Previous work on the mechanism of sulphonium salt solvolysis is reviewed briefly. Rate data, determined by two independent methods, is presented for the solvolysis of dimethyl-t-butyl sulphonium iodide, bromide, and chloride in water and various ethanol–water mixtures. Rate dependence on the anion character and concentration of salt is shown to develop as the dielectric constant of the medium is lowered. The results are interpreted in terms of the increasing importance of an ion-pair mechanism as the composition of the medium is changed. The interpretation is substantiated by independent evidence for ion-pair formation.
