Large Synergism of 3,5-Dichlorophenol in the Extraction of Gallium(III) with 2-Methyl-8-quinolinol Derivatives

Abstract

The large synergistic effect of 3,5-dichlorophenol (Hdcp) in the extraction of gallium(III) with 2-methyl-8-quinolinol derivatives (HA), such as 2-methyl-8-quinolinol (HMQ), 2-methyl-5-ethoxymethyl-8-quinolinol (HMO₂Q), 2-methyl-5-butyloxymethyl-8-quinolinol (HMO₄Q), and 2-methyl-5-hexyloxymethyl-8-quinolinol (HMO₆Q), from a weakly acidic solution into heptane and chloroform was investigated. The acid-dissociation constants of HA in an aqueous solution, the distribution constants of HA between heptane and water, and the association constants between HA and Hdcp in heptane were determined. The extractability of gallium(III) with HA increased with an increase in the hydrophobicity of HA. The extractability of gallium(III) with HA was remarkably enhanced upon the addition of Hdcp. The synergistic effect of Hdcp was quantitatively evaluated in terms of both a mixed ligand complex formation of Ga(dcp)(A)₂ in an aqueous phase and the formation of an association-complex in an organic phase. The mixed-ligand complex formation and the association constant were determined at I = 0.1 M (H,Na)ClO₄ (1 M = 1 mol dm⁻³) and 25°C. The compositions of gallium(III)-HA complexes extracted in both the absence and presence of Hdcp were assigned to be Ga(OH)(A)₂ and Ga(dcp)(A)₂•Hdcp, respectively. Moreover, the association constants of the synthesized Ga(OH)(MQ)₂ with Hdcp in anhydrous chloroform were also determined by FT-IR spectrometry and the association-complexs were to be Ga(OH)(MQ)₂•mHdcp (m = 1, 2).