Synergistic extraction of gallium(III) and indium(III) with 2,4-pentanedione and 3,5-dichlorophenol on the basis of outer-sphere complexation

The synergistic extraction of gallium(III) and indium(III) with 2,4-pentane dione (Hacac) in heptane and carbon tetrachloride has been studied using 3, 5-dichlorophenol (DCP) as the synergist. A remarkable enhancement of the ex traction of both metals(III) with 0.01 mol dm(-3) Hacac was observed upon t he addition of 0.05 mol dm(-3) DCP, especially in heptane. From an extracti on-equilibrium study, the synergistic enhancement was ascribed to the forma tion 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 hy drogen-bond formation between M(acac)(3) and DCP was observed by IR and H-1 NMR in carbon tetrachloride. The effect of DCP on the separation efficienc y of gallium(III) and indium(III) from aluminium(III) was discussed by mean s of the equilibrium constants such as the formation constants of outer-sph ere complexes as well as the extraction constants obtained so far. It was c oncluded that the present synergism caused by outer-sphere complexation imp roved not only the extraction efficiency, but also the separation efficienc y of those metals(III).