Conversion of CO₂ with epoxides to cyclic carbonates catalyzed by amino acid ionic liquids at room temperature

CO₂ utilization plays an important role in rational use of carbon resources and reduction of carbon emissions. It is still a challenge to achieve efficient CO₂ utilization by amino acid ionic liquids (AAILs) under room temperature and atmospheric pressure with cocatalyst- and solvent-free conditions. Herein, the newly developed AAILs including 1,1,3,3-tetramethylguanidine cation ([HTMG]⁺) together with both amino acid and halogen as anions, were simply synthesized by neutralization reaction. Under mild conditions (30 °C, 20 h and 1 MPa CO₂), the cycloaddition reaction of CO₂ and propylene oxide could be efficiently catalyzed by [HTMG][His][I] with 99 % propylene carbonate yield and selectivity in the absence of additional solvent and cocatalyst. Notably, even at room temperature and atmospheric pressure for 72 h, [HTMG][His][I] also displayed 96 % yield and 99 % selectivity due to the cooperation of [HTMG]⁺, [His]^2– and [I]^–. Meanwhile, [HTMG][His][I] performed excellent universality of various epoxides and reusability. Based on the characterization results of ¹H and ¹³C NMR, it was verified that propylene oxide and CO₂ were simultaneously activated by the functional groups in [HTMG][His][I]. Hence, the reaction mechanism for CO₂ cycloaddition with epoxide catalyzed by [HTMG][His][I] was proposed. This work provided a simple strategy to prepare sustainable AAILs for efficient CO₂ utilization under very mild conditions of room temperature and atmospheric pressure (even the low CO₂ concentration at simulated flue gases).