Extraction of alkali metal picrates with 18-crown-6, benzo-18-crown-6, and dibenzo-18-crown-6 into various organic solvents. Elucidation of fundamental equilibria governing the extraction-ability and -selectivity.

TAKEDA Yasuyuki

doi:10.2116/bunsekikagaku.51.515

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１８‐クラウン‐６，ベンゾ‐１８‐クラウン‐６及びジベンゾ‐１８‐クラウン‐６のアルカリ金属ピクリン酸塩に対する抽出能及び抽出選択能の素平衡定数による原因解明
18-クラウン-6,ベンゾ-18-クラウン-6及びジベンゾ-18-クラウン-6のアルカリ金属ピクリン酸塩に対する抽出能及び抽出選択能の素平衡定数による原因解明
18 クラウン 6 ベンゾ 18 クラウン 6 オヨビジベンゾ 18 クラウン 6 ノアルカリキンゾクピクリンサンエンニタイスルチュウシュツノウオヨビチュウシュツセンタクノウノソヘイコウテイスウニヨルゲンインカイメイ

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Abstract

In order to quantitatively study the effects of diluents as well as the size, structural flexibility, and benzo groups of 18-crown-6 (18C6), benzo-18-crown-6 (B18C6), and dibenzo-18-crown-6 (DB18C6) concerning their extraction-ability and -selectivity for alkali metal ions from the standpoint of equilibrium, constants of the overall extraction (K_ex), the distribution for various diluents of low dielectric constants (K_D,MLA), and the aqueous ion-pair formation (K_MLA) of crown ether (L)-alkali metal picrate (MA) 1 : 1 : 1 complexes (MLA) were determined at 25°C; the partition constants of the crown ethers themselves were also measured at 25°C. The distribution behavior of the crown ethers and their MLA complexes can be clearly explained by regular solution theory, except for chloroform. The specific interactions of chloroform with L and MLA were observed. The molar volumes and solubility parameters of the crown ethers and the MLA complexes were determined. A relation between the molar volumes of the MLA complexes and K_MLA was considered. For the same alkali metal, the K_MLA value decreases in the order 18C6>B18C6>DB18C6 with an increase in the number of benzo groups. The orders of decreasing K_MLA value are K⁺≥Rb⁺≥Cs⁺>Na⁺>Li⁺ for 18C6, K⁺>Rb⁺>Na⁺ for B18C6, and K⁺>Rb⁺>Cs⁺>Na⁺ for DB18C6. The K_MLA values make major contributions to the extraction selectivity of the three crown ethers (K⁺>Rb⁺>Cs⁺>Na⁺>Li⁺). For 18C6 and B18C6, the magnitude of K_ex is determined largely by that of K_MLA, whereas, for DB18C6, K_D,MLA contributes most favorably to K_ex. The extraction-ability and -selectivity for the alkali metal picrates and their change with the diluent of these three crown ethers were completely elucidated by the four fundamental equilibrium constants and regular solution theory.

Journal

BUNSEKI KAGAKU

BUNSEKI KAGAKU 51 (7), 515-525, 2002

The Japan Society for Analytical Chemistry

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