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

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 CuSO 4 and CoSO 4 catalysts in an electrolyte. Co 3+ generated at the anode from oxidation of Co 2+ diffuses to the solution and reacts with phenol to form hydroquinone, which is subsequently oxidized by Cu 2+ in the solution selectively to p ‐benzoquinone. The active metal ions (Cu 2+ and Co 3+ ) 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 Cu 2+ reacts with hydroquinone immediately, and p ‐benzoquinone remains stable in CuSO 4 solution. By optimizing catalyst concentrations and reaction temperatures (0.2 M CuSO 4 , 0.005 M CoSO 4 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.