Nucleophilic substitution reactions of a-chloroacetanilides with benzylamines in dimethyl sulfoxide

초록

Kinetic studies of the reactions of a-chloroacetanilides (YC6H4NRC(=O)CH2Cl; R = H (5) and CH3 (6)) with benzylamines (NH2CH2C6H4X) are carried out in dimethyl sulfoxide at 55.0 oC. The Br?sted bX values are in the range from 0.6 to 0.9 and cross-interaction constants rXY are positive, rXY = +0.21 and +0.18 for 5 and 6, respectively. The rates are faster with 6 than with 5 and inverse secondary kinetic isotope effects involving deuterated benzylamine (ND2CH2C6H4X) nucleophiles, kH/kD < 1.0, are obtained. Based on these and other results a stepwise mechanism with rate-limiting expulsion of the chloride leaving group from a zwitterionic tetrahedral intermediate, T? is proposed. In this mechanism a prior carbonyl addition to T?is followed by a bridged type transition state to expel the chloride.