Synthesis of lipophilic acyclic diionizable polyethers and selective transport of alkaline-earth cations in bulk liquid membrane system

Selective transport of alkaline-earth cations in a bulk liquid membrane system by lipophilic acyclic polyether dicarboxylic acids is reported. Introduction of proton-ionizable groups into such polyethers shows a distinct advantage over neutral macrocycles in that transfer of a metal ion into an organic medium does not require concomitant transport of an aqueous phase anion. A new organic ligand 1,5-bis[2-(2′-carboxypentadecyloxy)phenoxy]-3-oxapentane (8) which bears a tetradecyl group as an alkyl chain at the α-position of the carboxylic acid side-arm unit is sufficiently lipophilic to avoid loss of the complexing agent into the aqueous phase during solvent extraction and exhibited a calcium selectivity over other alkaline-earth cations.