Kinetics of oxidation of phenoxyacetic acids by pyridinium hydrobromide perbromide

Article abstract of DOI:10.1002/(SICI)1099-1395(199602)9:2<105::AID-POC758>3.0.CO;2-A

The oxidation of several monosubstituted phenoxyacetic acids by pyridinium hydrobromide perbromide (PHPB) was studied in aqueous acetic acid. The reaction is first order with respect to PHPB. Michaelis-Menten-type kinetics are observed with respect to phenoxyacetic acids. The oxidation of [2,2-²H₂]phenoxyacetic acid exhibits a substantial kinetic isotopic effect. The effect of solvent composition indicates that the transition state is more polar than the reactants. The formation constants of the intermediate phenoxyacetic acid-PHPB complexes and the rates of their decomposition were determined at different temperatures. The rates of oxidation of para- and meta-substituted phenoxyacetic acids were correlated with Hammett's substituent constants. The ρ value is -2.59 at 35 °C. The rates of oxidation of ortho-substituted compounds are correlated with Charton's triparametric equation. A mechanism involving transfer of a hydride ion from the substrate to the oxidant is proposed.