Kinetics and Mechanism of Oxidation of Methyl Mandelate by Manganese(III) Pyrophosphate

Department of Chemistry, S. B. S. H., University of Udaipur, Udaipur

Manuscript received 14 May 1976 accepted 26 September 1977

Where as a ketoester is the product of oxidation of the ester of an hydroxy acid by chromium(VI) and by vanadium(V), benzaldehyde is the product of oxidation of methyl mandelate by manganese(III) pyrophosphate. Kinetics of the oxidation of the methyl mandelate by manganese(III) pyrophosphate has been studied. The reaction is first order each in ester and in manganese(III) pyrophosphate. The rate is proportional to the square of the concentration of hydrogen ion but it is inversely proportional to the concentration of free pyrophosphate in the solution. Addition of manganese(II) ion has no effect on the rate of reaction. The rate is also affected by the composition of the solvent acetic acid water mixture, the rate decreases in increase in the proportion of acetic acid in the solvent mixture. The kinetic isotope effect kH/kD has a value of 1.90 and shows that C-H is not involved in the rate determining step. The heat of activation and entropy of activation have values of 25.0 k.cals mole^-1 and 15.0 e.u. res­pectively. A mechanism which is consistent with the observed rate laws and other experimental facts has been proposed.