Synthesis of dimethyl carbonate catalyzed by carboxylic functionalized imidazolium salt via transesterification reaction

We investigated the dependence of cations and anions of ionic liquids (ILs) on catalytic activity for the synthesis of dimethyl carbonate (DMC) via the transesterification of ethylene carbonate (EC) with methanol (CH ₃OH), and demonstrated that an easily prepared carboxylic functionalized imidazolium salt exhibited higher activity, 82% yield of DMC together with 99% selectivity was obtained under the metal-free and halogen-free conditions. The reaction mechanism was also proposed according to experimental and DFT studies. In addition, in order to simplify the catalyst separation and evaluate the catalyst stability, we also covalently anchored the functionalized imidazolium salt onto a highly cross-linked polystyrene resin (PS) as a heterogeneous catalyst for DMC synthesis, and continuously performed the reaction in a fixed bed reactor for 200 h without obvious loss of activity, which would have potential applications in industry. The process thus represented an environmentally friendly pathway for the synthesis of DMC via a transesterification reaction.