Kinetics and Mechanism of the Aminolysis of Aryl N,N-Dimethyl Thiocarbamates in Acetonitrile

= alkyl or aryl group. Kinetic studies on the aminolysis mechanisms of aryl carbamates, 1, are however relatively scarce, albeit they (1) are structurally similar to the corresponding esters and carbonates. Recent works on the aminolysis of aryl thiocarbamates, 1a, with R = Et and Ph have indicated that the aminolysis rates with benzylamines in acetonitrile are more than 3 times faster with R = Et than with R = Ph in concerted processes. This rate enhancement with R = Et relative to R = Ph has been attributed mainly to a stronger push to expel the thiophenoxide leaving group by EtNH than by PhNH in the tetrahedral transition state. It is, however, not well understood that (i) exactly what type of electronic effect is responsible for this push, e.g. is it a polar or a charge transfer effect? and (ii) whether there is a steric inhibition effect operative with a bulkier phenyl group relative to an ethyl group or not. In order to shed more light on the aminolysis mechanism of aryl N,N-dimethyl thiocarbamates by elucidating effects of the nonleaving (RNH) group in 1a, we carried out kinetic studies on the aminolysis of aryl N,N-dimethyl thiocarbamates (ADTC; RH = (CH3)2 in 1a) with benzylamines in acetonitrile, eq. (1). We varied