Kinetics of oxidation of phenoxyacetic acids by pyridinium hydrobromide perbromide

✍ Scribed by K. Karunakaran; K. P. Elango

• Publisher: John Wiley and Sons
• Year: 1996
• Tongue: English
• Weight: 366 KB
• Volume: 9
• Category: Article
• ISSN: 0894-3230
• DOI: 10.1002/(sici)1099-1395(199602)9:2<105::aid-poc758>3.0.co;2-a

✦ Synopsis

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-Mententype kinetics are observed with respect to phenoxyacetic acids. The oxidation of [2,2-*H,]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 puru-and rnetu-substituted phenoxyacetic acids were correlated with Hammett's substituent constants. The p value is -259 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.