Kinetics and Mechanism of the Aminolysis of Phenyl Dithioacetates in Acetonitrile

Abstract

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 zwitterionic 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 leaving group with βX = 0.80−0.86 and βZ = −0.71 to −0.84 for ANs and DMAs to rate-limiting attack by the nucleophile with much smaller magnitudes of βX and βZ for BAs. The relatively large βXZ values for the former series and a smaller βXZ for the latter series support the proposed mechanistic change.