Nucleophilic Substitution at Sulphonyl Sulphur. Part 2. Hydrolysis and Alcoholysis of Aromatic Sulphonyl Chlorides

Kinetics of hydrolysis, methanolysis and ethanolysis of furan-2- and -3-, thiophen-2- and -3-, and benzenesulphonyl 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 SN2 type mechanism takes place which is shifted toward an SN1 process (looser transition state) or an SAN process (tighter transition state) in the hydrolysis and alcoholysis reactions, respectively.