Ion-Pair Extraction by Use of Liquid Crystals as Extracting Solvent

• Published in: Analytical Sciences 1990/04/10, Vol.6(2), pp.283-286
• Main Authors: OHKI, Akira, TAKENAKA, Shigeori, TSUKADA, Kadzuya, MAEDA, Shigeru, TAKAGI, Makoto
• Format: Article
• Language: English
• Subjects: Chemistry; Exact sciences and technology; extracting solvent; Ion-pair extraction; Kinetics and mechanisms; liquid crystal; Organic chemistry; phase transition; Reactivity and mechanisms
• ISSN: 0910-6340; 1348-2246
• DOI: 10.2116/analsci.6.283

By using a liquid crystal, 4-cyano-4′-hexylbiphenyl (abbreviated as CHB), as an extracting solvent, the following ion-pair extraction reaction was investigated: (QClO4)o+(Pi-)w_??_(QPi)o+(ClO4-)w (Q+: cationic species such as Crystal Violet (CV+), Methylene Blue (MB+) and tetrabutylammonium (TBA+); Pi-: picrate anion; subscripts o and w denote organic and aqueous phases, respectively). The above extraction equilibrium was confirmed to hold in the case of a liquid crystal (CHB) solvent as well as in an ordinary solvent (hexylbenzene/cyanobenzene 1:1 mixture for comparison; abbreviated as MIX). The dependence of the extraction constant on the temperature was investigated. Only in the CV+-CHB system, the extraction constant discontinuously changed around a phase transition temperature of CHB (29°C; nematic/liquid). When an MIX solvent was used, such a phenomenon was not observed; the extraction constant gradually increased with an increase in temperature. The effect of the molecular orientation of the extracting solvent is discussed.