627-632A series of m- and p-substituted phenyl thiolacetates have been prepared. The kinetics of aminolysis of these acetates by imidazole have been followed at 20ᵒC and an ionic strength of 0.1 mol dm-3 at different pH in water containing traces of dioxan. The non-linear Hammett plot and the nonlinear plot between log k2 and log k(OH) indicate the possibility of two types of mechanism, viz., unassisted nucleophilic substitution for the compounds having electron-withdrawing groups in the leaving moiety and general acid-assisted nucleophilic substitution for the compounds having electron-releasing groups in the leaving moiety
