Nucleophilic Substitution Reactions of Thiophenyl Dimethylacetates and Trimethylacetates with Benzylamines in Acetonitrile

摘要

The kinetics and mechanism of the reactions of thiophenyl dimethylacetates (TDA) and trimethylacetates (TTA) with benzylamines in acetonitrile are studied. The reactions are first order in both the amine and the substrate. Relatively large values of モ_X (モ_nuc = 1.1-1.5; TDA and 1.1-1.5; TTA) and モ_Z (モ_lg = -1.8~-2.0; DTA and -1.3~-1.6; TTA) for benzylamines, significantly large k_H/k_D values (=1.2-1.5; DTA and 1.2-1.5; TTA) involving deuterated benzylamines, and large ヱ_XZ (=0.82; TDA and 1.05; TTA) values are interpreted to indicate stepwise acyl transfer mechanism, but with the hydrogen bonded four center type transition state for benzylamine. The relatively greater magnitudes of ヱ_XZ and the secondary kinetic isotope effects involving deuterated nucleophiles are in line with the proposed mechanism.