John G. Tillett

KINETICS AND MECHANISMS OF THE ACID- CATALYSED HYDROLYSES OF 4-NITROPHENYL- N-AROYL-ARENEIMINOSULPHONATES

Abstract The acid catalysed hydrolyses of N-acetyl and a series of N-aroylsulphonimidic esters have been studied in aqueous 40% (v/v) dioxane solutions of mineral acids. At low acidity all the esters studied are considered to hydrolyse by an A-2 mechanism. At higher acidities a changeover to an A-1 mechanism is observed for N-aroylsulphonimidic esters.

Acid-catalysed hydrolysis of some aromatic cyclic sulfamates

The acid catalysed hydrolysis of some cyclic sulfamates, X-3-(p-tolylsulfonyl)-1,2,3-benzoxathiazole 2,2-dioxides ( 1a , X = Me; 1b , X = H; 1c , X = Cl; 1d , X = NO 2 ) have been studied in concentrated aqueous sulfuric and perchloric acid solutions. Analysis of the data by the Excess Acidity Method, activation parameters, substituent, solvent deuterium isotope effect and order of the catalytic effects of the acids are all in agreement with an A-1 mechanism in the studied range.

Nucleophilic substitution at sulphinyl sulphur. Kinetics and oxygen-18 tracer studies of the alkaline hydrolysis of some sulphinate esters

The rates of alkaline hydrolysis of some simple aliphatic sulphinate esters have been studied at various temperatures. The enthalpies and entropies of activation have been determined. The main difference in reactivity between the five- and six-membered rings is shown to be due to entropy strain. Oxygen-18 experiments demonstrate that 1,2-oxathiolan 2-oxide does not undergo 18O exchange with solvent during hydrolysis.

THE REDUCTION OF CYCLIC DISULPHIDES WITH TRIARYLPHOSPHINES IN AQUEOUS ORGANIC SOLVENTS

Abstract The kinetics of the reduction of cyclic disulphides with triphenylphosphine have been studied in aqueous ethanol at various temperatures. Solvent effects on the reaction of 4-phenyl-1,2-dithiolane with tris-(4chlorophenyl) phosphine in a number of aqueous organic solvents have been analysed in terms of the Kirkwood, Y and EN T functions.

ACID-CATALYSED HYDROLYSIS AND ALCOHOLYSIS OF 4-NITROPHENYL-N-ACETYL-PHENYLIMINOSULPHONATE

Abstract The acid-catalysed hydrolysis of the title compound (1) has been studied in aqueous (20% v/v) dioxane solutions of mineral acids. The kinetic data were analysed in terms of the Bunnett-Olsen approach, activation parameters and solvent isotope effects and were consistent with a bimolecular (A-2) mechanism. The kinetics and products of alcoholysis of 1 have also been investigated.

REACTIVITY OF SULFUR HETEROCYCLES

Abstract The relationship between ring strain and the reactivity of alicyclic compounds has been of fundamental importance in the development of modern organic chemistry. Because of their biological interest, the reactivity and stereochemistry of cyclic phosphorus compounds have been extensively studied.1,2 In recent years the reactivity of cyclic sulfur compounds has also begun to attract considerable interest. In 1966 it was pointed out that the common feature of sulfur-containing heterocycles is that nucleophilic attack at sulfur, be it di-, tri-, or tetra-coordinated, is always faster than the corresponding open-chain analogues.3 The present review attempts to discuss some fo the factors which affect the reactivity of cyclic sulfur compounds towards nucleophilic attack and to draw attention to some of the recently observed exceptions to this generalization.

Solvent effects on the alkaline hydrolyses of 4-nitrophenyl N-aroyl-areneiminosulfonates

Abstract Second-order rate constants have been determined for the alkaline hydrolyses of N-aroyl-p-toluenesulfonimidic esters in aqueous organic solvents. Rate minima were observed with decreasing water concentration in aqueous acetonitrile, dioxane and t-butanol mixtures whereas rates of hydrolysis decrease continuously in MeOH-H2O and increase in DMSO-H2O. Solvent effects, Arrhenius parameters, and substituent effects are consistent with either an addition-elimination or a concerted SN2-type mechanism.

Nucleophilic substitution at sulphur. Part 3. The alkaline hydrolysis of some cyclic and open-chain sulphonate esters

The rates of alkaline hydrolysis of a number of aryl cyclic and open-chain sulphonate esters have been studied at various temperatures. The enthalpies and entropies of activation have been determined. The difference in reactivity between the five-membered sultone and other cyclic and open-chain analogues is shown to arise from a combination of both enthalpy and entropy strain. The detailed mechanism of alkaline hydrolysis of sulphonate esters and the cause of ring strain in sultones are discussed in some detail.

Hydrolysis of N-Phenylalkanesulfinamides in Aqueous Mineral Acids

Abstract The acid-catalyzed hydrolysis of N-phenylalkanesulfinamides (RSONHPh; 1, R = iPr; 2, R = tBu; 3, R = 1-adamantyl) has been studied in aqueous mineral acids. Hydrolysis was found to proceed via a slow spontaneous (uncatalyzed) pathway, an A-2 (bimolecular) acid-catalysis pathway, and an acid-dependent nucleophilic catalysis pathway, the last of which predominates in hydrobromic and hydrochloric acid solutions. A mechanistic switch over from A-2 to A-1 was detected for compounds 2 and 3 in concentrated sulfuric acid. Order of catalytic activity, effect of added salts, Arrhenius parameters, kinetic solvent isotope, and solvent effects are all consistent with the proposed mechanisms. GRAPHICAL ABSTRACT

A PROTON INVENTORY STUDY OF THE WATER-CATALYSED HYDROLYSIS OF A SULPHITE ESTER IN AQUEOUS DIOXANE

Abstract The water-catalysed (spontaneous) hydrolysis of bis(p-nitrophenyl) sulphite in aqueous dioxane exhibits a solvent deuterium isotope effect of K H2O/k D2O =3.21 and is second order in water concentration. The proton inventory plot for mixtures of protium oxide—deuterium oxide shows significant downward curvature and suggests the involvement of three equivalent protons. Several possible transition states are considered.