The structure of acidified ionic liquid [emim]BF4 and its catalytic performance in the reaction for 4,4′-MDC synthesis

Acidified ionic liquid [emim]BF4 (H+[emim]BF4) was prepared and its structure was ascertained using 1H NMR analysis and experimental verification. It was found that the cation of H+[emim]BF4 is composed of a central immidazole molecule surrounded by a water layer in which excessive HBF4 molecules are dissolved. H+[emim]BF4 showed high catalytic performance in the condensation of methyl N-phenyl carbamate (MPC) and formaldehyde (HCHO) to methylene diphenyl dimethylcarbamate (4,4′-MDC). Under the suitable reaction conditions of 70 °C, molar ratio of MPC to HCHO = 4, weight ratio of H+[emim]BF4 to MPC = 4, and reaction time 1.5 h, the yield and selectivity of 4,4′-MDC attained 71.7% and 71.9%, respectively. Besides, H+[emim]BF4 could be reused for 4 runs after being treated by ultrasonic extraction with CHCl3 and no significant catalytic activity loss was observed after the second run.

Graphical abstractAcidified ionic liquid (H+[emim]BF4) was prepared and its structure was first ascertained. The cation of H+[emim]BF4 is composed of a central immidazole molecule surrounded by a water layer in which excessive HBF4 molecules are dissolved. H+[emim]BF4 showed high catalytic performance in the synthesis of methylene diphenyl dimethylcarbamate (4,4′-MDC). It could be reused 4 times after being purified.Figure optionsDownload full-size imageDownload as PowerPoint slide