Solvolyses of Secondary Sulfonates in Aqueous Ethanol and Acetone. Nonlinear mY Relationships due to Leaving Group and Medium Effects

Article abstract of DOI:10.1021/jo00314a008

Solvolitic rate constants for secondary mesylates and tosylates in aqueous ethanol and in aqueous acetone are correlated with Winstein-Grunwald Y values.Curvature of these plots is greatest for tosylates in aqueous ethanol, especially for 2-adamantyl.Because mesylates show little or no curvature, it is argued that the results cannot be explained by mechanistic changes but by solvation effects of the leaving group in the mixed solvents.The parameter, m, measuring response to solvent ionizing power varies from 0.68 for isopropyl to 1.21 for 2-adamantyl mesylate in aqueosus acetone at 25 deg C.An alternative solvent ionizing power parameter for tosylates, Y_OTs , and the solvent nucleohpilicity parameter, N_OTs, are evaluated for 20percent ethanol/water, 20percent acetone/water, and 40percent acetone/water.It is proposed that solvolyses of substrates having the same (or very similar) leaving group should be compared if reliable mechanistic information (e.g., nucleophilic solvation effects) is required.The tendency for "dispersion" of correlation lines for various binary mixed solvents appears to be due to both leaving-group effects and to variations in solvent nucleophilicity.By helping to account for curvature and dispersion in mY correlations, this work supports recent work in which mechanistic information was deduced from similar correlations.