One-step synthesis of dimethyl carbonate from carbon dioxide, propylene oxide and methanol over alkali halides promoted by crown ethers

• Crown ethers were used as cocatalysts in DMC synthesis catalyzed by alkali halides.
• DMC yield of KCl catalyst promoted by DBC increased by more than five times.
• The increase is due to good complexing ability of crown ethers for alkali metal ions.
• Crown ethers promote reaction rate and equilibrium, while preventing side reaction.
• Crown ethers conveniently achieved high recovery ratio and excellent reusability.

Crown ethers (i.e. [2,4]-dibenzo-18-crown-6 (DBC), 18-crown-6, 15-crown-5 and 12-crown-4) show obvious co-catalytic effect for alkali halides catalyzing one-step synthesis of dimethyl carbonate (DMC) from CO2, propylene oxide and methanol. Especially, the DMC yield of KCl catalyst promoted by DBC can increase by more than five times and reach about 40% under mild reaction conditions (i.e., low mole ratio of methanol and epoxieds: 7:3, low initial pressure of CO2: 1.5 MPa, reaction temperature: 140 °C, time: 10 h). The optimized molar ratio of KCl to DBC is 2: 1. Due to the good complexing ability between DBC and K+, KCl and DBC formed an organometallic complex. Actually, DBC can not only promote the reaction rate and equilibrium of cycloaddition and transesterification reactions, but also prevent side reaction. Importantly, DBC can conveniently achieve high recovery ratio and show excellent reusability.

Crown ethers were used as cocatalysts in one-step DMC synthesis catalyzed by alkali halides. Especially, the DMC yield of KCl catalyst promoted by DBC can increase by more than five times, due to the good complexing ability between DBC and K+. Crown ethers promote reaction rate and equilibrium, while preventing side reaction. Crown ethers conveniently achieved high recovery ratio and excellent reusability. In other words, crown ethers achieve a homogeneous co-catalytic effect and a heterogeneous recovery.Figure optionsDownload as PowerPoint slide