Synthesis of diethyl carbonate from CO₂ and orthoester promoted by a CeO₂ catalyst and ethanol

The combination of a CeO₂ catalyst and ethanol effectively promotes the direct synthesis of diethyl carbonate (DEC) from CO₂ and an orthoester. The reaction temperature, initial CO₂ pressure, and the ethanol/orthoester volume ratio were found to significantly influence DEC formation and were systematically studied to determine the optimum conditions. DEC amount of 5.2 mmol was obtained at 160 °C, 5 MPa of CO₂, and a reaction time of 20 h, providing high productivity (1.21 mmol_DEC mmol_catalyst⁻¹ h⁻¹) using a CeO₂ catalyst. The recovered CeO₂ catalyst was recyclable at least four times without any significant loss of activity when both triethyl orthoacetate and triethyl orthovalerate were used. A series of orthoesters bearing various alkyl substituents, aromatic substituents and halide moieties were evaluated for their activities with and without ethanol. In the presence of ethanol, orthoesters bearing longer alkyl substituents led to higher DEC yields, and orthoesters bearing aromatic and halide moieties negatively impacted DEC formation. In the absence of ethanol, triethyl orthoacetate provided the highest DEC yield; in all cases, the use of ethanol resulted in a greater DEC formation than when the reaction was performed without ethanol.