1,3-Bis(2,4,6-trimethylphenyl)imidazolinium Chloride

Typical procedure: 1,3-bis(2,4,6-trimethylphenyl)imidazolinium chloride (17 mg), dried potassium carbonate (138.2 mg) and DMSO (1 mL) are added into a dry reaction tube (10 mL). The mixture is stirred at room temperature for 1 h to generate the carbene, which is then reacted with carbon dioxide (in balloon). After the mixture is stirred for 2 h at room temperature, trans-cinnamaldehyde (62 micro-L) is added into the mixture. Then the reaction mixture is stirred for 4 days at room temperature, and quenched with HCl solution (1 M, 4 mL). The quenched mixture is extracted with ethyl acetate (3 x 4 mL). The combined organic layers are washed with brine (5 mL), dried over Na2SO4 and filtered. The solution is concentrated in vacuo to give crude trans-cinnamic acid in 95% yield (determined by the 1H NMR based on cinnamaldehyde). The residual gas in the balloon is　analyzed by GC to determine the concentration of CO in the mixture. The CO concentration in the mixture is consistent with the yield of trans-cinnamic acid.