Solvent Extraction of Sr²⁺ and Cs⁺ Based on Room-Temperature Ionic Liquids Containing Monoaza-Substituted Crown Ethers

Abstract

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 Sr(2+) 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 Sr(2+) 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(+) >> Sr(2+) > 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 Sr(2+) >> K(+) > Cs(+) > Na(+) in 1-ethyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]amide and 1-butyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]amide and K(+) > Sr(2+) > 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 Sr(2+).

Application of ionic liquids in analytical chemistry

“…Because of the pH-sensitive complexation capability of these ligands, it was possible to develop a facile stripping process, permitting both the macrocyclic ligands and the ILs to be recycled. A highly selective system toward Sr 2þ was developed after optimizing selection of the macrocyclic ligands and ILs [7]. The same authors also studied the extraction of Cs þ from aqueous solution to hydrophobic ILs, without introducing an organophilic anion in the aqueous phase, by using calix- [4]arene-bis(tertoctylbenzo-crown-6) as an extractant and sodium 6 ] enhances the extractability and the selectivity of lanthanide cations compared to when dissolved in conventional organic solvents [20], and pyridinocalix- [4]…”

Ionic Liquids in Chemical Analysis

“…A series of N-alkyl aza-18-crown-6 ethers in ILs were investigated as recyclable extractants for separation of Sr2 + and Cs + from aqueous solutions (48). The pH-sensitive complexation capability of these ligands allows for a facile stripping process to be developed so that both macrocyclic ligands and ILs can be reused.…”

Physicochemical properties and toxicities of hydrophobic piperidinium and pyrrolidinium ionic liquids

“…Water-immiscible ionic liquids used previously for metal-ion extraction from water exhibit solubilities in water that are too large for industrial extraction processes. [29][30][31][32][33] Previous work described the synthesis of new hydrophobic imidazolium and pyridinium ionic liquids that show low solubilities in water. 15,16 In this work, we report some physico-chemical properties and toxicities of ionic liquids [MOPip] + cations with selected anions.…”