Effect of side chain in ionic liquid anion on ionic liquid chelate 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 composing an IL. In the solvent extraction of metal ions, it is considered that IL anions affect extraction by the interaction IL anions and metal ions. However, the structural effect of the IL anions on extraction is hardly clarified. In this study, the effect of the side chain of the IL anions on the IL chelate extraction of trivalent lanthanoids using 2-thenoyltrifluoroacetone was investigated. Four 1-butyl-3-methylimidazolium bis(perfluoroalkanesulfonyl)imides with different carbon number of side chain n (n = 1-4) were synthesized and used as extraction solvents. When n was even, the extracted species were different from those when n was odd. This result was considered to be due to the different IL solvation effects on the extracted complexes depending on n. It was implied that the side chain in the IL anions was involved in the extraction mechanism by affecting solvation of extracted complexes.