Direct synthesis of diphenyl carbonate by mediated electrocarbonylation of phenol at Pd2+-supported activated carbon anode

Mediated electrocarbonylation of phenol to diphenyl carbonate (DPC) at a PdCl2-supported activated carbon anode in 1 atm CO at 298 K was studied. A dry CH2Cl2 or CH3CN solvent and a galvanostatic electrolysis of 1 mA were necessary for formation of DPC, while the addition of a base and a supporting electrolyte was also essential. A combination of triethylamine (Et3N) and tetrabutylammonium perchlorate (Bu4NClO4) was suitable in various combinations. The addition of 2 equiv. of Et3N to the electrolyte (C6H5OH/Bu4NClO4/CH2Cl2) at 1-h intervals was more efficient in the formation of DPC than a single initial addition of the same amount of Et3N. The yield of DPC was 130% based on Pd and its current efficiency (CE) was 42% for 6 h. The CE of the CO2 formation was only 3%. Sodium phenoxide (PhONa) showed dual functionality as a base and supporting electrolyte. When the mediated electrocarbonylation was conducted in a C6H5OH/PhONa/CH3CN electrolyte, DPC was produced in 172% yield and 40% CE for 6 h. The CE of the CO2 formation was 10%. DPC formed continuously after a single initial addition of 4 equiv. of PhONa. Li or K phenoxide also worked as promoters for the mediated electrocarbonylation of phenol to DPC.