ZnBr₂-Based Choline Chloride Ionic Liquid for Efficient Fixation of CO₂ to Cyclic Carbonate

Abstract

In this work, ZnBr₂-based choline chloride (CH) was first investigated to catalyze the synthesis of cyclic carbonates from CO₂ and epoxides under solventless conditions. It was demonstrated that ZnBr₂-based CH was very efficient and selective. Under the optimum reaction conditions, 99% yield of propylene carbonate was achieved. The catalyst can be reused five times without loss of catalytic activity. It was proved to be very active in a variety of terminal epoxides with CO₂. In addition, a synergistic catalytic mechanism by Zn²⁺ and -OH was proposed.

GRAPHICAL ABSTRACT

Keywords:

• Carbon dioxide
• choline chloride
• cycloaddition
• epoxide
• zinc bromide

ACKNOWLEDGMENTS

We gratefully acknowledge the National Natural Sciences Foundation of China (20876162 and 20625618), National Basic Research Program of China (973 Program, 2009CB219901), and Key Projects in the National Science and Technology Pillar Program in the Eleventh Five-Year Plan Period (2008BAF33B04).

Notes

^a Reaction conditions: PO (140 mmol), CH (1.4 mmol), ZnBr₂ (0.28 mmol), CO₂ (1.5 MPa), 110 °C, 60 min.

^b Isolated yield.

^c Moles of propylene carbonate produced per mole of catalyst per hour.

^d ZnBr₂ (0.14 mmol).

^a Reaction conditions: PO (140 mmol) and CH (1.4 mmol).

^b CH/ZnBr₂: molar ratio of CH to ZnBr₂.

^c Isolated yield.

^d The first run of the catalyst.

^e The second run of the catalyst.

^f The third run of the catalyst.

^g The fourth run of the catalyst.

^h The fifth run of the catalyst.

^a Reaction condition: epoxide (140 mmol), CH (1.4 mmol), ZnBr₂ (0.28 mmol), CO₂ (1.5 MPa), 110 °C, 60 min.

^b Isolated yield.

^c 12 h.

^d 24 h.