Rate and Equilibrium of the Distribution of 2-Thenoyltrifluoroacetone in Carbon Tetrachloride-Aqueous Perchlorate Solution Systems

Abstract

The rate and equilibrium of the liquid-liquid distribution of 2-thenoyltrifluoroacetone (Htta) was studied in carbon tetrachloride-aqueous 0.1 mol dm-3 sodium perchlorate solution systems at 298 K. The distribution equilibrium of Htta reached after two-phase agitation for 90 min and the distribution constant of the total Htta was 2.2X10; however, that of the enol form of Htta was higher than 2X102 and that of the keto form of Htta was 5.8X10'. By a spectrophotometric method and by a liquid-liquid partition method, the rate constant of the enolization and ketonization in the organic phase was measured. The former was 102 times higher than that of the latter; both were several orders lower than those in the aqueous phase. From these results, it was assumed that when Htta was initially added to the organic phase the main route of the two-phase distribution reaction was a transference of the enol form from the organic to the aqueous phase and its change to the keto form. In contrast to the change in the distribution ratio of Htta during two-phase agitation, the solvent extraction of metal ions from the aqueous phase with Htta did not change very much after a transient equilibrium was reached within a short time. This was examined with the extraction of indium(III). KeywordsKeto-enol tautomerism, 2-thenoyltrifluoroacetone, solvent extraction, kineticsBoth the keto and enol forms are present in a solution of a f3-diketone, and the molar ratio of these species is dependent on the nature of the medium. Several experimental methods were employed in order to determine the molar ratio of the keto and enol forms of the /3-diketones at equilibrium, such as titration methods/ as well as UV2 and NMR spectrometry.3 From these previous studies, it is known that in a waterimmiscible nonpolar organic solvent the enol form is predominant, while in an aqueous solution the keto hydrate form is predominant.This distribution process of a f3-diketone should affect the distribution ratio of $-diketone as well as the solvent extraction of certain metal ions with the /3-diketone when complex formation of the metal ions with the f3-diketone is not slow. Thus, when a f3-diketone transfers from an organic solution to an aqueous solution by agitation of the two solutions, the chemical form should be changed; since this does not proceed very rapidly, the distribution ratio of the /3-diketone as well as the solvent extraction of copper(II) with the extractant changed during the twophase agitation.4In the present paper, the effect of such a tautomeric transformation on the distribution ratio of 2-thenoyltrifluoroacetone (Htta) in carbon tetrachloride-aqueous perchlorate solution systems was studied by spectrophotometry and by measuring the change in the distribution ratio as a function of the two-phase agitation time. The effect of a tautomeric transformation of the extractant on the solvent extraction of metal ions in these systems was examined with indium(III) as an example. Experimental ReagentsAll of the reagents were of an analytical grade. ...

Rate of Association of 2-Thenolytrifluoroacetone and Trioctylphosphine Oxide in Carbon Tetrachloride-Aqueous Solution Systems and Its Effect on the Solvent Extraction of Copper(II)

“…The observed rate constant of ketonization in water-saturated carbon tetrachloride was 1070 s-1, as was given in ref. 9. This is more than two orders lower than the values of kobsd in Fig.…”

“…This is due to the absorption by the enol form Htta; the absorption by the keto form is negligible at this wavelength. 9 It was also found that the absorption of carbon tetrachloride solution of TOPO at this wavelength was negligible.…”

TTA solvation kinetics in the ionic liquid BumimTf2N

“…Such a chemical equilibrium is illustrated by the presence of an isobestic point in figures 1 and 2. As already mentioned in literature, one of the parameters driving the keto/enol equilibrium is the polarity of the solvent [14]. In addition, obviously, the enol/hydrate equilibrium depends on the total water amount in the solvent in which TTA is dissolved.…”

Solvent extraction and stripping of lithium ion from aqueous solution and its application to seawater

“…It is well known that TTA forms adduct or ion-pair with trioctylphosphine oxide (TOPO) to create a synergistic effect, which increases the extraction efficiencies of metallic ions. Many researchers studied solvent extraction of metallic ions using TTA and TOPO [7][8][9][10][11][12][13][14][15][16]. Noro and Sekine [11] studied the synergistic extraction of lanthanide using TTA with TOPO or tetrabutylammonium ions (TBA ? )…”

“…and reported the distribution coefficient and equilibrium constant. Sekine et al [12][13][14][15] also performed several researches on the solvent extraction of metallic ions with the same extractants. Takazawa et al [16] reported thermodynamic study on the synergistic extraction of cobalt (II) with b-diketone and TTA.…”