Kinetics and mechanism of the aminolysis of thiophenyl 2-thiopheneacetatesin acetonitrile

Kinetic studies of the reaction of Z-thiophenyl 2-thiopheneacetates with X- benzylamines in acetonitrile at 45.0 degreesC have been carried out. The re action proceeds by a stepwise mechanism in which the rate-determining step is the breakdown of the zwitterionic tetrahedral intermediate, T+/-, with a hydrogen-bonded four-center type transition state (TS). These mechanistic conclusions are drawn base on (i) the large magnitude of rho (X) and rho (Z ), (ii) the normal kinetic isotope effects (k(H)/k(D) > 1.0) involving deut erated benzylamine nucleophiles, (iii) the positive sign of rho (XZ) and th e larger magnitude of rho (XZ) than that for normal S(N)2 processes, and la stly (iv) adherence to the reactivity-selectivity principle (RSP) in all ca ses.