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

Abstract Acidified ionic liquid [emim]BF 4 (H + [emim]BF 4 ) was prepared and its structure was ascertained using 1 H NMR analysis and experimental verification. It was found that the cation of H + [emim]BF 4 is composed of a central immidazole molecule surrounded by a water layer in which excessive HBF 4 molecules are dissolved. H + [emim]BF 4 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]BF 4 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]BF 4 could be reused for 4 runs after being treated by ultrasonic extraction with CHCl 3 and no significant catalytic activity loss was observed after the second run.