| Acidic functional ionic liquids as an effective catalystwhich is an efficient alternative to conventional organic solvents havea good prospect. To explore the general rules of acid strength and molecular microstructure insingle-core and dual-core ionic liquidswhich hasthe same functional groups, four types of acidic ionic liquid were synthesized, and the acid strengths were determined by Hammett indicator associated with UV spectroscopy, the configurations of single-core ionic liquid and dual-core ionic liquid were systematically studied, the results of this project were testified by systematically analysis in the scale of micro-molecule.The single-core sulfate acidic ionic liquid [MIM(CH2)4HSO3][HSO4](IL1) and single-core carboxyl acidic ionic liquid [MIM(CH2)4COOH][HSO4](IL3) were obtained by a two-step process. The dual-core sulfate acidic ionic liquid(CH2)4[IM(CH2)4HSO3]2[HSO4]2(IL2) and dual-core carboxyl acidic ionic liquid(CH2)4[IM(CH2)4COOH]2[HSO4]2(IL4) were obtained by a multi-step process.The acid strength of single-core ionic liquids with different concentrations and dual-core ionic liquids with same concentrations were determined by Hammett indicator associated with UV spectroscopy. The results indicated that the acid strength of dual-core ionic liquids show a much stronger than the acid strength of single-core ionic liquids in the same concentration, as well as the acid strength of dual-core ionic liquidswere not stronger than the acid strength of single-core ionic liquids in the same concentration of HSO4-, when the functionalized groups of cations were the same.The acid strength of the ionic liquids will be influenced by differentfunctional groupsof cations, but not significantly; the acid strength of sulfate acidicionic liquidsare stronger than carboxyl acidic ionic liquids at the same concentration of acid.The cations of single-core ionic liquids[MIM(CH2)4HSO3]+ and [MIM(CH2)4COOH]+ and the ion pairs of single-core ionic liquids[MIM(CH2)4HSO3][HSO4] and [MIM(CH2)4 COOH][HSO4], cations ofdual-core ionic liquids(CH2)4[IM(CH2)4HSO3]22+ and(CH2)4[ IM(CH2)4COOH]22+ and the ion pairs of dual-core ionic liquids(CH2)4[IM-(CH2)4HSO3]2 [HSO4]2and(CH2)4[IM(CH2)4COOH]2[HSO4]2were studied systematically by B3LYP/ 6-311++G(d, p) of density functional theory. The structure optimization, frequency analysis and energy calculation were obtained, then interaction energy and atomic charge were analyzed.It was found that hydrogen bonding was an important factor in the stable structure of the cations and ionic liquids. The more amount of hydrogen bonds, the shorter the length, the more stable geometries of ionic liquids.The strongest interaction in the ionic liquid was found between the anion and the functional group of cations. When the strong intramolecular hydrogen bonds were formed, the hydrogen of HSO3- was prone to combined withoxygen atom of HSO4-. The finalexisting form was the interaction between zwitterion and H2SO4.It was found that the hydrogen atomsof cationic functional groups and anionic functional groups in ionic liquidsshowed a strong acid, followed by H connected the carbon atoms of N-C-N also showed strong acidity; electrophilic inductive effect was be strengthened by the co-existence of bis-imidazole rings in dual-core ionic liquid, which enhancedthe ability of electrons to move to the imidazole ring, theelectronegativity of-HSO3 and-COOHwas decreased and theelectronegativity of HSO4- was increased,the acidity of dual-core ionic liquid was decreased; the basic laws of acidic strength of single-core ionic liquids anddual-core ionic liquids was the same in conclusions of experiment and charge analysis. |
PDF Full Text Request