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Efficient transformation of CO₂ to cyclic carbonates using bifunctional protic ionic liquids under mild conditions

Meng, Xianglei, Ju, Zhaoyang, Zhang, Suojiang, Liang, Xiaodong, von Solms, Nicolas, Zhang, Xiaochun, Zhang, Xiangping
Green chemistry 2019 v.21 no.12 pp. 3456-3463
ambient temperature, anions, carbon dioxide, carbonates, catalysts, cycloaddition reactions, epoxides, flue gas, green chemistry, hydrogen bonding, infrared spectroscopy, ionic liquids, nitrogen
A series of 1,8-diazabicyclo-[5.4.0]undec-7-ene (DBU) based bifunctional protic ionic liquids (DBPILs) were easily prepared by acid–base reactions at room temperature. They were used to catalyze the cycloaddition reaction of CO₂ with epoxides under mild conditions. As a metal free catalyst, the best DBPIL showed a 92% yield of products within 6 hours at 30 °C and 1 bar CO₂ without any solvents and co-catalysts. It could afford carbonates in good yields with broad epoxide substrate scope and CO₂ from simulated flue gas (15% CO₂/85% N₂). IR spectroscopy and DFT studies were carried out to investigate the mechanism of the cycloaddition reaction. The results showed that the DBPILs could activate both CO₂ and epoxides by alkoxy anions and powerful hydrogen-bonding, which was well consistent with experiments.