Extraction and Liquid Membrane Transport of Transition Metal Ions by Proton-Ionizable Noncyclic Diamides

Abstract

Solvent extraction and liquid membrane transport abilities of the synthesized noncyclic diamides (L¹, L², L³, L⁴, L⁵) having pyridine ring as ligand were examined for transition metal ions (Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺) and the structural effect of the ligand on the metal binding ability was discussed. Even in acidic ran ge, L₁L₄ formed neutral complex with Cu²⁺- accompanied with the release of two amide-proton and extracted Cu²⁺ with the excellent selectivity and efficiency even in the absence of lipohilic picrate ion. The extraction and the transport abilities for CIO decreased in the following order: L²>L¹>L⁴>L³ and L³>L⁴>L¹>L², respectively. This result implies that the balance of the rates of uptake and release of CIO at the interfaces between aqueous and membrane phases is of substantial importance. The discrepancy of the orders will be explainable by the ease of the conformation change in the complex formation and the coordination ability of donor nitrogen atom of each ligand. In the extraction of the solution containing single ion species (Co²⁺, Ni²⁺, C u²⁺, Zn²⁺), L¹ and L² extracted Cu²⁺ Ni²⁺ (40%), Zn²⁺ (15%) and Co2+ (12%), while they specifically extrated Cu²⁺ from the mixed solution of these ions. L³ and L⁴ extracted only Cu²⁺ from either the single or the mixed solutions. L⁵ extracted Cu²⁺ only when picr ate ion is present at the neutral range of pH and the two amide-proton did not dissociate.