Kinetics and mechanism of oxidation of hydroxy acids by pyridinium hydrobromide perbromide

1086-1088The oxidation of glycollic, lactic, mandelic and malic acids by pyridinium hydrobromide perbromide (PHPB) in acetic acid water mixture (3:7, v/v) leads to the formation of corresponding oxoacids. The reaction is first order each in PHPB . nd the hydroxy acid. Addition of pyridinium hydrobromide does not affect the rate indicating that PHPB itse fis the reactive oxidizing species. The oxidation of ɑ-deutriomandelic acid shows the presence of a primary kinetic isotope effect (kH/kD = 5.07). The reaction does not exhibit solvent isotope effect (k(H2O)/k(D2O) = 1.011. The rate decreases with an increase in acetic acid content in the solvent mixture. A mechanism involving hydride ion transfer to the oxidant is proposed