Analytical Sciences

Evaluation of the Hydrophilic Property of Sodium Ion-pair Complexes with 3m-Crown-m Ethers (m = 5, 6) and Their Benzo-derivatives by Solvent Extraction

Yoshihiro KUDO,* Ryo FUJIHARA,** Toshiaki OHTAKE,*** Shoichi KATSUTA,* and Yasuyuki TAKEDA*

*Graduate School of Science, Chiba University, Chiba 263-8522, Japan
**Graduate School of Science and Technology, Chiba University, Chiba 263-8522, Japan
***Department of Chemistry, Faculty of Science, Chiba University, Chiba 263-8522, Japan

The ion-pair formation constants {K_j⁰: j = MA (metal salt), MLA} of NaO₂CCF₃ (Na⁺tfa^-) and its ion-pair complexes (MLA) in water (w) were determined potentiometrically at 25°C and an ionic strength (I) of zero. 15-Crown-5 (15C5), 18-crown-6 ethers (18C6), and their mono-benzo derivatives were used as crown ethers (L). The extraction of Natfa by these four L from w into 1,2-dichloroethane was done at 25°C, and then the extraction constants (K_ex) for NaLtfa were calculated by using the K_j values, which were estimated from the corresponding K_j⁰ ones at I of the w-phases, and other equilibrium constants. Also, the distribution constants (K_D,MLA) of NaLtfa between the two phases were obtained from a thermodynamic cycle expressing K_ex. An interaction of w-molecules with NaLA was considered using a relation of log K_D,MLA with log K_D,L, derived from the Scatchard-Hildebrand equation, where K_D,L denotes the distribution constant of L between the two phases. The interaction increased in the order of NaL (picrate) < free L ≤ NaLMO₄ (M = Mn, Re) < NaLtfa for L = 15C5 and 18C6.

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