KINETICS AND MECHANISM OF THE AMINOLYSIS OF PHENYL DITHIOACETATES IN ACETONITRILE

The aminolysis reactions of phenyl dithioacetates with anilines (AN), N,N-dimethylanilines (DMA), and benzylamines (BA) in acetonitrile are investigated. The mechanism is relatively simple, involving a zwitteri onic tetrahedral intermediate, T+/-, and is uncomplicated by the fast proton transfer step which may become rate limiting in the aminolysis of thiono and dithio esters and carbonates with poor leaving groups in water. The mechanism changes from rate-limiting expulsion of the leav ing group with beta(X) = 0.80-0.86 and beta(Z) = -0.71 to -0.84 for AN s and DMAs to rate-limiting attack by the nucleophile with much smalle r magnitudes of beta(X) and beta(Z) for BAs. The relatively large beta (XZ) values for the former series and a smaller beta(XZ) for the latte r series support the proposed mechanistic change.