KINETICS OF CERIUM(IV) OXIDATION OF MANDELIC-ACID - IONIC-STRENGTH AND SPECIFIC CATION EFFECTS

The kinetics of the redox reaction between mandelic acid (MA) and ceric sulfate have been studied in aqueous sulfuric acid solutions and in H2SO4MClO4 (M+ = H+, Li+, Na+) and H2SO4MHSO4 (M+ = Li+, Na+, K+) mixtures under various experimental conditions of total electrolyte concentration (that is, ionic strength) and temperature. The oxidation reaction has been found to occur via two paths according to the following rate law: rate = k[MA] [Ce(IV)], where k = k1 + k2/(1 + a)2[HSO4−]2 = k1 + k2/(1 + 1/a)2[SO42−]2, a being a constant. The cations considered exhibit negative specific effects upon the overall oxidation rate following the order H+ ⩽ Li+ < Na+ < K+. The observed negative cation effects on the rate constant k1 are in the order Na+ < Li+ < H+, whereas the order is in reverse for k2, namely, H+ ⩽ Li+ < Na+. Lithium and hydrogen ions exhibit similar medium effects only when relatively small amounts of electrolytes are replaced. The type of the cation used does not affect significantly the activation parameters. Copyright © 1979 John Wiley & Sons, Inc.