Kinetics and Mechanism of Oxidation of Chloramphenicol by 12-Tungstocobaltate(III) in an Acidic Medium

Abstract

The oxidation of Chloramphenicol (CAP) by Keggin-type 12-tungstocobaltate(III) anion was investigated spectrophotometrically under pseudo-first-order conditions in perchloric acid at 303K.  Under these reaction conditions, CAP exists in unprotonated form. The reaction was found to proceed via the formation of a weak complex between the reactants. A direct electron transfer from CAP to the 12-tungstocobaltate(III) anion generated a 3-(4-nitrophenyl)-2,2-dichloroacetamido-1-propanol-3-oxy free radical in the rate-determining step. This free radical was further oxidised to give 4-nitrobenzaldehyde, dichloroacetic acid, and glycoaldehyde. The rate constant increased with an increase in concentration of the substrate. The reaction rate remained constant with an increase in hydrogen ion concentration, and was independent of the ionic strength. The products of the reaction were confirmed by LC-MS, FT-IR and 1H NMR spectroscopy. The thermodynamic parameters were evaluated by temperature variation kinetic data. A detailed mechanism and rate equation are proposed for the reaction.