The kinetics of the chromium(III) catalysed oxidation Of L-leucine and L-isoleucine by alkaline permanganate were studied and compared, spectrophotometrically. The reaction is first order with respect to (oxidant) and (catalyst) with an apparently less than unit order in (substrate) and zero order with respect to (alkali). The results suggest the formation of a complex between the amino acid and the hydroxylated species of chromium(III). The complex reacts further with the permanganate in a rate-determining step, resulting in the formation of a free radical, which again reacts with the permanganate in a subsequent fast step to yield the products. The reaction constants involved in the mechanism were obtained. There is a good agreement between observed and calculated rate constants under different experimental conditions. The activation parameters with respect to slow step of the mechanism for both the amino acids were calculated and discussed. Of the two amino acids, leucine is oxidised at a faster rate than the isoleucine. (c) 2004 Elsevier B.V. All rights reserved.