CHARACTERIZATION OF CARBOHYDRATE OXIDATION AT COPPER ELECTRODES

The electro-oxidation of carbohydrate compounds at copper electrodes i n strongly alkaline solution was investigated by cyclic voltammetry, h ydrodynamic voltammetry and coulometry experiments. Product analysis w as carried out by H-1 and C-13 nuclear magnetic resonance spectroscopy . Model carbohydrate compounds examined included, in addition to simpl e monosaccharides, alditols and aldonic, aldaric and uronic acids. All these oxidations were found to consist of many-electron processes. Fo r glucose itself, 12 electrons were involved in complete oxidation at + 0.60 V vs. Ag \AgCl\ 13 M NaCl, and the sole product appeared to be the formate ion, with no partial oxidation species seen as either inte rmediate or final products. For other carbohydrates, carbonate was ass umed (but not observed) to be a possible oxidation product as well. In view of the fact that various alditol compounds were oxidized even mo re readily than glucose and other monosaccharides, it appeared that th e aldehyde or ketone functionality is not required for oxidation at th e Cu electrode. Rather, voltammetry results obtained for a series of p olyhydroxyl compounds revealed that the minimum structural requirement for facile oxidation is the presence of at least two, and preferably more, nearby hydroxyl groups in the compound to be oxidized.