SOLVENT-EXTRACTION OF EUROPIUM(III) ANIONIC COMPLEXES WITH SEVERAL BETA-DIKETONES AS ION-PAIRS WITH TETRABUTYLAMMONIUM INTO CHLOROFORM

The solvent extractions of europium(III) in 0.1 mol dm-3 sodium nitrate solutions with acetylacetone (Hacac), benzoylacetone (Hbza), benzoyltrifluoroacetone (Hbfa), trifluoroacetylacetone (Htfa), and hexafluoroacetylacetone (Hhfa) into chloroform were measured in both the absence and presence of tetrabutylammonium (tba+). From the results and those with 2-thenoyltrifluoroacetone (Htta) in a previous study it was concluded that extractions with the CF3- containing beta-diketones, Hbfa, Htfa, Hhfa, and Htta are greatly enhanced by the addition of tba+. This could be explained in terms of the extraction of a ternary complex, EuA4- tba+ (A- is a beta-diketonate ion). However, extractions with Hacac and Hbza were nearly the same when tba+ was added. The enhancement of extraction was statistically treated by assuming an association of EuA3 and A-tba+ in the organic phase. The equilibrium constants for an association with different beta-diketones were compared, and the reasons for the difference in the association equilibrium as well as the enhancement of extraction are described.