NUCLEOPHILIC-SUBSTITUTION REACTIONS OF THIOPHENYL BENZOATES WITH BENZYLAMINES IN ACETONITRILE

The kinetics and mechanism of the reactions of thiophenyl benzoates wi th benzylamines in acetonitrile are reported. The signs of rho(XY) (>0 ), rho(YZ) (<0) and rho(XZ) (>0) are consistent with the acyl transfer mechanism involving rate-limiting breakdown of a tetrahedral intermed iate, T-+/-. Moreover, the large magnitude of rho(X) (rho(nuc)) and rh o(Z) (rho(lg)), the small, normal secondary kinetic isotope effect, k( H)/k(D) > 1.0, involving deuterated benzylamines, and the general vali dity of the reactivity-selectivity principle are all found to support the mechanism proposed. The benzoate group, YC6H4C=O, is considered to play the role of a relatively strong electron donor to induce such me chanism, despite the fact that the reactions involve basic nucleophile s (benzylamines) relative to less basic nucleofuges (thiophenoxides).