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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.