Enhancing the Basicity of Ionic Liquids by Tuning the Cation–Anion Interaction Strength and via the Anion-Tethered Strategy

详细信息    查看全文

• 作者：Dan Xu ; Qiwei Yang ; Baogen Su ; Zongbi Bao ; Qilong Ren ; Huabin Xing
• 刊名：Journal of Physical Chemistry B
• 出版年：2014
• 出版时间：January 30, 2014
• 年：2014
• 卷：118
• 期：4
• 页码：1071-1079
• 全文大小：478K
• ISSN：1520-5207

文摘

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鈥揳nion 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鈥揳nion interaction strength was weakened. For the acetate anion-based ILs, the hydrogen-bonding basicity scale (尾) increased by 29% when the cation changed from 1-butyl-3-methylimidazolium ([Bmim]) to tetrabutylphosphonium ([P₄₄₄₄]), achieving one of the highest reported 尾 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.