Synergistic Extraction of Gallium(III) and Indium(III) with 2,4-Pentanedione and 3,5-Dichlorophenol on the Basis of Outer-Sphere Complexation

Abstract

The synergistic extraction of gallium(III) and indium(III) with 2,4-pentanedione (Hacac) in heptane and carbon tetrachlo-ride has been studied using 3,5-dichlorophenol (DCP) as the synergist. A remarkable enhancement of the extraction of both metals(III) with 0.01 mol dm^-3 Hacac was observed upon the addition of 0.05 mol dm^-3 DCP, especially in heptane. From an extraction-equilibrium study, the synergistic enhancement was ascribed to the formation of outer-sphere complexes, M(acac)₃·n(DCP) (M=Ga or In; n=1–3), in the organic phase. Furthermore, using the synthetic metal(III) chelates hydrogen-bond formation between M(acac)₃ and DCP was observed by IR and ¹H NMR in carbon tetrachloride. The effect of DCP on the separation efficiency of gallium(III) and indium(III) from aluminium(III) was discussed by means of the equilibrium constants such as the formation constants of outer-sphere complexes as well as the extraction constants obtained so far. It was concluded that the present synergism caused by outer-sphere complexation improved not only the extraction efficiency, but also the separation efficiency of those metals(III).