Carboxvl-imidazolium Functionalized Ionic Liquids For Solubilizing Metal Oxides

As a class of novel “green” solvents, room temperature ionic liquids （RTILs） have found wideapplications in organic synthesis, catalytic reaction, electrochemical devices, separation technology, andfunctional materials because of their excellent physical and chemical properties such as good thermalstability, negligible vapor pressure, dissovling ability, and wide electrochemical window. However,conventional ionic liquids show a low solubility for metal oxides or metal salts due to their weaklycoordinating properties of anions and cations. The carboxyl-imidazolium functionalized ionic liquids havereceived increasing attention in view of their strong coordinating ability to metal ions.In this research, a series of carboxyl-imidazolium functionalized ionic liquids were designed andsynthesized, and their chemical and physical properties were characterized. The miscibility with water forsome carboxyl-imidazolium functionalized ionic liquids were studied and can be controlled by changingthe number of the carboxyl, the alkyl chain length, and the type of the anion. The liquid-liquid equilibriumphase diagrams for the ionic liquid-water system were drawn. The solubilities for the seven metal oxides incarboxyl-functionalized ionic liquids were determined in order to investigate the probalitiy of the selectiveseparation for metal ions. As a part of the project supported by the National Natural Science Foundation ofChina （No.21173069）, the major content of the present work is as follow:1. In this article, thirteen kinds of carboxyl-imidazolium functionalized ionic liquids were designedand synthesized.[mimCH₂COOH]Cl （with crystal water）,[mim（CH₂）₅COOH]Br,[mim（CH₂）₅COOH]Tf₂N,[CH₂COOHimCH₂COOH]Cl and [CH₂COOHimCH₂COOH]Br （synthesized under MW irradiation） werefirst reported. The thermal stability of eight ionic liquids, and pKavalues of six ionic liquids weredetermined. The structures of the [mimCH₂COOH]Cl crystal and the isolated gas molecule obtained usingDFT theory are compared.2. The structure of cation and cation-anion ion-pairs of [mimCH₂COOH]Cl were optimized at theB3LYP/6-311++G**level, and the most stable geometry was obtained. Based on the crystal structure andthe calculated vibrational spectra, the observed infrared and Raman bands were assigned.3. The solubilities of two hydrophobic ionic liquids in water were determined, and the liquid-liquid equilibrium phase diagrams were drawn. The separation of metal ions from aqueous was tested.4. In order to investigate the selectively separation for metal oxides. The solubilities of seven metaloxides （CuO, Fe₃O₄, Cr₂O₃, Co₂O₃, CdO, MnO₂and ZnO） in six kinds of carboxyl-imidazoliumfunctionalized ionic liquids were studied, and the difference in solubility was analysied.