Correlation of the Specific Rates of Solvolysis of Trimethylsilylmethyl Trifluoromethanesulfonate Using a Two-Term Grunwald–Winstein Equation

Abstract

The specific rates of solvolysis of trimethylsilylmethyl trifluoromethanesulfonate have been measured at 25.0 °C in ethanol, methanol, and 2,2,2-trifluoroethanol (TFE) and their mixtures with water. Determinations were also made in aqueous acetone and in TFE–ethanol mixtures. An extended (two-term) Grunwald–Winstein equation correlation gave sensitivities towards changes in solvent nucleophilicity and solvent ionising power as expected for an S_N2 pathway, consistent with a previous proposal. For four solvents specific rates were determined at three or four additional temperatures and appreciably negative entropies of activation were observed, consistent with the proposed mechanism. At −20 °C, the specific rate of methanolysis is almost identical to that for methyl trifluoromethanesulfonate, suggesting a fortuitous balance between steric hindrance effects and a favourable electronic effect upon the introduction of the trimethylsilyl group.