A series of sulfonic acid-functional ionic liquids (ILs) were prepared and their acid strength was determined by the Hammett method combined with UV-visible spectroscopy.Then the catalytic activity of the ILs for the synthesis of methylene diphenyl dimethylcarbamate (MDC) from methyl phenyl carbamate (MPC) and formaldehyde (HCHO) was evaluated.The result showed that the acid strength of the ILs was well consistent with their catalytic activity.The acidity of ［HSO3-bpy］CF3SO3 was the strongest and its catalytic activity was the highest.The reaction conditions for the synthesis of MDC were optimized using ［HSO3-bpy］CF3SO3 as reaction media.Under the suitable reaction conditions of 70℃

60 min

molar ratio of MPC to HCHO 12 and mass ratio of ILs to MPC 4

the yield of MDC was 91.5％.［HSO3-bpy］CF3SO3 could be reused more than five times after the removal of water by vacuum distillation.