Nucleophilic substitution at sulphonyl sulphur. Part 2. Hydrolysis and alcoholysis of aromatic sulphonyl chlorides

Abstract

Kinetics of hydrolysis, methanolysis and ethanolysis of furan-2- and -3-, thiophen-2- and -3-, and benzene-sulphonyl chlorides have been measured. Fair correlations with Taft σ* values for heterocycles are found; more satisfactory trends are observed by applying the two-parameter (polar and steric) Taft–Pavelich equation, particularly for the hydrolysis reaction including data for aliphatic sulphonyl chlorides. In this case the negative δ value, which is related to the steric parameter, is consistent with steric acceleration due to relief of strain in the transition state. Alcoholysis rates of substituted thiophen-2-sulphonyl chlorides (5-CH₃, 5-Cl, 4-NO₂, and 5-NO₂) have been also measured in order to compare the substituent effects with those already observed for hydrolysis. The data are in accord with previous findings, that an S_N2 type mechanism takes place which is shifted toward an S_N1 process (looser transition state) or an S_AN process (tighter transition state) in the hydrolysis and alcoholysis reactions, respectively.