Highly efficient conversion of carbon dioxide catalyzed by polyethylene glycol-functionalized basic ionic liquids

Abstract

A series of polyethylene glycol (PEG)-functionalized basic ionic liquids (ILs) were developed for efficient CO₂ conversion into organic carbonates under mild conditions. In particular, BrTBDPEG₁₅₀TBDBr was proven to be a highly efficient and recyclable catalyst for the synthesis of cyclic carbonates without utilization of any organic solvents or additives. This is presumably due to the activation of epoxide assisted by hydrogen bonding and activation of CO₂ by the ether linkage in the PEG backbone or through the formation of carbamate species with the secondary amino group in the IL cation on the basis of in situ FT-IR study under CO₂ pressure. In addition, the subsequent transesterification of cyclic carbonate e.g. ethylene carbonate (EC) with methanol to dimethyl carbonate (DMC) can also be effectively catalyzed by BrTBDPEG₁₅₀TBDBr, thanks to the activation of methanol by the secondary and tertiary nitrogen in the IL to easily form CH₃O⁻, realizing a so-called “one-pot two-stage” access to DMC from CO₂ without separation of cyclic carbonate by using one kind of single component catalyst. Therefore, this protocol represents a highly efficient and environmentally friendly example for catalytic conversion of CO₂ into value-added chemicals such as DMC by employing PEG-functionalized basic ILs as catalysts.