Highly selective synthesis of dimethyl carbonate from urea and methanol catalyzed by ionic liquids

Direct synthesis of dimethyl carbonate from methanol and urea using ionic liquids, such as Et3NHCl–FeCl3, Et3NHCl–ZnCl2, Et3NHCl–CuCl2, Et3NHCl–SnCl2 and emimBr–ZnCl2, as catalysts were investigated. Among the ionic liquids, Et3NHCl–ZnCl2 or emimBr–ZnCl2 exhibited higher activity for the synthetic reaction and surprisingly high selectivity to DMC. The effects of the various reaction conditions, i.e. reaction temperature, molar ratio of methanol to urea, and amount and composition of catalysts, on the synthesis of DMC were discussed in a systematic way. The reaction mechanism and the reasons why raised activity and high selectivity of the catalyst are maintained were explored.