Reaction mechanism studies involving the correlation of the rates of solvolysis of benzoyl and p-nitrobenzoyl p-toluenesulfonates

摘要

The solvolyses of benzoyl and p-nitrobenzoyl p-toluenesulfonates (tosylates) are considerably slowerthan those of the previously studied mixed anhydride of acetic and p-toluenesulfonic acids (acetyl tosylate), which, even with application of rapid-response conductivity, could only be studied at considerably reduced temperatures. For the presently studied compounds, the specific rates over a wide variety of solvents could be conveniently studied at -10 °C. For solvolyses of benzoyl tosylate, application of the extended (two-term) Grunwald-Winstein equation gives sensitivities to changes in solvent nucleophilicity and solvent ionising power consistent with an ionisation (S_NI) pathway. Indeed, a good correlation is obtained against only solvent ionising power. For the solvolyses of the p-nitro-derivative, very different sensitivities are obtained, with an appreciable dependence on solvent nucleophilicity, and a dominant biomolecular pathway for the substitution is proposed for all of these solvolyses, except for those in solvents rich in fluoroalcohol. Studies of solvent deuterium isotope effects in methanolysis, of leaving-group effects relative to a halide and of temperature variation effects are consistent with the proposed mechanistic pathways.