Synthesis And Properties Of Aryl-substituted Imidazolium-based Ionic Liquids

Ionic liquids, usually known as green solvents have become a research hotspot in the field oforganic synthesis, electrochemistry and separation process. It also shows great potential inradionuclide separation and modern industrial lubricants preparations. Compared with the alkyl group,the π-electron in aromatic compound can dissipate the radiant energy in the form of light, heat, etc,thus maintaining the aromatic compound in a stable structure under radiation conditions.In this paper, we proposed an aryl-substituted imidazolium-based ionic liquid1-benzyl-3-phenylimidazolium tetrafluoroborate [BnPhIm]BF₄, and investigated the radiation effects of it. Two otherionic liquids of1-benzyl-3-methyl imidazolium tetrafluoroborate [BnMeIm]BF₄, and1-butyl-3-methyl imidazolium tetrafluoroborate [BuMeIm]BF₄are also experimented as referencematerials. It was found that after irradiation the colors of these three ionic liquids are significantlydarker and UV-Vis absorbance increased; meanwhile¹H NMR and FT-IR spectra of [BnMeIm]BF₄and [BnPhIm BF₄before and after irradiation at400kGy show no change except chemical shift.Through Fluorescence and TG analysis, it is also revealed that due to the aggregation behaviorchanges caused by γ-radiation,[BnPhIm]BF₄shows an obvious “red edge effect” and thendisappeared after dilution, and the thermal stability of ionic liquids also increased as well as theelectrochemical stability. HPLC spectra of [BnPhIm]BF₄show the existence of minority radiationfragments, ESI-MS and MS²analysis show the primary radiolysis of ionic liquids in γ-radiationenvironment mainly are N-Bn and C-Ph. In summary, the introduction of aromatic ring groupsimprove the radiation resistance of imidazole cation, enhancing the radiation stability of[BnPhIm]BF₄.We also synthesized ten borate salts ionic liquids, divided into four categories: bis（mandelato）borate salts [BuMeIm][BMB],[BnMeIm][BMB],[BuPhIm][BMB] and [BnPhIm][BMB];bis（salicylato） borate salts [BuMeIm][BScB],[BnMeIm][BScB],[BuPhIm][BScB] and[BnPhIm][BScB]; bis（oxalato） borate salt [BuMeIm][BOB]; bis（malonato）borate salt[BuMeIm][BMLB], and then characterize the structrue properties of these ionic liquids.