Quaternary Ammonium Ionic Liquids as Bi-functional Catalysts for One-step Synthesis of Dimethyl Carbonate from Ethylene Oxide, Carbon Dioxide and Methanol

One kind of novel ionic liquids (ILs) with a tertiary amino moiety and a quaternary ammonium group were synthesized and identified by FT-IR, H-1 and C-13 NMR. The elemental chemical state and basicity of ILs were determined by XPS and Hammett indicator method, respectively. Then the catalytic performance of these bifunctional catalysts was investigated in one-step synthesis of dimethyl carbonate (DMC) from ethylene oxide (EO), carbon dioxide and methanol. The best catalytic performance with 99% EO conversion and a maximum of 74% DMC selectivity was obtained using [N-111,N-6N11]I as catalyst under optimized reaction conditions. And the catalyst could be reused for several times. Normally, stronger basicity could be obtained by altering the anions with different nucleophilicity in ILs and a better catalytic activity could be achieved correspondingly. A mechanism that both the ring opening of epoxide through nucleophilic attacks and the transesterification play an important role in the reaction was proposed based on experimental results.