Enhancing the basicity of ionic liquids by tuning the cation-anion interaction strength and via the anion-tethered strategy.
Enhancing the basicity of ionic liquids by tuning the cation-anion interaction strength and via the anion-tethered strategy.
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DOI：
10.1021/jp4096503
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发表时间：
2014-01
期刊：
影响因子：
--
通讯作者：
Danqian Xu;Qiwei Yang;Bao-gen Su;Zongbi Bao;Qilong Ren;Huabin Xing
中科院分区：
文献类型：
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作者：
Danqian Xu;Qiwei Yang;Bao-gen Su;Zongbi Bao;Qilong Ren;Huabin Xing
离子液体具有较强的碱度，在化学过程中往往表现出优异的性能，因此通过分子设计来提高离子液体的碱度具有重要意义。在这里，我们提出了两种有效的方法来提高离子液体的碱性：通过削弱阳离子-阴离子相互作用强度和采用阴离子拴系策略。值得注意的是，两个量子化学参数--最负的表面静电势和最低的表面平均局部电离能--被用作有力的工具，分别在微观水平上证明了碱度的静电和共价方面。结果表明，对于相同阴离子(醋酸酯或三氟乙酸酯)的离子液体，随着阴阳离子相互作用强度的减弱，离子液体的碱性增强。对于基于乙酸酯阴离子的ILS，当阳离子从1-丁基-3-甲基咪唑([BMIM])变为四丁基膦([P4444])时，氢键碱性标度(β)增加了29%，达到了ILS的最高β值之一。此外，还证明了当胺基团与IL的阴离子相连时，它的碱性比它与阳离子相连时的碱性更强。这些结果对于设计强碱性离子液体和提高离子液体吸收二氧化碳、SO2和乙炔吸收、纤维素溶解、生物活性物质提取等过程的效率具有重要的指导意义。
Ionic liquids (ILs) with relatively strong basicity often show impressive performance in chemical processes, so it is important to enhance the basicity of ILs by molecular design. Here, we proposed two effective ways to enhance the basicity of ILs: by weakening the cation-anion interaction strength and by employing the anion-tethered strategy. Notably, two quantum-chemical parameters, the most negative surface electrostatic potential and the lowest surface average local ionization energy, were adopted as powerful tools to demonstrate the electrostatic and covalent aspects of basicity, respectively, at the microscopic level. It was shown that, for the ILs with the same anion (acetate or trifluoroacetate), the basicity of the ILs could be enhanced when the cation-anion interaction strength was weakened. For the acetate anion-based ILs, the hydrogen-bonding basicity scale (β) increased by 29% when the cation changed from 1-butyl-3-methylimidazolium ([Bmim]) to tetrabutylphosphonium ([P4444]), achieving one of the highest reported β values for ILs. Moreover, it was also demonstrated that, when an amine group was tethered to the anion of the IL, its basicity was stronger than when it was tethered to the cation. These results are highly instructive for designing ILs with strong basicity and for improving the efficiency of IL-based processes, such as CO2 capture, SO2 and acetylene absorption, dissolution of cellulose, extraction of bioactive compounds, and so on.