Solvent effect correlations and the mechanism of solvolysis of alkyl chlorosulfates

The rate of hydrolysis of the series of alkyl chlorosulfates ROSO2Cl (R = ethyl, n-propyl, isobutyl, neopentyl) has been measured as a function of solvent composition in dioxane–water media. The solvent effect is examined from the viewpoint of dielectric constant, solvation number, and solvent ionizing power. The results point to a continuous variation of solvolytic mechanisms (from SN2, through borderline, to SN1) along the series. The correlations are also considered with respect to the 'entropy criterion' for multiple bond scission previously advanced for solvolysis of the alkyl chlorosulfates. Solute–solvent interactions are identified as a possible alternative origin of the abnormally large ΔS≠ values observed in chlorosulfate solvolysis.