No description available.

No description available.

The reactions of several nitro-aromatic substrates with the aliphatic amines, n- butylamine, pyrrolidine and piperidine in DMSO have been studied. Reaction of the amines with trinitroaromatic compounds, such as ethyl thiopicrate, phenyl thiopicrate and phenyl 2,4,6-trinitrophenyl ether, was shown to occur in two well separated processes. A rapid reaction, occuring at an unsubstituted ring position, resulted in the formation of a a-adduct; this was followed by a slower substitution reaction, resulting in the displacement of the 1-substituent to give the amino-substituted compound. Kinetic results show that in the formation of the σ-adduct, the rate determining step changes from nucleophilic attack by amine with n-butylamine to proton transfer from the zwitterionic intermediate with piperidine; with pyrrolidine the proton transfer step is partially rate limiting. The substitution reaction involving n-butylamine is not base catalysed indicating nucleophilic attack, the k(_1) step, is rate determining. However, the reactions with pyrrolidine and piperidine are subject to general base catalysis showing proton transfer is involved in the slow step. The rate limiting step is thought to be the proton transfer from the zwitterionic intermediate to base. A single substitution reaction was seen for the reaction of the less activated 1-substituted 2,4-dinitrophenyl and 1-substituted 2,4-dinitronaphthyl compounds. The rate limiting step again changes from nucleophilic attack with n-butylamine to proton transfer with pyrrolidine and piperidine. The uncatalysed, k(_2), pathway was detected during the reaction of the 1-substituted 2,4-dinitrophenyl compounds. Those were the least activated substrates studied and as the effectiveness of the base catalysed step relative to the uncatalysed decomposition of the intermediate decreases with decreasing activation of the substrate, detection of the uncatalysed step became possible. Kinetic and equilibrium studies were also made on the reaction of morpholine with several phenyl ethers. Results were compared with those for piperidine with the same substrates, the values of the kinetic and equilibrium constants were as expected considering morpholine has the same steric requirements as piperidine but is considerably less basic.

No description available.

No description available.

The aim or the thesis was to produce accurate rate measurements, from which an accurate value of ∆Cp* at constant atmospheric pressure could be calculated and so obtain more information concerning the activation process for the S (_n) l solvolysis of benzhydryl chloride. It was hoped that the data would be accurate enough to determine any possible temperature coefficient of ∆Cp*.The solvolysis of benzhydryl chloride can be followed accurately via the development of acidity, either by titrimetric analysis or conductance measurement of the reaction mixture. It was calculated assuming that conductance and concentration are linearly related, that conductance measurements were capable of producing rate coefficients with a fractional error better than 1 x 10 (^-4) Whilst such an assumption has been used in the past, it was found not to be applicable in this case. It was therefore decided to computer fit the rate data using equation I, a relationship between conductance (L) and concentration (c): c = AL + BL (^3/2) + C I together with the rate equation, equation II: ln (P - P) = A - kT II which when combined together yield equation III which was computer fitted: y = ln (l - X) = A(_l) T + A (_2) – ln (l – A (_3). X (_1+x(^2)) III where X = L/L A (_1) = -k A (_2) Involves all the Xo terms A(_3) = A 1/3 / 1 + A 1/3 A 1/ = B/A. L ½. The rate coefficients calculated from equation III had a fractional error in the range 0.001 to 0.0008, whilst being an order of magnitude better than any obtained in the past, were not as good as the 1 x 10 (^-4) that had been expected. This in turn meant that the activation parameters, particularly ACP*, had disappointing accuracies. One of the causes is without doubt the limited temperature range (now 25, normally 50), over which the rate coefficients were determined due to experimental difficulties. Also the introduction of the parameter B/A, is also partly responsible for the poor accuracy of the activation parameters. In the event, no conclusions as to the magnitude of d/dT (ACp*) were possible. It was also the aim of this thesis to study the same reaction under conditions of constant volume, since suggestions had been made that activation parameters at constant volume might be easier to interpret. However, even greater experimental difficulties were encountered, it was therefore decided to limit the study to obtain accurate rate data at constant atmospheric pressure.

This thesis is divided into four chapters. In Chapter 1 the calculation of the acidities of a series of substituted methyl styryl ketones and some miscellaneous carbon acids using a semi-empirical allvalence electron molecular orbital approach is described. Satisfactory correlation is obtained between the calculated and experimental acidities for these molecules. It has also been shown that the order of relative acidities is determined by the facility of negative charge delocalisation in their corresponding carbanions. In Chapter 2 the base-catalysed rates of detritiation of some substituted methyl styryl ketones are reported. The results clearly show that by comparison with the structurally similar acetophenones the interposing of the vinylic linkage in the substituted methyl styryl ketones reduces the effect of the substituent on the hydroxide-catalysed rates of detritiation. In Chapter 3 an account of the synthesis of some substituted benzoylacetones is given. In addition the thermodynamic and kinetic acidities for these 3-diketones have been measured. The primary kinetic isotope ratio k[H]/k[D] values for benzoylacetones are approximately half the k[H]/k[T] values and the Swain-Schaad ratio is close to the expected value of 1. 44. The magnitude of the solvent kinetic isotope effect in the case of anion catalysis is very small (1.22-1.09) and for water catalysis the value is appreciably higher (1.68). In view of the relatively high primary kinetic isotope effects and values near 0. 5 obtained for the Bronsted B parameter a symmetrical transition state is postulated for these B-diketones. In Chapter 4 the rates of detritiation of (alpha-[3]H)-p-dimethylamino-acetophenone in methanolic and ethanolic solutions of potassium, sodium and lithium alkoxides at 25° C are reported. In all the cases considered the alkoxide ion pairs are more reactive than the corresponding free ions. The reactivity of ion pairs follows the order KOR > NaOR > LiOR.

The glucose/valine reaction was investigated as an exampie of a reaction between organic solids. The reactions between glucose and other amino acids were studied in less detail. Both, the kinetics of the reaction and the chemical composition of the products were investigated. Contrary to previous results, dry crystals of glucose and valine reacted readily at a temperature below the melting point of either reactant. Increase of humidity appeared to decrease the rate of reaction. Water, CO2 and isobutyraldehyde were the major gaseous products. The rate of reaction was followed by measurement of pressure change on a vacuum line and also by measurement of weight loss on a thermogravimetric balance, The kinetic curves obtained on both systems were of sigmoid shape and seemed to be similar. The reaction did not go to completion. The activation energy obtained was 34 Kcal/sole and did not vary with particle size. The approximate "orders" of reaction were 0.5 and 1.0 with respect to valine and glucose. Observation by optical microscope and electron microscope suggested the reaction might occur on the surface of glucose and photographs taken showed a build up of inert product which hinders further reaction. Analysis of reaction products showed that (X-amino acids and glucose react to give water, CO2 and the aldehyde containing one fewer carbon atoms than the amino acid, Carbon-l4 labelling showed the CO2 to arise from the carboxyl group of the amino acid. A number of minor products were partly or wholly identified. There was some evidence that the glucose was being degraded as well as reacting with valine" Efforts were made to find out the kinetic rules for the reactions of this kind, and the data were fitted with varying degrees of success to equations suggested by Avrami and Erofeyev and others" A mechanism of reaction involving the Strecker degradation was outlined. The mass spectra of several hexoses and some pentoses and disaccharides were obtained and analysed. No molecular ion peaks were obtained and the most abundant ions generally appeared at mass numbers 73, 60, and 31, The differences between the sugars were insufficient for this to be an acceptable method of analysis.

The SE2 reaction (1) between tetra-alkyltins and mercury(II) salts has been studied kinetically (R = Me, Et, Prn, Pri, Bun, Bui, Peneo; X = OAc in solvents methanol and tertiary butanol at 30 °C and R = Me, Et; X = Cl, I, OAc in solvents methanol, ethanol, n-propanol, n-butanol and tertiary butanol at 25 °c). R4Sn + HgX2 → R3SnX + RHgX (l) The following order of reaction rates was observed for (1), X = OAc, in solvent methanol: R = Me > Et > Prn > Bun > Bui > Peneo > Pri (2) Although this sequence is probably steric in origin, it is not the same sequence as is observed in SN2 reactions, and in SE2 reactions which proceed with inversion of configuration at the substituted carbon atom (SE2(open)Inv reactions). It is suggested that reaction (1) in methanol proceeds with retention of configuration at the substituted carbon atom, by mechanism SE2(open)Ret. It is further suggested that the stereochemical course of SE2(open) reactions of substrates RMXn may be deduced from a consideration of the constitutional effects of alkyl groups (R) on the rate of reaction; if these effects parallel steric effects in SN2 reactions, then mechanism SE2(open)Inv is indicated, but if the constitutional effects parallel those found for reaction (1) in methanol (sequence (2)) then mechanism SE2(open)Ret is indicated. In this way, stereochemical assignments for a number of other SE2(open) reactions have been deduced. Calculations have shown qualitatively and semi-quantitatively that the reactivity sequence (2) does indeed arise from steric effects, mainly in the transition state, in reaction (1). Similar calculations were also carried out on the SN2 reaction between bromide ion and alkyl bromides, and it was demonstrated that the different steric effects in inversion and retention reactions are a result of the different geometrical shapes of the transition states. Standard free energies of the reactants in (1) (R = Me, Et; X = Cl, I, OAc) were determined for transfer between the five alcoholic solvents, and combination of these initial state solvent effects with the kinetic data enabled transition state solvent effects to be calculated for the reactions. It was concluded that the transition states in these SE2(open)Ret reactions behave as polarisable species, with quite a high degree of charge separation. The SN2 reaction (3) was also studied kinetically, in solvents water, methanol, ethanol, n-propanol, isopropanol, n-butanol, tertiary butanol, ethyl acetate, ethyl benzoate and acetonitrile, at 25 °C. Et3N + EtI → Et4N+I- (3) Gas-liquid chromatography was used to determine terminal values of Raoult's law activity coefficients for both reactants, in a large number of solvents, thus permitting a dissection of solvent effects on the reaction into initial and transition state effects, for more than 30 solvents. It was concluded that the transition state in this Menschutkin reaction behaves as though it were a polarisable non-electrolyte, rather than an ion pair, and that in many solvents, the effects are due to specific solvent-solute interactions.

The kinetics of the reactions between tetra-alkyltins, R4Sn, (R = Me, Et) and mercury(II) halides, HgX2,(X = Cl, I) in solvent ethyl acetate have been studied kinetically at various temperatures. The stoichiometry of the reactions is expressed by equation (1): R4Sn + HgX2→RHgX + R3SnX . (1) The reactions in ethyl acetate follow second-order kinetics, first-order in each reactant. From the kinetic salt effect studies on reaction (1) (R = Et and X = Cl) in ethyl acetate, it is shown that the reaction proceeds through a polar transition state. The sequence of reactivity among the alkyl groups for reaction (1) (R = Me, Et and X = Cl, I) is shown to be Me > Et. This sequence has been used by previous workers as evidence for mechanism S E2(open). By analogy, this mechanism is suggested for the reactions in ethyl acetate; the salt effect studies, above, provide confirmation for this suggestion. Activation parameters for reaction (1) (R = Me, Et and X = Cl, I) in ethyl acetate were shown to be consistent with mechanism S E2 (open) . The solvent effects on the variation of the activation parameters DeltaG+, DeltaH+ and DeltaS+ for reaction (1) (R = Me, Et and X = Cl, I) when solvent methanol or acetonitrile is replaced by ethyl acetate have been dissected into initial- and transition-state contributions. It is shown that in nearly all cases both initial- and transition-state effects are important, but the major solvent effect is on the transition state. Reaction (2) (R = Et and R' = Me, Et, Bu t, ClCH2CH2) and (2) (R = Me and R' = Me, Et) in ethyl acetate has been studied at 25C. R4Sn +Hg(OCOR')2 →RHgOCOR' + R3SnOCOR' (2) From the effect of the substituents (R') on the rate of reaction, mechanism SE2(open) is postulated. Reactions of phenyltriethyltin with mercury(II) halides have been studied kinetically in methanol at various temperatures. The stoichiometry of the reaction is represented by equation (3) (X = Cl, I): PhSnEt3 + HgX2 → PhHgX + Et3SnX (3) Reaction (3) follows second-order kinetics, first-order in each reactant. When X = I the reaction is followed by a fast equilibrium, equation (4): Et3SnI + Hgl2 ↔ Et3Sn + Hgl3 (4) It is shown that mercury(II) chloride reacts only via the covalent species HgCl2. The order of reactivity among the mercury(II) salts for reaction (3) in methanol was found to be: Hg(OAc)2 > HgCl2 > Hgl2 > Hgl3 (5) Added water mildly accelerates reaction (3) (X = Cl) whilst inert salts tend to retard it; the activation enthalpy of reaction (3) (X = Cl, I) is quite low, and it is suggested that the transition state of the reaction resembles a pi-complex rather than a sigma-complex. Reaction (3) (X = Cl, I) has also been investigated in solvents acetone and ethyl acetate at various temperatures. Results are similar to those found in methanol and similar mechanistic conclusions are drawn. It is concluded that reaction (3) is a suitable electrophilic aromatic substitution for studies of salt effects and solvent effects.