(700f) Mechanistic Study of Se-Catalyzed Oxidative Carbonylation of Alcohol for Producing Dialkyl Carbonate

As one of the C1 chemistry reactions which play a critical role in the chemical and energy industry, oxidative carbonylation of alcohols to corresponding dialkyl carbonates (DACs) has been studied due to DACs’ myriad applications, such as aprotic solvents, alkylation reagents, alkoxycarbonylation reagents, solvents for Li-ion batteries, monomers for polycarbonates, and gasoline additives.

Conventionally, DACs have been produced via the phosgenation of corresponding alcohols. Although this process is simple and low cost, it causes harmful effects to the environment due to using the lethal phosgene and generation of corrosive HCl as a by-product. Therefore, several alternative approaches have been developed, and oxidative carbonylation of alcohols is considered as the most feasible reaction owing to high atomic efficacy. Meanwhile, EniChem has commercialized dimethyl carbonate (DMC) production via Cu salt-catalyzed oxidative carbonylation since the early of 1980s, but this process suffers from low activity and high corrosion due to its halide content.

To overcome these issues, Se-based catalysts have been investigated due to the generation of SeCO which easily reacts with nucleophiles. However, they are still limited by the low yield of DACs. Thus, we studied Se/tertiary amine catalytic system for oxidative carbonylation of 2-methoxyethanol (MEG). Notably, Se/DMAP catalytic system for oxidative carbonylation of MEG afforded bis(2-methoxyethyl) carbonate (BMEC) with 60.9% yield at 50 °C. This catalytic system highlights higher turnover frequency (TOF) values under milder conditions than any other previous catalytic system. To unravel the role of DMAP and suggest a plausible mechanism of Se/DMAP-catalyzed oxidative carbonylation, ¹H NMR, in situ or ex situ ATR-FTIR, and DFT calculations were studied. Throughout these studies we could identify the key DMAP intermediate resulting from DMAP-mediated esterification and revealed that DMAP exhibits a unique triple functionality, acting as a base, a hydrogen bond (HB) acceptor, and a nucleophile.