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 N 2 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.

Correlation of the rates of solvolysis of α-bromoisobutyrophenone using both simple and extended forms of the Grunwald-Winstein equation and the application of correlation analysis to related studies

“…The extended Grunwald-Winstein equation [3-6], which has been found to be very useful in its application to the specific rates of solvolysis of a wide variety of substrates, such as phosphorus compounds [34], silicon compounds [35], acid chlorides [36], chloroformate esters [37], chlorothioformate esters [38], and heterocyclic compounds [39], is here applied to the solvolyses of tertiary alpha-substituted ketones, some of which have, contrary to earlier opinions summarized elsewhere [12], been found to be capable of forming carbocations with the charge formally adjacent to the carbonyl group under solvolytic conditions [10-12]. …”

Nucleophilic Aliphatic Substitution

“…83 The two-term Grunwald-Winstein equation indicated that the rates were strongly dependent on the nucleophilicity and only slightly dependent on the ionizing power of the solvent. This, and the large negative S = found in four solvents, suggest the reactions occur by an S N 2 mechanism.…”