Kinetics and mechanism of oxidation of methionine by pyridinium hydrobromide perbromide

The oxidation of methionine (Met) by pyridinium hydrobromidc perbromidc (PHPB) has been studied in acetic acid-water (1 : 1) solutions. The oxidation reaction leads to the formation of the corresponding sulfoxide. The reaction is first order each in PHPB and Met, The reaction rates have been determined at different tcinperaturcs and the activation parameters calculated. A mechanism involving the formation of a halogen-sulfonium cation in the rate-determining step has been proposed.