Electrochemical Capture and Release of Carbon Dioxide Using a Disulfide-Thiocarbonate Redox Cycle.

We describe a new electrochemical cycle that enables capture and release of carbon dioxide. The capture agent is benzylthiolate (RS-), generated electrochemically by reduction of benzyldisulfide (RSSR). Reaction of RS- with CO2 produces a terminal, sulfur-bound monothiocarbonate, RSCO2-, which acts as the CO2 carrier species, much the same as a carbamate serves as the CO2 carrier for amine-based capture strategies. Oxidation of the thiocarbonate releases CO2 and regenerates RSSR. The newly reported S-benzylthiocarbonate (IUPAC name benzylsulfanylformate) is characterized by 1H and 13C NMR, FTIR, and electrochemical analysis. The capture-release cycle is studied in the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BMP TFSI) and dimethylformamide. Quantum chemical calculations give a binding energy of CO2 to benzyl thiolate of -66.3 kJ mol-1, consistent with the experimental observation of formation of a stable CO2 adduct. The data described here represent the first report of electrochemical behavior of a sulfur-bound terminal thiocarbonate.