Aliphatic carboxylic acid as a hydrogen-bond donor for converting CO2 and epoxide into cyclic carbonate under mild conditions

Abstract

The coupling of CO₂ and epoxides is a promising way to reduce atmospheric carbon by converting it into value-added cyclic carbonate. Pursuing efficient catalysts is highly attractive for the title reaction. Herein, we developed simple and inexpensive catalyst systems of aliphatic carboxylic acids as the hydrogen-bond donor (HBD) and quaternary ammonium halides as the nucleophile to catalyze the CO₂-epoxide coupling reaction with high efficiency and selectivity under mild conditions (80 °C and 4 bar CO₂). The high activity of this catalyst system is retained even under ambient conditions. The effects of the acidity and steric hindrance of acids on the catalysis of CO₂-epoxide coupling were systematically investigated. Lastly, the reaction mechanism was deduced and its rationality was further reinforced by exploring the interaction between a representative system AA/TBAB (acetic acid/tetrabutylammonium bromide) and propylene oxide (PO). The study of aliphatic carboxylic acids/quaternary ammonium halides provides a new way to design catalyst systems for the title reaction.