Nucleophilic substitution reactions of α-chloroacetanilides with pyridines in dimethyl sulfoxide

The kinetic studies of the reactions of alpha-chloroacetanilides (YC6H4NRC(=O)CH2Cl; R=H (4) and CH3 (5)) with pyridines have been carried out in dimethyl sulfoxide at 95 degrees C. The pyridinolysis rates are faster with 4 than with 5 whereas the arninolysis rates with benzylamines are faster with 5 than with 4. The Br circle divide nsted beta(X) values are in the range from 0.30 to 0.32 and the cross-interaction constants, rho(XY), are small negative values; rho(XY) = -0.06 and -0.10 for 4 and 5, respectively. Based on these and other results, the pyridinolyses of achloroacetanilides are proposed to proceed via a stepwise mechanism with rate-limiting addition of the nucleophile to the carbonyl group to form zwitterionic tetrahedral interinediate (T-+/-) followed by a bridged type transition state to expel the leaving group.