A series of N-alkyl aza-18-crown-6 ethers were synthesized and characterized by NMR spectroscopy and mass spectrometry. These monoaza-substituted crown ethers in ionic liquids were investigated as recyclable extractants for separation of Sr2+ and Cs+ from aqueous solutions. The pH-sensitive complexation capability of these ligands allows for a facile stripping process to be developed so that both macrocyclic ligands and ionic liquids can be reused. The extraction efficiencies and selectivities of these monoaza-substituted crown ethers for Na+, K+, Cs+, and Sr2+ were studied in comparison to those of dicyclohexano-18-crown-6 under the same conditions. The extraction selectivity order for dicyclohexano-18-crown-6 in the ionic liquids investigated here was K+ ≫ Sr2+ > Cs+ > Na+. The extraction selectivity order for N-alkyl aza-18-crown-6, in which the alkyl group is varied systematically from ethyl to n-dodecyl, was Sr2+ ≫ K+ > Cs+ > Na+ in 1-ethyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]amide and 1-butyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]amide and K+ > Sr2+ > Cs+ > Na+ in 1-hexyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl] amide and 1-octyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]amide. The strong dependence of selectivity on the type of ionic liquid indicates an important role played by solvation in solvent extraction processes based on ionic liquids. The optimization of macrocyclic ligands and ionic liquids led to an extraction system that is highly selective toward Sr2+.
一系列N-烷基硝基-
18-冠-6醚类化合物被合成并通过NMR波谱和质谱进行表征。这些单硝基取代的
冠醚在
离子液体中被研究作为可回收的萃取剂,用于从
水相中分离Sr²⁺和Cs⁺。这些
配体的pH敏感复合能力使得能够开发出简便的去萃取过程,从而使得宏环
配体和
离子液体均可重复使用。在相同条件下,这些单硝基取代的
冠醚对Na⁺、K⁺、Cs⁺和Sr²⁺的萃取效率和选择性与二
环己烷-
18-冠-6进行了比较。在这里调查的
离子液体中,二
环己烷-
18-冠-6的萃取选择性顺序为K⁺ ≫ Sr²⁺ > Cs⁺ > Na⁺。N-烷基硝基-
18-冠-6的萃取选择性顺序在1-乙基-3-甲基
咪唑二[(三
氟甲基)磺酰]胺和1-丁基-3-甲基
咪唑二[(三
氟甲基)磺酰]胺中为Sr²⁺ ≫ K⁺ > Cs⁺ > Na⁺,在1-己基-3-甲基
咪唑二[(三
氟甲基)磺酰]胺和1-辛基-3-甲基
咪唑二[(三
氟甲基)磺酰]胺中为K⁺ > Sr²⁺ > Cs⁺ > Na⁺。选择性强烈依赖于
离子液体类型,这表明溶剂化在基于
离子液体的溶剂萃取过程中起着重要作用。宏环
配体和
离子液体的优化导致了一个对Sr²⁺高度选择性的萃取系统。