Kinetics and Mechanism of Oxidation of Methionine by Chromium(VI): Edta Catalysis

The kinetics of the oxidation of DL-methionine to sulfoxide by CrVI has been studied in aqueous acetic acid in the presence of sodium salt of ethylenediaminetetraacetic acid (edta). It appears that CrVI-edta is the active electrophile. The low dielectric constant of the medium favours the reactivity. Ionic strength and MnII have no significant effect on the conversion. The ratio k(D2O) / k(H2O) ≈ 1 does not seem to indicate any significant solvent isotope effect. Highly negative ΔS# values indicate a structured transition state. A ternary intermediate has been envisaged for describing the enhanced reactivity