Analytical Sciences

Structural Control of Schiff Base Ligands for Selective Extraction of Copper(II)

Syunichi OSHIMA,*¹ Naoki HIRAYAMA,*²  Koji KUBONO,*³ Hisao KOKUSEN,*⁴ and Takaharu HONJO*²

*1 Division of Basic Sciences, Graduate School of Natural Science and Technology, Kanazawa University, Kanazawa 920-1192, Japan
*2 Department of Chemistry, Faculty of Science, Kanazawa University, Kanazawa 920-1192, Japan
*3 Division of Natural Science, Osaka Kyoiku University, Kashiwara 582-8582, Japan
*4 Department of Environmental Engineering, Kanazawa Institute of Technology, Nonoichi, Ishikawa 921-8501, Japan

Structural control of Schiff base ligands for selective extraction of copper(II) was investigated by changing pendant arms and the distance between two imine-N donor atoms in ligands. Di-Schiff base ligands, N,N'-bis(2-quinolylmethylidene)-1,2-diiminoethane (BQIE), N,N'-bis(2-pyridylmethylidene)-1,3-diimino-2,2-dimethylpropane (BPMP) and N,N'-bis(2-quinolylmethylidene)-1,3-diimino-2,2-dimethylpropane (BQMP), were used as complexation reagents for ion-pair extraction of divalent transition metal cations into nitrobenzene with picrate anion. The pendant arms affected the lipophilicity of ligand to nitrobenzene, due to their polarity. The distance between two imine-N atoms, on the contrary, was a factor of controlling the extraction selectivity. BQMP has both 2-quinolyl pendant arms and trimethylene backbone structure; use of BQMP as a complexation reagent led to the selective extraction of Cu²⁺ in the system.

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