Kinetics and Mechanism of the Aminolysis of Phenyl Dithioacetates in Acetonitrile

Article abstract of DOI:10.1021/jo970413r

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 β_X = 0.80-0.86 and β_Z = -0.71 to -0.84 for ANs and DMAs to rate-limiting attack by the nucleophile with much smaller magnitudes of β_X and β_Z for BAs. The relatively large β_XZ values for the former series and a smaller β_XZ for the latter series support the proposed mechanistic change.