Oxidative mechanism of glycolic acid and formaldehyde by acid bromate: A critical study

Abstract

Kinetics and mechanism of oxidation of glycolic acid (GA) by acid bromate (free from the autocatalytically generated molecular bromine oxidation) is studied in detail. The reaction exhibits first order each in [GA] and [oxidant] and second order in [acid]. Reaction rates are very much susceptible to change in dielectric constant (<i>ɛ</i>) of the medium. The reaction exhibits solvent isotope effect (1.8 ± 0.01 at 303 K) but primary isotope effect is absent. The rate determining step is the esterification of glycolic acid with acid bromate, followed by a fast disproportionation of the ester through a C - C bond cleavage to yield formaldehyde. This product undergoes oxidation with a faster rate than glycolic acid ending up with formic acid, inert towards further oxidation. An independent study of oxidation of formaldehyde is also made and results are correlated with the observations of the later part of the reaction. Related activation parameters are evaluated and discussed. An attempt is also made to compare the similar oxidations of other substrates and oxidants.