Role of Ethylenediammonium Dichromate in the Kinetic and Mechanistic Analysis of the Oxidation of Glycolic and Lactic Acids in Aqueous AcOH Medium

Abstract

In aqueous acetic acid medium, the kinetics of oxidation of glycolic and lactic acid by ethylenediammonium dichromate [enH₂Cr₂O₇] have been explored. The oxidation product is the corresponding oxoacid. The conventional UV–vis spectrophotometric method is used to study the reaction kinetics. First-order kinetics has been observed concerning [enH₂Cr₂O₇] and with substrate the order is less than two. The fractional-order dependency with respect to substrate confirms the binding of oxidant and substrate to form a complex before rate-determining step. The rate of reaction increases with an increase in [H⁺] concentration. The existence of primary kinetic isotope effect, k_H/k_D = 5.97 at 298K for glycolic acid (ratio of rate constants for protio- and deuterio-glycolic acid) indicated a C–H bond cleavage rather than C–C bond cleavage. Variation of solvent polarity is found to impose a remarkable impact on the rate of oxidation. From the experimental data, formation of an unstable cyclic transition state followed by intra-molecular proton transfer has been proposed. Under similar conditions oxidation of lactic acid was studied.