Kinetics and mechanism of the oxidation of alpha-hydroxy acids by benzyltrimethylammonium chlorobromate

The oxidation of glycollic, lactic, malic and a few substituted mandelic ac ids by benzyltrimethylammonium chlorobromate (BTMACB) in acetic acid-water (1:1) leads to the formation of the corresponding oxoacids. The reaction is of first order in BTMACB as well as the hydroxy acid. Addition of benzyltr imethylammonium chloride or bromide ion does not affect the rate indicating that BTMACB itself is the reactive oxidizing species. The oxidation of alp ha-deuteriomandelic acid shows the presence of a primary kinetic isotope ef fect (k(H)/k(D) = 5.27 at 303 K). The reaction does not exhibit the solvent isotope effect [k(H2O)/k(D2O)= 1.01]. The rate decreases with increase in the amount of acetic acid in the solvent mixture. A mechanism is proposed w hich involves hydride ion transfer to the oxidant.