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

We propose a concerted mechanism with a hydrogen bonded cyclic transition state for the aminolysis of aryl N-allyl thiocarbamates with benzylamines in acetonitrile based on the negative cross-interaction constant, failure of RSP, the kinetic isotope effects greater than unity and relatively low ΔH≠. with large negative ΔS≠. values. The aminolysis mechanism of aryl carbamates, 1, is quite similar to that of aryl carbonates, 2, and aryl esters, 3. A change in the mechanism of the aminolysis with benzylamines in acetonitrile has been observed from stepwise through a tetrahedral intermediate, T±, to concerted for the carbamates (1 with R = Ph) as well as for the carbonates (2 with R = Et) when leaving group is changed from phenoxides (a : -OAr) to thiophenoxides (b : -SAr). This suggests that the strength of push provided to expel the leaving group from T± by PhNH is similar to that by EtO, and the destabilization of T± due to this push is strong enough for -SAr but is too weak for -OAr to lead the aminolysis to a concerted process