Solvolysis of Sulphonyl Halides. I. The Hydrolysis of Aromatic Sulphonyl Chlorides in Aqueous Dioxan and Aqueous Acetone

Abstract

The hydrolysis of benzene, p-toluene, p-bromobenzene, and p-nitrobenzene sulphonyl chlorides in 10-60 wt. % water-dioxan and water-acetone has been shown to follow an S_N2 mechanism. The reaction does not show acid catalysis or any " salt " effect. Hammett?s equation does not describe fully the effects of substituents on the reaction rate. For solutions in which water has the same molarity, aqueous acetone gives lower rates than aqueous dioxan when the molarity of water is high but higher rates when the molarity of water is low. Change in the water content of the solvent produces only small changes in the enthalpy of activation except in solutions of low dielectric constant. The reduction in rate as solutions become less aqueous is mainly determined by the entropy of activation becoming more strongly negative.