Contrasting solvent effects on the kinetics of oxidation of methionine by quinolinium fluorochromate

Abstract

The oxidation of methionine by quinolinium fluorochromate (QFC) has been studied, in the presence of chloroacetic acid. in water-DMSO and water-acetic acid mixtures of varying mole fractions. The reaction is first order each with respect to methionine, QFC and acid. The reaction rates have been determined at different temperatures and the activation parameters have been computed. The reaction rate increases with increase In mole fraction of acetic acid in the mixture, where the specific solvent-solvent-solute interactions were found to dominant (56%), while In water-DMSO mixtures the rate decreases with increasing mole fraction of the organic co-solvent, where the transition state was stabilized only to a lesser extent by solvation. A solvation model and a suitable mechanism for the reaction are postulated.