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The rates of hydrolysis of model sulphonate esters in aqueous solutions of concentrated sulphuric acid were studied. Data for these compounds were used to calculate the solvent parameters Y<SUB>OTs</SUB> and N<SUB>OTs</SUB> in 0-60% w/w sulphuric acid using the Grunwald-Winstein approach. The small increases in hydrolysis rates of sulphonate esters were found to be due to medium effects with no acid catalysis occurring below 50% w/w sulphuric acid. The product distribution of 6-octyn-2-ol benzene sulphonates were predicted from Y<SUB>OTs</SUB> and N<SUB>OTs</SUB> parameters in sulphuric acid solution. Phosphonate esters were found to be sensitive to acid catalysis in dilute acid solution. Phosphonate rate data in dilute acid solution were dissected into the contributions arising from solvolytic and acid-catalysed reaction pathways. The rates of hydrolyses of phosphonate esters in 0-98% w/w sulphuric acid solution were measured and discussed in terms of acidity function theory. A novel approach, using an extension of the Grunwald-Winstein method, to correlate reaction kinetics of protonated substrates in concentrated acid solution was developed. The similarities between this novel approach and the more traditional acidity function method are discussed. The relevant background in the preparation and use of phosphonic acid containing compounds as intermediates for reactive dyestuffs is briefly discussed and the dyeing of cotton fabrics is outlined.

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A fair amount of research has been carried out on the reactions of nitrous acid with aryl hydrazines, with marked differences in mechanism between the reaction of nitrous acid with 2,4-dinitrophenylhydrazine, and the reaction of nitrous acid with alkyl and halogen substituted aryl hydrazines. It was hoped that study of the electrophilic nitrosation of 2-nitrophenylhydrazine would serve as a link between the two sets of results. A large range of electrophilic nitrosating agents are known, and the spectra of two of these; dinitrogen trioxide (N<SUB>2</SUB>O<SUB>3</SUB>) and nitrosyl thiocyanate (ONSCN), have been studied using stopped flow spectrophotometry. Earlier studies of the nitrosation of hydrazine using sodium acetate/acetic acid buffers, produced discrepancies between observed rates compared to a rate calculated from measurements made in much more acidic conditions in HC1O<SUB>4</SUB>. Consequently the original study has been re-investigated and extended. There is considerable current interest in the electrophilic nitrosation of sulfur compounds, which leads to the formation of sulfur-nitroso intermediates, and in the subsequent decomposition reactions of these intermediates. Preliminary work on the reaction of nitrous acid with tetramethylthiourea (NMe)<SUB>2</SUB>CS, showed some unexpected <SUP>1</SUP>H NMR spectra for the products. A likely product of the decomposition of the S-nitrosothiouronium ion intermediate (NMe<SUB>2</SUB>)<SUB>2</SUB>CSNO<SUP>+</SUP> is [(NMe<SUB>2</SUB>)<SUB>2</SUB>CSSC(NMe<SUB>2</SUB>)<SUB>2</SUB>]<SUP>2+</SUP> and this species should also be formed in the oxidation of tetramethylthiourea by bromine. This led to an investigation of the reaction of (NMe<SUB>2</SUB>)<SUB>2</SUB>CS with bromine in aqueous solution, with a comparison made between the products gained by bromination and nitrosation, using <SUP>1</SUP>H NMR.

An introduction to a range of inorganic solids as heterogeneous catalysts in aromatic bromination reactions is given in Chapter 1. These solids involve silica, alumina, zeolites, clays, and heteropolyacids. Aromatic bromination over these solids is discussed. Regioselectivity towards the <I>para</I>-isomer of various alkylbenzenes is the main theme but the advantages and disadvantages of each brominating system are also discussed. In Chapter 2 the bromination of phenyl acetate (PA) is tested using zeolites, clays and AlCl<SUB>3</SUB> as catalysts. Zeolite NaY was found to be the most efficient catalyst for the <I>para-</I>selective bromination of PA in the presence of dichloromethane. Use of NaY zeolite allows the bromination of PA to give almost exclusively the <I>para</I>-isomer in quantitative yield. Additionally, the effect of the counterions, activation temperature of the zeolite, and solvent on the reaction were also investigated. In Chapter 3 the bromination of PA <I>via</I> a solvent-free process has been investigated. Additives (<I>i.e.</I> acetate anhydride, NaHCO<SUB>3</SUB> and NaOCOCH<SUB>3</SUB>) as HBr scavengers can markedly increase the selectivity for <I>para</I>-isomer. In particular, a mixture of zinc acetate and bromine is shown to be an efficient reagent for <I>para</I>-selective bromination. In Chapter 4 the separation of 4-bromophenyl acetate (4-BPA) is studied. 4-BPA can readily be separated in pure form from industrial distillation residues by selective sorption into ZSM-5 from a cyclohexane solution of the residues and subsequent desorption with acetone. Additionally, the effect of the zeolite parameters, solvent, and temperature on selective adsorption of 4-BPA, as well as re-generation of the used zeolite, have been investigated. In Chapter 5 transbromination of bromo-substituted phenols and phenyl acetates has been discussed using large-pore zeolites and AlCl<SUB>3</SUB> as catalysts. The reactions involve intermolecular transbromination. HZSM-5 zeolite shows shape selectivity for the <I>para</I>-isomer.

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Rate Constants for the solvolysis of standard compounds have been used as a measure of solvent polarity. The Grunwald and Winstein equation utilized <i>tert</i>-butyl chloride for the Y scale. Y<SUB>X</SUB> scales for the 1- and 2-adamantyl derivatives have been established to correlate various substrates with different leaving groups. This thesis presents Y<SUB>OMs</SUB> results for binary aqueous mixtures of acetonitrile and dioxane which are classified as dipolar aprotic solvents. Y<SUB>Cl</SUB> values have also been obtained. When compounds containing one aromatic ring such as <i>p</i>-methoxybenzoyl chloride are correlated against Y<SUB>Cl</SUB> the plot splits into separate lines for each binary mixture. It is shown that <i>p</i>-methoxybenzyl chloride eliminates this effect because positive charge can be delocalized onto the benzene ring. There is a notably good correlation with Z values: the solvent polarity scale based on the charge transfer absorption band of a pyridinium ion. Free energy relationships like rate-rate profiles can indicate a change in mechanism if a break occurs. This is observed for benzoyl chloride which reacts by a dissociative pathway in highly aqueous media and an addition-elimination pathway in less aqueous media. The compositions of acetonitrile and dioxane where the competing reaction channel contributes 50% to the overall rate have been located and the dissociative channel dissected. The benzhydryl system has been used to provide a rate ratio for tosylates and <i>p</i>-nitrobenzoate leaving groups. The reactive mesylate was prepared on a small scale and transferred to a conductivity cell without isolation. the <i>p</i>-nitrobenzoate was analysed by HPLC which is suitable for much slower reactions. The ratio obtained was compared to previous values for which steric and temperature considerations are important. Also studied were the solvolyses of bicyclo[2.1.1] hexyl and tricyclo[23.1.00<SUP>2,6</SUP>] hexyl tosylates which proceeded with anchimeric assistance. The corresponding ditosylates had rate constants 3 x 10<SUP>3</SUP> smaller in 80% ethanol-water at 25<SUP>o</SUP>C mainly due to inductive effects.

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