Electrocatalysis of Anodic Oxygen‐Transfer Reactions: Oxidation of Phenol and Benzene at Bismuth‐Doped Lead Dioxide Electrodes in Acidic Solutions

Abstract

The electrocatalytic activities are compared for pure β‐lead dioxide electrodes and bismuth‐doped lead dioxide electrodes for oxidation of dimethylsulfoxide (DMSO), phenol, and benzene in acidic media. A correlation is observed between the bismuth content of films on Au disk electrodes and the apparent heterogeneous rate constant for conversion of DMSO to . The oxidation of phenol occurs at a transport‐limited rate for both the and film electrodes; however, the electrodes exhibit significantly greater stability against surface fouling by polymeric films. This is a direct benefit of the greater electrocatalytic activity of electrodes for oxidation of phenol beyond the phenolic radical. A ring‐disk experiment for benzene oxidation at a disk demonstrates that o‐benzoquinone and p‐benzoquinone are produced at the disk in the ratio ca. 0.25. However, the total ring current for reduction of these products from the disk reaction is significantly below that predicted from the disk current, and it must be concluded that a significant amount of electroinactive species is produced at the disk. This production is speculated to occur with and probably corresponds to a ring‐opening reaction with production of one or more organic acids. The product solution from exhaustive electrolysis of benzene contains p‐benzoquinone as the only electroactive product; hence, the o‐benzoquinone is concluded to undergo further oxidation at the electrode to one or more electroinactive products.