Thenoyltrifluoroacetone equilibrium

In natural U, the radionuclides of the uranium family and the actinium family are present, and sometimes also radionuclides of the thorium family. Therefore, direct determination of U in ores without chemical separation is difficult, especially since the absorption of the radiation depends on the nature of the minerals. Generally, the samples are dissolved and Th is separated, e.g. by coprecipitation or by extraction with thenoyltrifluoroacetone (TTA). Radioactive equilibrium between " Th and the daughter nuclide 234mp jg rather quickly attained, and the high-energy yS" radiation of the latter can easily be measured. A prerequisite of the determination of U by measuring the activity of either " Th or 234mp jg establishment of radioactive equilibrium. This means that the uranium compound must not have been treated chemically for about 8 months. 

The author has used liquid-liquid extraction with thenoyltrifluoroacetone (TTA) and potentiometry using a fluoride selective electrode to determine the stoichiometiy and equihbrium constants of the fluoride complexes of Th(lV) and U(1V) only the Th(IV) data will be discussed here as the U(1V) data have been reviewed previously in [1992GRE/FUG]. The experiments have been made in a 4 M HCIO4 ionic medium at 20°C. The experimental data are described in detail and this study provides very useful information on the quality of the two experimental approaches used. The same author has previously studied the Zr(lV) and Hf(lV) systems using the same experimental approach. The slope of the ion selective electrode was determined experimentally and equilibrium was assumed to be attained when the emf changed by less than 0.1 mV/h. The experiments were made at three different total concentrations of Th(lV), 0.90, 1.79 and 4.48 mM and with the total concentration of HF varying from 0.406 to 225 mM. This corresponds to a concentration of free fluoride, 8 x 10 < [F ] < 5 x 10 M. The analysis of the experimental emf data is straightforward and the conditional equilibrium constants for the two reactions ... 

Replacement of the terminal methyl groups of acacH by an electron-withdrawing or aromatic group such as CF3, C4H3S (2-thienyl), and CfiHs shifts the equilibrium in favor of the enol tautomer. Hexafluoro-acetylacetone (hfacH), thenoyltrifluoroacetone (in carbon disulfide), and dibenzoylmethane (dbmH) (in carbon tetrachloride), for example, exist entirely in the enol form. °" ... 

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