Solvolysis of Sulphonyl Halides. IV. The Hydrolysis of Some Substituted Aliphatic Sulphonyl Chlorides and of Ethanesulphonyl Bromide in Aqueous Dioxan

Abstract

The effects of substitution in the alkyl group of an alkanesulphonyl chloride, on the rate of hydrolysis, vary with the solvent composition. The relative rates can be explained in terms of the theory of Grunwald and Winstein that there is a continuous range of transition complexes, with " bond making " between the water molecule and the sulphur atom controlling the rate in the less aqueous media, while the stretching and charging of the sulphur to chlorine bond controls the rate in solvents of higher water content. The inhibition of the simple S_N2 reaction, which gives rise to a maximum rate constant as the composition of the solvent approaches pure water, resembles that noted with methane- and ethanesulphonyl chlorides. The hydrolysis of ethanesulphonyl bromide, at 25 °C, proceeds at three to eight times the rate for the corresponding sulphonyl chloride in solvents varying in composition from 0.99 to 0.2 mole fraction of water with dioxan. Over most of the solvent range both the entropy and enthalpy of activation are favourable to a higher rate of solvolysis for the sulphonyl bromide.