Tatsuya Sekine

Solvent extraction of lead(II) and strontium(II) as dibenzo-18-crown-6 complexes with picrate ion

Abstract The solvent extraction of lead(II) and strontium(II) from aqueous lithium picrate solutions with dibenzo-18-crown-6 (DBC) in chloroform or benzene has been measured. From slope analysis, the extracted species are found to be Pb(DBC)(Pic)2 and Sr(DBC)(Pic)2. The distribution ratio of lead(II) is about forty to fifty times that of strontium(II). This is ascribed to the higher stability of the lead(II) DBC complex, and to weaker hydration of the lead(II) DBC complex. The extraction of both metals is stronger into a benzene than into a chloroform solution of DBC.

Formation and two-phase distribution equilibria of cobalt(II) and zinc(II) complexes with β-diketones in several solvent extraction systems

Abstract The equilibrium constants for the complex formation of cobalt(II) and zinc(II) with several β-diketones in 1M sodium perchlorate solution ( β n ), the two-phase distribution constants of the bis-chelates of these metals between carbon tetrachloride and the above aqueous solution ( Kdm ), and the adduct formation of the bis-chelates with trioctylphosphine oxide (TOPO) in the organic phase ( β n ( org ) ) have been determined at 25°C. The distribution constants of the bis-zinc(II) chelates were also determined when the solvent was hexane, chloroform or benzene. The weaker the acidity of the ligand the higher the β n value for these complexes. The relationship, log Kdm = 2 log Kd + C , where Kd is the distribution constant of the extractant is obeyed for each of the zinc(II) chelates when the solvent is different. The Kdm values of the metal chelates with the same ligand are always lower for cobalt(II) than for zinc(II), and among the series of bis-chelates of the same metal ion, there is a tendency for β n ( org ) of TOPO adducts to be higher when the β 2 is lower, but the stability order of the adducts of a set of cobalt(II) and zinc(II) chelates with the same β-diketone is not always the same.

Kinetic studies of the solvent extraction of metal complexes—V: Rate of solvent extraction of iron(III) with several β-diketones

Abstract The rate of extraction of iron(III) in acid aqueous perchlorate solutions with acetylacetone, benzoylacetone, trifluoroacetylacetone, benzoyltrifluoroacetone, 2-thenoyltrifluoroacetone and hexafluoroacetylacetone into carbon tetrachloride has been studied at 25°C. The rate was found to be − d [ Fe 3+ ] d t = K 0 ∗ [ Fe 3+ ][ HA ] org [ H + ] −1 (where HA is a β-diketone) when the acidity was not very high, and the rate constants were calculated by assuming either that the reaction was controlled by the association of (i) hydrated Fe3+ with a β-diketonate anion, or (ii) hydrated FeOH2+ with an enol form of β-diketone molecule. It was concluded that the reaction (ii) was, in general, more acceptable although it could not explain previously reported observations on the rate of iron(III) extraction with 2-thenoyltrifluoroacetone.

The effect of hydrophobic picrate on the extraction and separation of lanthanides(III) with carbamoylmethylene phosphine oxide

The effect of a hydrophobic anion, such as picrate (pic−), on the extraction and separation of Ln(III) ions with a carbamoylmethylene phosphine oxide (CMPO) from aqueous nitric acid solutions into benzene has been examined in the present study. The metal extraction with the CMPO was greatly enhanced by adding a small amount of pic−, which did not coordinate with the metal ions but only played the role of a counter-anion in the ion pair extraction. Furthermore, the separation of the Ln(III)-series was also improved, which is a great advantage of the anion effect: On the contrary, a synergism by using two extractants, both of which can coordinate with a metal ion, generally decreases such selectivity. From analyses of the distribution data of Ln(III) ions and picric acid, the mechanism of the cooperative effect was clarified. The strong cooperative effect originates from the difference in the hydrophobicity between pic− and NO3−. Indeed, the Eu(III)–CMPO complex cation paired with pic− was much less hydrated than that paired with NO3−; besides, the binding number of CMPO to the Ln(III) ions also seemed to be affected by the hydration. From these results it is concluded that the metal ions can be dehydrated by the effect of hydrophobic pic−, to a great extent, when its ion pairs are formed. This can be the origin of the great enhancement of the extractability by adding pic−. Metal dehydration can also produce the improved selectivity for the Ln(III) ions, i.e., the coordination of the CMPO can be performed more effectively with much fewer water molecules hydrated to the metal ions, and, thus, the inherent selectivity of the extractant can be exhibited more clearly. Metal dehydration can be induced under the influence of pic−, which is quite inert in coordination, electrostatic interaction, and hydration properties.

Seasonal and longitudinal changes in copper and iron in surface water of shallow eutrophic Lake Kasumigaura, Japan

Abstract The concentrations of copper and iron in surface water of the eutrophic Lake Kasumigaura, the second largest lake in Japan, have been monitored at three sites monthly from April 1989 until March 1994. The metals were analyzed by a graphite furnace AAS after filtration with a 0.45-μm membrane filter. The concentrations of copper in the water were in the range 10 −9 to 5 × 10 −8 M and showed clear seasonal changes, being higher in summer and lower in winter. The concentrations of copper did not decrease on passage through the lake. The values of dissolved chemical oxygen demand (COD Mn ) showed a similar behavior, an interaction of copper in the lake water with organic matter was estimated. The concentration of copper in the lake became sometimes higher than the value of EC 50 for Microcystis , however, the metal forms stable complex species with organic matter and the toxic effect may be reduced. The concentrations of iron, on the other hand, showed wide variation, but no obvious seasonal change. The concentrations of iron decreased very markedly during flow of water through the lake.

Kinetic studies of solvent extraction of metal complexes—VI: Equilibrium and rate of solvent extraction of iron(III) perchlorate with trioctylphosphine oxide in hexane

Abstract The equilibrium and rate of solvent extraction of iron(III) in 4 M aqueous perchlorate media with trioctylphosphine oxide (TOPO) in hexane have been studied at 25°C. Although the distribution ratio of iron(III) was apparently dependent on the hydrogen-ion concentration, the extracted species was found to be Fe(ClO 4 ) 3 (TOPO) 4 after correction for the decrease in the free TOPO concentration caused by extraction of perchloric acid. The rate was found to be first order with respect to TOPO and inverse first order with respect to hydrogen-ion, and the controlling reaction was assumed to be association of FeOH 2+ with TOPO in the aqueous phase. The extraction was accelerated by chloride, bromide, or nitrate ions (X − ) and this was explained by another extraction mechanism controlled by association of FeX 2+ with TOPO in the aqueous phase. It was concluded that the rate of association with TOPO increases in the order of FeOH 2+ FeNO 3 2+ > FeBr 2+ > FeCl 2+ .

Kinetic studies of the solvent extraction of metal complexes—III: The rate of extraction and back-extraction of gallium(III) thenoyltrifluoroacetonate chelate in aqueous perchlorate solution-chloroform systems

Abstract The rate of forward extraction of Ga 3+ from 0·1 M aqueous perchlorate solutions into chloroform with TTA (thenoyltrifluoroacetone, denoted by HA) and of backward extraction of the tris-TTA chelate, GaA 3 , have been determined under various conditions. The distribution equilibria in the same systems have also been measured. The rate of forward extraction is proportional to [Ga 3+ ], [HA] org , and [H + ] −2 , whereas that of backward extraction is proportional to [GaA 3 ] org , [HA] org −2 , and [H + ]. On the basis of these results, the rate determining step in the forward extraction is believed to involve an association of the GaOH 2+ species with A − in the aqueous phase and that in the backward extraction to be the reverse reaction of this. The constants for both the rate controlling steps have been determined and the extraction constant computed from these values is found to agree with that computed from the equilibrium data.

SOLVENT EXTRACTION EQUILIBRIA OF TRIS(BENZOYL- TRIFLUOROACETONATO)COMPLEX OF COBALT(II) AND NICKEL(II) AS ION-PAIRS WITH TETRABUTYLAMMONIUM

Abstract Solvent extraction of cobalt(Il) and nickel(II) in aqueous 1 mol dm−3 NaCl solutions with benzoyltrifluoro-acetone(Hbfa) in carbon tetrachloride has been measured in the absence and presence of tetrabutylammonium(tba+). In the absence of tba+, M(bfa)2 species is extracted and the extraction of cobalt(II) is better in the higher Hbfa concentration range but in the presence, M(bfa)3 −tba+ type ion-pair is extracted and the extraction of nickel-(II) is always better. This is explained in terms that although the bis-nickel(II) complex is more stable, it is much more strongly hydrated than the bis-cobalt(II) complex and consequently its extraction is hindered but in the tris-complexes such a large difference of the hydration may not occur and the more stable nickel(II) complex is extracted better.

Solvent extraction equilibria of acids—II: Extraction of phosphoric acid from various aqueous solutions with trioctylphosphine oxide

Abstract Solvent extraction equilibria of phosphoric acid with trioctylphosphine oxide (TOPO) has been studied at 25°C. When the diluent was hexane, a trisolvate with TOPO was extracted but when it was benzene or carbon tetrachloride, both a trisolvate and a disolvate were extracted. Extraction into hexane was slightly enhanced by hydrochloric acid and greatly impaired by perchloric or nitric acid in the aqueous phase and the impairment was found to be due to a decrease in the free TOPO concentration caused by the extraction of the strong acid. It is concluded after the correction for this decrease in the free TOPO concentration that these strong acids enhanced the net extraction of phosphoric acid by forming a mixed acid species, H3PO4·HX·(TOPO)3 (where HX is a strong acid), which is assumed to have a hydrogen-bond between the phosphoryl oxygen of the phosphoric acid and HX, and that the order of enhancement is HClO4 > HNO3 > HCl. The constants for the above extraction equilibria were determined.

SOLVENT EXTRACTION OF ZINC(II) ANIONIC g-DIKETONATE COMPLEXES AS ION-PAIRS WITH TETRABUTYLAMMONIUM IONS

ABSTRACT Solvent extraction equilibria of zinc(II)with five 6-diketones(HA)in carbon tetrachloride-aqueous 1 mol dm−3NaN03systems are studied in the absence and presence of tetrabutylammonium ions(tba+The distribution data of zinc(II)in the absence of tba+ are explained in terms of extractions of uncharged ZnA2 complex from the aqueous phase where the ZnA+, ZnA2and ZnA3complexes are formed, and those in the presence of tba+ in terms of extraction of the ZnA3~tba+ ion-pairs in addition to the uncharged one. The extraction of the ZnA3-tba+species is better with hexafluoroacetylacetone than with trifluoroacetyl-acetone. It is better when the extractant is benzoyltri-fluoroacetone than when it is trifluoroacetylacetone and this is explained in terms of a greater increase in the hydrofobic character by formation of the tris-complex from the bis-complex with the larger ligand. However, the extraction with acetylacetone and benzoylacetone is not affected by though the formation of the tris-chelate with these lig...