ELECTROCHEMICAL AND INFRARED SPECTROSCOPIC QUANTITATIVE-DETERMINATIONOF THE PLATINUM-CATALYZED ETHYLENE-GLYCOL OXIDATION MECHANISM AT CO ADSORPTION POTENTIALS

The electrochemical mechanism for ethylene glycol oxidation by polycry stalline platinum at 0.30 V/SCE in 0.10 M HClO4 is investigated by ref lection infrared spectroscopic, coulometric, and voltammetric measurem ents of 0.10 M ethylene glycol, glycolaldehyde, glyoxal, glycolic acid , glyoxylic acid, and oxalic acid. CO2, glycolic acid, and adsorbed CO are identified as reaction products for ethylene glycol and glycolald ehyde oxidation. A two-path mechanism is proposed for 0.30 V oxidation of ethylene glycol and glycolaldehyde: either the reacting molecule u ndergoes direct oxidation to desorbing glycolic acid or it undergoes d irect dissociation of the carbon-carbon bond to form various amounts o f aqueous CO;! and adsorbed CO. Calculations are performed, assuming t he quantities of CO and CO2 depend statistically upon the identities o f the two functional groups comprising the two-carbon reactant molecul e and upon oxidation conditions. Calculation results for dissociation at 0.30 V show that nearly 100% of the carboxyl functional groups are oxidized to CO2, whereas 20% and 50-67%, respectively, of the alcohol and aldehyde groups are partially oxidized to adsorbed CO. About 20% o f the ethylene glycol molecules undergo bond dissociation, whereas 25- 40% of the glycolaldehyde molecules dissociate. In 70 s of electrochem ical oxidation, about three times as many ethylene glycol molecules re act as glycolaldehyde molecules.