Periodate Influencing Diperiodatocuprate(III) Oxidation of Sulfur Containing Amino Acid in Aqueous Alkaline Medium

The diperiodatocuprate(III) (DPC) oxidation of DL-methionine, a sulfur containing amino acid, was studied spectrophotometrically in alkaline solution. The reaction rate was first order in the concentration of DPC and fractional order in the concentration of DL-methionine. Increasing the OH⁻ concentration decreased the rate of reaction, whereas adding IO₄⁻ enhanced the rate. The reaction was preceded by a small initiation period of about 0.8 minutes. This initiation time decreased when the concentration of IO₄⁻ or DPC increased. Adding the reaction products did not alter the rate of reaction. A mechanism including the intervention of a DL-methionine free radical is proposed and the corresponding rate law is derived. The reaction rate constants are evaluated as well as the activation parameters.