Effect of side chain length in ionic liquid anion on extraction of trivalent lanthanoids

Eguchi, Ayano ; Okamura, Hiroyuki   ; Sugita, Tsuyoshi   ; Ueda, Yuki   ; Morita, Kotaro*; Shimojo, Kojiro   ; Naganawa, Hirochika  ; Hirayama, Naoki*

Physical and chemical properties of ionic liquids (ILs) can be tuned by changing the combination of an anion and a cation. In the solvent extraction of metal ions, it is well known that the structure and alkyl chain length of the IL cation have a great effect on the extractability. However, the structural effect of the IL anion on the extractability is hardly clarified. In this study, the effect of the side chain length of the IL anion on the IL chelate extraction of trivalent lanthanoids using 2-thenoyltrifluoroacetone was investigated. Four 1-butyl-3-methylimidazolium bis(perfluoroalkanesulfonyl)imides with different side chain lengths (n = 1-4) were synthesized and used as extraction solvents. When using ILs which side chain lengths n were even (n = 2, 4), the extracted species were different from those when using ILs that n were odd (n = 1, 3) and the IL having hexafluorophosphate anion. It was, therefore, implied that the extracted species can be controlled by the side chain length of the IL anion.