Studies on Synthetic Ionophores. VI. Synthesis of Polyether Carboxylic Acids and Their Use as Carriers for Alkali Metal Ion Transport through Liquid Membrane

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Abstract
ω-Hydroxy carboxylic acids (3, 5, 6, 7, 10, 12, 14, 17, 18, 20, and 22) bearing 2–6 ether oxygens and aromatic rings with or without a tetrahydrofuran ring and the ω-methoxy and ω-benzyloxy derivatives of 5 (8 and 9) were synthesized. These were employed as carriers for active and competitive transport of alkali metal ions through liquid membrane as well as for extraction of alkali metal ions to organic layers. Effect of hydrophobic group of aromatic and tetrahydrofuran rings, number of ether oxygens, and terminal hydroxyl group of the ionophores on the ion transport ability and selectivity were investigated. The hydrophobic groups increased total amount of transported ions as well as partition coefficients. The ionophore, 5, which contains five ether oxygens, two aromatic rings, and o-toluic acid moiety transported K+ selectively over Na+ and Li+ through 1,2-dichloroethane being consistent with the extraction experiments. The m- and p-substituted isomers, 6 and 7, exhibited no transport ability through 1,2-dichloroethane. The ω-alkoxy derivatives of 5 (8 and 9) exhibited less selectivity for K+ through 1,2-dichloroethane than 5 did. Through 1-hexanol, the ionophores, 5–9, including linoleic acid with no ether linkage transported alkali metal ions. The ionophores (3, 12, 20, and 22) containing 2–4 ether oxygens did not exhibit high transport ability.