An experimental and DFT study of the reaction between dichloroethylene carbonate and triethylamine in dimethyl carbonate†

The reaction between dichloroethylene carbonate and triethylamine is the key side process in the synthesis of vinyl carbonate. Quantitative experiments revealed a DCEC : TEA molar ratio of 1 : 2, indicating that the initial product, chlorovinyl carbonate (CLVC), further reacts with TEA. Triethylamine hydrochloride, CO₂, CO, chloroethane, and a small amount of chloromethane were identified as reaction products. Product analysis using alternative amines and solvents confirmed the origin of chloroethane from TEA and CO₂/CO primarily from DCEC, with chloromethane originating from DMC. Density functional theory (DFT) calculations elucidated the mechanism of triethylamine hydrochloride and chloroethane formation, revealing a chain propagation pathway for HCl elimination from chlorovinyl chloride (CLVC). Within this pathway, the initial activation is facilitated by triethylamine, while subsequent activations are mediated by a reactive intermediate generated in the preceding step. The initial HCl elimination from CLVC was identified as the rate-determining step. A competing pathway involving attack by TEA at the chlorine-bearing carbon of CLVC leads to a quaternary ammonium salt intermediate, which decomposes to chloroethane. This study provides significant theoretical insight for understanding the side reactions in the synthesis of vinyl carbonate.