Synthesis of carbonates by one-step transesterification

Synthesis of carbonates from methanol, CO₂ and ethylene oxide(EO) through one-step transesterification was studied and various catalysts used in alcoholysis and esterification were investigated. The results indicated that in the presence of quaternary ammonium salt or quaternary phosphonium salt catalysts, the reaction activity order for the cationic groups was: [Pr₄N]⁺ > [Et₄N]⁺ > [Me₄N]⁺ > [PPh₃Me]⁺ > [Bu₄N]⁺ and the order for the anionic groups was Br^- > I^-. Thereinto [Et₄N]⁺ showed the best target product selectivity, so it was selected as catalyst used in the one-step transesterification. Under the optimum conditions of temperature 150°C, pressure 4 MPa, the catalyst dosage 0.22 mol/L, mole ratio of methanol to EO 4 and time 4 h, EO conversion could reach 97.22% and total selectivity to both dimethyl carbonate and ethylene carbonate could be 86.54%.