(2gh) Se-Catalyzed Oxidative Carbonylation of C1-C4 Alcohols for Producing Dialkyl Carbonates

Oxidative carbonylation of alcohols is one of the carbon-neutral strategies that use carbon monoxide from syngas to produce value-added carbonyl compounds. The resulting dialkyl carbonates (DACs) have drawn considerable attention during the last few decades due to their environmentally benign characteristics as green reagents as well as various practical applications such as electrolyte solvents for Li-ion batteries, monomers for polycarbonates, and gasoline additives.

DACs have been prepared via the phosgenation of corresponding alcohols. However, this process accompanies harmful effects to the environment due to the generation and its neutralization of corrosive HCl as a by-product. To replace this method, several alternative approaches have been developed, including alcoholysis of urea, transesterification of ethylene carbonate, methylnitrite carbonylation, carboxylation of alcohols, and oxidative carbonylation. Among these, oxidative carbonylation of alcohols is considered as the most feasible reaction owing to practical viewpoints, i.e., high atomic efficacy. The Cu-based catalysts have been studied for oxidative carbonylation but suffers from low activity and high corrosion due to its halide content.

To overcome these issues, Se-based catalysts have been investigated as halide-free catalysts, however, they are still limited by the low yield of DACs. Thus, we studied Se/DMAP catalytic system for oxidative carbonylation of C1-C4 alcohols that produced 40-61% yields of C3-C9 DACs. This catalytic system highlights higher turnover frequency (TOF) values under milder conditions than any other previous catalytic system and showed the highest TOF reported to date for the oxidative carbonylation of methanol. Notably, oxidative carbonylation of 2-methoxyethanol (MEG, C3-alcohol) afforded bis(2-methoxyethyl)carbonate (BMEC, C7-DAC) with 60.9% yield at 50 °C. This catalytic system could be reused at least five times while retaining the majority of the original activity. A possible mechanism of the oxidative carbonylation of alcohols using Se/DMAP system was thoroughly investigated based on the catalytic results, in situ ATR-FTIR spectroscopy, NMR spectroscopy, and first principles density functional theory (DFT) calculations, and these studies revealed that DMAP exhibits a unique triple functionality, acting as a base, a hydrogen bond (H-bond) acceptor, and a nucleophile.

Research Interests

Carbonylation refers to carbon-neutral reaction that uses abundantly available carbon monoxide from syngas to produce value-added carbonyl group-containing chemicals, so it is widely used in industrial chemistry. As one of the carbonylations, oxidative carbonylation of alcohols are considered as practical approaches to produce dialkyl carbonates (DACs) and have been studied because of the increasing demand of DACs. Much of the work has been done on the oxidative carbonylation of alcohols to DACs using Cu-based catalysts, but these catalysts suffer from low activities and corrosion issues.

During my Ph.D., I investigated Se-based catalytic system for oxidative carbonylation of alcohols and found Se/DMAP catalytic system which shows over 40% yield of DACs under mild reaction conditions. Besides, I proposed a possible mechanism of Se/DMAP catalytic system on oxidative carbonylation of alcohols based on experimental results and first principles density functional theory (DFT) calculations. In my current postdoctoral research with Prof. Yong Jin Kim and Dr. Jayeon Baek in Korea Institute of Industrial Technology (KITECH), we investigate Se supported on DMAP-functionalized support for oxidative carbonylation of alcohols to make heterogeneous catalytic system from the practical point of view. Based on my recent understanding on catalysis for carbonylation, I envision my future research to span across carbonylation of biomass-derived chemicals and CO₂ conversion using homogeneous or heterogeneous catalysts. With the increasingly serious problems of environmental pollution and energy scarcity, C1 chemistry technology (containing conversion of CO and CO₂) will be considered more important research area for the production of highly pure chemicals.