Experimental and Quantum Chemical Calculations on the High-Efficiency Transesterification of Dimethyl Carbonate with Alcohol Catalyzed by Calcium Oxide.

Typical catalysts used in dimethyl carbonate (DMC) transesterification encounter challenges in terms of environmental sustainability and economic viability. Calcium oxide (CaO), being an environmentally friendly and cost-effective catalyst, exhibits favorable compatibility with the criteria above. It has been conclusively demonstrated that CaO performs high efficiency as a catalyst for the transesterification between alcohols and DMC. The optimal conditions for the CaO-catalyzed transesterification of DMC and 1-octanol were determined (90 °C, 17 h, and CaO/1-octanol/DMC molar ratio = 0.3:1.0:40.0), under which the conversion of 1-octanol reaches 98.3%, while the yield and selectivity of methyl octyl carbonate are 98.1 and 99.9%, and CaO has been proven to have the efficient ability to be recycled three times. Meanwhile, the CaO-catalyzed reaction mechanism of the transesterification of DMC with alcohol is illustrated in the quantum chemical method based on the M06-2X functional, and the structures of the corresponding transition states are simultaneously derived. The activation energy barrier is proven to be effectively decreased by the catalytic effect of CaO. In addition, the electrostatic potential diagram verifies the proposed reaction sites. This research constructs the theoretical basis for CaO-based DMC chemistry and expands the green catalysts available for the synthesis of dialkyl carbonates.