The reactions of so me aetivated aromatic halidaa wit3v Piperidins, and 2>Autylaniae in dipolar apsotic and dipolar protic solvents* 1 th&ais subaitted to th» Haiwrsitjr of Ibadan for the degreo of HASTEN OF SCIENCE By Modupe Adeola Adenle B,Sc» (üons.) Nee I'lo&upe Adeola Adelfeyo üniversity of Ibadan« UNIVERSITY OF IBADAN LIBRARY Ibis is to certify that the whole of the work öescrlbed in this thesis was done by Mrs. A.H. Adenlo under our supervision fron Deceaber 1968 to Decenber 1971. " K u M — T. i - u ^ S p Department of Che:aistry, University of Ibadan. UNIVERSITY OF IBADAN LIBRARY ACOOWLEDGEI'IMTS The author wishes to express her profound gratitude to her Supervisors Dr. T.O. Baiakole and Professor J. Hirst for their keen aupervision and patience during the whole period of the work« The author is also very grataful to the he ad of departraont Professor J« Beetlestone, relatives, friends, and all others, who, by their worda of encouragement and support, have made this work possible. May Go& bless then all. yinally the author tri3lies- to dedicate the work to the memory of her daughter. Adeola Adenle nee Adeola Adefclayo Chemistry Department, üniversity of Ihadan. Januar7 22, 1975 UNIVERSITY OF IBADAN LIBRARY Abstract Th© reactions of 2-chloro-5-nitro pyridine with piperidine have been studied in aceton© and in nethanol. In acetone, the rate constants are neasured as a function of the anine concentration. In nethanol, the Arrheniua paraneters are obtained. In nethanol, except for a very slight (alnost negligible) downward trend of rate constants at very high concentration which is explained in terms of Charge - transfer conplexes, there is no base catalysis and the observed rate constants are the rates of fornation of the internediate conplex. The rates of reaction of 1-X-2, 4-dinits,obenzene (X=F, Cl) with piperidine and n-butylanine in nethanol, acetone, and chloroforn (stabilised and destabilised) have been neasured as a function of the anine concentration. In acetone, the reactions of both Substrates with piperidine Show true base catalysis with ^3/^2^ 50 in both cases. In Chloroform with n-butylanine, there is very little rate increase with increasing anine concentration. For both Substrates, ^ A a This is explained in tems of hydrogen-bonding in the internediate state. In nethanol, the reaction of the chloro Substrate with piperidine gives a snall linear increase of rate constants with increasing anine concentration; whila for the fluoro Substrate, the graph of rate constants UNIVERSITY OF IBADAN LIBRARY against anine concentration gives a doubly sloped curve. This is due to Sone special unknown nediun effects. In acetone, the reactions with n-butylanine give rather peculiar results. The chloro Substrate appears to be norc sensitive to catalysis by anine than the fluoro Substrate - a Situation hitherto unknown. In general, for the reactions in nethanol and Chloroform, there is not nuch ba3e influence; while those in acetone are dependent on the base strength. UNIVERSITY OF IBADAN LIBRARY CONOENTS PAGE 1. Introduction 1 2. Solvent Effects 8 3. Literature Survey of Solvent Effects 17 4. Experimental Section (a) Preparation and Purification of Materials 28 (b) Description of Special Apparatus 34 (c) Investigation of Kinetics 37 (d) Kinetic Results 55 (e) Summary of rate constants 157 5. Discusion of Results 164 6 Referencos 190 UNIVERSITY OF IBADAN LIBRARY M 2S L . ; Arusatic Uucleophilic Substitution has been known since the second half of tho nineteenth Century; but systeuatic and intensive rese’arch in the field dates back to the werk of Brady and Cropper^ in 1950. Tlie"comprehensive Hiera ture on aromatic nucleophilic substitu• tions in,i c'ludes the reviews and studies of Bunnett and Zahler2 , Killeri A Berliner and Monack5 and Ross 6„ Initially, aronatic nucleophilic Substitution reactions were classified as S1T7! and ST2 7 by analogy with nucleophilic Substitution in the aliphatic series, The £N1 nechanism is the one proposed for the uncatalysed decomp.'. ~ition of diasonium salts 8 ’ 9 in aqueous Solutions. ArTfi ^ Ar+ + EL ....... (ii) The reacticn is first order in aqueous solution^’̂ '1''^ and its rate is unaffected by the concentration or even the Identity of the anicrs of the salts cven when these anictis enter into the forma/t ic-n of the products 7 * 13 . In the bimolekular reactions, two type3 were recognised: a) these t';at proceed with rocxzGr.aov.cri for esanplc the reactiers involvLng the : bensyne' intermediates 14 . These reactions proceed via the elimination - addition meehani and only take place either in the presence of ve-f - strong bases e.g. KaKE^/NH^ or under very UNIVERSITY OF IBADAN LIBRARY 2 üraotic oonditione, One such roaction can be roprosentod ty tlc l I nj below: b) those that take. place without roorraccoEont, These constitute the vast majority of aromatic nucleophilic Substitution reactions. In the 1950’s and early *60*s there was a lot of controversy as to the mechanism of this type of reaction. Initially, it was thought that bond - breaking and bond - making processes *ere syn- ohronous by analogy with the straight - forward Sl'Î mechanism. Quantum - mechanical considerations show that this type of mechanism is impossible, The transition states for thi3 mechanism would be either a:«b X UNIVERSITY OF IBADAN LIBRARY 3 In (a)jX - Y is perpendicular to the plane of the benzene ring and as such is impossible because the p-orbitals which are supposed to hold X and Y are those used for the 7T bonds and an acceptance of it will lead to a violation of the Pauli Principle. Also in (b)jX - Y is planar with the benzene ring and is impossible because Y and the benzene ring cannot occupy the same space. 15 Bunnett and Zahler have strongly advocated the Intermediate complex mechanism. This mechanism requires that in the formation of the transition state of the reaction, the benzenoid resonance of the ring is lost and is replaced by a pentadienate ion resonance. The reagent forms a complex, the intermediate complex, with the Substrate during the process. This intermediate complex then decomposes into products at a definite rate. The intermediate complex formulation with an amine as nucleo- phile and ca sativated halidö as tho Substrate is given belcw: UNIVERSITY OF IBADAN LIBRARY 4 At any given base concentration m , the rate of fonnation of (e ) is given by V = ko A 7£\7 ------- (15) where ko is the observed specific rate constant for the formation of E. Applying the steady state appro ximation to the above UNIVERSITY OF IBADAN LIBRARY 5 reaction scheine: V A comparison of equations (l(5) and (l'(6) will give Three different forms of the equation (17) arise depending on the relative magnitudes of k^, k-1, and kg. 1. When kg + k^ /~B_7 k-1 then equation (l7) become ko = k^ Under this condition, the reaction is insensitive to base catalysis regardless of the concentration or catalytic power of the base. 2. When k-1 kg + k^ then equation (17) becomes ko = and the rate is linearly dependent on the concentration of the base DJ as is the the case in the potassium acetate - catalysed reaction of 1- fluoro -2, 4 - dinitrobonzo with N - methylamine in ethanol."^ 3. When kj^ and kg + k^ £~B_7 are oomparablo in magnitude, the rate is curvilinearly dependent on the concentration of the base. All the recorded evidenoe is in favour of the inter- mediate complex mechanism. Biese have been summarüsad in various UNIVERSITY OF IBADAN LIBRARY 6 reviews and articles. 27-22 The relative ordere in which halogens are displaced in aromatic nucleophilic Substitution reactions have been advanced generally as arguments in favour of the intermediate complex mechanism. Generally, in protic solvents the Order Fvv Cl> Br^I has been observed 23 suggesting that the Formation rather than the decomposition of the complex is rate detennining supportlng the intermediate complex mechanism. The reverse order F < CI "•/'Br - is less frequent ly encountered. In fact, it has only been observed in f«r bases 24» 51 though there are several examples of this order in non - protic solvents such as benzene. In all cases where this sequence has been observed the reactions of the fluoro - Substrate are base catalysed. The effect of the solvent in aromatic nucleophilic Sub­ stitution reactions has been mcasured by many workers and in this department by Okafor2 6 and Ette 27 , In these studies>base catalysis has been observed in sorae solvents such as water - dioxane mixture and benzene. Except for the work of Suhr2 8, where base catalysis has been observed in methanol, most workers have observed no base catalysis in methanol and in most of the dipolar aprotic solvents. The aim of the present work is to investigate the kinetic UNIVERSITY OF IBADAN LIBRARY 7 form of the reactions between activated fluoro - and chloro - benzene and pyridine with amines in various solvente. The results will bo used to elucidate the changes which occur in the mechanism of aromatic nucleophilic Substitution reac­ tions as the solvent is vazied. UNIVERSITY OF IBADAN LIBRARY 8 CEIAPTER 2 ROTiVMT EFFECTS Liquid Solutions offer both practical and theoretical advantages for the study of Chemical rcactions. It is easy to obtain macroscopically homogeneous Solutions of many reactants, to vary the nature of the liquid, to add other reagents, to control physical conditions with great uniformity. Most of the physical organic Chemical theoriec aro baoed on the otudy of reactions carried out in liquid solution. The fomulation of many reaction mechanisms can be aided by data on the effect of solvents on the rates and products of the reactions. There are many parameters which can be utilised to predict solvent effects on reaction rates and mechanisms. EFFECT OF DIELECTRIC COl-iSTANT (D) OE THE SOLVENT ON REACTIOI? RATE: Forces between reactants are altered and their rates of reactions modified depending upon the medium in which the reaction is taking place, The greatest physical effect which a solvent exerts upon the reactants innorsed in it is the modification of the electrostatic forces among the reactant pai’ticlee ihreugh ihe Dielectric Constant influence of the medium. These electrostatic forces affect raarkedly the sbility, of reactant particles to contact each other. Tho dielectric constant does not provide a direct measure of the interactions on the molecular scale as is to be expected due to the complexity of the interactions. UNIVERSITY OF IBADAN LIBRARY 9 Many theoretical treatments of electrostatic interactions are available all based on the dielectric constant of the solvent. 30 Considering dipole - dipole reactions, a theory for the influence of the dielect3?ic constant of the medium on the free energy of a polar molecule has been given by Kirkwood. 31 By considering eloctiostatic forces only (neglecting van der waals’ forces) the change in free energy when a molecule with dipole moment yu and radius r passes from a medium of dielectric constant of unity 1 into a medium of dielect ic constnt D is given by AG = - /“ D - 1rr 11 (1) t* 2D + 1 Applying this to the transition - state theory for the reactionj A + B ------a M ̂ where A, B, and M#= are polar species and taking note that k = where k = rate constant in solution, the equation In k = In ko - (P ~ l) j yü2A yü2B (2D+ 1) / ~rT'A~ + rT B where ko is the constant in a medium of dielectric constant unity and where the non - electrostatic forces are the seme for the activated complex as for the reactants. This equation Xl(2)y prodioto that if the activated eomplex is more polar than the reactants, as is the case where the products are icns, then the rate of the reaction UNIVERSITY OF IBADAN LIBRARY 10 increases with the dielectric constant of the medium, Por reactions in solvent mixtures, a straight line is often obtained by plotting Ink versus (d - l/2D + l)^. This equation is not always obeyed and is not valid in general if reaction rates in different types of eolvonts of different dielectric 1 constants are compared. This and other instances 33» 34# 35# indicate the limited application of the dielectric constant as a measuro of the solvating power of the solvent. Por this rcason, the use of the lineal free energy relationship may be of tromenduons help. HÜGEES - nraOLD QUALITATIV3 SOLVENT THEORY: The qualitative solvent theory of Hughes, Ingold and their collaborators relates the relative solvation energies of the transi- tion and initial States to the mechanism and Charge - type of the reaction. It proposes that strongly solvating (ionising) solvents facilitate an increase in the magnitude of the charges, inhibit a decrease and retevrd the distribution of a given Charge in going from the ground state to the transition state. Also that a reaction in which the formation of the transition state involves an increase or decrease in the magnitude of the charges will be subject to stronger solvent influences than one wherein a given Charge is dis- tributed in the transition state. Por nucleophiüc Substitution reactions, it States that there are four possible oharge types. In the reaction: Y + HX— t>YR + X a) Initially Y negative x neutral UNIVERSITY OF IBADAN LIBRARY - Hfl - b) Initially Y neuttal ’vcXtnamtral c) Initially I . nogatUre X positive d) iDitJUaldy Y neutral X positive There are two types of mechanistic paths by which these reactions can oocur: 3N2 and Sjjl. For each mechanism and each Charge type the change in Charge distribution on going from the initial to the transition state has to be considered. When this is done, the general conclusions of the theoiy are summarised belows rredictec Solvent Effects on Nucleophilic S—u-b--s-t--i-t- -u--t-i--o--n-s . , Charge Charas I Change in Predicted effect of Type Initial Transition Distribu­ increased solvent State State tion (a) polaritv on rate Bimolecular Mechanism Sr2 a) y?RX y £ — a— Dispersed Small decrease b) Y+RX Ye& - R --- Increased Large Increase c) i+RX4- Y°— R---X ^ Reduced Large decrease d) Y+RX+ y^ sL r— Dispersed Small decrease Unimolecular Mechanism 2j\j1 a)and b) RX Increased Large increase c)and d) R2+ - Dispersed IM , * deffr^aaS. (a) on proceeding from the initial state to the transition state. The theory assumes that energy changes will be more important than entropy changesj äi^ough in nany systemsj the tiro effects would be In Opposition, and the theory therefore considered only solvation energies. This theory has been found to work well for many reations of attyl halides and *onium salts. However, it ignores specific interactions such as hydrogen-bonding and also entropy effects.^ UNIVERSITY OF IBADAN LIBRARY 12 SPECIFIC INTERACTIONS BETWEEH SOLVENT AND REACTANTS: All the relationships between the rate of reaction and the polarity of the solvent hitherto discussed take into account only some interactions and ignored all specific effects such as hydrogen - bonding and polaiisability and as such give only a rough picture of the effect of a solvent on a given reaction. The solvent effects on the rate of the Menschutkin reaction illustmtes the importance of these interactions. The Hughes - Ingold theory predicts that the rate should be greatest in more polar solvents. Por hydrolytic solvents the activation energy decreases with increasing dielectric constant, whilo the entropy of activation is little affected. The reaction is, as predicted, faster in ethanol than in benzene, However, if comparison is made between different types of solvents, the theory is less satisfactory. The Hughes - Ingold theoiy is based on electrostatic effects and does not take into account specific solvent - solute interactions such as hydrogen - bonding. These special interactions between solvent and reactants are of fundamental importance in bimolecular substitutions and hsnee limits the applicability of the theory. A theory of solvent effects on the rates of reaction based on specific solvent effects is due to Miller & Parker. UNIVERSITY OF IBADAN LIBRARY - 13 - PROTIC AND APROTIC SOLVENTS: Solvents are classified as protic or dipolar aprotic depending on whother they possess labile hydrogen atons or not. Hydrogen - donors e.g, methanol are classified as protic solvents and they have high dielectric constants. D methanol = 32.6. Solvents with D>15 which though containing hydrogen atoms but which cannot bo donated to form hydrogen - bonding with an appropriato species are known as dipolar aprotic solvents e.g. dimethyl formamide D = 38 acetone D = 21.5 Solvents like benzene which are non - polar may be classified as non - polar aprotic solvents. Parker^ has demonstrated that most anions in dipolar aprotic solvents are much less solvated than in protic solvents, but large polarisable charged transition states in dipolar aprotic solvents are more solvated than in protic solvents. The result is that bimolecular reactions of anioao which pass through a large polari- sable state containing that aniort' are much faster in dipolar aprotic solvents than in protic solvents.39, 40 Reactions of small aniotxs arcmost accelerated, but reactions of large polaiisable anions are least accelerated, in the change from protic to dipolar aprotic solvents. 39 In protic solvents aniojis are solvated by ion-dipole interac- tions on which ta superimposed a strong hydrogen - bonding which xs greatest for small cm.o ^s.3 9 Thus solvation by protic solvents UNIVERSITY OF IBADAN LIBRARY - 14 - decrease3 strongly in. the series 0H~, F**>^ Cl~> Br” > N^"*> I~ In dipolar aprotio 3olvents, anaons are solvated by ion - dipole interactions on which is superimposed an intoraction due to the mutual polarisability of the anion and the solvent molecule which is greatest for large ions. There is no significant contribution to solvation by hydrogen - bonding in dipolar aprotic solvents. Solvations of anions by dipolar aprotic solvents thus decreases slightly in the reverse Order to that given for protic solvents. QUANTITATIVE DETERMINATION OF SOLVENT EFFECTS (LINEAR FREE EHERST RET.ATT OTJSHTPfî • The formulation of many reaction mechanisms can be aided by data on the effects of solvont3 on the rates and products of the reaction. In Order to mnke use of data on solvent effects for reaching conclusions about mechanism3, an unambiguous way of defining what effect is expected for a given solvent is required. As of present, all parameters used to describe solvents result from experimental measurements. In Order to utilise these parameters properly, the molecular basis of the process which provided the data for defining the parameter must be understood.^ In order to havo a definite basis for comparison of solvent effects, linear free cnergy relatior«# ships are employod. These relationships do not provido a theoiy of Mnetic solvent effects; but they attempt to correlate solvent properties in terms of parameters which are independent of tho UNIVERSITY OF IBADAN LIBRARY 15 reacting Substrate. (Jrunwald and Winstein guggested the two parameter linear free energy equation log £ = mY --------(II (4)) where k is the rate constant for the solvolysis of a compound in any solventj;k0 is the rate constant for the solvolysis of the same compound in a Standard solvent (8Cffc ethanol); Y is a measure of the ionizing power of the solvent and m gives the sensitivity of the Substrates to changes in the medium. The application of the equation requires that Y values be determined with respect to a standared compound and this has been chosen as teart-butyl Chloride (m = 1.00) These Standard solvent and Substrate were chosen because of the numerous instances of reactions involving both of them. This equation is found to be satisfactory for correlating solvolysis rate for mahy simple SH1 reactions in which the carbonium ion is rapidly converted into the producta. The agreement for Sn 2 solvolysis is less general. Later on, other more complicated equations have been devised to correlate rates of solvolysis reactions. 43 Swain's original vxew was that all polar displac(nem) ent reactions involve concerted action of a nucleophilic reagent attacking the Substrate (s) as an electrophilic reagent (e ) pulls off the di3placed group JT + S E — ---------- /Transition S ta te 7— Products. This view led to the expectation that displacement rates could be correlate by the four parameter equation thus: UNIVERSITY OF IBADAN LIBRARY 16 log |■K- O = Sn + S1e ------- II 5 where k is the rate of reaction of the Substrate being considered,' ko is the rate of the reaction. of the same Substrate with water in which both N and E are water for xihich both n and e are defined as zero. n is a nucleophilic constant characteristic of N and e is an electrophilic constant charateristic of E. S and S1 represent the respective senstivity of the substrate (s) to the nucleophile (n ) and to the electrophilic reagent (e ). Fierens and hi3 co-workers 44 examined a number of features of the Grunwald - Winstein equation. Maile finding the cofrelations useful as a diagae-sis of mechanism in the solvolytic reactions studied, they consider the Y values to be so dependent upon the choice of Standard substrate as to have limited application. UNIVERSITY OF IBADAN LIBRARY - 17 - CHAFTER 3 Literature Survey of Solvent Effects in Aromatic Nucleophilic Substitution Many reactions of amines with nitro-activated halobenzenes have been iescribed as base catalysed i.e. the second-order rate constants increased with increasing amine concentration or on addition of other bases while other Systems do not show catalysis. Applying the steady-state approximation to the catalysed mechanism the observed rate constants ko is given by * The three cases which can arise depending on the relative magnitude Also three striking characteristics have been observed from the various studies of these reactions in many solvents namely: Many reactions are accelerated mildly by bases; some are strongly aocolerated and a few have been known to be slightly retarded. In the class of reactions where k _ 1 » ^ + ^3 KJ , there is a linear relationship between the base concentration and the rate* Experimentally, the many known reactions belonging to this class obey the mathematical expressions ko = k' + k" C H vhere ko is the observed second-order rate coefficient, k * and k tt are second- and third-order coefficients respectively. k"/k' is a measure of the relative magnitude of the accelerated and unaccelerated parts of the reaction UNIVERSITY OF IBADAN LIBRARY - *8. Bunnett and his co-workers 17 have pointed out that two types of this apparent catalysis can be distinguished based on the value of kn/k', Strongly accelerated reactions are those for which k"/k' >50. Mdldly accelerated reactions are those with k"/k' significantly lower than 50 and more commonly 5 or lower. Several factors such as polarity of solvents or medium effects, the nature of the leaving group and other factors such as basicity of the nucleophile are known to affect the base catalysis. For the strongly accelerated reactions there is at least a qualitative relationohip between the base strength of the catalyst and its catalytic effect, For instance, in the reactions 17 of 1-fluoro-2, 4-dinitro benzene with N-methylaniline and various Catalysts; when OH is the catalyst, k"/k, - 350, when CHjCOO"* is the catalyst, k"/fe* - 150. With N-methylaniline as nucleophile there was little acceleration. Thus the order of catalytic effect is 0H~ XJH^COO"* >BNH2» For the mildly accelerated reactions, the Chemical character is not yet clear. For instance, in many of the reactions of 2 ,4-dinitrohalobenzenes with various amines, there is little or no relationship between the base strength of the catalyst and its ability to increase the reaction rate. Amines, hydrozide ions and acetate ions appear to be equally effective as catalysts. Bunnett^* ^ suggests that for mildly catalysed reactions, the formation of the intermediate is rate-determining, and that the slight augmentation of rate with increasing concentration of various solutes is due to some unspecifi effects UNIVERSITY OF IBADAN LIBRARY 19 From the results discussed below, it would appear that kinetic rehaviour observed experimentally depends principally on the nature cf the group displaced i.e. whether it is a 'good' or a ’poor' leaving group; tut for border-line cases, e.g. fluorine, the solvent and/or nucleophile ased can have a large effect. A change of solvent can result in either a change in the kinetic form of the reaction, or, if the kinetic form of the reaction remains the same, the rate of reaction changes. A survey of the reactions producing the various types of kinetic effects iiscussed above is now given, Reactions in which the rate constant decreases with increasing base AC AC j\rj yiQ concentration have been recorded by many workers^- ’ * The reactions of 1 -fluoro-2,4-dinitrobenzene with aniline in methanol 45 Show a decrease in rate coefficient ko of about 30$ as the aniline concentration is increased from 5 x 10— 4 M to 1 x 10- 2 M. This Observation by Bunnett and Garst is in general agreement with the results of Ross and Kuntz 48 in the reactions of ‘:-chloro-2 , 4-dinitrobenzene with aniline in ethanol and in 50$ ethanol - 50$ ethyl acetate. Results of other workers including that by Bamkole and Hirst 46 on the reactions of 2-chloro-5-nitropyridine and 2-fluoro-5-nitropyridine with aniline in methanol at high temperatures (F at + 104.3°C, CI at +102.9°C) also show this decrease in rate with increase in amine concentration. Bemasconi47 also noticed this decrease in the reaction of piperidine with the ethers of 2-4-dinitrophenol in 10$ dioxane - 90$ water. Ross and Kuntz 48 explained their Observation in terms of charge-transfer complexes. This explanation is also assumed valid for all the other instances where this phenomenon is observed. UNIVERSITY OF IBADAN LIBRARY _ 20 - There are very many cases of mildly accelerated reactions reported by rarious workers^* These include the reactions of 1-chloro-2,4- dinitrobenzene with several amines in Chloroform11 7 and/or ethanol for which k"/k' raries from 0.24 to 4*6 and those of p-nitrofluorobenzene with piperidine in several polar solvente for which k"/4c't3.2, The reactions of 1-chloro-2,4- dinitrobenzene with amines in benzene^3 ’ ^ are at most mildly augmented by excess amines. The effects of neutral and basic salts on the rates of the reactions of 1-chloro-2,4̂ dinitrobenzene with aniline in methancl i3 mildj1 7 k"/k' ä 2. When the solvent is t-butanol, the rate was found to increase steadily with increasing aniline concentration but k"/k’ is still about 2.6. In the reactions 45 of N-methylaniline with 1-X_ 2,4-dinitrobenzene /(.X = F, 21, Br) in various hydsoxylic solvents, it was found that when X=C1, and Br, there were mild accelerations with kn/ik '4.5* Suhr5 1 reported work on the reactions of p-nitrofluorobenzene with piperidine in alcoholic solvents for which k"/k' <5 . Now, by Bunnett's Classification, only Systems for which k^/fe’ >50 are regarded as cases of true base catalysis, Therefore in the reactions reported by Suhr 51 , Bunnett 17, and other voikers for which k"/k' <5 , from our proposed mechanism in Chapter I, the formation of the intermediate is rate limiting: there is no base catalysis. These reactions belong to the dass of reactions with + k^fB] » k ^ - a Situation which is mostly encountered for 'good' leaving groups. Bunnett and Bemasconi^a’ ^ investigated the reactions of Piperidine with the ethers of 2,4-dinitro phenol in 10$ dioxane - 90$ water leading to 2,4-dinitrophenj^l piperidine. They shoved that the occurrence of base catalysis UNIVERSITY OF IBADAN LIBRARY — 2* ** iepends on the group displaced. Reactions with good leaving groups such as :l, Br, I, were little or not sensitive to catalysis by bases whereas base oatalysis was found to be strong for poor leaving groups such as the ethers. However, Ross 22 has studied the rates of reactions of l-chloro-2,4— iinitrobenzene with n-butylamine in Chloroform as functions of amine ooncentrations and added salts, viz, benzyl triethylammonium nitrate. He obBerved mild general base catalysis in these reactions and on this basis, proposed that base catalysis in the reactions involving a good leaving group is due to hydrogen bonding between the amine and the suitable acceptor for iydrogen bonding in this case, another molecule of nucleophile, in the rransition state for the intermediate complex formation. Pew instances of base catalysis involving the CI group have been reported. One unequivocal instance is reported by Bernasconi and Zollinger52 in the reaction of 1-chloro*-2,4-dinitrobenzene with p-anisidine in benzene. Other strongly accelerated reactions include the reactions 17 of 1-fluoro-2,4-dinitrobenzene with N-methyl aniline in ethanol in the presence of potassium acetate for which k"/k' = 150. The reaction is strongly catalysed by oxyanion bases^k"/k’ = 350 for the hydroxide catalysed System with 60$ water ■10$ dioxane as solvent. The corresponding chloro compound shows no such base catalysis. Reactions * of p-nitrofluoro benzene and 1-fluoro-2,4~dinitrobenzene with piperidine in benzene are so strongly dependent on amine concentration that they are second-order in amine except at very low amine concentration2 8« Pietra and Vitali 54 also showed that there is base catalysis in the reaction of 1-fluoro-2,4-dinitrobenzene with piperidine in benzene in the UNIVERSITY OF IBADAN LIBRARY presence of such addenda as ̂ V-pyridone and N-methyl Cf4- pyzidoae. Reactions of 4-fluoro-nitrobenzene with piperidine in benzene 55 Show linear increase of rate constants with increasing amine concentration. Bernasconi and others 56 investigated the reactions of 1-fluorO“2,4-”dinitro benzene with benzylamine and N-methylbenzjrlamine in benzene with and without the addition of pyridine and 1,4-diaza-bicyclo (2.2.2) - octane (DABCO) as catalysts. Both reactions are catalysed by the reacting amine, pyridine and by DABCO. The dependence of the reaction rate on base concentrations is linear for N-methylbenzylamine and curvilinear for benzylamine. The sensitivity of both reactions to base catalysis is much greater than that of the reaction of piperidine with 1-fluoro-2,4-dinitrobenzene but is found to be considerably smaller than in the reaction of p-anisidine with the same Substrate 52; thus auggesting a correlation between the basicity of the reacting amine and the sensitivity of the reaction to base catalysis. The reaction5 2 of 1 -fluoro-2,4-dinitrobenzene with morpholine in benzene have been studied with and without pyridine, and DABCO as catalysts. The reaction is catalysed by all three nucleophiles although the reaction is more sensitive to pyridine and DABCO catalysis than the same Substrate with the sterically identical but more basic piperidine. These obsrervations confirm a previously found trend of greater sensitivity to base catalysis with decreasing base strength of the reacting amine. The rates of reactions of 1-fluoro- and 1-chloro—2,4-dinitrobenzene with piperidine as influenced by the addition of dimethylsulfoxide and aqueous dioxane have been measured 57 in benzene solution. For the fluoro Substrate, the reaction is about as strongly catalysed by dimethylsulfoxide as by DABCO but UNIVERSITY OF IBADAN LIBRARY - 23* auch more strongly than by pyridine. A change in the dependence on piperidine concentration upon the addition of dimethylsulfoxide is an indication that a medium effect is operating. Another evidenee is fumished by the reaction cf the chloro Substrate. This Substrate, whose reaction is known to be insensitive to base catalysis, is nevertheless accelerated by dimethylsulfoxide. The dimethyl sulfoxide does not simply accelerate the rate of reaction via case catalysis but also via a medium effect notably its high polarity. It is less basic than pyridine in benzene therefore it cannot act as a base catalyst as proposed by Suhr“̂ . For the strongly accelerated reactions mentioned above, the Situation is that k_i » k2 + k5 CCJ and the Overall equation: ^ kg + k1 k3 fej k^1 + k2 + k5 Cßj reduces to; There is a linear relationship between the rate constants and the amine concentrations. Some reactions have been found to undergo base catalysis in such a way that ko increases less than linearly with increasing catalyst concentration. Among such are the reactions 58 of secondary amines and p-nitrophenyl phosphates and ethers of 2,4-dinitrophenol with piperidine in hydroxylic solvents which show strong dependence of rates on amine concentration. In these reactions, a limiting rate is obtained at high concentration of the catalyst. The plot of the rate constant versus amine concentration is curvilinear. This is interpreted as involving a change in the rate-determining step 'which in t u m requires that UNIVERSITY OF IBADAN LIBRARY - 24 there be an intemediate in the reaction pathway. Such observations constitute the most convincing evidence for the prediction that when k--| and 0*2 + k3CBJ ) are of comparable Order, of magnitude, then a non-linear relationship exists between the base concentration and the rate of reaction. And it is generally agreed2 2 that the observed rate accelerations are due to catalysis of intermediate decomposition to products. Curvilinear relationship between amine concentration and the rate constant arises when k—1 ü + k^ LB] At sufficiently high amine concentration, the condition kj Cb] » k 2 holds. If the original equation k + k k [B] ko = .k..,. ..+. .k. 2 + ^*- -H- is inverted to 1 ___1_ (-k»1 + k, + k^ [b] n k° k, k2 + pj > and the assunption k^ CB] » k ^ holds, then the equation above becomes — !_ =J — + k_i ko k. ------r 1 k1 k3 Cb] A plot of versus will be linear except at low amine concentration II. sJ when this assumption may not hold. Such plots would then be linear initially, and later deviate towards the B axis. From such plots, slope will be and intercept ^ From the equations above, the values of k1, k-i/kj, k-i/k2 and kj/k2 can be obtained. The ratio k.j/k.2 indicates UNIVERSITY OF IBADAN LIBRARY -25 the extent of acceleration by bases. Such predictions are now fully satisfied i S - 11 and observed by many workers among them Bunnett et al. In general, the order of halogen mobility in protic solvente is ? » Cl is Br >1* Por example, in methanol, a protic solvent, the departure of the smaller more strongly bound halide ion is favoured over the departure of the larger and more loosely bound halide ions. This suggests that the step at which the C - halide bcnd is broken is not rate limiting. In non-protic solvents such as benzene the reverse order i.e. P < CI ä I is observed. >Öien the reverse order is observed, the leaving group tends to depart slowly, (ku, + k^Cß)) being small, while the solvent e.g. benzene - a non-polar aprotic solvent with a dielectric constant of 2.28 causes K-1 to be large. Thus in non-polar aprotic solvents, strong accelerations have been found for the reactions of piperidine with 2,4-‘dinitroanisole and 2,4-dinitrophenyl ether 53 which possess poor leaving groups. The change from a non-polar aprotic solvent such as benzene to a protic and dipolar aprctic ones has a profound effect on the reactions of 4-fluoro and 4-cnloro nitrobenzenes 51 in various solvents such as methanol, iimethylsulfoxide and dimethylformamide. In methanol, and in dinethyl sulfoxide, the reactivity sequence ArP > ArCl is observed^' . From Parketts work"^a , it has been established that the increase in rate in changing from protic to dipolar aprotic solvent is general for anion-dipolar molecular reactions proceeding via a large negatively charged transition state. Paricer attributed this behaviour to the fact that solvation energy of simple ions are lower in dipolar aprotic solvents than in water. UNIVERSITY OF IBADAN LIBRARY - 26 - However, when reaction is between neutral molecules such as nitro- activated halides and amines, this is not always true as there are instances when reactivity is higher in protic solvents over dipolar aprotic solvente. More Support for this view is supplied by Habbersfield's work 29• On oarrying out the Menschutkin reactions of pyridine with six benzyl halides, he found a decrease in enthalpy of activation in changing from protic to iipolar aprotic solvents. This lower activation energy in dipolar aprotic solvent notably dime:'hylformamide is caused entirely by greater solvation of the transition complex in this solvent. The reactions of p-nitrofluorobenzene with piperidine2 8 proceed faster in the dipolar aprotic dimethylsulfoxide and dimethylformamide than in the protic solvents and solvents with similar dielectric constants - acetonitrile and nitromethane. suhr attributed this behaviour to base catalysis but Bunnett disagreed with this view 17. 45 . Bernasconi 57 has, in his woik, demonstrated that dimethylsulfoxide is not capable of accelerating reaction rates by base catalysis. Both Bunnett and Bernasconi conclude therefore that these solvents accelerate reaction velocity through their high polarity. Rates of reaction of many primary& 2q. and secondary6 2b amines with p-nitrofluorobenzene have been measured in dimethylsulfoxide. Addition of varying quantitie3 of dimethylsulfoxide to benzene was found to cause great increases in the rates of reaction. Addition of dipolar aprotic solvent notably dioxane also caused increase in rates though of a smaller Order than 61 by dimethylsulfoxide. The explanation given by Miller is in general agreement with previous views that the presence of dimethylsulfoxide in the solvents causes a relative enlancement of the solvation of the transition state. UNIVERSITY OF IBADAN LIBRARY 27 - Also, in the work of Ross 22 on the catalysis of the intermediate complex ;:rmation in Nucleophilic Aromatic Substitution, he found that in the mildly :=talysed reactions cf öalonitrobenzcno . with amines, solvent effects =re very large in general paralleling the polarity as indicated by their iielectric constant. For example, the reaction of p-nitrofluorobenzene and piperidine at 50°C is four tines faster in dinethylsu.1.foxide ( = 48.5) than in dibutylather ( = 3.06) There are few cases of exception to the rule of groater rate enhancement in dipolar aprotic solvents than in protic solvents. For example in the work of Bamkole and Hirst 59 on the reactions of 1-fluoro- and 1-chloro- 2,4-dinitro benzene with aniline, and piperidine and 2-chloro- and 2-fluoro-5-nitropyridine in acetone and methanol; also the work of Chapman and Parker^ on these Substrates with ethanol as solvent. In all cases, it was found that the rates :f reaction are greater in the hycüeoxylic solvents by factors ranging from to 30. For instance, in the reaction between 2-fluoro-5-nitropyridine and aniline at high temperatures =- 103°C, the rate of reaction in methanol at 104.3 C is 3.14 x 10 l.mol.” sec.” and in acetone, the corresponding rate is 2.38 x 10- 5 l.mol- 1 sec- i • Also in the reactions of l-chloro-2,4- iinitrobenzene with piperidine, the rate constant at 50 o C is 6.54 x 10- 5 1 zol” ̂ sec” ̂ in acetone and 5»53 x 10 ^ lmol ^sec ̂ in methanol. In these instances, reactions are faster in protic solvents than in dipolar aprotic ones. Despite these exceptions, in general, in reactions between unchaxgsd nolecules, e.g. activated halides with amines, the trend of rate enhancement in dipolar aprotic solvents over protic solvents is established. UNIVERSITY OF IBADAN LIBRARY KN 28 CHAPTER 4 EXPERIMENTAL SECTION ) Prenaration and Purification of Materials i) 1 - fluoro -2. 4- dinitrobenzene: This yellow liquid was purified by crystallisation at low temperature (-10°C)* Since the compound is stored in sealed tubes, one of the tubes was chilled, cut open, and the yellow liquid quickly filtered into 100-ml. of sodium dried ether in a 250 ml. round bottomed flask. The flask was scratched with a glass rod to facilitate crystallisation, stoppered and finally stored in a deep freeze (about -10°c) for 24 hours. Pine yellow crystals separated, were quickly filtered off by suction to avoid moisture gathering on it, stored in a quick fit specimen bottle and dried in a vacuum desiccc.tor aver phosophorus pentoxide for 2 hour3. The substance was stored as a liquid in the vacuum desiccator. melting point - 27°C Literature6 0m .pt. - 26.5 - 27o C ii) 1 - chloro -2. 4- dinitrobenzene: Commercial 1—chloro 2, 4—dinitrobenzene (60 gms) was dissolved in hot methanol and decolourising charcoal. The mixture was heated to boiling and while still hot, filtered by suction into a preheated receiver. The pale yellow liquid was kept in a quick fit conical flask. On cooling, pale yellow crystals UNIVERSITY OF IBADAN LIBRARY - 2 9 - separated, which were filtered off by suction, stored in a quick fit specimen bottle, and dried by suction over CaClg grains. The substance was then stored in the vacuum dessicator. Melting point - 49-50°C Literature4 4mb. pt. - 50-51 oC iii) 2-chloro -5 - nitropyrj dine; Commercial 2-chloro- 5 nitropyridine (20 gm.) was dissolved in 30 ml. of Analar methanol. A small sample was left undissolved. Decolorising charcoal was added and the mixture boiled for about 2 minutes. The hot mixture was filtered and the filterate stored in a quick fit conical flask. On cooling, flakes of a pale yellow substance separated, were filtered by suction and then vacuum dried over CaCl^. The substance was then stored in a quick fit specimen bottle. Melting point - 110 - 110.5°C Literaturtum.pt. - 109 - U0°C iv) Pineridine: Analar Piperidine (100 ml.) was refluxed with sodium metal for six hours and then distilled in an all quick fit distilling assembly. The distillate was protected from atmospheric moisture by a CaCl2 guard tube. UNIVERSITY OF IBADAN LIBRARY 30 - The middle portion of the distillate, distilling at 105°C was collected in a 100 ml. quick fit round bottomed flask and kept for kinetic runs. The procedure was repeated after three weeks of storage to maintain a high degree of purity. v) N-Butylamine; Analar N-hutylamine (lOO ml.) was distilled in an all quick fit distilling asserfbüy ovor eine dust and potassium hydroxide pellets. The distillate was protected from moisture by a CaClg guard tube. The middle portion distilling at 77°C was collected for kinetic runs. The procedure was repeated after three weeks to maintain high degree of purity. vi) Acetone; Analar acetone (l.5 litre) was refluxed with KMh04 until the violet colour of the permanganate persisted. The acetone was then distilled off. Magnesium perchlorate (anhydrone) was added to Saturation point and then the acetone was distilled in an all quick fit assemblage. The middle portion distilling at 56°C was collected and used for kinetic runs. vii) Methanol: The method of Luud and Bjerrum^Hlao used. Into a 3- litre quick fit round bottomed flask was put dry magnessium tumings (lO gm.) resublimed iodine (0.5 gm.) and Analar methanol (300 ml.). The methanol was conyerted to the methoxide and the UNIVERSITY OF IBADAN LIBRARY - 31 - reacting mixture had to be cooled. More analar methanol (2 litres) was added to the flask and the contents refluxed for 30 minutes using a double surface condenser. Methanol was distilled and the middle portion which distilled at-64°C was collected into a dry quick fit flask. (2 litres) viii) Absolute Chloroform: Chloroform is stabilised with 2$ ethanol. To destabilise it, analar Chloroform (2 litres) was shaken up with 50$ sulphuric acid (400 ml.). This shaking was repeated three times after which thero was no more reaction in the flask. The Chloroform was then waohed several times with distilled water; the washings being tested with blue litmus paper. When the washing was neutral to litmus, calcium Chloride (lOO grams) was added and shaken up. The cloudy Chloroform became clearer. The calcium Chloride was filtered off. A further 100 gm of calcium Chloride was shaken up with the Chloroform and left over night. The calcium Chloride was filtered off and the already dry Chloroform was distilled gentl.y in an all quick fit assemblage. The middle portion distilling at 6l°C was collected for kinetic runs. The following tests were conducted to show that there was no more OH radical present in the Chloroform: a) The N.M.R. spec';?um was obtained and this showed no OH peak. b) The Vapour Phase Chromatograph showed only one peak. UNIVERSITY OF IBADAN LIBRARY 32 c) The I.R. spectrum showed no OH peak. These three tests showed the solvent to be free from any mixtures hence to be 100$ pure. ix) Pre-paration of Piperidine Hydrochloride: HCl gas formed by dropping concentrated H2SO4 onto concentra— ted HCl and dried by being passed through two jars containing concentrated H2SO4, was bubbled into a solution of piperidine in dry acetone. The white precipitate which formed was filtered off and washed with dry acetone. This product, being hygroscopic was quickly collected and stored in a well stoppered reagent bottle for use. x) 2. 4 -dinitrophenylpiperidine: 50 ml. each of Standard Solutions of 1-chloro-2, 4-dinitro- benzene (2N) and Piperidine (2N) in sodium dried ether, were mixed in a 100 ml quick fit conical flask and left in a thermostat at 30°C overnight. The contents were then poured into 100 mls of distilled water, the orange precipitate filtered off, recrystallised from methanol and dried in a vacuum dessicator. Melting poing 44e Literature m.pt. a 9 2 - 94°C xi) Preparation of 2. 4 djnjtrophenyl ~I»-butylar3i.ne: 1 gram of 2,4-dinitrochlorobenzene was weighed into a beaker and very cautiously enough n-butylamine to dissolve it was added. UNIVERSITY OF IBADAN LIBRARY 33 The contents on cooling were stirred with dry acetone and the precipitate of n-butylamine hydrochloride was filtered off. The filtrate was evaporated down to an oil which solidified on stirring with dilute HCl. The precipitate was filtered off and recrystallised fron boiling methanol and decolorising charcoal. The product, bright yellow crystals, was stored for runs. Molting Point - 81 - 82°C Litl^mpt. ts 81 ̂ C xii) Preoaration of 2-nipcridino -5 -nitropyridine: 2- chloro - 5-nitropyridine (l.O gm) and piperidine (l,5 gm.) were heated on the water bath for 30 minutes. The product was then dissolved in the mininun amount of 8C$ ethanol, heated with decolorising charcoal, filtered and then allowed to cool. Yellow crystals separated. Melting point - 82°C ‘Literature 4m4efl ting point 5 84o C xiii) Prenaration of Quenching Mixturo; A mixturo of known proportion of concentrated H^SO^ in dry methanol was employed in quenching the reactions in this Work. The acidity of the medium was depondent on the particular rcaction. For 2-chloro -5-nitrophyridine the concentration of the EgSO^ was O.OBI. For all the other reactions the concentration was 0.05H. The quenching mixture acted by fixing the amine as amine hydrogen sulphate and rendering it inoffectivo as a nucleophile. UNIVERSITY OF IBADAN LIBRARY ~ 2>4"— (b) DBSCRIPTIOIT OF SPECUL APPARATUS i) Thornostats; Two types of thermostats were uscd for the temperature ränge of -30°C to +50° C at which the kinetic Studios reported höre were carried out. Por work carriod out from +20° C to 4-50° C a well lagged glass bath containing water was used. Renting was done by an electric coil and a mechanical stirror kept the tenperaturo uniform. The electric coil heatod tho fluid to a fraction of a degreo lower than that required before control was effected by an intejsaitterrt fteator, a Sunvic relay and a regulator.. ^or work carried out below room teraperature, a *black box' thermostat containing methanol was used. Thore was a cooling System which continually withdrow heat until a fraction of a degree below that required. Control was then effected by a Sunvic relay and a regulator. In each oaso, the required temperatures were maintained to mithin + 0,05°C and readings were taken with Standard thorraonoter with an accuracy of + 0.01°C. ii) The Dreischenkolrohr called D.R. tube: Por fast runSj this apparatus was used. It consisted of a glass tube with three separate compartments. ^wo tubes, about 1.5 cm« in diameter and 5 cm* long were UNIVERSITY OF IBADAN LIBRARY 3 5 joined to a stem which was about 3 cm. in diameter at a .common juncture so that they were inclined at about 60° to each other but about 120° to the stem. About 4 cm* to this juncture along the main stem, another tube about 5 cm. long and of the same diameter as the stem was joined. This third tube pointed in an opposite direction to the other smaller tubes and was inclined to the stem at about 60°. The ends of the three tubes were then roundod up and the stem provided with a B24 socket and stopper. The apparatus thus had three legs on which it could stand solidly. Different Solutions could be pipetted into each compartment without them mixing until so desired. By tilting the stem side ways, the Solutions in the lower arms can be mixed when also desired. The third larger compartment which is normally used to hold the quenching solution was not used in this reaction. iii) ffllford (2400) Recording Spectronhotometer; For runs, for which the D.R. tube technique was too slow, the Gilford Instrument was used. The reaction took place in the cell compartment whose temperature had been regulated via the thermostat. The instrument simply recorded the optical density against time. UNIVERSITY OF IBADAN LIBRARY - 36-- iv) Gibson Spectrophotometer; For runs for which even the Gilford Instrument proved too slow, the Gibson Durrurd's Stopped - Flow Spectrophotometer was used. The dead time of the instrument was 2 m. sec. UNIVERSITY OF IBADAN LIBRARY 37 - (c) INVESTIGATION OF KENETICS Because the products of all the reactions in this work wore brightly coloured progress of reaction was followed spectrophotoao* trically in each caso. A. Reaction of 1 - fluoro -2. 4 -dinitrobonzene with Piperidine in dry Methanol: The optical absorptions of samples of the reaction mixture wore mcasured on a Unicara spectrophotometer S.P. 500. Choicc of Navelength: The wavelength at which the progress of the reaction was followed was one at which only the product absorbed and maximally too, to the exclusion of the reagents. Standard Solutions of Piperidine (0.0002M), 1- fluoro -2, 4—dinitrobenzene (O.OOOIM) and the product: 2,4 dinitrophenylpiperidine (0.0001M) werc prepared in acetono and Quenching Mixture 0.05M E^SO^ in Methanol. These Solutions wore used to scan tho spectrum fron 200 iyu to 450 npx, The product absorbed maximally at 380 cyu while the reagents did not absorb. Calibration Gurve or Beer*3 Law tost for 2»4 dinitrophenyl- Piperidine at 580 n/u: Prom the 10 -A M Standard solution used for scanning, dilute Solutions were prepared by making up 10 ml«, 20 ml», 30 ml‘* up to 90 ml» to 100 ml» with Quenching mixture. The final ooncen- trations are shown on the table. UNIVERSITY OF IBADAN LIBRARY 38.- Solutions and how they are Concentration of Mean optical prepared. diluted Solutions. density at 380 Eyu 10 ml, of 10**̂ M diluted to 1 x 10**5I'I 0.163 100 ml. 20 ml, of 10% " " 2 x 10"5M 0.315 30 ml, of IO“4!! " " 3 x 10~5M 0.456 40 ml. of IO"4» " " 4 x 10”5M 0.608 50 ml. of lO^M " " 5 x 10”5II 0.755 60 ml. of IO*"4!! " " 6 x 10”5M 0.901 70 ml. of IO"4» " " 7 x 10“5M 1.054 80 ml. of lO^M " " 8 x 10“5M 1.210 90 ml» of IO"4!'! " " 9 x 10**5H 1.360 10~4M 10“̂ 1.500 A plot of optical density agajnst concentrations in moles per litre was made. The slopc of this linear graph = 6,70 x 10 moles per litre per unit optical density and tliis t o s used t o convert optical density moasurements in the runs to moles per litre of product present, Procedure for a run: Exact quantities of piperidine and fluoro compound to mako 0.025M and 0.0025M respectively were weighed out. These were made into Solutions with diy mothanol (about 90 ml,) in 100 ml. UNIVERSITY OF IBADAN LIBRARY 5 9 - Standard flasks. These flasks were labelled with their respective Contents and immersed in the thermostat. After about 20 minutes, by which time, the Solutions must have attained thermostat tem~ perature, more dry methanol was added to make up to the marks. 5 ml. of each rcactant was carefully pipetted by means of a rubber pipette filter and deposited rather carefully into the small tubes of the D.R. tube taking care they did not mms. The D.R. tube was then stoppered. About 20 ml. of Q.M. was put in a 50 ml beaker. The D.R. tube was submerged in the thermostat such that the reactants in the small tubes were fully immersed. After some time, the D.R. tube was tilted to bring the contents into contact whilo at the same time, a stop clock was started. At the desired time, the 20 ml Q,N, in the beaker was used to stop the reaction. All the contents of the D.R. tube was then transferred to a 50 ml. dry Standard flask. The D.R. tube was then rinsed twice or more with small quantities of Q.M. and the washings added to the Standard flask care being taken not to overshoot the mark. The solution was then made up to the mark with more Q.M. 10 nl of this wa3 further diluted to 50 ml» in another 50 ml» Standard flask with Q.M. The optical density of this last solution was then takon. One such reaction in the D.R. tube was left ovomight and the optical density after appropriate dilution was found to agree with the theoretical UNIVERSITY OF IBADAN LIBRARY infinity obtained from the calibration cu^ve. This procedure was used for all the runs for this : Calculation of Rate Constants from Exnerimaatal data: The reaction can be represented by the equation: ArF + R̂ I'TH = AriTRg + HF R ^ H + HF ES R.NH2F“ where ArF s 1- fluoro -2, 4-dinitrobenzonc HgNH =r Piperidine ArNRg = 2, 4-dinitrophenylpiperidine. Let the initial concentrations of R^NH and ArF be a and b respectively. Then after time t let x moles of products be foxmod then the rate equation is dg = k (a- 2x) (b — x) , .JL(i), dt This is assuming that the piporidiniun fluoride so formed above is not as good as a nucleophilo as piperidine itself. But if it is assumed that HF is such a weak acid that it does not lead to the prOduction of piperidinium fluoride under the run conditions or that even if this is formed, it is as good a nucloophilo ao the piperidino itself, then the rate equation will be: dx = k (a - x) (b - x) .... A(ii) dt In either casc, if the concentration of the nucleophile s is very much greater than that of the Substrate b we can assume that a - 2x Clr n - x -£b- a So the equations (i) and (ii) become dx = k" a(b - x) .... A(iii) dt UNIVERSITY OF IBADAN LIBRARY - +1 - For truly first order reactions, the nucleophile is in such an excess that the rate equation: = k a(b - x) (where the notations above still apply) dt can be rewritten as dx = k^(b - x) .... . (iv) where ka = k̂ " dt first order rate constant. Comparison of this with that equation (iii) obtained fron 2nd order kinetics gives dx = k^(b - x) .. „.• .A(iv) dt dx = k"a(b - x) .. dt £ = 1 k"a k" = £ a Thus the second order rate constant can be obtained by dividing the first order rate constant by the amine concentration. For first order kinetics, dx = ka (b - x) or dt dx = k 1 (b - x) dt on Integration v/e have k1 = 1 m ( l ) t (b - x) UNIVERSITY OF IBADAN LIBRARY — 42 - A graph obtajned by plotting log.^ of opticai density at infinity lass that at the tine t versus time t will give a 3traight line whoso slope will be from hcre, can be obtained and hence 2.303 k". This was the raethod used to calculatc second Order rate constants for thi3 reaetion. UNIVERSITY OF IBADAN LIBRARY 43 - 3. The reaction of 1 -chloro -2. 4 - 46 *■* Test for Beer^ Law: Solutions of strengths ranging from 10-^M to 10~^M were also uaed. Solutions and how they are prepared Cortcentration of Mean optioal diluted solution density 0®. at 370 m/u 10 ml. of 10~4 diluted to 100 ml. 1 x 10“% 0,171 20 ml. of 10“4 <» n H 2 x 10~% 0.328 30 ml. of 10“4 u n b 3 x 10 - % •«.499 40 ml. of 10-4 rr n i» 4 x 1 0 - % 0.680 50 ml. of 10-4 n n n 5 x 10-% 0.890 60 ml. of 10-4 n ii n 6 x 10-% 1.055 70 ml. of 10~4 i i ti ti 7 x 10“ % 1.255 80 ml. of 10-4 i i n i i 8 x 10“% 1.450 90 ml. of 10-4 ii n ti 9 x 10-% 1.650 10-4 10“4M 1.950 Slope of plot of optical density against concentration = 1,750 x 10“4. The section of OB = 0.171 to Olk* '=1.055 was used. Procedure for a run: Standard Solutions of the reagents were prepared at thermostat temperatures as described earlier on with solvent also at thermostat temperature. In this way, there was no necessity for the calculation of coefficient of cubical expansion. 50 ml. of each of the reagents was mixed in a Standard flask and 5 ml. aliquots withdrawn at suitable time intervals into 20 ml. of Q.M. in a 50 ml Standard flask. More Q.M. was added to -make up to the mark. ’ 5 ml. of this was further 'dilti ted to UNIVERSITY OF IBADAN LIBRARY 47 - 50 ml, in another Standard flask and the OD of this latter solution was taken. Calculation of fcate Constants: This followed the same procedure as that of 1-fluoro- 2,4- dinitrobenzene. The slope of graph obtained by plotting the logi.u^ of (ODo e - OD.t ) versus time in seconds will give the vapue of k1 where 2.303 O P ^ = optical density at infinity obtained by leaving the reacting mixture for more than 48 hours. OD^ ss optical density at any time t and k^ = first order rate constant. *2 where RgNH is the amine. For the reaction of 2-chloro-5-nitropyridine with Piperidine in dry acetone, exactly the same procedure as that above was followed. D. The reaction of 1 - fluoro-2. 4 -dinitrobcnzcne and Piperidine in drv acetone. Choice of Wavelength: The same wavelength 380 nyu was used here as for the same reaction carried out in methanol since the products of both reactiong are the same, Procedure for a run: Gilford (2400) Recording Spectrophotometer, was used* UNIVERSITY OF IBADAN LIBRARY — 4P • It contains a cell - compartment whose temperature can be regulated by a flow of water to that desired. This regulation was aehieved by means of a water thermostat whose temperature was 3lightly thigher than that required in the cell. The cell temperature gave the desired reading. 1.00 x IO**2!! of the fluoro compound was prepared in a 50 ml Standard flask. This was diluted a further 1,000 times to give 1.00 x 10- 5M; 2.5 ml. of this was carefully pipetted into a sxlica cell and placed in the cell compartment. Now, 0.2M of Piperidine was prepared and this was further diluted 10 times to give 0.02M. With an Agla Mierometer All - Glass Syringe used with Shardlow mierometer screw gauge 0.01 ml of this base was added to the fluoro compound in the cell and the Instrument started. The concentration of the base was then 0.01 x 0.02 M = 2.51 7.91 x 10”^M. Higher concentrations were obtained by dropping 0.01 ml of stronger Solutions onto the Substrate. The instrument gave a plot of optical density versus time in chosen units. Fron this graph, CD oC, and CD.t were obtained. And a plot of log (O.D^ - O.D^) versus time in seconds gave a graph whose slopo = k̂ ~ x 2.303 K being first Order rate constant. k2 , second Order rate constant wae then obtained fron this. UNIVERSITY OF IBADAN LIBRARY 49 Reaction of X - chloro-2. 4 - dinitrobenzene with Pit>eridine in dry acotone: Wavelength of 380 ayu was also used. The calibration curve used for the same reaction in dry methanol was also used. Procedure for a run: Enough reagents to give twice the desired concentrations in the run were weighed out. The Solutions were prepared in the thermostat as earlier described. 50 ml* of each of the reagents woro thon nizod and at ouitable time intervals 5 ml* aliquote were withdrawn and diluted 100 fold with quenching mixture before the optical densities were taken. Calculation of rate constants: The equation B(iii) was used here also k . 1- 1 . 2*222 0.5^ » OD^ 1 log F f X-2 O.D^t 1° 0DöC ** ^ t where the Symbols retain their significance. F. Reaction of 1 - fluoro - 2.4 - dinitrobenzene with n-Butylaraine in acetone: This followed precisely the same pattem as the reaction of the fluoro compound with piperidine. The only difference is that here, since the products differed, the wavelength used also differed. The method used for scanning and calibration were precisely the same. The Optimum wavelength was found to be 350 ayu. Procedure for n y s : Enough reagents to give twice required run concentrations UNIVERSITY OF IBADAN LIBRARY - 50 - were weighed and prepared in the solvent. With 1 ml bulb pipettes, 1 ml. of each reagent was mixed in the cell and the optical density was recorded. Care was taken to maintain the cell at the required temperature. C^cu^Lation of Hate Constants: Plots of log (0D - 0D, ) versus time in seconds for each oc t concentration were obtained. From the slopes of these graphs, first order rate constants wero obtained. From these, second Order rate constants were calculated. G. Reaction of 1 - chloro 2.4 - dinitrobenzene with n-Butylamine in acetone; The wavelength used was also 350 nyu and the calibration curve gave a slope of 5.548 x 10- 3 moles per litre per unit optical density. Procedure for a run: The nethod of mixing 50 ml., of Standard Solutions of the reagents and quenching 5 ml. aliquots at predetermined time intervals was used. Calculation of Rate Constant; 2nd Order rate constants were calculated using equation B(iii).. k2 = 1 . 1 . 2,303 F f X-2.0D UNIVERSITY OF IBADAN LIBRARY 51 H. Reaction of 1 - chloro-2.4 -dinitrobenzene with n - Butylamine Cftlorqjfoqn: The wavelength used was 350 nyu and the slope of calitration curvo has 1, 5.548 x 10 noles per litre per unit optical density as above. The procedure for runs was the same as that above. Calculation of Rate Constants; The run concentration of the chloro compound in each case was 2.5 x 10"^M. The equation B(iii) is only applicable in cases when the concentration of the anine concentration was less or the same as the Substrate concentration, then a modification of B(iii) was employed. k2 = 1 . I * 2.5Q5 . 1 log O-D ̂. <- ÖD 0.5X - OD, B(iii) P f X-2 t 0.5X - 0Do O D ^ - OD̂ . where the Symbols still retain their usual significance. This modification would be ODj* m ÖD Y - ÖD k2 = 1 . I • 2s2£L log ge., X * ...H(i) P D 2(Y-0d^ t Y - o d c OD ^ - 0R£ where 0do in this case is the optical density corrosponding to half of the initial concentration of n-Butylamine going to Products and Y is the calculated optical density corresponding to conversion of all the chloro compound into products. I. Reaction of 1 - fluoro-2.4 -dinitrobenzene with R-Butylaaiae, in Chloroform. Wavelength used = 350 nyu Calibration curve used was the same as that for H. Slope UNIVERSITY OF IBADAN LIBRARY - „52. - = 5.546 x 10„ 3 moles per litre per unit optical density. Anine Concentration 0.0251*1 and 0.10M: These reactions were carried out in the cell compartment of the Gilford (2400) recording spectrophotometer. Amine concentratjons 0.20M up to l.,QCM The Gibson X>urrurd*s otoppcd - flow spectrophotometer was used. The dead time of the instrument was 2 m.sec. Optical Densities: The optical densities of each reaction at infinity were calculated fron the calibration curve. The experimental infinity optical densities in the runs were also obtained. Theoretical optical density at infinity is denoted OD calc. m Experimental optical density at infinity is denoted OD 0«' ex- periment. In cases where OD calculation were used, both vaiues were written. In cases where no 0Do experimental was obtained but inferred, then O D ^ calculated only were written. Calculation of linits of accuracv: 1. Por those rate constants calculated using the equation B(iii) or its modification H(i) the limit of error was simply the maximum deviation of any of the separate rate constants fron the average obtained. 2, Por the graphical determinations, the error of the slope may be calculated fron the scatter of the points by the formula Sg = (3 n *• 12) nR UNIVERSITY OF IBADAN LIBRARY .--53 - wfaore n = number of points w s= ränge of vertical scatter R = total ränge of the x coordinate between the first and last points of the graph. ss 2.303 x slope error in is then tho relative error calculated from above. where T bJ is concentration of amine in runj error in k2 is then the fractional or relative error calculated using the oquation (i). UNIVERSITY OF IBADAN LIBRARY - 54 - Calculation of Arrhenijis Parameters is made from the Arrhenius | j » equation k = B©” /RT. The activation energy E for a reaction ean be calculated fron the rate constants for the reaction at two different renperatures. Thus, if and kg are the two rate constants at kelvin tenperatures T^ and T^ respectively, then iog i - j l (Ta 8 kt 2.303R T1 T2 where R is the molar gas constant = 1.987 cal, gram mol ^. The pre-ezponential factor B can be calculated at any temperature T where E is known from the equation log k = log B - E 2.303 RT UNIVERSITY OF IBADAN LIBRARY 55 (a) kinbtic results. EKPERIMSHT 1 Reaction of 1 - fluoro - 2, 4 - dinitrobenzene xrilth Piperidine in the presence of piperidine hydrochloride in duy methanol at 29.6- + 0.05°C. Wavelength = 580 ryu Initnal Concentr tions: Piperidine 1.25 x 10»_2M Pluoro = 1.25 x 10“5M Pip. Hel. = 1.00 x 10r1^ O Do^c calc.=0.754 f = 25. OD GXpv•= 0.755 ( O D ^ - OD ) is expressed as optical density units at 500 cyu per 10 ml of reaction mixture after appropriate dilution. Rate constants are calculated on OD^oxperiaent. Tine (secs) ODoc- 0Dt 2 + log (OD^- 30 0.625 1.7945 90 0.476 1.6776 180 0.417 1.6201 240 0.589 1.5899 560 0.262 1.4183 480 0.225 1.3483 600 0.165 1.2175 750 0.129 1.1106 900 0.093 0.9685 of 2 + log (OD <»- OD.t ) versus ti.me in secs Kl = 2.11 x 10 = 9.17 + 0.5 x 10 = 1.69 + 0.09 x 10 1 litre mole~1sec~^ Duplicate kg = 1.65 ± 0.09 x 10 litre mole ^sec Mean k g = 1 .6 7 x 10_ 1 litre mole _■) sec_■] UNIVERSITY OF IBADAN LIBRARY - 56 - EXPERIHEHT 2 Reaction of 1 - fluoro - 2 , 4 - dinitrobenzene with Piperidine in the presence of piperidine Hydrochloride in dry methanol at - 29.6 + 0.05°C. Wavelength = 330 Initial Concentrations: Piperidine = 2.50 x 10 Pluoro 1.25 x 10“5M Pip. HCl 1.00 x 10“1M OD^calc. = 0.754 OD^expt. 0.755 f = 25. (ODo c. - OD.o) is expressed as optical density units at 330 m /ai per 10 nl of reaction mixture after appropriate dilution. Rate constants are calculated on 0I> OCexperinent. Tine (secs) OD oc - OD.t 2 + log OD - 15 0.594 1.7738 30 0.540 1.7324 45 0.440 1.6474 90 0.372 1.5705 180 0.238 1.3766 300 0.140 1.1644 450 0.090 0.9542 600 0.030 0.4771 Slope of 2 + log (OD — OD.) versus time in secs = 2.15 + 0.06 x 10-3 k, = 4.96 f I O ’3 kg' = 1.99+0.02 x 10 -1 litre mole -1 sec-1 Duplicate kg = 1.99+0.01 x 10“1 " " " Mean kg = 1.99 x 10_1 " " " UNIVERSITY OF IBADAN LIBRARY - 57 - EXFBRIiIEI'IT 3 Reaction of 1 - fluoro - 2 , 4 - diaitrobenzene with Piperidine in the presence of piperidine Hydrochloride in dry methanol at - 29.6 + 0.05°C. Wavelength = 380 myu Initial Concentrations j Piperidine 3.75 x 10-2M Fluoro 1.25 x 10“3M Pip. HCl 1.00 x IO”2!!. OD calc. = 0.754 OD QP cxp1t. = 0.755 f = 2 5 (OD^ - OD^) is expressed as optical deflaity units at 380 nyu per 10 ml of reaction raixture after appropriate dilution. Rate constants are calculated on ODQ_Pexperincnt. Time (secs) OD oe - OD.t 2 + log (OD^- 0Dt) 10 0.583 1.7657 30 0.507 1.7050 45 0.402 1.6042 60 0.350 1.5441 90 0.275 1.4393 150 0.194 1.2878 300 0.099 0.9956 450 0.060 0.7782 Slope of 2 + log (OD — 0D̂ _) versus time in secs = 3.63 + 0.41 x kj = 8.35 x 10 ^ k„ = 2.22 + 0.09 x 10 2 litre mole ^sec 2 Duplicate k2 = 2 . 2 2 + 0 . 0 8 x 1 0 -1 UNIVERSITY OF IBADAN LIBRARY - 58 - EXPERIMENT 4 Reaction of 1 - fluoro - 2, 4 ~ dinitrobenzene with Piperidine in the presence of piperidine Hydrochloride in dry methanol at - 29.6 + 0«05°C Wavelength = 380 ma/u. Initial Concentrations: Piperidine 4.40 x 10“^! Fluoro 1.25 x 10“'\ Pip. HCl 1.00 x 10" "S l OD^calc. = 0.755 ODC_Cexpt. = 0.748 f = 2 5 (OD^ - 0D̂ _) expressed as optical density units at 380 nyu per 10 ml of reaction mixture after appropriate dilution. Rate constants are calculated on OD experincnt. Tine (secs) OD oc.- OD.t 2 + log (OD oc- 5 0.648 1.8116 15 0.580 1.7634 30 0.458 1.6609 45 0.384 1.5843 60 0.330 1.5185 90 0.239 1.3734 180 0.130 1.1159 Slope of 2 + log (OD - OD.) versus time in sees = 5*651 ± kj = 1?30 x ^1 0-2 1 1 k2 = 2.96 + 0,01 x 10 litre mole sec Duplicate k2 = 3.20 + 0.03 x 10"1 " " " Mean k2 = 3.08 x 10“1 " " " UNIVERSITY OF IBADAN LIBRARY - 59 - EXPERIMENT 5 Reaction of 1 - fluoro - 2, 4 - dinitrobenzene with Piperidine in the presence of Piperidine Hydrochloride in dry methanol at - 29.6 + 0.05°C. Wavelength = 380 myu. Initial Concentrations: Piperidine = 4.75 x IO”2!-! F'luoro = 1.25 x 10"5M Pip. HCl = 1.00 x IO-3!! 01) occalc. = 0.754 OD^expt. = 0.755 f = 2 5 (OD^ *• OD^) is expressed as optical density units at 380 nyu per 10 ml of reaction mixture after appropriate dilution. Rate conatants are calculated on OD 0cexnerinent. Time (f3ecs) OD <80 - OD.t 1 + log (OD - ODt.) 5 0.625 0.7959 . io 0.529 0.7235 20 0.448 0.6513 50 0.394 0.5955 45 0.267 0.4265 60 0.248 0.3945 90 0.198 0.2967 180 0.142 0.1510 Slope of 1 + log (OD__ — OD.) versus time in secs = 9.29 + 1.4 x k1 = 2.13 x 10~> k2 = 4.46 + 0.01 x IO”1 litre mole^sec"1 Duplicate k2 = 4.38 + 0.01 x IO"1 11 !1 II Mean k2 ;>«= 4.42 x IO"1 »1. tl tt. UNIVERSITY OF IBADAN LIBRARY EXPERIMENT 6 Reaction of 1 - fluoro - 2, 4 - dinitrobenzene with Piperidine in the presence of Piperidine Hydrochloride in dry methanol at - 29.6 + 0.05°C. Wavelength = 380 nyu. Initial eonocntrcticns: Piperidine = 5.00 s 10 -2M Pluoro = 1.25 x 10 \ Pip. HCl = 1.00 x 10"^ OD^calc. = 0.755 OD expt. = 0.748 f = 2 5 ( 0 D ^ ‘- OD̂ . ) is expressed as optical density units at 380 nyu per 10 mls of reaction mixture after appropriate dilution. Rate constants are calculated on 00O_G_cxperinent. Time (secs) 00 9Q- 00,t. 1 + log (QD^ 5 0.591 0.7716 10 0.497 0.6964 15 0.452 0.6355 20 0.347 0.5410 25 0.324 0.5100 30 0.282 0.4500 40 0.258 0.4112 60 0.201 0.3010 90 0.111 0.0410 Slope of 1 + log (03^ - 0 0 versus time in secs = 1.441 + 0.113 x 1( kn * 3.33 x 10-2 k21 * 6.60 + 0.01 x 10- 1 litre mole -1 sec-1 Duplicate k2 =* 6.40 + 0.00 x 10"1 ,! » " Mean k2 =6.50 x IO-1 " " ” UNIVERSITY OF IBADAN LIBRARY - 61 - EXPERIMENT 7 Reactions of 1 - fluoro - 2, 4 - dinitrobenzene with Piperidine in dry oothanöl at - 29.6 + 0.05°C. Wavelength. = 380 cyu. Initial Concentrations: Piperidine = 1.25 x 10 Fluoro = 1.25 x 10-5M OD^ calc. » 0,755 ° öb 0Xpt* = 0.749 f = 2 5 (OD^ - OD^) is expressed as optical dencity units at 380 nyu per 10 mls of reaction mixture after appropriate dilution. Rate constants are calculated on OP experiment. e c te (secs) OD CK - ODt 2 + log (0D(OG 30 0.619 1.7917 90 0.469 1.6712 180 0.415 1.6180 240 0.381 1.5809 360 0.256 1.4082 480 0.217 1.3365 600 0.158 1.1987 900 0.085 0.9294 Slope of 2 + log (ODC G - ODt ) -zversus time in secs = 1.02+0.04 x 10k = 2.34 x 10"^ k12 <= 1.80 + 0.01 x 10 -1 litre mole -1 sec-1 Duplicate kg * 1.72 + 0.01 x 10~1 " " " Mean k2 =* 1.76 x 10“1 " " UNIVERSITY OF IBADAN LIBRARY - 62 - EXPERIMENT 8 Reaction of 1 - fluoro - 2, 4 - dinitrobenzene with Piperidine in dry methanol at - 29.6 + 0.05°C. Wavelength = 380 m^u. Initial Concentrations: Piperidine = 2.50 x 10 Sl Fluoro = 1.25 x 10"5M ODc o calc. = 0.755 ODC O expt. = 0.760 f = 2 5 (°Doc “ ° V is expressed as optical density units at 380 myu per 10 mls of reaction mixture after appropriate dilution. Rate constants are calculated on OD ouexperiment. Time (secs) OD oo- OD,t 2 + log (0D( 15 0.633 1.8014 30 0.603 1.7803 60 0.500 1.6990 90 0.447 1.6503 120 0.375 1.5740 180 0.279 1.4456 240 0.235 1.3711 300 0.155 1.1903 420 0.095 0. 977 Slope of 2 + log \0D^ - OD ) versus time in secs = 2.05 + 0, k., = 472 x 10 ^ k^1 * 1.88 +0.00 x 10 -1 litre mole -1s ec -1 Duplicate k2 = 1.96 + 0.01 x 10r 1 Me an 1.92 x 10,-i UNIVERSITY OF IBADAN LIBRARY - 63 - EXPERIMENT 9 Reaction of 1 - fluoro - 2,4 - dinitrobenzene with Piperidine in dry methanol at - 29.6 + 0.05°C. Wavelength = 380 myu. Initial Concentrations; Piperidine = 3.75 x 10 Fluoro 1.25 x 10 3M OD^calc. = 0.755 OD^expt. = 0.760 f = 2 5 (OD^ - OD^) exPresse< ̂as °pliQal density units at 380 myu per 10 mls of reaction mixture after appropriate dilution. Rate constants calculated on ODaß' exprerinent. Time (secs) ° V - 0Dt 2 + log (OD^ 10 0.552 1.7259 20 0.498 1.6972 30 0.474 1.6758 40 0.395 1.5968 60 0.340 1.5315 90 0.269 1.4298 120 0.195 1.2906 150 0.165 1.2175 240 0.090 0.9542 Slope of 2 + log (OD CSC - OD t ) -z versus time in secs = 3.683 +0.16 x 10 k. = 8.47 x 10 ^ = 2.26 + 0.03 x 10 litre mole sec Duplicate k2 = 2.35 ± 0.02 x 10“1 " " " Mean k2 = 2.30 x 10 M " " UNIVERSITY OF IBADAN LIBRARY ~ 64 ~ EXPERIMENT 10 Reaction of 1 - fluoro - 2, 4 - dinitrobenzene with Piperidine in dry methanol at - 29.6 + 0.05°C. Wavelength = 380 myu. Initial Concentrations: Piperidine = 4.40 x 10 Fluoro = 1.25 x 10"5M OD^calc. = 0.755 OD expt. = 0.750 f = 2 5 (OD^ - OD^) is expressed as optical deff-sity units at 380 m p e r 10 mls of reaction mixture after appropriate dilution. Rate constants are calculated on OD^experiment. ?ime (secs) ° v - 0I)t 1 + log (OD - QL 5 0.652 0.8142 10 0.628 0.7980 15 0.580 0.7634 20 0.542 0.7340 30 0.462 0.6646 45 0.379 0.5789 60 0.312 0.4942 90 0.245 0.3892 120 0.177 0.2355 180 0.120 0.0792 of 1 + log (OD Oö - OD.) versus time in secs = 6.11; kl = 12.80 x 10-^ k2 = 3.19 + 0.00 x 10 -1 litre mole-1sec-1 Duplicate *2 = 3.07 + 0.01 x io”-11 t! 1» t! Mean k2 = 3.13 x 10 1 tl I I UNIVERSITY OF IBADAN LIBRARY V vl - 65 - EXPERIMENT 11 Reaction of 1 - fluoro - 2, 4 - dinitrotenzene with Piperidine in dry methanol at - 29.6 + 0.05°C. Wavelength. = 380 myu. Initial Concentrations: Piperidine = 4.75 x 10 Fluoro = 1.25 x 10 M OD calc, = 0.754 OD O-'expt. = 0.749 f = 2 5 (OD CP_ - OD.v) . ' is expressed as optical density units at 380 m//u per 10 mls of reaction mixture after appropriate dilution. Rate constants are calculated on OD^experinent me (secs) 0D<*- ° v 1 + log (OD< 5 0.622 0.7938 10 0.529 0.7235 15 0.490 0.6902 20 0.448 0.6513 30 0.389 0.5899 45 0.267 0.4265 60 0.245 0.3892 90 0.190 0.2788 180 0.135 0.1303 Slope of 1 + log (qD ^ - OD^) versus tine in secs = 8.75 + 0.50x10 -3 k = 2.02 x 10"2 k„ = 4.24 + 0.00 x 10 litre mole sec Duplicate k^ = 4.09 + 0.01 x 10-1 Mean k2 = 4.17 x 10-1 UNIVERSITY OF IBADAN LIBRARY EXPERIMENT 12 Reaction of 1 - fluoro-2,4 - dinitrobenzene with Piperidine in dry nethanol at -29.6 + 0.05. ¥avelength = 380 nyu Initial Concentrations: Piperidine = 5.00 x 10“^ OD = 1.63 ,+ 0.08 x 10~2 litre mole -1 aec-1 Huplicate k 0 C.= 1.70 ± 0.05 x 10"2 " " ” Mean k^ = 1.6? x 10~2 litre; mole'*^sec""^ UNIVERSITY OF IBADAN LIBRARY §l - 68 r EXPERIMENT 14 Reaction of 1 - chloro -2, 4 - dinitrobenaene with Piperidine in the presence of Peridine Hydrochloride in dry methanol at + 30.2 + 0.05°C. Wavelength = 380 npi Initial Concentrations: Piperidine « 0.075M Chloro = 5 z 10~^M Pip. Hel = 1.00 x 10*”̂ M 05 o and “ 0Dt) are expressed as optical density units at 380 nyu per 5 nl of r< Lction nixture after appropriate dilution. Rate constants are calculated on 0 .D00 experinent. Tine (secs) 0.5X - OP̂ . ° V ° V k? x 10- 2 litreä nol, e -1 sec-1 0 2.577 0.643 - 300 2.480 0.547 1.61 600 2.396 0.462 1.68 900 2.338 0.404 1.59 1,500 2.231 0.297 1.64 2,400 2.122 0.189 1.67 3,300 2.060 0.126 1.66 5,100 1.993 0.058 1.64 Average ^2 == 1.64 ± 0.05 X 10“2 litre nole^sec“’*'Duplicate 1.62 ± 0.03 X IO“2 « «i ttk 2 Mean 1.63 X io“2 " tt ti^2 ~ UNIVERSITY OF IBADAN LIBRARY EXPERIMENT 20 Reaction of 1 - chloro - 2,4 - dinitrobenzene with Piperidine in dry nethanol at 30.2 + 0.05°C Vavelength = 380 ryu Initial Concentrations - Piperidine = 0.075M Chloro = 5 x 10"5M CDcc. calc. S 0.754 expt. = 0.750 F = 6.67 x IO"5 f SS 100 X = 11.31 (0.5X and (CD oz - OD.) are expressed as opticald ensity units at 380 npx per 5 nl of reaction nixture after appropriate dilution. Rate constants are caiculated on O P ^ j experinent. Tine (secs ) 0.5X - 0Dt ° V 0Dt k2 x io”2 : nole"1! 0 5.557 0.652 - 180 5.134 0.530 1.58 480 5.279 0.375 1.61 660 5.171 0.266 1.63 1,080 5.078 0.183 1.68 1,395 5.034 0.129 1.68 1,980 4.967 0.062 1.70 2,880 4.944 0.040 1.65 Average k2 = 1.65 + 0.07 x 10“2 litre nole'-1 sec-1 Duplicate 3s2 = 1.64 + 0.08 x 10~2 1? II i» Mean k2 = 1.65 x 10"2 II II II UNIVERSITY OF IBADAN LIBRARY -75 - EXPERIMENT 21 Reaction of 1 - chloro - 2,4 - dinitrobenzene with Piperidine in dry nethanol at + 30.2 + 0.05°C ¥avelength 380 ryu Initial Concentrations - Piperidine = 0.15CM Chloro = 5 x 1 0 - \ DD calc. = 0.754 0D0_^„. expt. = 0.748 F = 6.67 x 10"5 f = 100 X = 22.61 (0.5X - OD.t) and (OD ec* - OD,u). aro expressed as optical denöity units at 380 ryu per 5 nl of reaction mixture after appropriate dilution. Rate constants are calculated on O D ^ experinent. Sine (secs) 0.5X - OD,V ODO G- OD,t kL x ,1 0“-12 litre 2 nole sec-1 0 11.12 0.564 90 11.01 0.457 1.62 210 10.90 0.343 1.66 360 10.74 0.240 1.64 660 10.68 0.120 1.68 960 10.61 0.058 1.67 1,380 10.57 0.02C 1.63 Average kg = 1.65 ± 0.03 x 10- 2 litre nole -1 sec-1 Duplicate kn = 1.68 ± 0.04 x IO”2 " "■ » Moan 1$2 = 1.66 X 10“2 n n n UNIVERSITY OF IBADAN LIBRARY 16 EXPERIMENT 22 Peaction of 1 - chloro - 2, 5 - dinitrobenzene with Piperidine in dry nethanol at + 30.2 + 0.05°C Wavelength es 380 cyu Initial Concentrations - Piperidine = 0.300M Chloro = 5 x 10~5M ODC P calc. = 0.754 OD oc expi. = 0.748 P = 6.67 x 10“5 f « 100 X = 45.23 (0.51 - 0Dt) and (0Jpj -- OD^) are expressed as optical density units at 380 nyu per 5 Ql of roaction mixture after appropriate dilution. Rate constants arc caleulated on ODo c calculation. Tine (secs) 0.5X - oDt OD OC OD.t k2 x io“2 litre mol, e -1 sec-1 0 22.48 0.623 - 30 22.41 0.545 1.76 60 22; 36 0.494 1.74 90 22.26 0;399 1.76 150 22.16 0.304 1.78 210 22.07 0.212 1;69 270 22.02 0.157 1.75 330 21.96 0.103 1.72 390 21.93 0.076 (1.52) 450 21.91 0.052 1.78 Average « 1.75 ± 0.06 x 10- 2 litre mole -1a ec-1 Duplicate k^ = 1.73 + 0.05 x io“2 " " " Mean k^ = 1.74 x 10“2 nn. •n, t"i UNIVERSITY OF IBADAN LIBRARY - 77 - EXPERIMENT 25 Roaction of 1 - chloro - 2 , 4 - dinitrobenzene with Piperidine in iry methanol at + 50.2 + 0.05°C Vavelength = 580 iyu Initial Concentrations - Piperidine =, 0.60®! Chloro == 5 x 10~5M OB calc. = 0.754 CJE* OD expt. = 0.748 P = 6.67 x 10”5 f = 100 X = 90.46 (0.5X - 0Dt) and (OD - 0Dt) are expressed as optical density Ofc units at 580 nyu per 5 ml of reaction mixture after appropriate dilution. Rate constants are calculated on OD experiment. Q fc Tine (secs) 0.5X - ODt OD •» OD.t k 20 x 10 litreO 0 . , 1 nole’ sec" 0 45.04 0.557 - 5 45.00 0.521 1.92 10 44.95 0*484 1.98 20 44.91 0.445 1.95 50 44.80 0.526 1*95 80 44.71 0.251 1*96 110 44.62 0.159 1.94 170 44.54 0.670 1.94 Average k2 = 1.95 + 0.05 x 10"* litre nole“''sec-1 Duplicate kj> = 1.96 + 0.05 x IO"2 " Mean k2 = 1.96 x 10"2 tt» UNIVERSITY OF IBADAN LIBRARY 78 EXPERIMENT 24 Reaction of 1 - chloro -2,4- dinitrobenzene with Piperidine in dry methanol at + 30.2 ± 0.05°C Wavelength =3 380 ryu Initial Concentrations - Piperidine = 1.20M Chloro = 5 x 10~3M Ob calc. = 0.755 ObC a« expt. = 0.751 P = 6.67 x 10“3 f = 100 X «* 180.92 (0.5X - 0Dt) and 0I> 01 - QD.t are expressed as optical donsity unit; at 380 nyu per 5 ml of reaction nixture after appropriate dilution Rate constants are calculated on O D ^ experiment. Time (secs) 0.5X - QD. -2t °D0C- °Dt k2 x 10mol, litre e -1 sec-1 0 90.09 0.388 - 5 90.00 0.332 2;20 10 89.98 0.329 2.22 15 89.89 0.262 2;28 20 89.82 0.230 2.25 30 89.79 0.211 2.26 40 89.77 0.172 (2.42) 50 89.74 0.116 2.27 60 89.71 0.08Ö 2.29 Average = 2.25 + 0.05 x 10 litre mole -1sec-1 Duplicate lo> = 2.23 + 0.01 x io“2 " " !t. Mean k. = 2.24 x 10“2 " " II UNIVERSITY OF IBADAN LIBRARY EXPERIMENT 25 Reaction of 2 - chloro - 5 - nitropyridine with Piperidine in dry nethanol at 20.80 j; 0.05°C Wavelength = 370 ryu Initial Concentrations - Piperidine = 1.00 x 10-2M Chloro <= 5.00 x 10“5M ODq c ca-1-G • = 1.089 f = 400 < ° V - ® t> ia expressed as optical density units at 370 nyu per 5 nl of reaction mixture after appropriate dilution. Rate constants are calculated on 01) OL ealculation. Tine (nina) OD 0*L- OD,t 1 + log O D ^ - 0Dt 45 1.042 1.018 90 1.023 1.010 120 0.955 0.981 180 0.912 0^960 300 0.812 0.908 390 0.743 0.871 480 0.681 0.833 600 0.571 0.756 720 0.551 0.741 Slope of 1 + log (OD - OD.) versus time in secs - 6.943 + 0.44 x k~ = 1.60 x 10 3 kU, = 1.60 ± 0.00 x 10_ ■* litre molo «.isec Duplicate k 2 = 1.64 ± 0.00 x IO"*? » !» II Mean = 1.62 + 0.00 x IO**5 " ?» n UNIVERSITY OF IBADAN LIBRARY 80“ EXPERIMENT 26 Reaction of 2 - chloro - 5 nitropyridine with Piperidine in dry nethanol at 30.50 + 0.05°C Navelength = 370 nyu Initial Concentrations - Piperidine 1.00 x ltf^M Chloro 5.00 x 10**^ OD at oalc. = 1.089 f = 40 iß expressed as optical density units at 370 per 5 ml of reaction mixture after appropriate dilution. Rate constants are calculated on calculation. Time (nins) <*>*- ® t 1 + log O D ^ - ( 15 1.047 1.020 30 1.009 1.004 45 0.968 0.986 60 0.938 0.972 90 0.886 0.947 175 0.744 0.872 235 0.692 0.840 310 0.579 0.763 370 0.531 0.725 480 0.431 0.634 Slope of 1 + log (OB Ĝ -~ OBt ) vertrsus kLne in secs = 1.390 + 0.05 x 10 -5 k = 3.20 x 10 0 1 = 3.20 + 0.00 x 10- tJ lltre nole -1 sec-1 Duplicate k^ = 3.36 + 0.01 X 10~5 " " " Mean = 3.28 x IC”5 " " ” UNIVERSITY OF IBADAN LIBRARY - 8 t - 2fif5d2!i'UMENT 27 Reaction of 2 - chloro - 5 - nitropyridine with Piperidine in dry aethanol at 40.22 ± 0.05°C Vavelength = 370 nyu Initial Concentrations - Piperidine = 1.00 x IO“2!! Chloro = 5.00 x IO"3!! O D ^ calc. a 1.089 = 40 QD^ - 0D_j_ is expressed as opticc.1 denöity units at 370 nyu per 5 nl of reaction mixture after appropriate dilution. Rate constants are calculated on OD oc, eolculation. Time (mins) OD <*£.— QDX. 1 + log ODO C - ODt. 5 1.059 1.025 10 1.033 1 . 0 1 4 20 0.993 0.997 35 0.932 0.969 66 0.824 0.916 100 0.733 0.865 160 0.580 0.761 204 0.550 0.740 270 0.466 0.668 330 0.408 0.611 Slope of 1 + log (0D( - OD. ) vercusi- tine in secs = 2.710 ± 0.06 xo c t Iĉ = 6.24 x 10 ? ^2 = 6.24 + 0.00 x 10"3 litre mole"^sec~^ Duplicate kg = 6.39 + 0.00 x 10"3 ff ii n Mean b 6.32 x ° * 0 0 x 10“3 ff B II UNIVERSITY OF IBADAN LIBRARY 8 2 Reaction of 2 - chloro - 5 nitropyridine with Pipcridine in dry nethanol at 50.55 + 0.05°C Wavelength = 370 nyu Initial Concentrations - Piperidine = 1.00 x 10*"Sl Chloro = 5.00 x 10~5M 0I)c& 09,10• ~ 1,089 f = 4 0 (OD - OD^) is expressod as optical density units at 380 n per 5 nl of reaction mixture after appropriate dilution. Rate constants are calculated on OD CK- calculation. Timo (nins) ° V - 0Dt 1 + log OD OB- 01 5 1.044 1.019 10 0.995 0.998 15 0.953 0.979 20 0.912 0.960 30 0*843 0.926 45 0.747 0.873 60 0.681 0.853 90 0.563 0.751 120 0.481 0.682 Slope of 1 + log (CO oc - OD.t) ve~rmis time in eecs = 5.426 k- = 12.5 x 10*° kg = 12.5 ± 0.0 s io-5 litre mole^sec"1 Duplicate k„ = 12.1 ± 0.0 X 10~3 !f fl II Mean =12.3 X IO*""5 n ii it UNIVERSITY OF IBADAN LIBRARY EXPERIMENT 29 Peaction of 1 - fluoro - 2,4 - dinitroben2ene with Pipcridine in dry acetone at + 30.0 + 0.05°C Vavelength = 380 npx Initial Concentrations - Piperidine = 7.97 x 10“% Pluoro 1.00 x 10“5M ODcc 0.880 (OD - OP.) is expreosed as optical density units per 2.51 ml of the reaction nixture. Tine (seca) ° V - 0Dt 2 + log ( O D ^ - 0Dt) 96 0.730 1.8633 168 0.636 1.7993 264 0.530 1.7243 408 0.410 1.6128 504 0.330 1.5185 600 0.280 1.4472 768 0.210 1.3222 954 0.150 1.1761 1,390 0.080 0.9031 Slope of 2 + log (ODo * - OD.t) versus tine in secs = 7.69 —+ 0.15 x 10 *1 = 1.77 x 10"5 k2 *= 22*0 + 0.8 litre mole~^sec~^ Duplicate = 22,0 + 0 . 8 " •i t. Mean k>> = 22.0 + 11 M tt UNIVERSITY OF IBADAN LIBRARY - 84' EXPERIMENT 30 P.eaction of 1 ~ fluoro - 2,4 - dinitrobenzene with Piperidine in dry acetone at + 30.0 + 0.05°C Vavelength = 380 ryu Initial Concentrations - Piperidine « 1.594 x IO“4* Fluoro = 1.00 x IO"5!-! OD = 0.890 OK (OD Of - CH)t. ) ia expressed as opticai density units at 380 m//u per 2.51 nl of reaction nixture. Tine (secs) OD o* - OD,t 1 + log OD05 25 0.74 1.8693 50 0.67 1.8265 60 0.63 1.7993 70 0.59 1.7709 120 0.51 1.7076 170 0.41 1.6128 240 0.31 1.4914 340 0.22 1.3424 480 0.13 1 . 1 1 3 9 625 0.08 0.7782 Graph of 1 + log (OD^ - CtD̂ ) versus tine in secs = 1.77 x 10“^ + 0.05 *1 = 4.08 x 10“° = 24.30 ± 1.2 litre nole*"^sec”^ Duplicate = 24.00 ± 1.2 11 ir 11 Mean k2 = 24.2 + 1.2 11 11 n UNIVERSITY OF IBADAN LIBRARY - 85 - EXPERIMENT 31 Reaction of 1 - fluoro - 2,4 - dinitrobenzene vrith Piperidine in dry acetone at + 30.0 + 0.05°C Wavelength = 380 nyu Initial Concentrations - Piperidine = 2.446 x k T S i Fluoro = 1.00 x 10**^ OD Ob = 0.900 (OD^ - 01t) is expressed as optical density units at 380 cyu per 2.51 ml of reaction mixture. Time (secs) ODa u. - OD.t log O D ^ - 15 79 1.8976 30 71 1.8513 55 61 1.7853 70 55 1.7404 100 46 1.6628 130 39 1.5911 180 30 1.4771 245 22 1.3424 295 18 1.2553 345 15 1.1761 Slope of 1 + log (OD^ - OD^) versus time in secs = 2,80 x 10• •3 + 0.07 ki. = 6.45 x 10~5 kg = 27.00 + 1.3 litre aolo aec Duplicate kg = 27.0 jb 0.9 " ” " Mean kg = 27.0 » " » UNIVERSITY OF IBADAN LIBRARY - 36 - EXPERIMENT 32 Reaction of 1 - fluoro - 2,4 - dinitrobenzene with Piperidine in dry acetone at 30.0 + 0.05°C Wavelength = 380 npx Initial Concentrations - Piperidine == 31..01081 x io10“*"̂ M Fluoro x 5k 0Doc- “ °*840 (OD oc - OD,t ) is expressed as optical density units at 380 m//u. per 2.51 ml of reaction mixture. Time (secs) ° V * 0I)t 1 + log OD oe - 20 0.610 1.7853 40 0.510 1.7076 55 0.420 1.6232 75 0.350 1.5441 95 0.280 1.4472 125 0.210 1.3222 175 0.140 1.1461 270 0.070 0.8451 *Z Slope of 1 + log (OD Qk - OD."C) versus time in sece = 4.21 + 0.11 x 10~^ kj. = 9.70 x 10“3 k-, = 30.1 + 0.08 litre mole -1 gec-1 Duplicate = 2 9 . 9 + 0 . 0 4 Mean k̂ =30.0 tt *T II UNIVERSITY OF IBADAN LIBRARY EXPERIMENT 53 Reaction of 1 - fluoro - 2, 4 - dinitrobenzene with Piperidine in dry acetone at 30,0 + 0.05°C. Wavelength = 380 m /u. Initial Concentrations: Piperidine = 3.984 x 10"4M Fluoro =1.00 x io“5m OD = 0.87 (OD o» - OD t) is expressed as optical density units at 380 myu per 2.51 ml of reaction mixture Tine (secs) OD OK - OD.t log (OD oc - ODtj 5 0.63 1.7993 20 0.54 1.7324 30 0.47 1.6721 40 0.40 1.6021 65 0.30 1.4771 95 0.21 1.3222 125 0.15 1.1761 160 0.10 1.0000 Slope of log (OD 06 ~ CDt.) versus time in secs = 5«373 +0.12 x 10 kx = 1.24 x IO-1 k2 = 31.0 + 0.5 litre molG -1 sec-1 Duplicate = 31.0 + 0.5 litre ti t» Mean k„ - 31.0 II Jf 1! UNIVERSITY OF IBADAN LIBRARY - 88 - EXPERIMENT 54 Reaction of 1 - fluoro - 2, 4 - dinitrobonzene with Piperidine in dry acetone at + 30.0 + 0.05°C. Wavelength = 380 myu. Initial Concentrations: Piperidine = 4.781 x 10- 4M Fluoro = 1.00 x 10 _5M OB O* = 0.87 oe OB^) is expressed as optical density units at 380 m /u per of reaction mixture. Time (secs) OB oc- OB t 1 + log (OB - OB OP t) 10 0.58 1.7634 20 0.51 1.7076 30 0.44 1.6435 40 0.37 1.5682 60 0.28 1.4472 80 0.21 1.3222 100 0.15 1.1761 125 0.11 1.0414 160 0.07 0.8151 1 + log (OD 0® - OBt.) . versus time in secs == 6.613 + 0.31 x >-3 kx = 1.54 x 10'-2 k„ 8 ‘8 8 -9 4 - EXPERIMENT 40 Reaction of 1 - fluoro - 2, 4 - dinitrobenzene with Piperidine in dry acetone at 30.0 + 0.05°C. Wavelength. = 380 m/u. Initial Concentrations: Piperidine = 1.25 x 10- 3M Fluoro = 1.00 x 10“5M OD o<* = 0.78 (ÖD oa - QDt. ) is expressed as optical density units at 380 m/'u 2.51 ml Of reaction mixture. Time (secs) 0Doe * 0Dt 1 + log (OD< 5 0.33 1.5185 15 0.25 1.3979 20 0.16 1.2041 25 0.12 1.0792 30 0.09 0.9542 60 0.03 0.4771 Slope of 1 + log (oD - OD t) versus time in secs = 2.27 + 0.21 x 10 -2 dt k2 = 5.22 x 10~2 k„ = 41.7 + 0.2 litre nole**^sec"’̂' Duplicate = 42,1 +0.1 Mean k2 = 42 .0 UNIVERSITY OF IBADAN LIBRARY 95 EXPERIMENT 41 Reaction of 1 - fluoro - 2, 4 - dinitrobenzene with. Piperidine in dry acetone at 30.0 + 0.05°C. Wavelength = 380 n/u, Initial Concentrations: Piperidine = 2.00 x 10 _3M Fluoro = 1.00 x 10"5M OD QKS = 0.85 (ÖD oc OD.t) is expressed as optical density units at 380 m>/u per 2.51 ml. of reaction :>ixture. Time (secs) OD «. - ÖD.t 1 + log (ODeo ■ ® t > 6 0.27 1.4314 9 0.20 1.3010 12 0.15 1.1761 18 0.09 0.9542 30 0.04 0.6021 Slope of 1 + log (OD^ «• OD X) versus time in secs = 4.00 + 0. 27 x IO" = 9.21 x 10"2 k2 = 46.2 + 0.4 litre mole’̂ sec'’’1' Duplicate k2 = 46.8 + 0.3 " " " Mean k2 =» 46.5 tt H II UNIVERSITY OF IBADAN LIBRARY - 9 6 - EXPERIMENT 42 Reaction of 1 - chloro - 2, 4 - dinitrobenzene with Piperidine in dry acetone at + 50 _+ 0.05°C. Wavelength. = 380 n zu. Initial Concentrations; Piperidine = 0,0105 M Chloro = 5 x 10“5M OD4 ja •al'i. = 0.733 OD (V expt. = 0.733 F = 6.878 x IO*"5 f 100 X = 1.552 ( O D ^ - 0Dt) and (0.5 x -.OD^) are expressed as optical density units at 380 n p e r 5 ml of reaction nixtu.re after appropriate dilution. Rate constants are calculated on ODO ttoxporicent. Tine (secs) 0.5 x - 0 OD^- QDt k2 x IO"”’1' nole"'*'sec’"̂ 0 0.4990 0.456 - 120 0.3650 0.322 (5.010) 240 0.3050 0.262 4.37 360 0.2590 0.216 4.33 480 0.2370 0.194 (3.91) 720 0.2240 0.181 (3.68) 960 0.1670 0.124 4.22 1,200 0.1240 0,081 4.29 1,440 0.1150 0.072 4.48 1,740 0.1050 0.062 4.48 1,980 0.093 0.050 4.56 2,280 0.089 0.046 4.36 Average = 4.40 +0.16 x 10“1 litre nole”*^sec’-1 Duplicate kQ = 4.31 + 0.09 x 10"1 tr n ii Me an = 4.36 x IO“1 litre nole^sec*-1 UNIVERSITY OF IBADAN LIBRARY ** i05T̂ r EXPERIMENT 43 Reaction of 1 - chloro - 2, 4 - dinitrobenzene with Piperidine in dry acetone at + 30 + 0.05°C. Wavelength - 380 nyu. Initial Concentrations: Piperidine = 0.015M Chloro = 5 x 10”% OD Oc calc. = 0.733 OD expt. = 0.735 F = 6.878 x io”5 f = 100 X = 2.240 (0.5 x - OD.t) and (OD.o c - OD.X) are expressed as optical density units at 380 m/u por ml of reaction mixture after appropriate dilution. Rate constants are calculated on OD eacperinent. Time (secs) 0.5X - OD k2 X 10“^litro mole”% e c 0 0.981 0.596 - 30 0*884 0.499 4.65 60 0.809 0.423 4;79 90 0.746 0.361 4.82 150 0.666 0.281 4.63 210 0.607 0.222 4.60 330 0.522 0.137 4.84 450 0.485 0.100 4.67 570 0.460 0.075 4.40 Average = 4.61 +, 0.22 x 10"1 litre mole^sec“1 Duplicate = 4.87 ± 0.21 x 10"1 II t! 1! Mean = 4.76 x 10”1 !t ft II UNIVERSITY OF IBADAN LIBRARY EXPERIMENT 44 Reaction of 1 - chloro - 2, 4 - dinitrobenzene with Piperidine in dry acetone at +30 ,+ 0.05°C. Wavelength = 380 cyu. Initial Concentrations: Piperidino = 0.020M Chloro = 5 x 10' 05 oc calc. = 0.733 &> expt. = 0.742 P = 6.878 x 10“5 f 100 X = 3.056 (0.5X - GDt) and (QD Ul - Oh,v) are expressed as optical density units at 380 nyu per 5 ml of reaction mixture ,after appropriate dilution. Rate constants are calculated on OD^expcrinent. Tine (secs ) 0.5X - Qht kg x 10”^ litre mole 0 1.389 0.634 - 15 1.317 0.541 5.18 45 1.194 0.408 (5.54) 75 1.106 0.320 5.39 105 1.053 . 0.267 5.02 135 0.996 0.210 5.19 165 0.956 0.170 5.21 225 0.902 0.116 5.16 285 0.864 0.070 5.23 Average kg * 5.24 + 0.12 x 10"'*' litra mole-1 sec-1 Duplicate kg * 5.19 + 0.08 x io“1 " » !> Mean kp = fi. 22 x 10"^ IStra mole'-1 sec-1 UNIVERSITY OF IBADAN LIBRARY EXPERIMENT 45 Reaction of 1 - chloro - 2, 4 - dinitrobenzene wit& Piperidine in dry acetöne at +30 + 0.05°C. Wavelength = 380 nyu. Initial Concentrations: Piperidine = 0.026M Chloro = 5 z 10“5M OD ne. calc. = 0.733 QD ec exprt. = 0.730 P = 6.878 x IO“5 f 100 X = 3.939 (o.5X - 0Dt) iand (OD - CD.) are expressed as optical density units at 380 nyu per 5 ml of reaction mixture after appropriate dilution. Rate constants are calculated on QD oxperinerrt. Tine (secs) 0.5X - 0Dt OD< rc — 'OD t k20 = IO“1 litre moje^sec 0 1.861 0.622 10 1.756 0.516 (7.49) 20 1.714 0.474 5.54 30 1.658 0.415 5.62 50 1.563 0.526 5.57 70 1.495 0.255 5.51 100 1.420 0.181 5.52 130 1.389 0.148 5.46 170 1.352 0.112 5.48 Average k^ = 5.57 + 0.11 x 10**̂ litre nole^sec-^ Duplicate k2 = 5.41 ± 0.10 x 10- 1 litre mole -1 sec-1 Mean k^ = 5.49 .x 10-^ litre mole”^sec~‘̂ UNIVERSITY OF IBADAN LIBRARY -100 - EXPERIMENT 46 Reaction of 1 - chloro - 2, 4 - dinitrobenzene with Piperidine in dry acetone at +50 +. 0.05°C. Wavelength = 580 m/u. Initial Concentrations: Piperidine = 0.050M Chloro = 5 x 10“^M OD ’ calc. = 0.755 O L . OD expt. = 0.755 F = 6.878 x 10"5 o c f = 100 X = 4.450 (0.5X - ÖD.t) and (OD - OD.t) are expressod as optical density 06 units at 580 n/u per 5 nl of reaction nixture after appropriate dilution. Rate constants are ealculated on OD öüoxporinent. Time (sees) 0.5X - 0Di QD m. * ODt. k2 x 10-1 litre mole” '̂sec"’* 0 2.121 0,651 10 2.029 0.559 5.66 20 1.961 0.471 5.64 50 1.891 0.401 5.67 40 1,855 0.544 5.62 50 1.784 0.299 5.67 65 1.759 0.249 5.70 80 1.695 0.207 5.62 95 1.655 0.165 5.58 Average Iĉ 5.64 + 0.06 x 10"1 litre mol. e -1 sec-1 Duplicate k2 5.72 + 0.08 x 10”1 litre cole”^sec Mean k2 5.68 x 10“^ litre nole’̂ sec UNIVERSITY OF IBADAN LIBRARY - 101 - EXPERIMENT 47 Reaction of 1 - chloro - 2, 4 - dinitrobenzene with Piperidine in dry acetone at +30 + 0,05°C. Wavelength = 380 m yu. Initial Concentrations % Piperidine = 0.035M Chloro = 5 x 10"~^M OC oc calc. = 0.733 OD expt. = 0.735 P = 6.878 x 10~5 Q m f = 100 X = 5.212 (0.5X - OdJt and (OD Qß - OD^) are expressed as optical density units at 380 myu per 5 ml. of reaction mixture after appropriate dilution. Rate constantsare calculated on OD^cxperinent. Time (secs ) 0.5X - ODt.. OD -1 -l _i OD » CD.t k2 x 10 litre mole sec 0 2.556 0.685 - 5 2.473 0.602 (7.68) 15 2.377 0.508 5.87 25 2.272 0.401 5.85 35 2.222 0.351 5.84 45 2.183 0.312 5.80 55 2.111 0.241 5.81 65 2.080 0.209 5.79 75 2.048 0.178 5.86 Average k2 = 5.83 + 0.06-x 10”1 litre nolc"■1 ooc-1 Duplicate = 5.87 + 0.01 3? IO”1 litre mole’■1 sec-1 Mean = 5.85 x 10 ^ litre mole ^sec”'*' UNIVERSITY OF IBADAN LIBRARY 102 - EXPERIMENT 48 Reaction of 1 - fluoro - 2, 4 - dinitrobenzene with N - Butylamine in dry acetone at 24.82 + 0.01°C. Wavelength = 350 nyu. Initial Concentrations: n - Butylamine = 5 x 10“4li Fluoro = 5 x 10”5M Cbo c* = 0.895 (OD^ - OD^) is expressed as optical density units at 350 reaction nixture. Time (mins) OD aß. - OD t 1 + log (ODflc 20 0.796 0.901 60 0.758 0.880 120 0.729 0.863 180 0.682 0.837 240 0.644 0.809 300 0.610 0.786 360 0.580 0.764 420 0.542 0.734 480 0.513 0.710 Slope of 1 + log ( QD OG - 0D_j_) versus time in secs = 6.75 : k2 - 1.55 x 10- 53 k? = 3.11 + 0.00 x 10~2 litre mole"’1sec""'1" Buplicate k„ = 3.21 + 0.00 x 10 2 litre ELole~4sec~4 Mean k2 = 3.17 x 10 2 litre jaole~1sec~1 UNIVERSITY OF IBADAN LIBRARY - 103 - EXPERIMENT 49 Reaction of 1 - fluoro - 2, 4 - dinitro'benzene with n - Butylamine in dry acetone at +24.32 + 0.01°C. Wavelength = 350 myu. Initial Concentrations; n - Butylamine = 10- 31 Eluoro = 5 x 10 = 0.895 (OD Oo - OD.t) is expressed as optical density units at 350 m/.u of reaction mixture. Time (mins) OD Ol - OD,t 1 log (0DÄ - 15 0.667 0.824 30 0.643 0.808 60 0.603 0.780 90 0.570 0.756 120 0.537 0.730 180 0.450 0.654 240 0.417 0.620 300 0.366 0.564 Slope of 1 + log (OD - OD.) versus time in secs = 1.52 + 0.11 x 10-5 CK. k1 = 3.50 x 10“ kg - 3.50 + 0.00 x 10 -2 litre mole -1 sec-1 Duplicate kg - 3.58 + 0.00 x 10 -2 litre mole -1 sec -1 Me an k0 =3.3.5544 x 10“2 litre mole ^sec ^ UNIVERSITY OF IBADAN LIBRARY 104 - EXPERIMEM1 50 Reaction of 1 - fluoro - 2,4 - dinitrobenzene with n - Butylanine in dry acetone at + 24.8 + 0.01°C Wavelength = 350 nyu Initial Concentrations - n - Butylamine = 2,5 x 10 -3M Fluoro ss 5 X 10~5M OD = 0.895 (0Dk - 0Dt) is expressed as optical density units at 350 m reaction mixture. Tine (nins) ° v - 0Bt 2 + log (OD^ - OD^) 10 0.570 1.756 20 0.520 1.716 40 0.458 1.661 60 0.421 1.624 90 0.356 1.550 120 0.300 1.477 180 0.219 1.341 240 0.150 1.176 300 0.110 1.041 360 0.084 0.905 Slope of 1 + log (ob OC - OD",Ü) /ersus time in secs = 4.08 + 0.02 x 10 -5 = 9.40 x 10r5 k2 =s 3.76 + 0.00 x 10- 2 litre mole -1 sec-1 Duplicate kX 3.89 + 0.00 x 10-2 Mean ko = 3.82 x 10 n ii ii UNIVERSITY OF IBADAN LIBRARY -;o5 -- EXPERIMENT 51 Reaction of 1 - fluoro - 2, 4 - dinitrobenzene with n - Butylamine in dry acetone at 24.82 + 0.01°C Wavelength = 350 nyu Initial Concentrations - n - Butylamine = 5 x 10 Fluro = 5 x 10’ 0Doe = °*895 (OD - OB.) is expressed as optical density units at 350 n^u of reaction nixture. Tine (mins) OB m - OB.t 2 + log (OB - OBX.) 5 0.747 1.8733 10 0.672 1.8274 15 0.590 1.771 30 0*507 1.705 45 0.415 1.618 60 0.330 1.519 75 0.290 1.462 90 0.235 1.371 120 0.160 1.204 150 0.110 1.041 180 0.090 0.954 Slope of 2 + log (OB QC - ° V versus time in secs = 9.29 + 0.5 x k^ = 2.14 x 10J ' kg = 4.28 + 0.00 x IO“2 litre nol, e -1 sec-1 Duplicate kg =4.16 0.00 x 10~2 » i! n Mean kg =4.22 x 10~2 « t* ti UNIVERSITY OF IBADAN LIBRARY 106 - EXPERIMENT 52 Reaction of 1 - fluoro - 2,4 - dinitrobenzene with n - Butylamine in dry acetonc at 24.82 + 0.01 C Wavelength = 350 ryu Initial Concentrations - n - Butylamine = 10"^ Fluoro = 5 x 10“^1 OB oc = 0.895 (OB - OB ) is expressed as optical density units at 350 m/u of oc ^ ' reaction mixture. Time (mins) OB OK.- OB,t 2 + log (OD^ - 0Dt) 5 0.565 1.752 10 0.490 1.690 15 0.422 1.625 20 0.360 1.556 25 0.320 1.505 30 0.260 1.415 40 0.200 1.301 50 0.150 1.176 60 0.115 1.061 75 0.085 0.924 Slope of 2 + log (OB aC- — OB.t) versus time in secs =2.3 k 2 = 4.91 x 10“4 kg = 4.91 + 0.00 x IO“ litre mole sec Duplicate kg « 4.80 ± 0.00 x: IO"2 » " 11 Mean kg = 4.86 x 10”2 " " II UNIVERSITY OF IBADAN LIBRARY 107*- ESCPERIMI3CT. _ 33. Reaction of 1 - fluoro - 2, 4 - dinitrobenzene with n - Butylanine in dry acetone at 24.82 + 0.01°C Wavelength = 350 mpx Initial Conccntiations - n - Butylamino = 5 s IO*“2!'! Fluoro = 5 x 10*"% OB OC' - 0.895 (OD^.- OD^) is expressed as optical density pnits at 350 ryu of reaction mixture. > (secs) OD (X, - OD t 1 + log (ODoc 0 0.754 0.877 60 0.654 0.816 120 0.565 0.752 180 0.482 0.686 240 0.408 0.618 300 0.348 0.550 360 0.301 0.480 420 0.208 0.332 540 0.182 0.260 600 0.150 0.190 660 0.128 0.114 mJT Slope of 1 + log1 (OD OL - OD.T) versus time in secs = 1.17 + 0.01 x 10 kj_ = 2.69 x 10“5 k2 ss 5.37 i 0.00 x 10- 2 litre mole -1sec Duplicate *2 = 5.67 + 0.00 x IO-2 " " " Mean kg = 5.52 x 10“2 " » " UNIVERSITY OF IBADAN LIBRARY -> 108 BXPERIMEHT 54 Eaecsxor. of 1 - fluoro - 2, 4 - dinitrobenzene with n - Butylanine : ciry aeeione at 24.82 + 0.01°C Wav ;lv af'th = 350 nyu ln: vinl Ooncentrations - n - Butylanine = 10**^M Fluoro = 5 x lO“*5^ OD 0= = 0.895 (0. OC - OD TT) is expressed as optical density units at 350 nyu of r-saeiaon mixture. Tine (secs) ODOC- ~ ÖD.t 1 + log (OD GO- -ODt.) 0 0.750 0.875 50 0.595 0.775 60 0.470 0.672 90 0.370 0.574 120 0.300 0.477 150 0.244 Qw3S7 180 0.200 0.301 210 0.170 0.230 240 0.142 0.152 270 0.123 0.086 300 0.108 0.033 'JA C sz ,f 1 + log (qBo o - OD.) versus time in secs = 3.16 + 0.09 x 10"r l kx = 7.28 x 10"3 k> *= 7.28 + 0.00 y; 10 o litre mole« ■! sec—1 J> ulcafce kg - 7.12 + 0.00 ,'x 10,#-2 Mean kg = 7.20 x 10 UNIVERSITY OF IBADAN LIBRARY ~ 3 P 9 - EXPERIMENT 55 Reaction of 1 - fluoro - 2, 4 - dinitrobenzene with n — Butylanine dry acetone at 24.82 ± 0,01°C Wavclength = 350 nyu Initial Concentrations - n - Butylanine = 2 x IO“1! Fluoro = 5.0 x 10“% 0J)oe " ° ’895 (OD^ — OD^) is expreß.sed as optical density units at 350 cyu of reaction mixture. Tine (secs) ° v - 1 + log OD. 0 0.570 0.756 3 0.550 0.740 6 0.505 0.703 9 0.458 0*661 12 *0.410 0.613 18 .... 0.340 .:Ll 0.532 24 0.27 5 0.439 30 0.224 0.350 42 . . , 0.148 0.170 54 0.100 0.000 Slope of 1 + log (OD - ÖD.) -versus time in secs = 1.47 + 0.04 x IO"* ©G "C k1 = 3.39 x IO“2 ■ ̂ 2 = 1.69 + 0.00 x 10— 1 litre nole —1 sec— l Duplicate k 2 = 1.56 + 0.00 x IO*“1 " " " Mean k2 =» 1.63 x 10 f! I! II UNIVERSITY OF IBADAN LIBRARY . oo.*- EXPERIMENT 56 Reaction of 1 - fluoro - 2, 4 - dinitrobenzene with n - Butylanine in diy acetone at 24.82 £ 0.01°C Wavelength = 350 m Initial Concentrations - n ~ Butylamine = 3 x 10“1!! Fluoro = 5 z 10“% OD ®s> - 0.895 (OD (jo - ÖDx,) is expressed as optical density units at 350 of reaction nixture. Time (secs) OD oc - OD t 2 + log (OD^ 3 0.350 1.544 6 0.290 1.462 9 0.235 1.371 12 0.195 1.290 15 0.160 1.204 18 0.130 1.114 21 0.115 1.061 24 0.095 0.978 27 0.085 0.903 30 0.065 0.813 33 0.056 0.748 log (öD , - 00.t)p versus time in secs = ; fcj_ «= 6.72 x X O k2 = 2.24 ± 0,02 x IO**1 litre mol. e- isec Duplicate = 2.19 i 0.01 x lCrl " I» 1! Mean fl*2 «2.21 X IO"1 " ft UNIVERSITY OF IBADAN LIBRARY -111 - EXPERIMENT 57 Reaction of 1 - fluoro - 2, 4 - dinitrobenzene with n - Butylamine in dry acetone at 24.82 + 0.01°C Wavelength = 350 m/U Initial Concentrations - n - Butylamine = 4 J 10~^M Fluoro = 5 x 10" *5K OD^ =0.895 (OD Oc - OD.t) ' is expressed as optical density units at 350 n//u of reaction mixture. Tine (secs0 OB OC - OB,t 2 + log OD «3P — 5 0.220 1.342 6 0.180 1.255 9 0.130 1.114 12 0.100 1.100 15 0.070 0.845 18 0.054 0.732 21 0.040 0.602 24 0.028 0.447 27 0.020 0.301 30 0.015 0.176 Slope of 2 + log (OD OG- - OD V), versus time in secs = 4.52 + 0.15 x 10 •2 kl = 1.04 x 10“2 R>> = 2.60 ± 0,00 x IO”1 litye nole ^sec ^ Duplicate *2 = 2.66 ± 0.00 x 10“1 tl II 1» Mean *2 = 2.63 x 10"1 n ii, ii UNIVERSITY OF IBADAN LIBRARY 112 - EXPERIMENT . _5S Reaction of 1 - chloro - 2, 4 - dinitrobenzene with n - Butylamine in dry acetone at + 30°C Wavelength = 350 nyu Initial Concentrations - n - Butylaraine = 10 %1 Chloro = 2 x 10“%! OD calc. =3.63 6 P = 5. 548 x 10”3 f = 2 5 X = 14.54 (OD Oct - O Dt;.) and (0.5X -■ OD ) are expressed as optical densityt units at 350 nyu per 5 ml of reaction mixture after appropriate dilution. Rate constants are calculated on OD calculation. Time (nins) 0. 5X - 0Dt OD - OB.t kP x 10- 5litre mol, e -1 sec-1 0 14.50 3.546 •- 90 14.43 3.523 2.77 180 14.41 3.499 2 . 7 7 300 14.36 3.4 66 2.86 420 14.35 3.447 2.62 540 14.32 3.420 2.63 660 14.30 3.396 2.62 1,440 14.12 3.218 2.80 1,920 14.03 3.124 2.71 • Average kg> = 2.72 + 0,10 x 10- 7 litre mole -1 sec-1 Duplicate kg = 2.73 + 0.08 x 10“5 ff 13. !1 Mean kg = 2.73 x IO”5 t? !» ft UNIVERSITY OF IBADAN LIBRARY - 113 - EXPERIMENT 59 Reaction of 1 - chloro - 2, 4 - dinitrobenzonc with n - Butylaminc in dry acetone at + 30° C Wavelength = 380 ryu Initial Concentrations - n - Butylamine = 5 x 10” -1M Chloro — 2 x 1CT*T/L O D ^ calc. » 3,636 P = 5.548 x 10"*5 f = 100 X = 9.09 (0.5X ** OD^) and (OD^ - OD^) are expressed as optical density units at 350 m/u per 5 ml of reaction mixture after appropriatc dilution. Rate constants are calculated on OD (P calculation. Tine (nins) 0. 5X - QDt OD 00- OD.t k - 6.97 ± 0.10 x ; .0“^ 11 lt U Mean k2 =6,95 x l O ••5 *r n i! UNIVERSITY OF IBADAN LIBRARY - 114 EXPERIMENT 60 Reaction of 1 - chloro - 2,4 - cinitrobemrene with n - Butylamine in dry acetone at + 30°C ¥avelength = 380 nyu Initial Concentrations - n - Butylamine = 1.0 x 10**^M Chloro = 2 x 10-2M OB oc calc. = 3.636 F = 5.548 x 10"5 f = 100 X = 18.180 (0.5X - OB.x ) and (OD■ o*» - OB.t) are expresscd as optical density units at 350 m/u per 5 ml of reaction mixture after appropriate dilution. Rate constants are calculated on OB calculation. Tine (nins) 0.5X - OB, «4t OB Dö- OB t ko^ x 10 - litrcmole 1se-c1 0 8.995 3.541 -- 10 8.971 3.516 1.22 15 8.954 3.501 1.24 30 8.915 3.461 1,28 55 8.820 3.367 1.28 85 8.772 3.317 1.27 145 8.572 3.127 (1.44) 205 8.494 3.040 1.24 295 8.335 2.881 1.26 415 8.116 2.655 1;22 595 7.819 2.356 1.24 Average kj> = 1.25 ± 0.03 x IO“4 litre mole”"̂ sec'*̂ Buplicate ^ - 1,24 + 0.05 x 10"4 11 11 n Mean lo> = 1.25 x 10“ ' IT II II UNIVERSITY OF IBADAN LIBRARY - Uß - EXPERIMENT 61 Reaction of 1 - chloro - 2, 4 - dinitrotensene with. n - Butylamine in dry acetone at + 30°C Wavelength = 380 nyu Initial Concentrations - n - Butylanine = 1,5 x IO"2!-! Chloro = 2 x 10~2M OB QC calc. = 3»636 F = 6.667 x 10" ,- 3 f = 100 X = 22.5 (0.5X - OB^) and (OB^ - CED̂ ) are expressed as optical density units at 350 nyu per 5 ml of reaction mixture after appropriate dilution. Rate constants are calculated on OBoc calculaticc. Tine (rains) 0. 5X ►* OBt. OD OC - 0Bta K x io“4 litre2 moli e -1s 0 11.175 2.925 ■- 5 11.148 2.898 (1.33) 15 11.103 2.853 1.70 25 11.068 2.818 1.71 35 11.033 2.783 1.62 45 10.994 2.744 1.67 55 10.956 2.706 1.69 65 10.914 2.664 1.69 75 10.869 2.619 1.61 85 10.822 2.572 1.76 95 10.734 2.534 1.74 105 10.743 2.493 1.75 115 10.707 2 .457 1.76 Average I .67 + 0.09 x IO”4 litre moleV^sec"*'*’ Duplicate *2 “ 1.68 + 0.06 x 10“4 tt ir 1 Mean *2 = 1.68 x IO"4 i» it n U hr1 Nro II IVERSITY OF IBADAN LIBRARY - 116 - EXPERIMENT 62 Reaction of 1 - chloro - 2, 4 - dinitrobenzene with n - Butylamine in dry acetone at + 30°C Wavelerrgth = 380 nyu Initial Concentrations ~ n - Butylamine = 2.00 x 10 Chloro = 2 x 10"^ OD oc calc. = 3.636 P = 6.667 x IO**5 f = 100 X = 30 (0.5X - OD ) and (OB - OD ) are expresoed as optical density units u O L u at 350 nyu per 5 ml of reaction mixture after appropriate dilution. Rate constants are calculated on OD.. calculation. Time (mins) 0.5X - OB.t OD OC - OD^t ^fc j x 1 0 -^«5-I litre mole 30c 0 14.903 2.903 mm 5 14.851 2.851 (3.07) 15 14.781 2.781 (2.42) 25 14.720 2.720 (2.20) 35 14.667 2.667 2.00 45 14.599 2.599 2.09 55 14.510 2.540 2.07 65 14.479 2.479 2.07 75 14.420 2.420 2.07 85 14.360 2.360 2.08 95 14.312 2.312 2.05 105 14.256 2.256 2.06 115 14.194 2.194 2.09 Average kg = 2.07 + 0.02 x io“4 litre mole^sec“^ Duplicate k>> = 2.09 ± 0.01 x 10"4 1 1 «. tt Mean k>> = 2.08 x IO*“4 !1 ff? tf UNIVERSITY OF IBADAN LIBRARY - 117 - EXP5REF5TT- 65 Reaction of 1 - chloro - 2,4 - dinitrohenzene with n - Butylamine in dry acetone at + 30°C Wavelength = 380 mpx Initial Concentrations - n - Butylamine = 2.50 x 10 "Sl Chloro = 2 x 10 TI OD calc. = 3.636 F = 6.667 x 10,"-3 f = 1 0 0 X = 37.5 (0.5X - OD.t)' and (cd OC! - CD V) are exnressed as optical density units at 350 nyu per 5 ml of reaction mixture after appropriate dilution. Rate constants are calculated on qd oe calculation. Time (mins) 0.5X - OD. OD oe - 0DtA Ru x IO"4 litre mol» e -1 sec-1 0 18.577 2.827 - 2 18.530 2.800 (3.11) 4 18.525 2.775 (3.11) 6 18.505 2.775 2.72 8 18.483 2*733 Zi 71 10 18.465 2.715 2.65 12 18.444 2.694 2.63 14 18.426 2*676 2.64 16 18i409 2.659 2.70 18 18.388 2.638 2.60 20 18.375 2.625 2.59 22 113.350 2.600 2.58 24 18.355 2.585 2.71 Average k2 = 2.65 + 0.07 x IO”4 litre mol, e- 1 seo-1 !*2 = 2.67 + 0.06 x. I O 4 n 1t »» Mean Rg = 2.66 x 10“4 w w, u UNIVERSITY OF IBADAN LIBRARY - 118 - EXPERIMENT 64 Reaction of 1 - chloro - 2, 4 - dinitrobenzene with n - Butylamine in dry acetone at + 30°C Wavelength = 380 nyu Initial Concentrations - n - Butylamine = 3.00 x 10“^M Chloro = 2 x 10*"Sl OD 0» oalc. = 3.636 F = 6.667 x 10 ,"-3 = 100 X = 45.00 (0.5X - ODt. ) and (OD Oe> - ODt.) are expressed as bptical density units at 350 nyu per 5 ml of reaction mixture after appropriate dilution. Rate constants are calculated on OD©3 calculation. Time (mins) 0.5X - OD.t OD - OD. ,-4 t k2 x 10 litre00 mole-1sec-1 0 22.342 2.842 - 2 22.314 2.814 (2.81) 4 22.276 2.776 3.32 6 22.250 2.750 (3.10) 8 22.215 2.715 3.23 10 22.184 2.684 3.21 12 22.154 2.654 3.21 14 22.118 2.618 3.31 16 22.090 2.590 3.26 18 22.057 2.557 3.32 20 22.025 2.525 3.34 ihre rage k2 s= 3.26 + 0.08 x IO*4 litie moln e -1 sec-1 Duplicate k2 = 3.21 + 0.06 x IO*4 fl ir ft; Mean k2 = 3.24 x IQ“4 1* ff; H UNIVERSITY OF IBA AN LIBRARY - r : - EXPERIMENT 65 Reaction of 1 - chloro - 2,4 - dinitrobenzene with n - Butylamine in dry acetone at + 30°C Wavelength = 380 npx Initial Concentrations - n - Butylamine = 3.50 x 10 ri Chloro = 2 x IO”2! C ®o_c calc. - 3 .636 E 1 f “ 100 X (0.5X - CD.,) and ('O B oc - CDOj at 350 mpa per 5 ml. of reaction mixture after appropriate dilution. Rate constants are calculated on ■ CSDe_c calculation. Time (mins) 0.5X - OB, OB oc. - OB,i k2 x IO”4 litre mole -1 sec-1 0 26 .158 2 ;9 0 8 ■ »>• 2 26.114 2 ; 864 3 .6 5 4 26.072 2.-822 3 .6 6 6 26 .028 2 .7 7 8 3 .6 5 8 25.983 2 .733 3.-72 10 25 .942 2 .692 3 .7 0 12 25 .896 2.646 3 .7 2 14 2*5.855 2 .605 3 .7 5 16 25VJ11 2 .5 6 1 3 .7 8 18 2 5 .7 6 9 2 .5 1 9 (4 .0 3 ) 20 2 5 .7 26 2.476 3 .7 5 Average »1= 3 .7 2 + 0 .0 7 k IC” 4 litre mole "sec Buplicate hg - 3 .7 6 + 0 j0 2 x IG” 4 ?!’ n; !•: Mean k£ = 3 .7 4 * IO“ 4 t* ft ft UNIVERSITY OF IBADAN LIBRARY - 1 1 2 0 - EXPERIMENT 66 Reaction of 2 - chloro - 5 - nitropyridine with Piperidine in dry acetone at 11.2 + 0.05°C Wavelength = 370 myu Initial Concentrations = Piperidine = 5.00 x 10~^M Chloro = 5 x 10"5M 01) calc. = 0.895 OfJ OD expt. = 0.895 O S £ = 100 (OD^ - OD^) is expressed as opticai density units at 370 m per T 5 ml of reaction mixture after appropriate dilution. Rate constants are calculated on O D ^ experiment. Time (secs) OD OG - ODt 1 + log (OD^ - 120 0.735 0.8663 180 0.704 0.8476 240 0.678 0.8312 420 0.594 0.7738 720 0.500 0,6990 960 0.434 0.6375 1,320 0.349 0.5428 1,800 0.283 0.4518 2,400 0.189 0.2765 Slope of 1 +- log (CD o£ - ODt.) versus time in secs = 2.71 i 0 ^ = 6.25 X IO*4 k2 » 1,25 i 0.00 x 10— 2 litre mole »1 sec< Duplicate k2 =* 1,30 ± 0.00 x 10"2 « " Mean k 2 ft 1.28 x IO*“2 * " ■ UNIVERSITY OF IBADAN LIBRARY - 121 - EXPERIMENT 67 Reaction of 2 - chloro - 5 - r&tropyridine with Piperidine in dry acetone at 11.2 + 0.05°C Wavelength = 370 uyu Initial Concentrations - Piperidine = 1.0 x IO"3!! Chloro = 5.0 x 10~3M OD 0- caic. = 0.895 OD expt. = 0.895 f = 1 0 0 (03 _ - OP ) is expressed as optical density units at 370 m/u per 5 ml of reaction mixture after appropriate dilution. Rate constants are calculated on O D ^ experiment. Time (secs) OP Ov — OD.X 1 + log (OD^, - 60 0 .7 0 5 0.8482 120 0 .644 0 .8089 180 0.602 0.7796 240 0 .5 4 8 0.7388 360 0 .475 0 .6749 480 0 .4 0 5 0 .6075 600 0.353 0 .5478 780 0 .274 0 .4378 960 0 .2 1 7 0.3365 1,200 0 .1 6 8 0.2253 1 ,500 0 .135 0 .1303 Slope of 1 + log (OP - OPt.) versus time secs = 5.54 i 0.1003 k,1 = 1 .2 7 X io “ 4 k2 = 1.27 ± 0.00 x .10"2 litre mol i e -1 sec-1 Duplicate k2 = 1.30 ± 0.00 y. i o “ 2 " tt fl Mean k> = 1 .2 9 x 10"2 ” n ir UNIVERSITY OF IBADAN LIBRARY - 122 - EXPERIMENT 68 Reaction of 2 - chloro - 5 - nitropyridine with Hperidine in diy acetone at 11.2 ± 0.05°C Wavelength. - 370 nyu Initial Concentrations Piperidine = 2.00 x 10""1K Chloro = 5 2C 10~3M OD calc. =OP 0.895 OD■oo expt. = 0.890 f = 100 (OD0^ - is exp]° V 5 ml of reaction mixture after appropriate dilution. Rate constants are calculated on ODc,- experiment. Time (secs) OD O''- ÖD.t 2 + log (OD co - OD t) 75 0.661 1.8202 150 0.542 1.7340 270 0.398 1.5999 420 0.277 1.4425 600 0.179 1.2529 840 0.098 0.9912 1,140 0,064 0.8062 1,500 0.035 0.5441 Slope of 2 + log (0DW - ODj.) versus time in secs = 1.08 + 0.01 x 10~3 = 2.49 s IO“*3 k2 « 1,25 ± 0.00 sc IO“2 litre mole^sec*“1 Duplicate k2 = 1.22 + 0.00 10“ Mean kg = 1.24 3C 10-2 I! UNIVERSITY OF IBADAN LIBRARY - 123 - EXPERIMENT 69 Reactions of 1 - fluoro - 2, 4 - dinitrobenzene with n - Butylamine in Stabilised Chloroform at 24.82 + 0.01°C Wavelengtn = 350 myu Initial Concentrations - n ~ Butylamine = 0.001K Pluoro = 2.5 x 10"Sl ObOs calc. = 0.895 OLoc expt. = 0.881 F ,-3 f = 5 X 3.636 (0.5X - O.û ) and ( O D ^ - ® t ) at 350 nyu per 10 ml of reaction mixture after appropriate dilution. Rate constants are calculated on 01 8 i - 135 - EXPERIMENT 80 Reaction of 1 - fluoro - 2, 4 - dinitrobenzene with n - Butylamine in destabilised Chloroform at 24.82 + 0.01°C. Wavelength = 350 myu. Initial Concentrations: n - Butylamine = 0.004M Pluoro = 2.5 x 10~4M ODGC calc. = 0.895 C t expt. = 0.872 F f = 5 X (0.5X - ODt. ) and (oD (K- - OB.t) are expressed as optical density units at 350 myu per 10 ml of reaction mixture after appropriate dilution. Rate constants are calculated on OD (K'cxperinent. Time (secs) 0.5X ~ oD.t/ OD oc.- OD,t • k2 x IO'1 li -1 sec-1 0 7.122 0.724 - 135 7.020 0.622 2.89 335 6.901 0.503 2.89 555 6.794 0.396 2.85 855 6,685 0.288 2.85 1,155 6.615 0.212 2.84 1,505 6.555 0.158 2.73 1,920 6.495 0.098 2.82 2,415 6.466 0.068 (2.67) Average k2 = 2.85 + 0.13 X 10-1 litre mol, e -1 sec-1 Duplicate k2 = 2.79 + 0«09 x 11 !1 Mean k2 = 2.82 + IO-1 litre moln e -1 sec-1 UNIVERSITY OF M O I M1 BADAN LIBRARY - 136 EXPERIMENT 81 Reaction of 1 - fluoro - 2, 4 - dinitrobenzene with n - Butylamine in destabilised Chloroform at 24.82 + 0.01°C Wavelength = 350 nyu Initial Concentrations - n - Butylamine = 0.01M Pluoro = 2.5 x IO*4 *! ODac. calc. = 0.895 OD Ol.. expt. = 0.887 F = 5.548 x 10"5 f = 5 X = 36.36 (0.5X - 0Dt) and (OD^ - ® t y are expressed as optical density units at 350 m/u per 10 ml of reaction mixture after appropriate dilution. Rate constants are calculated on OD calculation. Time (secs) 0.5X - OD ° V 0Bt *2 x io “ 1 litrew mole -1s ec-1 0 18.017 0.724 - 90 17.84 0.556 2.98 180 17.72 0.432 2.84 290 17.62 0.328 2.82 400 17.52 0.226 2.95 530 17.46 0.171 2.87 670 17.41 0.121 2.77 820 17.37 0.0Q4 2.72 1,040 17.34 0.04*6 2.76 Average = 2.84 + 0.14 x 10 •4L litre mole —1sec Duplicate = 2.83 + 0.10 x IO-*-1 " * "■ Mean = 2.84 z 10 .7 fli in I. UNIVERSITY OF IBADAN LIBRARY - 137 - EXPERIMENT 82 Reaction of 1 - fluoro - 2 , 4 - dinitrobenzene with n - Butylamine in destabilised C h l o r o f o r m at 24.82 + 0.01°C Wavelength = 350 nyu Initial Concentrations - n - Butylamine = 0.0125 M Fluoro = 2.5 x 10"'4M OB calc. = 0.895 OB03 expt. = 0.890 F = 5.548 x 10~3 f = 5 X = 45.44 (0.5X - OBt. ) and OB «X. - OBt'?) are expressed as optical density units at 350 nyu per 10 ml of reaction mixture after appropriate dilution. Rate constants are calculated on OB experimen t. Tine (secs) 0.5X - 0Dt GED oc~ OD t k,2 x io“1mole „1 : i 0 22.47 0.643 - 55 22 36 0.530 2.80 125 22.25 0.427 2.67 185 22.15 0.332 2.91 255 22.08 0.259 2.91 325 22.03 0.203 2.91 395 22.00 0.171 2.75 460 21.53 0.149 2.67 Average k 2 = 2.81 + 0.14 x 10*"̂ litre mole^sec-" Buplicate k2 = 2.81 + 0.08 x 10“1 w 1(1 Mean ^2 = 2.81 x 10"1 ,s w n UNIVERSITY OF IBADAN LIBRARY - 138 - EXPERIMENT 83 Reaction of 1 - fluoro - 2, 4 - dinitrobenzene with n - Butylamino in destabilised Chloroform at 24.82 + 0.01°C Wavelength = 350 nyu Initial Concentrations v n - Butylamine = 0.025M Fluoro = 2.5 z IO*"4!! OD OS- calc. := 0.895 OD expt. := 0.870 F = 5.548 x IO”5 X = 90.880 (0.5X - OD t) and (OD 08 - ° v are expressed as optical density units at 350 nyu per 2 ml of reaction mixture. Rate constants are calculated on OD^ experiment. Time (secs) 0.5X - OD^ OD CR- OD.t k x IO“1 litre mole sec 0 45.21 0.640 - 30 45.08 0.516 2.89 60 44.98 0.415 2.91 90 44.89 0.332 2.93 120 44.83 0.266 2.96 150 44.78 0.215 2.92 180 44.73 0.175 2.94 240 44,68 0.112 2,94 33 44.62 0.056 2.99 Average = 2.94 + 0.05 x 10~^ litre mole"“̂ sec”"̂ Duplicate = 2.90 + 0.06 x 10”^ '* " Mean k‘2 = 2, 92 x 10.-1 UNIVERSITY OF IBADAN LIBRARY CB* - 139 - EXPERIMENT 81 Reaction of 1 - fluoro - 2,4 - dinitrobenzene with n - Butylanine in deatabilised Chloroform at 24-82 + 0.01°C Wavelength = 350 nyu Initial Concentrations - n - Butylamine = 0.1M Fluoro = 2.5 x IO”4!! ODoc calc. = 0.895 F = 5.548 x 10~^ ODQC expt. = 0.884 X = 363.6 (0.5X and (öD oc - OD ) are expressed as optical density units at 350 cyu per 2 ml of reaction mixture. Rate constants are calculated on OD ce experiment. Time (secs) 0.5X - OD. OD oc- OD t k x 10~ ̂litro^ mol. e -1 sec-1 0 181.42 0.499 - 6 181.4 0.408 3.30 12 181.3 0.337 3.28 18 181.1 Ow277 3.28 24 181.1 0.230 3.24 30 181.1 0.189 3.25 42 181.0 0.132 3.-20 54 181.0 0.090 3.29 m 180.9 0.056 3.15 Average Rg- = 3.25 + 0.15 x 10"1 litre mole~4sec""^ Duplicate 1<2 = 3.23 £ 0.09 x io“1 l!i It Mean 1̂ 2 = 3.24 x IO"1 *» II »*. UNIVERSITY OF IBADAN LIBRARY 8 l - HO - m m m w . m Reaction of 1 - fluoro - 2, 4 - dinitrobenzene with n - Butylanine in destabilised Chloroform at 24.82 £ 0.01°C Wavelength = 350 nyu Initial Concentrations - n - Butylamine = 0.2M Fluoro = 2.5 x irtl Time (secs) OB OC- ÖD t 1 + log (OD^ - QDt) 1 1.790 1.253 2 1,653 1,218 5 1.522 1.182: 4 1.398 1 . 1 2 7 5 1.287 1.110 6 1.196 1.078 7 1.079 1.033 8 1.029 1.012 9 0.919 0.963 10 0.887 0.948 Slope of 1 4- log (OD - OB.) versus time in secs = 3.50 j; 0.12 x io“ k^ = 4.03 + 0.*Q 0 x 10„ i litre mole -l sec-l Duplioate = 4.02 ± 0.00 x 10'-1 Mean kg = 4.03 X 10-1 lt: »ts UNIVERSITY OF IBADAN LIBRARY - 141 - EXPERIMENT 86 Reaction of 1 - chloro - 2, 4 - dinitrobenzene with n - Butylamine in stabilised Chloroform at 24.82 + 0.01°C Wavelength = 350 mpx Initial concentrations - n - Butylamine = 0.002H Chloro = 5 x 10“^M OD eC calc. 0.895 OD oc expt. = 0.909 P = 5.548 x 10 ,-3 f = 1 0 X = 90.90 (X - OD.0 ) and (OD Oti - OD u) are expressed as optical density units at 350 nyu per 5 ml of reaction mixture after appropriate dilution. Rate constants are calculated on OD cC experiment. Time (mins) X - OD OD oc- OD t k . x IO’4 l1itreT» 2 mol-i e -1 i 0 90 .83 0 .8 4 2 -- 60 90,76 0 .7 8 7 1 ;7 5 120 90 .74 0 .732 1 .8 0 210 90.63 0 .6 6 7 1.72 360 90.53 0 .552 1 .83 490 90.46 0 .4 8 5 1.72 600 90.40 0 .4 1 9 1.82 720 90 .35 0 .3 7 0 1 .7 8 1 ,570 9 0 .18 0.206 (1 .6 1 ) 1 ,820 9 0 .0 4 0 .150 (1 .4 9 ) Average X i o " 4 litre mole' Duplicate k. = 1 .8 2 ± 0 .0 2 X IO*4 ii it fl Mean = 1 .8 0 X IO*4 11 r* I I UNIVERSITY OF IBADAN LIBRARY S0 0 + 1 1—•1 II - 142 - E7PERIHERT . Ql Rcaction of 1 - chloro - 2, 4 - dinitrobenzene with n - Butylamine in atabilised Chloroform at -f- 24.82 + 0.01°C Eavelength = 350 ryu Initial Concentrations ~ n ~ Butylamine = 0.005 M Chloro = 5 x IO”2!'! 00 oc calc. = 0.895 <7 00 oc expt. = 0.909 F = 5.548 x 10~p £• 50 X = 18.180 (x - 00,.c)' and are expressed as optical density unita< ° £ - ° V at 350 uyu per 5 ml of reaction mixture after appropriate dilution. Rate constants are calculated on OD oc experiment. Time (mins) x - oot 00 Oc- OD, k. x 10 - 4 litre t d. _2. molo aec 0 18.10 0.834 - 60 18.05 0.780 1.88 120 17.99 0.729 1.88 210 17.93 0.659 1.89 360 17.82 0.560 1.87 480 17.75 0.488 1.89 600 17.70 0.430 1.87 750 17.64 0.375 1.81 1,420 17.47 0.205 (1.70) 1,710 17.42 0.165 (1.63) Average k 2 = 1.87 ̂ 0.06 x 10r 4 litre mole -1a ec -1 Duplicate k 2 = 1.85 -v 0.03 x 10'r* Mean k2 = 1.8? x 10 it \r !t5 UNIVERSITY OF IBADAN LIBRARY - 143 - EXPERIMENT 8^ Reacticn of 1 - chloro - 2 , 4 ” dinitrobenzene with n - Butylaraine in stabilised Chloroform at + 24«82 + 0.01°C Waveler.g'Lli = 350 m/u Initial Ccncsntraticna n « Butylamine = o.om Chloro = 5 x 10-2M COo c calc. = 0.835 COf at exptc = 0,905 F = 5.543 x 10"5 „(x 200 X « 9.09- aotj and (00 OC « 00,.' are expressed as optical density unitsC at 350 tyu per 5 ml of r-eaction mixtare after appropriate dilution. Rate constants are calculated or OD oc experiment. Time (secs) X - CD,.1/ OD - 0DA k *= x 10"4- mole i litr-esec i ■ 0 8.914 0.734 «• 1,800 8.892 0.713 1.8 3,600 3; 865 0.687 1.889 6,600 3,816 0.643 1.93 10,2^0 8.7'2 0,603 1.98 13,800 8,7T,5 0.568 1.91 21,700 8.653 0.489 1.97 32,520 8.602 0,423 1.95 37,000 8.239 0.153 1.87 Average k~c,i- - 1.92 + 0..06 j 'j litre mole -1s ec-1 Duplicrto k.k. 1,Q3 o 0* •v :i Ui IT? Mean k0 *= 1.93 r: K*4 w !i ff UNIVERSITY OF IBADAN LIBRARY - 144 - * EXPERIMENT 89 Reaction of 1 - chloro - 2, 4 - clinitrobenzene with n - Butylamine in stabilised Chloroform at + 24.82 0.01°C Wavelength 350 nyu Initial Concentrations - n - Butylamine = 0.025M Chloro = 5 x IO"2*! OD oc calc. = 0.895 OD oc expt. = 0.909 P = 5.548 x 10"3 f = 250 X = 3.636 (X - 0Dt) and OD OB - QD t) are expressed as optical density units at 350 nyu per 5 ml of reaction mixture after appropriate dilution Rate constants are calculated on OD ̂experiment. Time (secs) X - ODt. ODc c - ODt. K2 x IO*"4 l-i1tr enol© sec- 1A 0 3.492 0.767 - 3,600 3.438 0.713 2.13 7*200 3.390 0.665 2.10 10,800 3.352 0.627 1.98 19,800 3.248 0.524 2.08 25,200 3.200 0.474 2.08 31,800 3.152 0*428 2.03 37*800 3.098 0.377 2.08 79,800 2.912 0.193 2.00 Average k2 = 2.06 + 0.08 x IO“4 litre mole^sec"'*' Duplicate kg = 2.04 + 0.02 x IO*4 I»? Mean kj = 2.05 x IO“4 tts «»• UNIVERSITY OF IBADAN LIBRARY - 145 - EKffTOWT , ,22 Reaction of 1 - chloro - 2, 4 - dinitrobenzene with n - Butylamine in er stabilised Chloroform at + 24.82 _£ 0.01 C Wavelength = 350 nyu Initial Concentrations - n - Butylamine = 0.05 M Chloro ss 5 x 10*^M OB QL> oalc. = 0.448 ODQ t expt. = 0.454 P = 5.548 x IO"5 f = 1000 X = 0.909 (X - 01) t ) and (OD vC- - OD X ) are expressed as optical density units at 350 m/u per 5 ml of reaction mixture after appropriate dilution. Rate constants are calculated on OD Ov experiment. Time (secs) X - 0 D t C® oc- 0D+*fc k2 x IO”4 litre mole'-1s ec••1 • 0 0.874 0.420 «r 3*600 0.846 0.392 2.03 7,200 0.820 0.366 2.05 16,080 0.764 0.3095 2.12 26,880 0.712 0.2575 2.11 38,400 0.658 0.2035 2.20 82,800 0.5^ 0.1285 2.09 Average kg = 2.10 ,± 0.10 x 10< -4 litre mole -hec"1 Duplicate = 2?. 18 + 0,01 x IO*4 " Mean kg = 2.14 x IQ"4 ,,f UNIVERSITY OF IBADAN LIBRARY - 146 - EXPERIMENT Ql Reaction of 1 - chloro - 2, 4 - dinitrobenzene with n - Butylamine in stabilised Chloroform at + 24.82 + 0.01°C Wavelength = 350 nyu Initial Concentrations n — Butylamine = 0.2M Chloro = 5 x 10"^M OD< - 152 - EXPERIMENT 97 Reaction of 1 - chloro - 2, 4 - dinitrobenzene with n - Butylamine in destabilised Chloroform at + 24.82 £ 0.01°C Wavelength » 350 nyu. Initial Concentrations n Butylamine = 0.025M Chloro = 5 x IO-2! ODOG calc. = 0.895 °Desc expt. = 0.909 P = 5,548 x 10*"' f = 250 X = 3.636 (X - OD^) and (OD — OD^) are expressed as optical density xmits at 350 m/u per 5 ml of reaction mixture after appropriate dilution. Rate constants are caleulated on 01)o^c experimont. Time (secs) X - OD. 01) QO- OD. k- x 10"4 litred mol, e -1s ec-1 0 3.491 0.766 - 3,600 3.441 0.715 2.02 7,200 3.389 0.664 2.10 10,800 3.352 0.627 2.12 19,800 3.252 0.527 2.16 25,200 3.200 0.475 2-. 08 31,800 3.151 0.426 2.08 37,800 3.100 0.375 2.10 79,800 2.920 0.195 2.12 Average k^ = 2.09 £ 0.07 x 10- 4 litre mole -1s ec-1 Duplicate Rr2 = 2,12 £ 0.05 x IO"4 w !t ra Mean k 2 = 2.11 x IO-4 • w ff? UNIVERSITY OF IBADAN LIBRARY - 153 - EXPERIMENT 98 Reaction of 1 - chloro - 2, 4 - dinitrobenzene with n - Butylamine in destabilised Chloroform at 24.82 + 0.01°C Wavelength = 350 myu Initial Concentrations - n - Butylamine = 0.05M Chloro = 5 x IO”2!-! OBQG caio. = 0.448 ODoc expt. sa 0.437 P = 5.548 x 10-3 f = 1000 X = 0.909 ( X - 0Dt) and (OB^ - ODt) are expressed as optical density units at 350 lyu per 5 ml of reaction mixture after appropriate dilution. Rate constants are calculated on OB QC oxperiment. Time (secs) X - OBt OB OG - OB.t kl2 x IO"4 litre mole" 0 0.886 0.410 Mt 2,760 0.863 0.387 2,18 8,100 0.818 0.358 (2.40) 15,840 0.763 0.287 2.30 23,580 0.721 0.245 2.30 36,720 0.675 0.199 2.35 80,280 0.585 0.109 2.16 111,780 0.546 0.071 2.17 Average k^ = 2.24 + 0.11 x IO"4 litre mole’4 3ec’4 ' Buplicate kg = 2.28 + 0.09 x 10“4 ft ft ft Mean kg = 2.26 x 10“4 tr it ft UNIVERSITY OF IBADAN LIBRARY - 154 - EXPERIMENT 99 Reaction of 1 - chloro - 2, 4 - dinitrobenzene with n - Butylanine in destabilised Chloroform at 24.82 + 0.01°C Wavelength = 350 nyu Initial Concentrations - n - Butylamine 0.2M Chloro 5 x Kf^M. OB calc. = 0.895 OBoe expt. = 0.870 E = 5.548 x 10~5 f = 1000 X « 3.636 (0.5X and (OB 0C - 0Dt) are expressed as optical density units at 350 nyu. per 5 ml of reaction mixture after appropriate dilution. Rate constants are calculated on experiment. Time (secs) 0.5X ~ OB,t CB oc- OB.t kc0 x io“ 4 •; mole 0 1.770 0.820 ■- -680 1.743 0.793 (2.50) 1,620 1.699 0.-749 2*92 3,100 1.639 0.689 3.00 4,900 1.574 0.624 3.04 6,720 1.509 0.559 3.18 8,500 1.468 0.517 3.08 15,480 1.315 0.365 3.17 21,060 1.248 0.307 2.89 Average R;, = 3.04 ± 0.13 x 1io0-“ 44 litre mole -1 sec-1Buplicate K , = 3.05 + 0.10 x " w tr. Mean R̂ , = 3.05 x IO"4 is UN lIV 8ERSITY OF IBADAN LIBRARY - 155 - EXPERIMENT 100 ReactibTT*of''Yw~ chloro - 2, 4 dinitrobenzene with n - Butylamine in destabilised Chloroform at + 24.82 ̂ 0.01°C Wavelength = 350 isyu Initial Concentrations n - Butylamine = 0.5M Chloro = 5 x lO“2!̂ ODOC calc. = 0.895 ODoc 6Xp*fc • = 0.875 F = 5.548 x 10"5 f = 1000 X = 9.090 (0.5X - ° Dt ) and (OD^Ö.l - OD V) are expressed as optical density units at 350 nyu per 5 ml of reaction mixture after appropriate dilution. Rate constants are calculated on OD oc experiment Time (secs) 0.5X - OD, OD oe- OD.t k, x 10"4 litreZ mol, e -1 sec-1 0 4.462 0.777 - 420 4.387 0.707 4.53 960 4.312 0.632 4.44 1,620 4.236 0.547 4.54 2,520 4.133 0.453 4.53 3,720 4.042 0.356 4.51 5,240 3.952 0.272 4.35 7,020 3.872 0.192 4.42 9,120 3.787 0.135 4.39 Average 1t, = 4.46 + 0.11 x 10*4 litre mole^sec*4 Duplicate = 4.56 i 0.15 x 10*4 tr tr. tt Mean lo. = 4.51 x IO-4 ff ff ff! UNIVERSITY OF IBADAN LIBRARY - 156 - EXPERIMENT 101 Reaction of 1 - chloro - 2, 4 - dinitrobenzene with n - Butylanine in destabilised Chloroform at 24.82 + 0.01°C Wavelength = 550 uyu. Initial Concontrations - n - Butylamine = 0.8 M Chloro = 5 x IO**2!! °v calc. = 0.895 °v expt. = 0.865 F = 5.548 X 10**5 f = 1000 X = 14.544 (0.5X -0Dt and (OD oc - ODX.) are expressed as optical density units at 550 nyu per 5 ml of reaction mixture after appropriate cilution. Rate constants are calculated on ODoc experimait. Time (secs) 0.5X - 0Dt ° V ~ 0Dt k2 x IO“4 litre mole-1 -1 0 7.180 0.765 - 220 7.104 0.687 6.07 520 7.001 0.595 6.21 •940 6.905 0.490 6.09 1*420 6.806 0.590 6.16 2,020 6.714 0.298 6.15 2,760 6.654 0.217 6.05 5,640 6.561 0.144 6.14 4,540 6.518 0.100 6.04 Average Rj, = 6.11 ± 0.07 x IO**4 litre mole^sec*4 Duplicate R̂ > = 6.10 + 0.05 x IO*4 »1 n; f»; Mean R^ = 6.11 x IO**4 ff ff* rr UNIVERSITY OF IBADAN LIBRARY 157 SUMMET OF RATE C O M T S TABLE I The reaction of 1-fluoro-2,4-dinitrobenzene with Piperidine in the presence of Piperidine Hydrochloride in dry methanol at - 29.6 °C Substrate concentration is 1.25 x 10”^ 10 2 / Piperidine/ ZTPiperidine IICl7 10 kg 1 mol mole litre mole litre ^ 1.25 0.10 1.67 2.50 0.10 1.99 3.75 0.10 2.22 4.40 0.10 3.09 4.75 0.10 4.42 5.00 0.10 6.56 Table 1a The reaction of 1 -fluoro-2,4-dinitrobenzene with Piperidine in dry methanol at - 29.6°C. Substrate concentration is 1,25 x 10 % 10 2 Piperidine 10 ^2 m°l -1 sec-1 mole litre 1.25 1.76 2.50 1.92 3.75 2.30 4.40 3.13 4.75 4.17 5.00 6.63 UNIVERSITY OF IBADAN LIBRARY 158 - TABLE 2 The reaction of 1-chloro-2,4-dinitrobenzene with Piperidine in the presence of Piperidine hydrochloride in dry methanol at + 50.20 + _0.05°C Substrate concentration is 5.00 x 10 -3 M piperidine/ piperidine HCi/ 10 -2 k2 litre mole mole litre _1 mole litre sec”^ 0.0355 0.10 1.66 0.075 0.10 1.67 0.150 0.10 1.72 0.300 0.10 1.72 0.600 OilO 2.07 1.200 0.10 2.17 TABLE 2a The reaction of l-chJ.oro-2,4-dinitrobonzene with Piperidine in dry menthanol at 30.20 + 0.05°C Substrate concentration is 5.00 x 10- 3M piperidine/ 10 2 k2 litre 0.0355 1.63 0.075 1.65 0.150 1.66 0.300 1.74 0.600 1.96 1.200 2.24 UNIVERSITY OF IBADAN LIBRARY - 159 - TABLE 3 The reaction of 1-fluoro-2,4-dinitrobenzene with Piperidine in dry acetone at +30,0°C Substrate concentration is 1.00 z 10 _5M 10 5 /Piperidin^ k2 litre mole-1 -1 mole litre ^ 7.97 22.0 15.94 24.2 24.46 27.0 31.81 30.0 39.84 31.0 47.81 32.1 55.77 33.0 63.74 35.2 71.71 36.1 79.68 39.1 100.00 41.0 125.00 42.0 200.00 46.5 TABLE 4- The reaction of 1 --chloro-2,4-dinitrobenzene with Piperidine in dry acetone at + 30.0 o„C Substrate concentration is 5.00 z 10 10 2. /y-Piperidine7 10 k2 litre mole -1 sec-1 mole litre-1 1.05 4.36 UNIVERSITY OF IBADAN LIBRARY - 160 - 1.53 4.76 2.05 5.22 2.65 5.49 3.05 5.68 3.55 5.85 TABLE 5 The reaction of 1-fluoro-2,4-d.initrobenzene with n-Butylamine in dry acetone at 24-82 + 0.05°C Substrate concentration is 5.0 x 10- 5M 10 ^ ^n-Butylaminey7" 10 2 k2 litre mole -1 sec-1 mole litre-1 0.05 3.17 0.10 3.54 0.25 3.82 0.50 4.22 1.00 4.86 5.00 5.57 10.00 7.20 20.00 16.4 30.00 22.1 40.00 26.3 UNIVERSITY OF IBADAN LIBRARY - 164 - TDUiJ 6 The reaction of 1-chloro-2,4-dinitrobenzene with n-Butylamine in dry acetone at + 30.0 0.05°C Substrate concentration is 2.00 x 10 “TVI 10 /n-Butylamine/ 10 4 k2 ütre mole-11 sec-1 mole litre ^ 0.10 0.27 0.50 0.69 1.00 1.24 1.50 1.68 2.00 2.08 2.50 2.66 3.00 3.24 3.50 3.74 TA3LE 7 The reaction of 1-fluoro-2,4-dinitrobenzene with n-Butylamine in stabilised Chloroform at 24.82 + 0.05°C Substrate concentration is 2.5 x 10 /n-Butylamine/ 10 Je, litre mole -1 sec-1 mole litre 0.001 2.64 0.004 2.68 0.01 2.65 0,0125 2.78 0»(T~ 2.91 0.100 3.06 UNIVERSITY OF IBADAN LIBRARY 162 0.200 5.86 0.500 5.88 0.800 7.94 1.00 11.33 TABLE 7a The reaction of 1-fluoro-2,4-dinitrobenzene with n-Butylanine in destabilised Chloroform at 24-82 + 0.05°C Substrate concentration is 2.5 x 10 /n-Butylanine/ 10 lc, litre mole ̂ sec more litre“1 0.001 2.55 0.004 2.81 0.010 2.84 0.0125 2.81 0.025 2.92 0.100 3.24 0.200 4.03 TABLE 8 The reaction of 1-chloro-2,4-dinitrobenzene with n-Butylanine in stabilised Chloroform at + 24-82 + 0.05°C Substrate concentration is 5 x 10 II UNIVERSITY OF IBADAN LIBRARY 163 /n-B utylamin§7' 10^ kg litre more litre ^ 0.001 .1.80 0.005 1.87 0.010 1.93 0.025 2.05 0.050 2.14 0.200 2.90 0.500 4.42 0.800 6.02 1A.BLE 8a The reaction of 1-chloro-2,4“dinitrobenzene with n-Butylamine in destabilised Chloroform at + 24.82 + 0.05°C Substrate coneentration is 5. x 10 Sl /n -B uty lan in_y 1Q4 l i t r e mol.-1 se c ' mole litre- 0.001 1.82 0.005 1.89 .... 0.010 1.93 0.025 2.11 0.050 2.26 0.200 3.05 0.500 4.51 . 0.800 6.11 UNIVERSITY OF IBADAN LIBRARY 16‘3 A - TABLE 9 The reaction of 2-chloro-5-nitropyridine with Piperidine in try acetone at + 11.2°C Substrate concentration is 5.00 x 10 % 10J2 . //Pri. peri.d.i. ne~^7 .1„02“ 1c, litre mole ̂ sec ^ mole5 .0l0itre 1.28 10.00 1.28 20.00 1.23 TABLE 10 The reaction of 2-chloro-5-nitropyridine with Piperidine in dry methanol Temperature o C 10 3 litre mole ̂ sec-1 log A 10 20.80 1.62 6.72 30.50 3.28 6.75 40.22 6.32 6.73 50.55 12.28 6.74 Temperature Range Activation Energy E (Kcal ) 50.55 - 40.22 12.8 40.22 - 30.50 12.8 30.50 - 20.80 12.9 Mean log A r- 6.74 10 Mean E 12.8 kcal UNIVERSITY OF IBADAN LIBRARY 164 CHAPTER 5 DISCUSSION OF RESULTS In the work reported in this thesis, the kinetics of the following reactions were studied: 1. 2-Chloro-5-nitropyridine with piperidine in acetone. 2. 2-Chloro-5-nitropyridine with piperidine in methanol. 3. 1-fluoro-2, 4-dinitrobenzene with piperidine in acetone. 4. 1-chloro-2, 4-*dinitrobenzene with piperidine in acetone . 5. 1-fluoro-2, 4-dinitrobenzene with piperidine in methanol. 6. 1-chloro-2, 4-dinitrobenzene with piperidine in methanol. 7. 1-fluoro-2, 4-dinitrobenzene with n-butylamine in acetone. 8. 1-chloro-2, 4-dinitrobenzene with n-butylamine in acetone. 95b 10. 1-fluoro-2, 4-dinitrobenzene with n-butylamine in stabilised and in destabilised Chloroform. 11&12. 1-chloro-2, 4 - dinitrobenzene with n-butylamine in stabilised and in destabilised Chloroform. Bach reaction can te represented by the following equations: ArX + R2NH ____ Ss A 1ÜR2 + HX HX + R2N H ____ i r2 H+ H2X~ The reactions wer® studied spectroscopically by following the absorbance of the orang<3-jrellow products of reaction ArNR2, at a wavelength region where it is the only species which absorbed. UNIVERSITY OF IBADAN LIBRARY - 165 - The experiments were carried out partly under second-order run conditions and under pseudo-first Order run conditions. The second Order rate coefficients obtained by employing conditions leading directly to second order kinetics and those giving pseudo-first order kinetics were the same within experimental error limits. The rate constants obtained for all thesc reactions increased with increasing amine concentration howbeit small except for the reactions of 2-chloro-5-nitropyridine with piperidine in acetone at 11.2 °C in which a small decrease in rate was obtained with increasing amine concentration. Since a reasonablo dogree of peculiarity attaches to the reactions of individual Substrates, the reactions are discussed seporately for the different Substrates. The reactions of 2-halo-5-nitro-pyridine with aniline and piperidine in acetone and in methanol: Bamkole and Hirst have reported 59 that the reactions of 1-X-2, 4- dinitrobenzenes (X, CI, F) and 2-fluoro-5-*uitropyridine with aniline and piperidine in methanol are not base catalysed; but that when the solvent is acetone 46, the reactions Show varying degrees of catalysis depending on the Substrate, and the nucleophile. For instance, in the reactions of the 5-nitropyridine Series, with aniline in acetone, their results show that the plots of the second order rate constants agaluet aniline concentrations are slightly curvilinear. UNIVERSITY OF IBADAN LIBRARY - 166 - When the nucleophile is changed to piperidine, a stronger base, the curvature of the plot increased for the reaction of 2-fluoro-5-nitropyridin and Bamkole and Hirst, from a plot of Vkobs vsreus ^ ( b ) found that ^/ k 2 = 612. From the results of the studies reported here, the data now available for the reaction of 2-chloro-5-nitro pyridine with piperidine in acetone Show that the rate constant do not increase with increasing piperidine concentration, Rather, there was an insignificant decrease in rate constant valu.es with increasing amine concentrations as shown in table 6a. Table 6a Reactions of 2-chloro-5-nitropyridine with piperidine in acetone at 11.2 °C Initial Substrate concentration — Tv— 5.00 x 10 102 (Piperidine) 5.00 10.00 20.00 102 k l mol-1 sec-1 1.28 1.28 1.23 Similal rate decreases with increasing amine concentrations have already been rocorded by Bernasconi4 -7/ Bamkole and Hirst 59 , Bunnett and Garst 1 7 and Ross and Kuntz A^ B in similar reactions. Ross and Kuntz explained thi;, Observation in terms of char.ge-transfer complexes. In terms of the general intermediate complex mechanism, these reactions belong to ''„he dass when kg + k^ (B) » k - 1. and the. general equation simplifies to k o = k.1 0? ta now avaflavle from the present work taken along with those in l.tterature make certain interesting comparisons possible for these UNIVERSITY OF IBADAN LIBRARY - 167 - reactions in methanol and in acetone. However, since the reactions in acetone show varying degrees of base catalysis, such comparisons are only valid provided corresponding steps are compared. This means comparing the rates of reaction in methanol with , the rate conetanto for the formation of the intermediate complex for the reactions in acetone. o\vj„ Such comparisons include the following: 1. The relative reactivities of the fluoro and chloro compounds in methanol and in acetone. 2. Comparison of the nucleophilicity of piperidine with that of aniline in methanol for both the fluoro and the chloro Substrates. 3. Comparison of the nucleophilicity of piperidine with that of aniline in acetone for both the fluoro and the chloro Substrates. 4. Comparison of aniline in methanol with aniline in acetone for both the fluoro and the chloro Substrates. 5. Comparison of piperidine in methanol with piperidine in acetone for both the fluoro and the chloro Substrates. 6. Comparison of partial rate coefficients for the reactions in acetone i.e. k1f k~1/k2 f k5/k2 etc. Since the reactions in methanol are not base catalysed, the activation energies as well as the pre-exponential factors (log B) can be obtained and these are assembled in table 6b below along with rate constants at 25°C and 50°C extrapolated from the Arrhonius equations: Table 6b The A.rrh,enius parameters and rate constants of reactions of 25°C and UNIVERSITY OF IBADAN LIBRARY and 50°C for the reactions of 2-X-5-nitro pyridine (X=F,Cl) with piperidine and aniline in methanol. Substrate Nucleophile E (kcal) log B ki25°C I ki 50°C X = CI Aniline 13.1 3.78 1.50 x 10"6 j 8.26 x 10" X = CI Piperidine 12.8 6.74 2.27 x 10“3 1.20 x 10“ Aniline 10.5 2.96 1.83 x 10 - 5i!7.18 x 10 Piperidine 10.6 7.46 4.89 x 10“1 j1.95 result fron author' s work Others from liturature reference 59, 63b Fron the table 6b above, it is seen that for a given Substrate, in methanol, tho activation energies appear to be the same whether the nucleophile is aniline or piperidine while log B fators are much higher (3-4.5 units) for piperidine. Below are assembled Arrhenius Parameters for the reactions of 1-X-2, 4-dinitrobenzeno (X *= F, CI, Br) with aniline ^ in 99.6$ ethanol and for the reactions of 1-X-2, 4-dinitrobenzeno with piperidine 44e, 63b (x = F, CI, Br) in methanol, The comparison of reactions in ethanol and methamjl is legitimate ae . Bamjcole and Hirst have already shown 59 that this change of solvent has little or no effect on the activation parameters. Table 6c Arrhenius parametoys for the reactions of 1-X-2, 4-dinitrobenzene (X = F, CI, Br) with aniline and Piperidine in 99*8 ethanol and methanol respectively and rate constants at 50°C U nN hJIVERSITY OF IBADAN LIBRARY II X! - 169 - Substrate Nucleophile S olvent E (k cal) log B k 50 °C X = F Aniline Ethanul 6.4 2.55 1.68 x 10"‘ X = F Piperidine Methanol 8.4 6.76 11.94 X = CI Aniline Ethanol 11.2 4.0 2.69 x 10" X = CI Piperidine Methanol 11.6 6.7 5.2 x 10-2 X = Br Aniline Ethanol 11.2 4.2. 4.05 x 10" X = Br Piperidine Methanol 11.8 8.5 3.36 From this table as for table 6B, it is seen that for the protic solvents ethanol and methanol, the activation energies are almost the same value for both piperidine and aniline with chloro and brouo substratee; whereas with the fluoro Substrate, the activation energy is even less with aniline in ethanol tlian with piperidine in methanol. The log B units are again about 3-4$ units higher for piperidine than for aniline. Since piperidine is a stronger base than aniline (pka for piperidine is 11.13*pka for aniline is 4.6) one would have expected this factor to operate in favour of piperidine to produce a lower activation energy; but this is not the case. Evidently this is an anomaly, the cause of which is not yet presently understoud. In table 6d below are assembled the Arrhenius parameters for the reactions of 4-nitrofluorobenzene with aniline and piperidine in the norJiydroxylic solvent dimethylsulfoxide ^ . UNIVERSITY OF IBADAN LIBRARY - 17« - Table 6d Arrhenius Parameters for the reactions of 4-nitro fluorobenzene with Aniline and piperidine in dimethylsulfoxide, Reagent E (k cal) log B Aniline 12.7 2.20 Piperidine 9.5 4.88 In this case, unlike the others in tables 6b and 6c above, the activiation energies Show the expected trend, that is the activation energy for piperidine is less than that of aniline. The anomaly mentioned above does not appear to hold here. Thus, correlating the facts from the tables 6b, 6c and 6d, this observed anomaly appoars to apply only when a hydxoxylio solvent suoh as nethanol or ethanol is used. For a discussion of the mobility of the fluorine atom relative, to ths ohloriao atom in methanol and in acetone, other useful data are assembled below: Table 6e A ccmparison of k^ (the rate of formation of the intermediate) for both the fluoro and the chloro compounds in methanol and in acetone. Solvent Methanol Acetone Substrate Reagent k1(l03.6°c) ^(11.2*^3) k1(l03.6°C) ^ ( n ^ c ) 2-P-5-N.P. Aniline 7.21 x 10"4 8.02 x 10"6 2.38x10-5 - 2-C1-5-NP Aniline .1.47 x 10"4 5.01 x 10"7 1.55x10“5 = 4.91 k1F = 16 kV rP = 1.51 - fcjci l^Cl k.,01 2-F-5-NP Piperidine 20.37 2.01 x 10"1 - 8.93 x 10“1 2-C1-5-NP Piperidine 2.07 x 10~1 7.78 x 10"4 - 1.28 x 10~2 k.F k.F k.F k^Cl = 98,6 kjci " 258*3 kjci = 69-7 UNIVERSITY OF IBADAN LIBRARY - 171 - results fram authors work Others are from reference 59. Two facts emerge from this table namely: (a) the relative rates of formation of the intermediate k^P decrease kjci as the solvent is changed from methanol to acetone and (b) Ignoring the fact that different temperatures are involved for reactions in acetone, the ratios k 1 F are considerably higher for k^Cl piperidine in the two types of solvent than for aniline. This is in agreement with the general conclusion that the greater the basicity of the nucleophile, the greater is the activation by fluorine relative to chlorine in bimolecular nuclephilic Substitution reactions. From the values in table 6e, it can also be seen that in each solvent, k^F ]>• k^Cl. This faster rate of reaction for the step 1 of the intermediate complex mechanism for the fluoro Substrate than for the chloro Substrate is likely to be due to the fact that the C-X bond is polarised (X = F, Cl). The degree of plarisation is greater for the fluoro Substrate than for the chloro sunstrate due to the greater electionegativity of the formcr halogen atom, Tho Polarisation can be shown as C ^ X where &+ , 5~- are sraall residual positive and negative charges induced by the Polarisation. The attack by a nucleophile BMHg is thus more enchanced for the fluoro Substrate than for the chloro. UNIVERSITY OF IBADAN LIBRARY - 172 Because the formation of the transition state involves Charge Separation* it is better favoured in methanol than in acetone because of the higher dielectric constant of the former, It might also be noted from the table that (Piperidine ),> (Aniline) for both Substrates and in both solvents; this is solely due to the greater basicity of piperidine which leads to a stronger interaction between the reactive partially positive carbon (l) atom (see above) of the Substrate and the basic nitrogen atom of the nucleophile. The widely different nucleophilicities of aniline and piperidine precluded the measurement of rate constants of these reactions at the same temperature. A much lower temperature was used for piperidine than for aniline. Nevertheless, one contrast looks obvious from table 6e. flhile methanol appears to be a faster solvent than acetone for reactions involving aniline the reverse is the case for reactions where piperidine is used as the nucleophile. The Hughes-Ingold Theory of Solvent Action predicts that methanol would be the faster solvent. The reVersed trend noted with piperidine as nucleophile suggests that a specific solvent effect is operating additionally and in Opposition to UNIVERSITY OF IBADAN LIBRARY - 173 the Hughes-Ingold effect. It is proposed here that this additional specific solvent effect is a ground state effect as explained below: Two types of hydrogen-bonds are possible when a primary or secondary amine is in contact with a solvent which has an electron- donor atom. The first type involves the lone pair of electrons on the nitrogen atom thus H - 0 - R It R - E ̂ H, + R-6'-H R - ¥ - H N R 1 ' l' While the second type involves the electrons on the donor atom of the solvent: H R"\ R N + :0 - H \ H H It is obvious that while ;both types of hydrogen-b onds are possible with a protic alcholic solvent, only the latter is possible with a dipolar aprotic solvent such as acetone. It can also be seen that while the formation of H-bonds of the fitst type can markedly reduce the mucleophilicity of the amine,the H-bondS of the second type cannot, barring the circumstance that its formation might hinder sterically the access of the donor site of the nucleophile to the electrophilic site of the Substrate, It is in these facts that the explanation of the anomalous ’fastnoss1 of acetone relative to methanol in the reactions under consideration lies,- H-bond of the first type reduces the reactivity UNIVERSITY OF IBADAN LIBRARY - 174 - of piperidine in methanol apparently to such an extent that the reduction outweighs the Hughes-Ingold accelerating effect expected for methanol. Hence acetone is a faster solvent than methanol in the reaction of piperidine with 2-halo-5-nitropyridines. When we consider aniline, H-bond cf the first type will be expected to reduce the reactivity of aniline also but here, its effect will be very small, if not negligible, because of the fact that the nitrogen lone pair electrons involved is part of an aromatic, resonating System and in therefore not really available as a lone pair for H-bonding. Hence the situations • • + + + NH, in methanol and acetone with respect to H-bonding are similar, leaving only the Hughes-Ingold effect operating in favour of methanol. As previously pointed out, there is little reason to expect that H-bonding of the second type will have much effect. A comparison of the partial rate constants in acetone can now be carried out. Prora the proposed mechanism, when k_-l » *2 + *3 (B) the original e quation UNIVERSITY OF IBADAN LIBRARY - 175 - reduces to *o . k1 2̂ + kl (B) T--- (611) k 1 k - 1 i.e. it is of the general form k o = k1 + k11 (B) ----(6III) and a plot of ko versus amine concentration will be linear and k^ will be the intercept i.e. the rate constant for the uncatalysed reaction G 1 k'1 1' /k1l is a measure of the relative magnitude of the accelerated and UBAcoolerated parta of tho reaction. ITow, if there is a factor such as the basicity of the amine which can increase k^ relative to k ̂, the relationship between rate constants and amine concentration deviates froa linearity bocause the relationship k k2 + (B) no longer holds. The more basic the amine, the more curvilinear is the plot and the relationship k- i > > ^ S (B) converts to -1 k2 + k3 (B) This explains the curvilinear plots obtained for piperidine in reference 59. Whenever the relationship .1 *2 + k.3 (B) holds, the general equation (6l) ceasos to lond itself to further simplification and a non-linear response of rate constants to base concentration is obtained. The majority of the reactions studied in UNIVERSITY OF IBADAN LIBRARY - 176 - qcetone conformed to this behaviour and the typical plots are illustrated in reference 59. If equation (61) is inverted, equation (6IV) is obtained 1 fco (IV) If it is further assumed that k3 ( B ) » ^ as is the case with good bases, then the equation (6IV) reduces to (6V) io ki 1 ( 6V)^ (B) and except at low amine concentrations when the equation (6V) ceases to apply, a plot of j1r versus 1 should respond linearly but deviating towards the -1j r̂ axis at low( Ba)m ine conc&rtferation; the slope is k___ 1_ k1 k3 and the intercept is _1_ V From the data at low amine concentrations and equation 6IV, ^2 and lc2 can be determined. From such a rate dissection, the figures given in the table below were obtained. Table 6f Partial rate constants for the reactions of 2-X-5-nitropyridine (X=C1,F) with piperidine and aniline. in acetone. UNIVERSITY OF IBADAN LIBRARY - 177 - Substrate Nucleophile T_ enp 0 k, kH * V k 2 2-F-5-nitrcpyridine Aniline 103.6 2.38x10“5 1.60 -31.3 1 9 .5 2-C1-5- " Aniline 103.6 1.55x10~5 3.17x10“1 1.53 4.95 2-F-5- " Piperidine 11.2 8.93x1O-1 1.17x10~5 7.19x10"1 612 2-C1-5- " Piperidine 11.2 1.28x10""2 - - The first and. second reactions in the table above can be compared. The greater 1 value obtained for fluoro compound is expected on general grounds. The greater strength of the C-F bond compared with that of the C-Cl bond and the fact that acetone solvates fluoride ions much less than Chloride ions 39b will reduce kg, the rate constant for the uncatalysed decomposition of the intermediate formed by fluoro compounds relative to the corresponding value for chloro compound. Even though reactions aro at different temperaturcs, the value of k for piperidine reaction with the fluoro Substrate is very much lower than that for the reaction of the same Substrate with aniline as nucleophile. As3uming 1̂ ) to be independent of amine, a change from an aliphatic amine such as piperidine to an aromatic amine such as aniline should result in an increase in the value of . The reason is that in the transition state for the reversion of the intenaediate complex to reactants, represented by k ^, by the principle of microscopic reversibility, there will be soae conjugation of thenitrogen lone pair of electrons with the benzene ring when aniline is the nucleophile. This will stabilise the transition state with respect to that formed by piperidine. UNIVERSITY OF IBADAN LIBRARY 178 Where this offect is not possible,then the ratios would be expccted to be greater for aniline than for piperidine. The ratio kylc> is the degree of base catalysis in the System. From Bunnetts’ Classification 45 , systömswhere k are said to be truly base catalysed. Where the value of the ratio falls appreciably below 50, these Systems are said to be mildly catalysed. Thus according to this Classification, the reaction of 2-F-5~nitropyridine with piperidine in acetone with 1 612 is the only case of true base catalysis. The otheiss are only mildly catalysed. However, in all cases, therolation k^F } k^Cl is observod, and the view is höre hold that all these cases are examples of the familiär intermediate complex mechanism in which the decomposition of the intermediate is base catalysed. To hold a different view is to say that the measured overall rate in acetone corresponds to the formation of the intermediate complex and one would then have to explain why the overall measured rate in the case of aniline is greater for the chloro Substrate than for the fluoro 59 , a sequence which has never been observed for the first step of the intermediate complex mechanism and which is contrary to the theoretical predictions already disccused. While the obscrved rate constants for the reactions in methanol are those for the formation of the intermediate complex, those for reactions in acetone are partly dependcnt on the rates of base assisted decomposition of the intesaaodiate to products except for the reaction of 2-Cl-5-nitropyridine with piperidine where ko = . In conclusion, the intermediate complex mechanism can be shown as UNIVERSITY OF IBADAN LIBRARY - 179 - (a) *2 Products R k~120 HH + Substrate =1sT=-s1 Intermediate C omplex (b) h . Products In mothanol, tho roactions of both fluoro and chloro Substrates with both amines go via path (a) and thore is apparently no base catalysis. In acetono, however, tho rates of reaction are partly dopendent on both paths; tho path which overrides tho othor deponds on tho Substrate, whether fluoro or chloro and the basic strength of tho nucleophile. The most favoured mechanism 17 proposed for the step in which base catalysis occurs can be fomulated as follows: >cv Jrt— X &-H—X i-Ra. II y + XNC k *N ° x This, in itself, comprises two steps - The intermediate I reacts reversibly with the base giving the second intermediate II and the conjugate acid of the base BH + In the second and rate determining step, the conjugato acid of the base B electro-philically assists the Separation of tho leaving group X front tho intermediate II. Thus each •j (B) term of the equation 61 above really ropresents the product ^ KB where ]ju is the equilibrium constant for the reaction of intermediate I with the base B to give intermediate UNIVERSITY OF IBADAN LIBRARY - 180 II and BET1- and lr̂ is the rate coefficient for the conjugate acid—catalysed expulsion of the leaving group X from the intermediate II. It follows that when B i s a good base, k^ is very mich greater than k^ and hence k^/k-j for piperidine is mich greater than for aniline. This trend has been confirmed for the fluoro Substrate (table 6f) for the reaction of the fluoro compound with aniline, is 3 1 but for reaction with piperidine, the ratio is much lower being only 0.7. For the readfckm of the chloro compound with aniline, is reduced to 1.5 i.e. approzimately io01 of the value for the fluoro compound. If the same reduction took place for the reaction with piperidine, then k -1 U- ^ i.e. it conforms to the condition when k -1 L*- ku, + kj (b ) and as explained earlier, no base catalysis will be observed as shown ln table UNIVERSITY OF IBADAN LIBRARY - t 80 II and BH4 * and k^ is the rate coefficient for the conjugate acid - catalysed expulsion of the leaving group X from the intermediate II. It follows that when B is a good base, ^ is very much greater than k^ and hence k̂ ŷ . for piporidine is much greaterthan for aniline. This trend has been confimed for the fluoro Substrate (table 6f). For the chloro Substrate however, k^/k for aniline is 4*95 while it is nil for Piperidins. Other factors, not presently known, must be responsible foor this reversed Order. Also when X is a good leaving group, the catqlytic ability of the base, if any, will not be nanifested; but when X is a poor leaving group this catalytic effeet can be rnore readily observed and hence for the same nucleophile, h (?) > h. (Cl) This is true for both nucleophiles as shown in table of. UNIVERSITY OF IBADAN LIBRARY - 181 - The reactions of 1-X-2. 4-dinitrob8nzene (x= F. Cl) with: (a) Piperidine in acetone (b) n-butylamine in Chloroform ( c) Piperidine in mothanol (d) n-butylamine in acetone The reactions of 1-X-2. 4 - dinitrobenzene (X = F . Cl) with Piperidine in acetone For the reactions of both fluoro and chloro Substrates, the second-order rate con3tants increased with increasing amine concentrations: this increase was non-linear and the curvilincar plots 3 and 4 were obtained from the data in tables 3 and 4 respectively. These reactions fall into the dass where k “ 1 k2 + k3 (B) Front the dissection of rate constants the results in table 6g were obtained. The reaction 59 of the fluoro Substrate with piperidine at - 30 öC is included for comparison. Also the reactions of 6b4oth Substrates withaniline at 50°C are included. Table 6g Partial rate constants for the reactions of 1-X-2, 4 - dinitrobenzene (X = F,Cl) with piperidine and aniline in acetone. Substrate Nucleophile Tenp °C k1 k-l/k3 k-Vk2 V k 2 1-C1-2-4-DMB Piperidine 30 7.27x10"1 8.31x 10~3 3.33 400 1 —F ,2—4—DNB Piperidine 30 55.02 3.67xlO~4 22.1 6.06x10 1-F,2 t4-DNB Piperidine -30 37.6 7.92x10-4 1.27 1.61x10 UNIVERSITY OF IBADAN LIBRARY I ~ FLUORO— 2 , 4 -DINITROBENZENE + PIPERIDINE IN ACETONE AT + 30°C FIG ■ 3 IO+ 5 [B} mok lü r e - ' lü re mol 1 sec UNIVERSITY OF IBADAN LIBRARY I -C*«H L O R O -21,.. ..4...-.D...I..N...I..T..R...O....B...E..N....Z...E..N....E... ....W....I.T..H... .....P...I.P...E...R...I.D...I.N...E.. ......I.N... ....D...R..Y... ....A...C...E...T..O...N....E.. .......A...T.. ....+...30°C [b3 molc litre 1 U litre m ol“NIVERSITY OF IBADAN LIBRARY 182 1-C1-2,4-DNB Aniline 50^ 6.54x10"5 1.09xl0_1 5.04 46.5 1-F-2,4-DNB Aniline 50 5.25x1O-3 1.60 - - i 30 °C Ü L k.p > 50°G(^Cl\) = 75.7 ( 80 piperidine Aniline There is base catalysis with both Substrates at 30 Cwhen the nuclecphile is piperidine as k„jS/kg ^ 50 in both cases, The results obtained for the fluoro Substrate with piperidine at -30 C compares favourably with those at +30, oC„ except. f.or. val. ues w.h ere one woul_ d_ .h ave expect, ed, ,k ^ at + „3„0o „C to be much greater than that at -30°C instead of the 1.5 increase observed. The catalysis of the fluoro Substrate is much greater than that of the chloro Substrate as expoctedon the basis of the proposed mechanism. as discussed ealier on in this chapter. The values of k-^/kg are also in the expected sequence i.e. greater for fluoro than for chloro; beCause of the greater strength of the C-F bond compared with that of the C-Cl bond and the fact that acetone colvatcs fluoridc 'Zt Qy. ions much less than Chloride Ions will reduce kg the unimolecular rate constant for the decompositon of the intermediate formöd bjr fluoro - compounds, relative to the corresponding value for the chloro - conpounds. The rate of formntion of the intermediate, k^, is greater for the fluoro Substrates than for the chloro Substrates with both nucleophiles. This is as expected, uS earlier discussed, because of the greater activation by the fluorine atom. The partial rate oonstant for the reactions of 2-X-5-nitropyridine UNIVERSITY OF IBADAN LIBRARY 183 (X = F, Cl) with piperidine and aniline in acetone assembled in table 6f earlier on can be compared with those in table 6g. Although the figures are not strictly comparable due to the vri.de spread of activity which precluded measurements of all the rates at the same temperature, some generalisationscan be made. Even though the values of ' F/Cl ratios for are expected to be temperature variable, this not withstanding, the figures indicate that for reactions with aniline, the ratio is higher in the 2,4 - dinitrobenzene than in the nitropyridine series. In the latter seriös, the value of this ratio is greater when the nucleophile is piperidine than ifhen it is aniline. In the former series, the present work gives about the same value for this ratio for aniline and piperidine. These results show that the greater the activation of the Substrate, the greater io the F/Cl ratio for lĉ . In contrast to an earlier notion 59, it does not appear unambiguously that there is a correlation of this ratio with base strength. Effect of change of solvent from acetone to mothanol/ethanol on the rate of formation of the intormediate can also be ohtained with the aid of table 6h below. The usoof the data obtained in methanol and ethanol is legitimate as Bamkole and Hirst have shown 59 that a change from methanol to ethanol has little or no effect on the activation parameters. The figures in table 6h are already included in those of table 6c. Table 6h Rate of formation of the intermdiate coiaplex for the reactions of 1-X-2, 4 - dinitrobenzene (X = Cl, F) with piperidine and aniline in UNIVERSITY OF IBADAN LIBRARY 184 methanol f) ̂ and ethanol respectively. Substrate Nuclaiphile Solvent Temp °C k1 1-F-2,4-DNB Piperidine Methanol 50 11.94 1-Cl-2,4-DNB Piperidine Methanol 50 5.2x10-2 1-P-2,4-DNB Aniline Ethanol 50 1.66x10“2 1-Cl-2,4-DNB Aniline E thanol 50 1.94x10-4 1_P_2,4_DNB Piperidine Methanol 30 5.02 1-C1-2,4-DNB Piperidine Methanol 30 1.55x10"2 - DNB is abbreviation for -dinitrobenezene ( 50 (kjci) 229.6 ( V ) 50 (k,Cl) 85.6 Piperidine Aniline Por the reactions in tables 6g and 6h, when the nucleophilo is aniline, the rates of formation of the intermediate complex is faster in the hydroxylic solvent ethanol than in acetone. This is consistent with the theory of Hughes' Ingold which predicts that for reactions anong neutral nolecules, going through charged Intermediateofa cliange to a more oolvating solvent such as fron acetone to methanol or ethanol, will result in an increase of rate of reaction. But whentfco nucleophile is piperidine,the aprotic solvent acetone is nuch faster than the protic solvent methanol. In the case of piperidine, it would appear that solvation effects acting via hydrogen bonding favour acetone over methanol. This sequence has already beon observed in the UNIVERSITY OF IBADAN LIBRARY 185 nitropyridino series earlier on and the discussion there also applies here. Also, as in the nitropyridine series, in both solvents, k1 F > k1 C], and also for both. solvents (Piperidine)^ k̂ (Aniline) From the results in tables 6f, 6g, and 6h, it will be gathered that the reactions of the 2-chloro-5-nitropyridine series are slower than those of the 2, 4 - dinitrobenzene series. This is easily explained as due to the greater activating ■ effect of an ortho nitrogroup relative to an ortho cyclic nitrogen atom. b. The reactions of 1-X-2. 4 -dinitrobenzene (X = F, Cl) with n-butylanine in stabilised and destabilised Chloroform. For both the fluoro and the chloro Substrates, there is a snall linear dependence of rate constants on anine concentration; tables 7 and 8 and the respective plots 7 and 8 illustrate this fact. The data derived fron these plots are given in table 6i below together with the result obtained 22 by S.D. Hoss with the chloro Substrate. k'* is the intereo_r i.e. the rate constant for the uncatalysed reaction and the unit i0 litro nol“1 ßec-15 k 11 i.s the slope i.e. the rate constant for the amine catalysed reaction and 2 the unit is litre 2 nol sec• “•1 . k 11 /k 1 is therefore the extent of base catalysis in the systen. Table 6i Surmiary of k 11 , k 1 , k 11 /k 1 for the reactions of 1-X-2,4—dinitrobenzene UNIVERSITY OF IBADAN LIBRARY I - FLUORO— 2 ,4 - DINITROBEN2ENE WITH p-BUTYL AMjNE IN STABU.ISED CHLOROFORM AT 24 82°C FIG- 7 QBj mol* litr«-I UNIVERSITY OF IBADAN LIBRARY I -CHLORO — 2 , 4 - DINITROBENZENE WITH n-BUTYLAMINE IN STABILISED CHLOROFORM AT 24B20C FIG- 8 £Bj molc Mir«-1 litre mol“ UNIVERSITY OF IBADAN LIBRARY 186 (X = P, Cl) with n-butylamine in stabilised chloroform. Substrate Nucleophile Temp °C k11 k1 P 7 ki 1-C1-2,4~DNB n-butylamine 24c82 5.29x10"4 1.90xlO“4 2.8 1-P-2,4-DEB n-butylamine 24.82 7.63x10~1 2.5x10™1 3.1 1~G1-2,4~DNB 22 n-butylamine 24.82 5.63x10"4 1.87x10~4 3.0 These reactions Show very mild base catalysis. Por both Substrates, stabilised and destabilised Chloroform were used; the rate constants obtained were the same within thelimits of experimental error in both solvents - compare figures in tables 7 and 7a, 8 and 8a. Por the fluoro Substrate, when the stabilised Chloroform is used, the molar concentration of tho oubctra' is 2.5 x 10- 4 while that of ethanol, the stabilising agent is 2.00 x 10- 2 M. The ethanol is therefore present in much lar&er concentration than the Substrate. This malces it possible, from the hydrogen-bonding point of view, for the internediatc complex to be preferentially solvated by ethanol when stabilised Chloroform is the solvent, and for the course of the rea.ction to follow essentially the same path as when ethanol is the solvent thus resulting in little or no catalysis. If this were so, then when the ethanol is renoved, i.e. the Chloroform is destabilised, a bigger response to the effect of increasing amine concentration may have been expccted, But the results show that the renoval of ethanol has no effect on the rate constants. This may mean that specific solvent effects such as hydrogen-bonding of the transition state by ethanol does not cccur in these reactions or if it does, such specific effect is also UNIVERSITY OF IBADAN LIBRARY - 187- equally possible with pure Chloroform. Ross, in his own work, attributed22 such mild accelerations in these reactions which involve a good leaving group and do not attain a limiting rate at high amine concentration as true base catalysis due to the presence of a hydrogen bond from the amine nucleophile to a suitable acoeptor in the transition state for the intermediate formation. The acoeptors can be a second amine molecule or an anion such as CH^COCT* or 01f" or even any neutral molecule with groups that can act as hydrogen bond aceeptor e«g. the NOg group in m - dinitrobenzene.® C. The reactions of 1-X-2. 4^dinitrobenzene (X « F. Cl) with Piperidine in methanol with and without Piperidine Hydrochloride. The results obtained for these reactions are given in tables 1 and 2. Fo* both the fluoro and the chloro Substrates, there is an increase in rate constants with increasing amine concentration. The plot of rate constants versus amine concentration for the chloro Substrate is linear with a single slope; for the fluoro Substratet however, there is first a gentle slope; then a steep slope see plots 1 and 2 respectively. The addition of Piperidine hydroChloride did not seem to have had any appreeiable effect on the rates of the reactions - see the plots of the values on the same graphs plots I and 2. If the presence of the hydrochloride had made any difference to the rates, this may have been attributed to electrophilic assistance by piperidine hydrochloride in the removal of F or Cl atom in the decomposition of the intermediate complex to produots. UNIVERSITY OF IBADAN LIBRARY I - FLUORO— 2. 4 - DINITROBENZENE 4- PIPERIDINE IN METHANOL AT -2 9 6° C WITH AND WITHOUT PIPERIDINE HYDROCHLORIDE FIG- I, I a with piperidinc hydrochloride without pipcridipe hydrochloridc IO2 [B l molc litrc 1 litrc UNIVERSITY OF IBADAN LIBRARY l - C H L O R O — 2. 4 - DINITROBENZENE WITH PIPERIDINE IN DRY M ETHANOL AT 3Q -2Q °C WITH PIPERIDINE HYDROCHLORIDE AND W ITHOUT I with piperidine hydrochloride without piperidine hydrochloride > 4427 23. J. Hine Phys. Org. Chen. 2nd Edition 1962, 393 24. G. S. Hanmond and L. R. Parks. J. Aner. Chen. Soc. 1955, 22» 540 25. Lewis and Suhr ibid 1960 82, 862 26. E. C. Okafor PH.D. Thesis 1966 27. S. I. Ette PH.D. Thesis 1972 28. H. Suhr Ber. Bun. Phys. Chen. 1963, .62, 893 29. P. Haberfield et al J. Org. Chen, 1971, 21> 1792 30. G. Scatchard J. Chen. Phys. 1939, 2.» 657 31. J. G. Kirkwood J. Chen. Phys. 1934, 2, 351 322 K. J. Laidler and H. Eyring. Ann. N.Y. Acad. Sei. 1940, 22, 303 33. G. Scatchard Chen. Revs. 1931, j3, 521 34. E. S. Anis and V. K. Laner J. Aner. Chen. Soc. 1939, 21» 905 35. C. V. King and J. J. Josephs Ibid 1944, 66, 767 36a. E. D. Hughes Trans. Farad. 1941, 21, 603 36b. C. K. Ingold; Structure and Mechanisn in Organic Chenistry, Bell, London, 1953, 345. 37. K. J. Laidler - Chenical Kinotics, - Mc Graw-Hill, N. T. 1950, 110 38. J. 0. Leffler J. Org. Chen. 1955, 20, 1202 39a. J. Miller and A. J. Parker J. Aner. Chen. Soc. 1961, 83, 117 39b. A. J. Parker J. Chen. Soc. 1961, 1328. 40. Canell and Speed Ibid 1961, 226 UNIVERSITY OF IBADAN LIBRARY - 192 - 41. An Introduction to Physical Organic Chemistry E. M, Kosomer, John Wiley and Sons, Inc. New York, 1968, 293 42a. E. Grunwald andS. Winstein J. Aner. Chen. Soc. 1948, JO, 846. 42b. E. Grunwald and S. Winstein Ibid 1951, 22» 2700 43. C. G. Swain, R. B. Moseley and D. E. Brown J. Aner. Chen. Soc. 1951» 2 2 » 3 7 3 1 . 44. Fierens et al Bull. Soc. Chin. Beiges 1955, Ü4, 308 44b. Vogel, A textbook of Practical Organic Chen. Longnan's 3rd Ed. 1956, 530. 44c. Caldnell and IConfield J. Aner. Chen. Soc. 1942 , 6̂ , 1696 44d. L. F. Fieser; Expts. in Org. Chen. 2nd Ed. D. C. Heath and Co. Boston, Hass. 1941, 360. 44e. J. F. Bunnett et al J. Aner. Chen. Soc. 1957, 22» 385 44f. Chapnan and Rees J. Org. Chen. 1954, 1190 45. J. F. Bunnet and H. Garst. J. Aner. Chen. Soc. 1965, 87. 3879. 46. T. 0, Bankoie, C.W.L. Bevan, J. Hirst, Nig. Journal of Science 1968, 2 , 11. 47. C. F. Bemasconi J. Org. Chen. 1967, 32, 2947 48. S. D. Ross and I kuntz J. Aner. Chen. Soc. 1954 , 2§> 3000 49a. F. Pietra and Fava Tet. Let. 1963, 1535 49b. F. Pietra and Fava Tet. Let. 1965, 745 50. C. F. Bernasconi and I Zollinger Tet. Let. 1965, 1083. 51. H. Suhr. Chen. Br. 1964, 22 , 3277 UNIVERSITY OF IBADAN LIBRARY 193 52. C. F. Bernasconi and I Zollinger Ibid 1967, .KJ, 50 53. J. F. Eunnett and C. F. Bernasconi J. Aner. Chea. Soc. 1965, 82, 5209 54. F. Piutra and D. Vitali Tet. Let. 1966, ĵ 6, 5701 55. P. Pietra and F. D. Cima Tet. Let. 1967, 4573 56. F. Bernasconi Helv. Chem. Acta. 1967, jjj, 50 57. F. Bernasconi and I. Zollinger Helv. Chea. Acta, 1966 4^, 2563 58. F. Pietra Quart. Revs. 1969, 22, 504 59. T. 0. Baakoie and J. Hirst, J.Chea. Soc. 1969, 848 60. N. B. Chapnan and R. E. Parker J. Chen. Soc. 1951, 3301 61. J. Miller, Nucleophilic Aromatic Substitution. Elsevier Publishing Co. New York 1948, 147 62a. H. Suhr Ann. Chen. 1965, 687. 175 62b. H. Suhr Ann. Chea. 1965.689. 109 63. Uba N^ Project 1967 63b. Yussuf N^ Project 1967 64. 0. Banjoko, L. Bevan, J. Hirst Nig. J. Sei. Vol. 2. No. 1 1968 UNIVERSITY OF IBADAN LIBRARY