Facile synthesis of zinc halide-based ionic liquid for efficient conversion of carbon dioxide to cyclic carbonates

Multifunctional monocomponent zinc halide-based ionic liquids, amidinothiourea-ZnI 2 (ATUI) and N-phenylthiourea-ZnI 2 (NTUI), were facilely developed as homogeneous catalysts for efficient conversion of CO 2 with epoxides to cyclic carbonates. On account of synergistic effects of multifunctional components in ATUI, the propylene carbonate yield could reach 95% under 110 °C, 1.0 MPa, 4.0 h or even mild conditions. There was a slight decrease of propylene carbonate yield because of the loss of ATUI during the reuse process. Additionally, the universality of ATUI was also studied to other terminal epoxides. Meanwhile, a plausible reaction mechanism was proposed where the synergistic effects involving cation structure and halogen anion of ATUI guarantee the cycloaddition reaction to proceed effectively under solvent and co-catalyst free condition. Finally, reaction kinetics were undertaken to compare the catalytic efficiency of ATUI and NTUI so as to compare the catalytic activity of different numbers of hydrogen bond donor in amidinothiourea and N-phenylthiourea.