Multifunctional Halogen-Free Guanidine-Based Ionic Liquids for the One-Pot Two-Step Synthesis of Glycerol Carbonate from CO2 and Glycerol under Mild Conditions

The conversion of greenhouse gas CO2 and biodiesel byproduct glycerol into high-value-added glycerol carbonate (GC) is an ideal strategy for carbon neutralization. In this work, a multifunctional halogen-free ionic liquid catalytic system was designed with different substituted phenols and organic strong bases, especially guanidines, for the one-pot two-step synthesis of GC. A 91% yield and 94% selectivity of chloropropylene carbonate (CHC) and a 93% GC yield were obtained with well-designed [HBTMG][mOH-PhO] after 3 h of cycloaddition and 2 h of transesterification under atmospheric pressure at 65/50 °C. A series of mechanism verification experiments showed that the synergistic activation of substrates by the anion and cation brought about the high catalytic activity of [HBTMG][mOH-PhO]. Moreover, the substrate scope suggested that the [HBTMG][mOH-PhO] system could be well applied to the synthesis of both terminal and internal cyclic carbonates under the same mild conditions. The [HBTMG][mOH-PhO] IL catalyst showed a good recovery performance. This work provided a halogen-free catalyzed green strategy with milder conditions for the synthesis of GC.