The mechanism of solvolysis of 2,2-dimethyl-3-pentyl and 1-(1-adamantyl)propyl sulfonates

Solvolysis rates, alpha and beta deuterium isotope rate effects and product yields have been determined for some 1-(1-adamantyl) propyl sulfonate esters, 4, in some ethanol-water, trifluoroethanol-water and hexafluoroisopropyl alcohol-water mixtures. For comparison, similar measurements have been made for solvolysis of 2,2-dimethyl-3-pentyl sulfonates, 5. For the esters 5, the alpha-d and beta-d(2) effects vary little with solvent in the ranges of 1.164-1.165 and 1.215-1.241, respectively, and only small yields of unrearranged products are formed; it is concluded that the mechanism involves rate determining formation of the secondary cation-ion pair followed by rapid rearrangement. For the adamantyl analogs, 4, the alpha-d effects vary in the different solvents from 1.162 to 1.213 and the beta-d(2) effects vary from 1.339 to 1.649; significant yields of unrearranged and Wagner-Meerwein rearranged (ring expansion) products are formed. The steady state treatment, which had been used previously to fit the results for 1-(1-adamantyl)ethyl esters, was applied to the results for 4; a mechanism which involves partially reversible ionization to the intimate ion-pair followed by competing elimination and solvent separation, to give the substitution products, fits the results reasonably well.