Pyridine-2-carboxylic acid mediated oxidation of α-hydroxy acids with pyridinium dichromate

The kinetics of oxidation of some alpha-hydroxyacids (mandelic, lactic and glycolic acids) with pyridinium dichromate (PDC) in the presence of pyridine-2-carboxylic acid [PA] has been studied in perchloric acid medium. PA enhances the rate of oxidation in the case of lactic acid (LA) and mandelic acid (MA). Kinetic solvent isotope effect studies (k(D2O)/k(H2O) greater than or equal to 1) imply a proton catalyzed reaction. Enhanced reactivity is explained by assuming the formation of a termolecular complex. Catalytic activity of PA is significant in the case of mandelic acid. By the way in glycolic acid (GA) oxidation the inverse dependence of the rate on [PA] is noted. At constant [H+] the reaction seems to follow the rate law, k(obs) = k(4)K(3)K(2)K(a)'[S][PAH(+)]/[PA](T) in glycolic acid.