Transesterification of dimethyl carbonate and ethanol to ethyl methyl carbonate with full product selectivity and high rate enabled by functionalized quaternary ammonium ionic liquids

Base-facilitated transesterification reactions hold a central position in the chemical industry, as they serve as crucial strategies for producing numerous chemicals, particularly for manufacturing ethyl methyl carbonate (EMC) electrolyte of lithium batteries from ethanol (EtOH) and dimethyl carbonate (DMC). However, reported catalysts face challenges including catalyst deactivation and environmental pollution. To tackle these challenges, we report functionalized quaternary ammonium ionic liquids with fine-tuned electronegativity and alkalinity via anion design and electron-withdrawing/donating substituents on the quaternary ammonium. N B222 Im achieves the fastest and highest catalytic performance to date; at an ultra-mild reaction time of 5 min and 58 ℃, its EMC yield reaches 55.61% with 91.57% product selectivity. We successfully correlate electrostatic attraction/electron delocalization ability of anions with the catalytic performance, visualizing the effective production of ethoxy group from EtOH, the selective cleavage of methoxy group from DMC, and their directional combination to form EMC by the nitrogen atoms in imidazole anions. Moreover, compared with the uncatalyzed system, DFT calculations on the proposed reaction mechanism demonstrate that N B222 Im can lower the reaction energy barrier for the conversion of DMC to EMC. This barrier is also lower than that of the EMC-to-DEC pathway, thus endowing this ionic liquid with high selectivity toward EMC formation. This work offers a viable strategy to overcome conventional catalyst drawbacks and new insights for efficient EMC synthesis catalyst design, and promotes electrode material development.