Extraction of Alkali Metal Ions and Tetraalkylammonium Ions with Ionic Surfactants Containing a Poly(oxyethylene) Chain

• Published in: Bulletin of the Chemical Society of Japan 2000-05, Vol.73 (5), p.1165-1169
• Main Authors: Sakai, Yukio, Ono, Kanako, Hidaka, Tamotsu, Takagi, Makoto, Cattrall, Robert W
• Format: Article
• Language: English
• ISSN: 0009-2673; 1348-0634
• DOI: 10.1246/bcsj.73.1165

The effect of the poly(oxyethylene) (POE) chain length of ionic surfactants, expressed as C12H25-(OCH2CH2)-nOCH2C6H3(OH)(NO2) (n = 2—9), on the extraction of monovalent cations, including alkali metal and tetraalkylammonium (TAA) ions, was investigated. The extraction constants (Kex) with surfactants having a POE chain of n ≥ 6 were almost constant for each alkali metal ion. The Kex sequence was Li+ < Na+ < Cs+ ≤ K+ = Rb+. The extractability and selectivity largely decreased as n in the surfactant decreased (n < 6). The effect of the POE chain length was related to the stability of the alkali metal-POE complex. Unlike an alkali metal ion, the Kex values for all TAA ions were almost constant with surfactants of n = 2—8. These facts indicated that the surfactant extracts alkali metal ions by both complex formation with its POE chain and ion-pair formation with a terminal p-nitrophenolate anion. On the other hand, TAA ions were extracted simply by ion-pair formation with a p-nitrophenolate anion of the surfactant. The proposed structures are discussed from the viewpoint of the spectrum shift of the extracted species.