Kinetics and mechanism of the oxidation of some α-hydroxy acids by 2,2′-bipyridinium chlorochromate

The oxidation of glycolic, lactic, malic, and a few substituted mandelic acids by 2,2'-bipyridinium chlorochromate (BPCC) in dimethylsulphoxide leads to the formation of corresponding oxoacids. The reaction is first order each in BPCC and the hydroxy acids. The reaction is catalyzed by the hydrogen ions. The hydrogen ion dependence has the form: k(obs) = a + b [H+], The oxidation of alpha-deuteriomandelic acid exhibited a substantial primary kinetic isotope effect (k(H)/k(d) = 5.29 at 303 K). Oxidation of p-methylmandelic acid was studied in 19 different organic solvents. The solvent effect has been analyzed by using Kamlet's and Swain's multiparametric equations. A mechanism involving a hydride ion transfer via a chromate ester is proposed. (C) 2002 Wiley Periodicals, Inc.