Kinetics and mechanism of oxidation of esters of α-hydroxy acids (mandelic acid) by peroxydisulphate

The kinetic study on Ag(I) catalysed oxidation of some esters such as methyl, ethyl, propyl, iso-propyl, n-butyl, iso-butyl and sec-butyl mandelates by peroxydisulphate revealed variation of first order rate constant with oxidant concentration. Kinetics is first order in ester and catalyst while half order in H+. A complex formed between ester and oxidant decomposing in a slow step to give products benzaldehyde, alcohol and carbon dioxide has been suggested. The nature and size of alkyl group of ester has been found to have a small effect on the rate of reaction. Thermodynamic parameters for the slow step have been evaluated. Free radical mechanism and suitable rate law have been suggested. rate = k[ester]/a+[ester] [S2O82-][Ag+][H+](1/2)/b+[S2O8] where 'a' and 'b' are constants.