A kinetic and mechanistic study on the oxidation of l-methionine and N-acetyl l-methionine by cerium(IV) in sulfuric acid medium

The kinetics of oxidation of l-methionine and N-acetyl l-methionine by Ce(IV) in sulfuric acid-sulfate media in the range of 288.1-298.1 K has been investigated. The major oxidation products of methionine and N-acetyl l-methionine have been identified as methionine sulfoxide and N-acetyl methionine sulfoxide. The major oxidation products have been confirmed by qualitative analysis and boiling point. The reaction was first order with respect to l-methionine, N-acetyl l-methionine and Ce(IV). Increase in [H+], ionic strength and HSO4- did not affect the reaction rate. Under the experimental conditions, Ce4+ was the effective oxidizing species of cerium. Increase in dielectric constant of the medium decreased the reaction rate. Under nitrogen atmosphere, the reaction system can initiate polymerization of acrylonitrile, indicating the generation of free radicals. Activation parameters associated with the overall reaction have been calculated.