Crown ethers as synergist in the 2-thenoyltrifluoroacetone extraction of lanthanoids in 1,2-dichloroethane

The solvent extraction of 14 trivalent lanthanoid ions (Ln(3+)) from a nitrate medium into 1,2-dichloroethane containing 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione (HTTA) was investigated at 25.0 degrees C. The extraction of Ln(TTA)(3) species was confirmed and the extraction constants were determined. The extraction of Ln with the synergistic mixture of HTTA and a crown ether (CE: 12-crown-4,18-crown-6, cyclohexano-18-crown-6 or benzo-18-crown-6) was also investigated at 25.0 degrees C. The 1:1 adducts of the complex and crown ether, Ln(TTA)(3)center dot(CE) are formed for all the lanthanoid ions and the CEs used in this study. The formation constants, beta(add), of the adduct Ln(TTA)(3)center dot(CE) from Ln(TTA)(3) in the organic phase were determined by nonlinear least-squares method. The stabilities and structures of the formed adducts were discussed with respect to the cavity size, steric effect, and basicity of the CE.