The aminolysis reactions of S-aryl N-arylthiocarbamates (YC 6 H 4 NH-C( --O)-SC 6 H 4 Z, 1) with anilines in acetonitrile are studied. The reaction rates are more influenced by the nucleophilicity of the nucleophile than the nucleofugality of the leaving group, but the change in the effective charge from reactants to the TS for formation of the tetrahedral intermediate is slightly greater in the leaving group (b Z fromÀ0.07 to À0.14) than in the nucleophile (b X ¼ 0.04-0.12). The magnitude of the Brö nsted coefficients are in the range of values that are consistent for a stepwise mechanism with rate-limiting formation of the zwitterionic tetrahedral intermediate. Signs of cross-interaction constants, r XY (>0), r XZ (>0) and r YZ (<0), are all consistent with a stepwise mechanism. It is concluded that the change of the amine from benzylamines to anilines causes a shift of the aminolysis mechanism from a concerted to a stepwise process.