Kinetics of the reaction of benzenesulphonyl chloride with pyridines in aqueous solution

Abstract

The hydrolysis of benzenesulphonyl chloride has been found to be catalysed by pyridines. The kinetics, stoicheiometry, and solvent isotope effect are consistent with a nucleophilic catalysis mechanism. This involves the formation of a sulphonylpyridinium intermediate which is subsequently hydrolysed, yielding sulphonic acid and regenerating the pyridine. The rate constants and activation parameters have been measured for the reaction of pyridine and nine 3- and 4-substituted pyridines. The rate constants are related to be pK_a of the pyridines and the σ° substituent constants giving Brønsted and Hammett plots with slopes of 0·45 and –2·68 respectively. Although the free energy of activation varies regularly with the substituents the effects on the enthalpy and entropy of activation are irregular.