Catalysis of nucleophilic aromatic substitution reactions in mixed solvents. Part 1. Reaction of phenyl 2,4,6-trinitrophenyl ether with aniline in benezene–methanol mixtures: strong evidence against the ‘dimer’ mechanism

Abstract

The reaction of phenyl 2,4,6-trinitrophenyl ether with aniline in benzene and benzene–methanol was studied at different amine concentrations. Addition of increasing amounts of methanol (from 0.1 to 90%) to benzene resulted in a continuous increase in rate. This trend is contrary to that expected on the basis of the dimer mechanism which predicts an initial diminution inrate followed by an increase in rate at higher methanol concentration (above 30%). In pure benzene and benzene–methanol mixtures of low methanol content, third-order kinetics with respect to the amine were observed, while at constant amine concentrations first-order kinetics with respect to methanol were observed. Addition of equivalent amounts of phenol in place of methanol at low methanol concentrations (0.1–0.4%) had no effect on the rate of reaction. These and other results herein described could not be satisfactorily explained on the basis of the dimer mechanism but are satisfactorily accommodated by a previously proposed reaction scheme involving single catalysing entities in a cyclic transition state.