Synthesis Of Imidazole-based Ionic Liquid Catalysts And Their Application

With the development of green chemistry, the research and application of ionic liquid has attracted more and more attention, especially on the catalytic field. The physical and chemical properties of ionic liquid could be changed by the modification on its structure. Indeed, the ionic liquid composed by different cations and anions may result in the distinct physical structure of ionic liquid. Previous researches have focused on the catalytic efficiency of ionic liquid and its derivatives, such as their activities, selectivity, and recycling yield. This thesis demonstrates some new foundings about ionic liquid and their catalystic applications:1) Imidazole bicarbonate ionic liquid-carbene (IL-NHCs)Theoretical and experimental researches reveal that imidazolium hydrogen carbonate ionic liquids (ILs) can be considered as an integration of ILs and N-heterocyclic carbenes (NHCs) (This combinant is denoted as IL-NHCs hereafter). These special ILs can spontaneously transform into a NHC-CO2 adduct, and a chemical equilibrium exists between ILs and NHC-CO2. This equilibrium is easy to be controlled because of the low transformation barrier height and small Gibbs free energy change. The NHC-CO2 contents in these IL-NHCs solution range from 3.0% to 95.5% depending on the functional groups and solvents. These IL-NHCs have the advantages of both ILs and NHCs, i.e., high reactivity, insensitivity to water and air, recyclability, and high thermal stability. Besides, they are cheaper comparing with the classical NHCs. The catalytic abilities of these IL-NHCs in benzoin condensation are comparable to that of classical NHC, and the IL-NHCs can be reused by a simple method. Besides, these IL-NHCs have good catalytic effective for transesterification reaction, oxidation of benzaldehyde, and so on. This IL-NHC is the first example that a compound contains both IL and NHC. The dual attributes of IL-NHCs provide a posibility to improve reactions catalyzed by classical ILs or NHCs.2) Preparation and application of a copper catalyst with an imdazole salt tagNew, simple, water-soluble copper catalysts with an imidazole salt tag [Cu-Imace-H][X] (X=Cl-, Br-,HSO4-, NO3-, and BF4-) were synthesized via an organic solvent-free method. They were characterized by 1H-NMR, 13C-NMR,FT-IR, UV-Vis, ESR, ESI-MS, elemental analysis, and melting point measurements. These catalysts are effective for phenol oxidation to dihydroxy derivates in water with H2O2 as oxidant, and 2,6-dimethyl-4-methyl phenol indirect oxidation with oxygen as the oxidant. The anion evidently affects the appearance and electronic structure of the catalysts, as well as their catalytic reactivity. Both the phenol oxidation and catalyst syntheses were organic solvent-free to ensure a green process.