Copper and Cobalt Co‐catalyzed Selective Electrooxidation of Phenol to p‐Benzoquinone Under Mild Conditions

Abstract Selective oxidation is still a challenge for targeted conversion of biomass derived substance to high‐value added products. Herein we report an efficient electrochemical strategy to transform phenol into p‐benzoquinone, by tandem oxidations of CuSO4 and CoSO4 catalysts in an electrolyte. Co3+ generated at the anode from oxidation of Co2+ diffuses to the solution and reacts with phenol to form hydroquinone, which is subsequently oxidized by Cu2+ in the solution selectively to p‐benzoquinone. The active metal ions (Cu2+ and Co3+) are continuously regenerated at the anode through electrooxidation and the targeted p‐benzoquinone is accumulated in the electrolyte solution. The Ultraviolet‐visible spectra and electrochemical test results reveal that Cu2+ reacts with hydroquinone immediately, and p‐benzoquinone remains stable in CuSO4 solution. By optimizing catalyst concentrations and reaction temperatures (0.2 M CuSO4, 0.005 M CoSO4 and 50 °C), the highest p‐benzoquinone yield was improved to 47 %. The developed copper‐cobalt co‐catalyzed system provides a promising approach to selectively prepare high‐value benzoquinone compounds under mild reaction conditions.