A Photocatalyzed Synthesis of Dialkyl Carbonates from Phosgene Generated in situ

The anion exchange resin Amberlite IRA-900, in the chloride form, catalyzes the photolysis of carbon tetrachloride in methanol, ethanol, and n-propanol under visible and near-UV irradiation to produce the corresponding dialkyl carbonate and alkyl chloroformate, the latter readily converted to the carbonate with base. For diethyl carbonate, the rate of reaction increases with the partial pressure of oxygen and is relatively insensitive to either the amount of catalyst present or the fraction of CCl4 in ethanol above approximately 10 mg/mL and 5%, respectively. A yield of 15% could be achieved for diethyl carbonate under appropriate conditions, accompanied by acetaldehyde and chloroform as major side products. The reaction in methanol was slower and that in n-propanol somewhat faster than in ethanol.