OXIDATION OF MANDELIC-ACID BY ALKALINE POTASSIUM-PERMANGANATE - A KINETIC-STUDY

The kinetics of the oxidation of mandelic acid (MA) by permanganate in aqueous alkaline medium at a constant ionic strength of 1.0 mol dm(-3 ) were studied spectrophotometrically. The reaction shows first-order kinetics in [permanganate ion] and fractional order dependences in [MA ] and [alkali]. Addition of products, manganate and aldehyde have no s ignificant effect on the reaction rate. An increase in ionic strength and a decrease in dielectric constant of the medium increase the rate. The oxidation process in alkaline medium under the conditions employe d in the present investigation proceeds first by formation of an alkal i permanganate complex, which combines with mandelic acid to form anot her complex. The latter decomposes slowly followed by a fast reaction between the free radical of mandelic acid and another molecule of perm anganate to give products. The reaction constants involved in the mech anism were derived. There is good agreement between the observed and c alculated rate constants under different experimental conditions. The reaction was studied at different temperatures and activation paramete rs were computed with respect to the slow step of the proposed mechani sm. (C) 1998 John Wiley & Sons, Ltd.