The Studies On The Hydrogen-bonding Interactions Between Ionic Liquids And Some Molecular Solvents

ILs exhibit many unique physicochemical properties, such as nonflammability, negligiblevolatility, high thermal stability, wide liquid range, and fine-tuning ability for the physical and chemicalproperties. Thus ILs have found wide applications in chemical synthesis, electrochemistry, and biomassdissolution. Many investigations have showed that the ionic liquid effect observed in the biomassdissolution, catalytic reaction and material preparation is closed related to the hydrogen bondinginteractions between the ionic liquids and molecules. In addition, some unique physicochemical propertiesof the ILs (such as melting point and viscosity) are also dependent on the hydrogen bonding interactionsamong ionic liquids. However, the studies on the hydrogen bonding interactions between ionic liquid andmolecular solvents are very scare and not systematic. Therefore, as a part of the project supported by theNational Natural Science Foundation of China (NO.21273062), the effect of anionic structure, ring typeand alkyl chain length of the cation, and nature of molecular solvents on the hydrogen bonding interactionsbetween ionic liquid and molecular solvents has been investigated in the prsent work. The interactionmodes and the interaction sites between water and ILs have been analyzed and the microstructure of ILssolutions was also determined. The main contents are as follows.1. The hydrogen bonding interactions between ionic liquids and water were investigated as afunction of mole fraction of water in aqueous ionic liquids (including [Bmim][CH3COO],[Bmim][CF3COO],[Bmim][HSO4],[Bmim][CH3OSO3],[Bmim][BF4],[Bmim][C2H5COO],[Bmim][OTf],[Bmim][NO3],[Bmim][N(CN)2],[Bmim][SCN]) solutions by Far-infrared,1H NMR and moleculardynamic simulation at293K. The influence of anion species of the ionic liquids on the hydrogen bondinginteractions between ILs and water has been analyzed and the microstructure of ionic liquids in water hasbeen determined. It was found that the formtion capability of hydrogen bonding of anion with watermolecules was decreased in the sequence: CH3COO-, C2H5COO-> HSO---4> CF3COO-> CH3OSO3, NO3>SCN-, N(CN)2-> OTf-> BF4-. With the increase of water mole fraction, the contact ion pairs of ionic liquidschanged into solvent-separated ion pairs.2. Far-infrared and1H NMR spectra have been determined at293K for the mixtures of[Emim][CH3COO]/H2O、[Bmim][CH3COO]/H2O and [Hmim][CH3COO]/H2O. The effects of the alkylchain length in the imidazolium cations on the hydrogen bonding interactions between water and ILs have been examined. In addition, Far-infrared and1H NMR spectra measurements as well as molecular dynamicsimulation have been carried out at293K for the mixtures of [BuPy][NO3]/H2O,[Py14][NO3]/H2O,[PP14][NO3]/H2O,[(Bu)3NH][NO3]/H2O,[Bu-choline-NO3]/H2O. The influence of cationic structures onthe hydrogen bonding interactions between ILs and water has been investigated, and the interaction modesand the interaction sites between water and IL molecules have been determined. The results showed that theeffect of the alkyl chain length on the hydrogen bonding interaction is neglectable. The hydrogen bondingformtion capability of cation with the water molecules decreased in the sequence:[Bu-choline]+>[Py14]+>[PP14]+>[BuPy]+>[Bmim]+>[(Bu)3NH]+.3. The hydrogen bonding interactions between [Bmim][CH3COO] and protic solvents (methanol,ethanol, glycol, acetic acid and propionic acid) or aprotic solvents (DMF, acetonitrile and DMSO) havebeen studied by Far-infrared,1H NMR and molecular dynamic simulation at293K. The interaction modesof the IL with these solvent molecules have been confirmed. It was found that the hydrogen bondinginteractions of cations and anions of the IL was destroyed by the protic solvents through the hydrogenbonding interactions between anions of the IL and the protic solvents. The order for the strength ofhydrogen bonding of the IL anion with different protic solvents was found to be: acetic acid> propionicacid> glycol> methanol>ethanol. The hydrogen bonding interaction of the IL with an aprotic solvent wasascribed to the interactions between H2atom of the IL cation and O/N atom in the aprotic solvent.