Design and Synthesis of Novel Ionic Liquids with Unique Structures and Excellent Catalytic Activity

We synthesis a series of novel ionic liquids with near-neutrality, moderate nucleophilicity, and zwitterionic structure through a one-step method. Interestingly, 1-methylimidazole can be readily activated by various esters, including carbonate esters, carboxylic acid esters, and oxalate esters. The structure and properties of the as-synthesized ionic liquids are qualitatively and quantitatively analyzed by FT-IR, 1H and 13C NMR, TG-MS, and the Hammett indicator method. The activation mechanism is proposed, and the negative charge density of these ionic liquids is calculated. Taking MI-EC as an example, the optimized synthesis conditions are at 85 °C for 18 h, and the pathway is determined through DFT calculations. MI-EC displays excellent catalytic activity in transesterification reaction. The EC conversion reaches 50.4%, the DMC yield is 30.5%, and the TOF is 127.8 h-1 with only 30 min, and the reaction kinetics are studied. The catalytic activity and the characterization results of MI-EC remain unchanged after six cycles, showing outstanding stability. Importantly, MI-EC has a wide range of substrate universality, such as carbonates, oxalates, and acetic esters. This study provides theoretical and practical support for the design and synthesis of ionic liquids and provides a new perspective for the preparation of alkaline catalysts.