Shoichi Katsuta

Equilibrium studies on complexation in water and solvent extraction of zinc(II) and cadmium(II) with benzo-18-crown-6.

The formation constants (K(ML)) in water of 1:1 complexes of benzo-18-crown-6 (B18C6) and 18-crown-6 (18C6) with Zn(2+) and Cd(2+), the sizes of which are much smaller than the ligand cavities, were determined at 25 degrees C by conductometry. Compared with Cd(2+), the crown ethers form more stable complexes with Zn(2+) although the size of Zn(2+) is less suited for the cavities. B18C6 forms a more stable complex with each metal ion than 18C6. Moreover, the extraction equilibria of these metal ions (M(2+)) with B18C6 (L) for the benzene/water system in the presence of picric acid (HA) were investigated at 25 degrees C. The association between L and HA in benzene was examined for evaluating the intrinsic extraction equilibria of M(2+) with B18C6. The extracted species were found to be MLA(2) and ML(2)A(2), and the overall extraction constants (K(ex,1) and K(ex,2), respectively) were obtained. The values of K(ex,1) for these metal ions are almost the same, but the K(ex,2) is larger for Zn(2+) than for Cd(2+). The extraction selectivity was interpreted quantitatively by the constituent equilibrium constants, i.e. K(ML), the ion-pair extraction constant of ML(2+) with A(-), and the adduct formation constant of MLA(2) with L in benzene.

Stabilities in Water of Alkali Metal Ion Complexes with Dibenzo-24-crown-8 and Dibenzo-18-crown-6 and Their Transfer Activity Coefficients from Water to Nonaqueous Solvents

Stability constants KML for the 1:1 complexes of Na+, K+, Rb+, and Cs+ with dibenzo-24-crown-8 (DB24C8) and dibenzo-18-crown-6 (DB18C6) in water have been determined by a capillary electrophoretic technique at 25°C. The KML sequence is Na+ < K+ < Rb+ < Cs+ for DB24C8 and Na+ < K+ > Rb+ > Cs+ for DB18C6. Compared with DB18C6, DB24C8 exhibits higher selectivity for K+ over Na+, but lower selectivity for K+, Rb+, and Cs+. To evaluate the solvation of the complexes in water, their transfer activity coefficients sγH2O between polar nonaqueous solvents and water have been calculated. The sγH2O values provide the following information: interactions with water of the metal ions and of the crown-ether oxygens are greatly reduced upon complexation and the complexes undergo hydrophobic hydration in water; the character of each alkali metal ion in solvation is more effectively masked by DB24C8 than by DB18C6, because of the larger and more flexible ring structure of DB24C8. Solvent effects on the complex stabilities are discussed on the basis of the sγH2O values.

Extraction of sodium and potassium picrates with 16-crown-5 into various diluents. Elucidation of fundamental equilibria determining the extraction selectivity for Na+ over K+

The constants of the overall extraction equilibrium (K(ex)), the partition for various diluents having low dielectric constants (K(D,MLA)), the aqueous ion-pair formation (K(MLA)), and the dimer formation in CCl(4) of 16-crown-5 (16C5)-alkali metal (Na, K) picrate 1:1:1 complexes were determined at 25 degrees C; the distribution constants of 16C5 were also measured at 25 degrees C. The logK(MLA) of Na and K are 4.14+/-0.19 and 3.05+/-0.28, respectively. The partition behavior of 16C5 and its 1:1:1 complexes with the alkalimetal picrates can be explained by regular solution theory, except for CHCl(3); the molar volumes and solubility parameters of 16C5 and the 1:1:1 complexes were determined. The magnitude of K(ex) largely depends on that of K(MLA). For every diluent, 16C5 always shows Na(+) extraction-selectivity over K(+). The K(MLA) value most contributes to the extraction selectivity of 16C5 for Na(+) over for K(+) among the three fundamental equilibrium constants, the aqueous 1:1 complex-formation constant of 16C5 with the alkali metal ion, K(MLA), and K(D,MLA). Furthermore, correct contributions of a methylene group to distribution constants of organic compounds between diluents of low dielectric constants and water were determined by the distribution constants of 16C5 and 15-crown-5; the additivity of the contributions of functional groups to the partition constant of a crown ether was verified.

Mechanisms and rules of anion partition into ionic liquids: phenolate ions in ionic liquid/water biphasic systems.

It is important to understand the mechanisms and general rules of ion partitioning in hydrophobic ionic liquid (IL)/water biphasic systems in order to predict the extractability of an ionic species with various ILs. In this study, we have investigated the partition of picrate ion (target anion, T(-)) from aqueous sodium picrate solutions into several ILs and the accompanying changes in aqueous concentrations of the IL component cation (C(+)) and anion (A(-)) at 298.2 K. The main ILs examined are 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide, 1-butyl-3-methylimidazolium hexafluorophosphate, and 1-methyl-3-octylimidazolium bis(trifluoromethanesulfonyl)amide. The aqueous concentrations of C(+) and A(-) decreased and increased, respectively, with the extraction of T(-) into the IL phase. From the standpoint of equilibrium, the partition behavior of T(-) can be explained both by the anion exchange with A(-) in the IL phase and by the ion pair extraction with C(+) in the aqueous phase. The aqueous concentrations of C(+) and A(-) are governed by the solubility product of the IL (K(sp)). The distribution ratio of T(-) is expressed as a function of Δ[T(-)](W), namely, the difference between the initial and equilibrium concentrations of T(-) in the aqueous phase; the distribution ratio of T(-) is nearly constant when Δ[T(-)](W) << K(sp)(1/2), but decreases with increasing Δ[T(-)](W) in the larger Δ[T(-)](W) region. The equilibrium constants of the ion pair extraction and the ion exchange extraction have been determined for picrate and other phenolate ions whose partition data were previously reported. The dependences of the extraction constants and extractability on the kinds of IL component ions can be quantitatively explained on the basis of the variations of K(sp).

Extraction of sodium and potassium perchlorates with benzo-18-crown-6 into various organic solvents. Quantitative elucidation of anion effects on the extraction-ability and -selectivity for Na+ and K+

To investigate quantitatively the anion effect on the extraction-ability and -selectivity of benzo-18-crown-6 (B18C6) for alkali metal ions, the constants for overall extraction into various diluents having low dielectric constants (K(ex)) and aqueous ion-pair formation (K(MLA)) of B18C6-sodium and potassium perchlorate 1:1:1 complexes (MLA) were determined at 25 degrees C. The K(ex) value was analyzed by the four fundamental equilibrium constants. The K(MLA) values were determined by applying our established method to this perchlorate extraction system. The K(M(B18C6)A) value of the perchlorate is much larger for K(+) than for Na(+), and is much smaller than that of the picrate. The K(M(B18C6)A) value makes a minor contribution to the magnitude of K(ex) for the perchlorate system, but a major contribution to that for the picrate one. The distribution behavior of the B18C6 1:1:1 complexes with the alkali metal perchlorates follows the regular solution theory. For the diluent with a high dipole moment, however, the 1:1:1 complexes somewhat undergo the dipole-dipole interaction. B18C6 always shows very high extraction selectivity for KClO(4) over NaClO(4), which is determined mostly by the much greater log/(log K(MLA)) value for K(+) than for Na(+). The extraction-ability and -selectivity of B18C6 for Na(+) and K(+) ions with a perchlorate ion were compared with those with a picrate ion in terms of the fundamental equilibrium constants. The K(+) extraction-selectivity of B18C6 over Na(+) for the perchlorate system is superior to that for the picrate one, which is caused largely by the greater log/(log K(K(B18C6)A))-log/(log K(Na(B18C6)A)) value for the perchlorate than for the picrate. The perchlorate system is recommended for extraction separation of K(+) from Na(+).

Solvent extraction of silver picrate by 3m-crown-m ethers (m = 5, 6) and its mono-benzo-derivative from water into benzene or chloroform: elucidation of an extraction equilibrium using component equilibrium constants

Ion-pair formation constant (K(AgPic) in mol(-1)dm(3)) of silver picrate (AgPic), those (K(AgLPic)) of its ion-pair complexes (AgLPic) with crown ethers (L) and complex formation constants (K(AgL)) of Ag(+) with L (15-crown-5 ether (15C5) and benzo-15C5) in water (w) were determined potentiometrically at 25 degrees C. Compounds used as L were 18-crown-6 ether (18C6), its benzo-derivative (B18C6) and the two 15C5 derivatives. Extraction constants (K(ex) in mol(-1)dm(3)) of AgPic with L (15C5, 18C6, B18C6) from acidic w-phases into either C(6)H(6) or CHCl(3) were recalculated from K(AgPic), K(AgL), K(AgLPic) and data opened in previous papers. Thus obtained K(ex) was divided into five component equilibrium constants containing K(AgL) and K(AgLPic) anew. Then, contributions of the component constants, K(AgL), K(AgLPic) and distribution constants of AgLPic between the w- and C(6)H(6)-phases, to K(ex) were discussed and compared with corresponding extraction systems of NaPic and KPic with18C6.

Solvent extraction of permanganates (Na, K) by 18-crown-6 ether from water into 1,2-dichloroethane: elucidation of an extraction equilibrium based on component equilibria

Ion-pair formation constants (K(MLA) mol(-1) dm(3)) of Na(+)- and K(+)-18-crown-6 ether (18C6) complexes with MnO(4)(-) in water (w) were determined potentiometrically at 25 degrees C. Simultaneously, extraction constants (K(ex) mol(-2) dm(6)) of the permanganates with 18C6 from w into 1,2-dichloroethane at 25 degrees C were obtained from the spectrophotometric determination of distribution ratios of the permanganates. These K(ex) values were divided into K(MLA) and other three component equilibrium constants and thereby extraction-selectivity and -ability were discussed in comparison with corresponding metal picrate-18C6 extraction systems reported before.

Extraction of sodium and potassium picrates with 15-(2,5-dioxahexyl)-15-methyl-16-crown-5 (lariat 16C5) into various organic solvents. Elucidation of fundamental equilibria which determine the extraction ability for Na(+) and K(+) and the selectivity.

To quantitatively elucidate the effects of the side chains and diluents on the extraction selectivity for sodium and potassium picrates of 15-(2,5-dioxahexyl)-15-methyl-16-crown-5 (L16C5) from the viewpoint of equilibrium, the constants for the overall extraction (K(ex)), the partition for various diluents of low dielectric constants (K(D,MLA)), and the aqueous ion-pair formation (K(MLA)) of L16C5-sodium and -potassium picrate 1:1:1 complexes were determined at 25 degrees C; the distribution constants of L16C5 were also measured at 25 degrees C. The log K(MLA) values for Na(+) and K(+) are 2.74+/-0.29 and 1.70+/-0.36, respectively. In going from 16-crown-5 (16C5) to L16C5, the side chains decrease the K(MLA) value, but do not increase the difference in K(MLA) between Na(+) and K(+). The distribution behavior of L16C5 and its 1:1:1 complexes with the alkali metal picrates closely obeys regular solution theory, except for chloroform. Molar volumes and solubility parameters of L16C5 and the 1:1:1 complexes were determined. The magnitude of K(ex) is mainly governed by the K(M(L16C5)A) value. For every diluent, L16C5 shows Na(+) extraction selectivity over K(+). The Na(+) extraction selectivity of L16C5 is determined completely by K(M(L16C5)A). The extraction ability and selectivity for sodium and potassium picrates by L16C5 are compared with those of 16C5 on the basis of the fundamental equilibrium constants.

A Micellar Electrokinetic Chromatographic Method for Determination of Solubilization Isotherms in Surfactant Micelles

We have devised a new micellar electrokinetic chromatographic method for determination of the solubilization equilibrium constants of neutral solutes in surfactant micelles as functions of the intramicellar mole fraction of the solute. In this method, the running solution in a capillary and in electrode vessels contains the neutral solute as well as the surfactant micelles, and the injected solution contains the surfactant micelles and the dilute marker compounds for aqueous and micellar phases but not the solute. The mobility of the solute can be measured from a negative peak recorded on the chromatogram. The solute concentration in the capillary is established, and the mobility of the micellar phase incorporating the solute, which depends on the intramicellar mole fraction of the solute, can be measured from the migration time of the micelle marker. These merits enable precise determination of the solubilization isotherms. This method has been used to study the solubilization equilibria of benzene, phenol, and a series of aliphatic ketones in sodium dodecyl sulfate solution, and the validity and effectiveness of this method for quantifying solubilization have been verified.

Solvent extraction of sodium perrhenate by 3m-crown-m ethers (m = 5, 6) and their mono-benzo-derivatives into 1,2-dichloroethane: Elucidation of an overall extraction equilibrium based on component equilibria containing an ion-pair formation in water

Equilibrium constants (K(MLA)(0)/mol(-1)dm(3)) for the ion-pair formation of a complex ion NaL(+) with ReO(4)(-) in water were determined potentiometrically at 25 degrees C and the ionic strength (I) of 0mol dm(-3) using a Na(+)-selective electrode. Here, crown ethers, L, were 15-crown-5 ether (15C5), benzo-15C5, 18-crown-6 ether (18C6) and benzo-18C6. Also, NaReO(4) was extracted by the L into 1,2-dichloroethane and then extraction constants (K(ex)/mol(-2)dm(6)) for the species, NaLReO(4), were determined at 25 degrees C by AAS. These K(ex) values were resolved into four component equilibrium constants containing K(MLA) calculated at given I values. Based on these data, extraction-abilities of the L against the perrhenate were discussed in comparison with those of sodium picrate-L systems reported previously.