超共轭强化氢键识别疏水离子液体的设计及萃取性能研究

The separation of hydrogen-bond acidic compounds from aqueous solution is very important for the environmental treatment, the purification of bioactive molecules, as well as the conversion and utilization of biomass. Liquid-liquid extraction is a separation method with advantages such as high throughput, easy scale-up and diverse operation mode. However, the kinds of conventional hydrophobic extractants are few and their molecular recognition abilities are weak, which hinders the application of liquid-liquid extraction in the aforementioned separation processes. Ionic liquids (ILs) are a promising class of physical extractant, due to their features such as ultralow vapor pressure, designability of structure and property and good molecular recognition ability, but the current hydrophobic ILs only have weak hydrogen-bond basicity which leads to poor extraction efficiency for the hydrogen-bond acidic compounds from aqueous solution. Therefore, in this project, we proposed a design strategy for synthesizing novel ILs with both strong hydrogen-bond basicity and good hydrophobicity, featuring the incorporation of hydrophobic electron-donating group to the anion and the synergic enhancement of hydrogen-bonding recognition ability by the cationic hyperconjugation effect. The relationship between the ILs’ structure and their physicochemical properties, including hydrogen-bond basicity, hydrophobicity, viscosity, melting point and interfacial tension will be researched. The extraction of several typical solutes in aqueous solutions by the developed ILs will be performed, and the underlying mechanism will be investigated. Besides, the efficient methods for recycling ILs will be explored. Some preliminary results have been obtained.

水溶液中氢键酸性化合物的分离是十分重要的化工分离过程，是水溶性化学品制备、环境治理、生物质资源转化等领域的关键步骤之一。液-液萃取是一种处理量大、容易放大、操作形式多样的分离方法，然而常规疏水萃取剂的种类较少，分子识别能力较弱，限制了液-液萃取在上述分离过程中的应用。离子液体具有几乎不挥发、结构和性质可设计、分子识别能力较强等特点，是一类具有良好发展前景的物理萃取剂，但瓶颈在于现有疏水离子液体的氢键碱性较弱，对氢键酸性溶质的萃取效率偏低。为此，本项目提出阴离子键合无氟疏水-供电基团、阳离子超共轭效应协同强化氢键识别能力的离子液体结构设计策略，设计合成兼具强氢键碱性与良好疏水性的新型功能化离子液体；深入研究离子液体结构与氢键碱性、疏水性、粘度、熔点、界面张力等物化性质的关系；研究典型溶质在离子液体-水两相体系的萃取平衡，探讨萃取机理，研究高效的离子液体循环利用方法。项目组已取得初步研究结果。

水溶液中氢键酸性化合物的分离是十分重要的化工分离过程，是水溶性化学品制备、环境治理、生物质资源转化等领域的关键步骤之一。液-液萃取是一种处理量大、容易放大、操作形式多样的分离方法，然而常规疏水萃取剂的种类较少，分子识别能力较弱，限制了液-液萃取在上述分离过程中的应用。离子液体具有几乎不挥发、结构和性质可设计、分子识别能力较强等特点，是一类具有良好发展前景的物理萃取剂，但瓶颈在于现有疏水离子液体的氢键碱性较弱，对氢键酸性溶质的萃取效率偏低。与此同时，结构相似脂溶性氢键酸性化合物的高效分离同样是化学工业的重要需求，其突破也有赖于强氢键碱性离子液体的设计和应用。. 本项目基于阴离子键合无氟疏水-供电基团、阳离子超共轭效应协同强化氢键识别能力的离子液体结构设计策略，合成了一系列氢键碱性强、疏水性/亲水性可调、低熔点的季鏻类功能化离子液体。构建了离子液体-水液-液两相体系，考察了离子液体及离子液体-分子溶剂复合萃取剂对水溶液中的结构相似氢键酸性化合物抗坏血酸和抗坏血酸葡糖苷的选择性萃取分离性能，抗坏血酸的分配系数可达常规疏水性离子液体和分子溶剂的60~680倍，同时分离选择性大于60。通过5级逆流萃取，抗坏血酸葡糖苷的纯度可由50%提高到96.2%，且收率高于98%。萃取机理研究显示，萃取分离过程是以氢键作用为主导的物理萃取。考察了离子液体萃取剂对水中弱酸性酚类污染物的脱除性能，分配系数是乙酸乙酯萃取的5.3倍，是常规含氟疏水离子液体的9~60倍。进一步拓展至结构相似脂溶性氢键酸性化合物的高效分离，考察了间甲酚、对甲酚和2,6-二甲酚的萃取分离性能，间甲酚/对甲酚同分异构体的分离选择性可达常规分子溶剂的两倍。. 在本项目的资助下，共发表6篇学术论文。项目成果有助于开发绿色、高效、低耗的氢键酸性化合物分离新工艺，对其它结构相似物质分离过程的研究也有借鉴意义。.