Electro‐Oxidation of Sulfite to Dithionate in the Presence of Copper Ion

The electro‐oxidation of sulfite catalyzed by copper ion has been investigated in neutral to weakly basic aqueous solutions. The catalysis by copper ion was observed at relatively low potentials at platinum and gold electrodes. Raman spectroscopic measurements and chemical analysis showed that dithionate was formed almost exclusively as the reaction product. A possible Cu(II) species was detected as a reaction intermediate by UV‐visible spectroelectrochemical methods. The steady‐state current‐potential relationship is interpreted assuming a quasi‐equilibrium of the redox couple Cu(I)/ Cu(II) at the electrode surface and a rate‐determining reaction of the Cu(II) species to give dithionate and Cu(I). The kinetics of the latter reaction suggests the formation of a binuclear Cu(II) complex in the reaction sequence.