Electrocatalytic oxidation of d-galactose in alkaline medium

Abstract

The electrocatalytic oxidation of d-galactose was investigated on platinum, gold and nickel electrodes in 0.1 M NaOH medium. The oxidation of galactose on nickel takes place in the NiOOH region and leads to the cleavage of the C–C bonds. This was confirmed by HPLC analyses of electrolyzed solutions which demonstrate relatively high amounts of low molar mass carboxylic acids, i.e., formic and glycolic acids. The oxidation of galactose on platinum is initiated at very low potentials, i.e., −0.8 V vs. SCE probably without oxygenated species on the electrode surface and gives moderate selectivity towards galactonic acid. The important effect of the lead adatoms on the electrocatalytic properties of platinum was demonstrated by the increase in the yield of galactonic acid from 34% to 67% with addition of 10 −5 M Pb 2+. On gold, galactose oxidation begins at approximately −0.5 V vs. SCE and is probably catalysed by the presence of hydrous gold oxides. The best yield of galactonic acid, 86%, was obtained after 6 h of electrolysis using a two potential program: −0.1 V vs. SCE for 30 s, 1.5 V for 1 s.