The kinetics and mechanism of the reactions of aromatic sulphonyl chlorides with anilines in methanol; Brønsted and Hammett correlations

Abstract

The rate of reaction of substituted benzenesulphonyl chlorides with various substituted anilines has been measured in methanol. Substituent effects in sulphonyl chloride and aniline are correlated by Brønsted and Hammett equations, respectively. The results are interpreted in terms of a direct bimolecular nucleophilic displacement mechanism. The sensitivity parameters, β and ρ, obtained from the free-energy relations, are inter-related and are themselves sensitive to the reactivity of the system. Thus β varies from 0·65 for p-methoxybenzenesulphonyl chloride to 0·96 for m-nitrobenzenesulphonyl chloride whereas ρ varies from 0·44 for m-nitroaniline to 1·14 for 3,4-dimethylaniline. These variations in β and ρ are interpreted to mean that electron-withdrawing substituents in the sulphonyl chloride increase bond formation whereas such substituents in the aniline leads to increased bond-breaking relative to bond formation in the transition state.