Effective separation of analogues structurally differing in a monounsaturated double bond remains challenging. In this study, hydrophilic ionic liquid (IL)/water mixtures were investigated as extractants for the extractive separation of hydrophobic analogues capsaicin and dihydrocapsaicin. A useful “diluent-swing” effect was introduced into the IL-based extraction and the recovery of solute for recycling the extractant. The extractive separation was performed at high IL concentrations where water behaves as a co-solvent, and back-extraction of the solute from the IL/water mixture was performed at low IL concentrations where water acts as an anti-solvent. The influences of IL structures (cations, anions, and substituent groups) and concentration, as well as the analogues concentration, on the separation efficiency were fully investigated. Selectivities of capsaicin versus dihydrocapsaicin of >2.0 were achieved by a number of IL/water mixtures, mainly because of the enhanced dipolarity/polarizability caused by the introduction of water to the extractant. Interestingly, a synergistic effect on the distribution coefficients and enhanced selectivities was achieved with N-ethylpyridinium bromide/water mixtures. This work sheds light on developing a feasible and effective large-scale separation method for compounds structurally different in their monounsaturated carbon–carbon double bonds.

中文翻译：

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以亲水性离子液体/水混合物为萃取剂分离单不饱和双键中不同的疏水化合物

有效分离单不饱和双键结构上不同的类似物仍然具有挑战性。在这项研究中，研究了亲水性离子液体（IL）/水混合物作为萃取剂，用于疏水性类似物辣椒素和二氢辣椒素的萃取分离。一种有用的“稀释剂摇摆”效应被引入到基于IL的提取和溶质回收中，以回收提取剂。萃取分离是在高IL浓度（水起助溶剂作用）下进行的，溶质从IL /水混合物中反萃取是在低IL浓度（水起反溶剂作用）下进行的。充分研究了IL结构（阳离子，阴离子和取代基），浓度以及类似物浓度对分离效率的影响。多种IL /水混合物可实现辣椒素对二氢辣椒素的选择性> 2.0，这主要是由于将水引入萃取剂引起的偶极/极化性增强。有趣的是，通过N-乙基溴化吡啶鎓/水混合物。这项工作为开发在结构上单不饱和碳-碳双键不同的化合物的可行，有效的大规模分离方法提供了启示。