Wu Bo, Zhang Yumei, Wang Huaping
State Key Laboratory for Modification of Chemical Fiber and Polymer Materials, Donghua University, Shanghai 201620, China.
J Phys Chem B. 2009 Sep 10;113(36):12332-6. doi: 10.1021/jp905252j.
In this contribution, we examined the effect of ethanol on the structural organization of aqueous solution of ionic liquids (ILs) using the near-infrared (NIR) technique and two-dimensional (2D) correlation spectra. The ILs used here are 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF(4)) and 1-allyl-3-methylimidazolium chloride ([Amim]Cl). It was easily found, from the distinct change tendency of NIR spectra for their aqueous solution, that the added ethanol exerted a different effect on the solution structure of [Bmim]BF(4) and [Amim]Cl. For [Amim]Cl/H(2)O, it was deduced that ethanol molecules prefer to compete with water by interacting with imidazolium C(2)-H rather than C(4,5)-H groups, accompanied by the formation of C(2)-H...O interactions with ethanol molecules, while ethanol molecules do not interact specifically with any imidazolium C-H groups for [Bmim]BF(4). Furthermore, it was shown that the nonpolar tail of [Amim]Cl is more sensitive to the decrease of polarity or dielectric constant of solvents than its polar head, whereas the converse is true for [Bmim]BF(4). However, for both ILs, ethanol molecules were capable of changing the interaction between cations and water, anions and water by introduction of C-H...O interactions with cations, as well as the strong hydrogen-bond interactions between the anions and the hydroxyls of the ethanol. This information is suggestive for recycling the hydrophilic ILs by distillation from their aqueous diluted solutions, as well as for purifying hygroscopic ILs.
在本论文中，我们使用近红外（NIR）技术和二维（2D）相关光谱研究了乙醇对离子液体（ILs）水溶液结构组织的影响。这里使用的离子液体是1-丁基-3-甲基咪唑四氟硼酸盐（[Bmim]BF₄）和1-烯丙基-3-甲基咪唑氯盐（[Amim]Cl）。从它们水溶液的近红外光谱明显的变化趋势很容易发现，添加的乙醇对[Bmim]BF₄和[Amim]Cl的溶液结构有不同的影响。对于[Amim]Cl/H₂O，据推测乙醇分子更倾向于通过与咪唑鎓C(2)-H而非C(4,5)-H基团相互作用来与水竞争，同时伴随着与乙醇分子形成C(2)-H...O相互作用，而对于[Bmim]BF₄，乙醇分子不与任何咪唑鎓C-H基团发生特异性相互作用。此外，研究表明[Amim]Cl的非极性尾部比其极性头部对溶剂极性或介电常数的降低更敏感，而对于[Bmim]BF₄则相反。然而，对于这两种离子液体，乙醇分子都能够通过与阳离子形成C-H...O相互作用以及阴离子与乙醇羟基之间的强氢键相互作用来改变阳离子与水、阴离子与水之间的相互作用。这些信息对于从其稀水溶液中通过蒸馏回收亲水性离子液体以及纯化吸湿性离子液体具有指导意义。
