Three-phase transport studies of benzimidazole ligands bearing hydrophobic N-alkyl substituents: transport of metal(II) ions (Ni, Cu, Zn, Cd) in single- and multiple-ion experiments †

Abstract

New ligands having two benzimidazole units, or one benzimidazole and one carboxylic acid unit, the two functions linked by a chain, and bearing hydrophobic N-alkyl substituents have been tested as transfer agents for metal(II) ions (Ni, Cu, Zn, Cd) using three-phase transport techniques. The transport was pH-dependent, so all comparisons were made with buffered feed and receiving phases at fixed pH. Variations in the nature and number [single and double N-alkyl-substituted bis(benzimidazole) ligands] of N-alkyl substituents, linker chain and its donor atoms were explored and resultant transport trends are discussed. While single-ion transport results were ambivalent (singly alkylated 2-oxapropane derivatives being the best extractants for copper, and the analogous 2-thiapropane ligands for zinc), in multiple-ion experiments copper was always transported in preference to zinc. Even for ligands with a longer linking chain (based on 2,5-dioxaoctane) the order for extraction of metal(II) ions was always Cu > Zn > Cd and the transport of Ni was negligible. From the benzimidazole ligands screened, those having a carboxylic acid moiety reveal the highest metal-ion selectivity.

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