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On the distribution coefficient of nickel dimethylglyoximate between an aqueous solution and organic solvents
Talanta, 1971, Vol. 18. pp. 1233 to 1235.
Per~amon Press. Printed in Northem
Ireland
SHORT COMMUNICATIONS
On the distribution coefficient of nickel dimethylglyoximate between an aqueous solution and organic solvents (Received 6 JuIy 1971. Accepted 1 August 1971) SUCCJZ.WVLapplications of the regular-solution theory to the distribution coefficients of chelating reagents such as B&ketones and oxine and their metal chelates have been made.‘-& ?n the present work, the theory is applied to the distribution of nickel dimethylglyoximate. EXPERIMENTAL Reagents The reagents and the solvents used were all of guaranteed reagent grade and were used without further purification. A **Ni radiotracer of 99.9 % purity was used. Distribution measurements of nickel-dimethylglyoxime
chelate
A (6-ml) volume of aqueous phase and an equal volume of an organic solvent were equilibrated by shaking in a glass-stoppered vial for 30 min. The aqueous phase contained nickel perchlorate labelled with O*Ni (2.0 x 10-sM) and dimethylglyoxime (DG) (2.8 x 10-BM). Its pH was maintained at about 10 with sodium hydroxide and its ionic strength was adjusted to be 0.1 with sodium perchlorate. The mixture was then centrifuged for 5 min. An aliquot (0.1 or 1 ml) of the organic phase was transferred to a stainless-steel planchet, heated at 300” to remove excess of DG and counted on a 2~ gas-flow counter. Part of the aqueous phase (2 ml) was transferred to another vial and the nickel in the solution was extracted into an equal volume of chloroform. The radioactivity of the organic extract, which was measured as described above, was taken as that of the aqueous phase. The distribution coefficients were obtained as the average of three independent runs. The experiments were all carried out in a temperature-controlled room at 20”. RESULTS The distribution
AND
DISCUSSION
ratio of nickel, DI. in terms of molarity is given by: D,“[A-]’ Dm = 1 + /%[A-1 + 8&4-l*
(1)
where DCo,p,, and [A-] represent the distribution coefficient of the nickel-DG chelate, the nth overall stability constant of the chelate and the concentration of the anion of DG, respectively. The preliminary experiments showed that the concentration of nickel (10-e-10-4M) did not affect the distribution ratio of nickel. The distribution ratio of nickel can be equated to the distribution coefficient of the chelate at pH 7-12 under the experimental conditions,’ and the pH of the aqueous phase was adjusted to about 10 for experimental convenience. The distribution coefficients of nickel-DG chelate for 6 inert solvents are given in Table I. The distribution coefficients of the chelate in terms of the mole fraction, PC”, are calculated from DC0by multiplying by the ratio of the molar volume of an organic solvent to that of water at 20”. The following formal relationship’ is given by the regular-solution theory:
(2) 1233
1234
Short communication
where V, is the molar volume of the chelate, S is the solubility parameter, and the subscripts aq, org and c refer to the aqueous phase, the organic phase and the chelate, respectively. The distribution data in Table I are successfully interpreted by equation (2). The numerical values obtained by the method of least squares are V, = 182 ml/mole, 6,, = 18.6 and 6, = 12.9. In this calculation, the 6 values for organic solvents at 25” were used, because the difference of the solubility parameters between 25” and 20” is so small as to be below 0.1 6 unit,O and the datum for TABLE~.-DI~TRI~UTION COEFPKXENTS OF Ni-DG CHELATEFORINERT ORGANICSOLVENTS
f%g Solvent 1 2 3 4 5 6
Chloroform Methylene chloride o-Dichlorobenzene Benzene Carbon tetrachloride n-Hexane
found 9.3
9.2 8.6 7.3
log DC0 calcd.
2.58 2.53 2.27 1.85 0.96 -0.79
1.92 2.39 2.39 1.78 1.08 -0.81
log P.0 found 3.23 3.08 3.07 2.54 l-69 0.07
chloroform was excluded, because the distribution coefficient of the chelate for chloroform was found to be much higher than that expected from the solubility parameter of chloroform. The empirical solubility parameter for an aqueous phase, daq, determined in this work is a little larger than those reported elsewhere. l** A study of the factors affecting the empirical solubility parameter for an aqueous phase is under way. The distribution coefficients of the chelate, calculated from equation (2) with the three values obtained above, are also given in Table I. These are seen to agree well with the observed values except in the case of chloroform. In a plot of log PCo/(& - CL,,,)against&r, practically all the experimental points fall on a single straight line, which is independent of the organic solvents used, as expected from equation (2). In the case of chloroform, a considerable deviation is observed, and a similar trend has also been found in b-diketone’ and oxineS systems with inert solvents. These facts suggest that chloroform has some specific interactions with these solutes and cannot be treated as a simple inert solvent. s. ORl Faculty of Engineering Shimoka University Hamamatsu, Japan Summary-The distribution coefficients of nickel dimethylglyoximate between an aqueous solution and 6 inert solvents were determined at 20”. The distribution coefficients of the nickel chelate were quantitatively interpreted in terms of solubility parameters. The solubility parameter for the nickel chelate was evaluated to be 12.9, that for the aqueous solution to be 18.6, and the molar volume of the chelate to be 182 ml/mol. Zusammenfassung-Die Verteilungskoeffizienten von Nickeldimethylglyoximat zwischen einer wmrigen LSsung und 6 inerten Liisungsmiteln wurden bei 20” bestimmt. Die Verteilungskoeffizienten des Nickelchelats wurden quantitativ an Hand von Loslichkeitsparametern interpretiert. Der Loslichkeitsparameter des Nickelchelats betrlgt 12.9, der der w%Wigen Liisung 18.6, das Molvolumen des Chelats 182 ml/mol. R&sum&-On a determine les coefficients de partage a 20” du dimethylglyoximate de nickel entre une solution aqueuse et 6 solvants inertes. On a interprete quantitativement les coefficients de partage du chelate du nickel en fonction de parametres de solubilite. Le parametre de solubilite pour le ch6late de nickel a 6te evaI& a 12,9, celui de la solution aqueuse a 18,6, et le volume molaire du chelate a 182 ml/mol.
Short communication
1235
REFERENCES T. Wakabayashi.
S. Oki, T. Omori and N. Suzuki, J. Inorg. Nucl. Chem., 1964,26,2255. S. Oki and N. Suzuki, ibid., 1964,26,2265. T. Wakabayashi, Bull. Chem. Sot. Japan, 1967,40,2836. i: N. Suzuki, K. Akiba and H. Asano, Anal. Chim. Acta, 1970,52,115, for reference. 5. D. Dyrssen, F. Krasovec and L. G. Sillen, Acta Chem. &and., 1959,13,50. 6. J. H. Hildebrand and R. L. Scott, The Solubility of Nonelecrrolytes, 3rd Ed., Dover, New York, 1964.
:: T. Omori, T. Wakabayashi,
Talattta,
1971 I Vol. 18, pp. 1235 to 1236.
Persamon
Press.
Printed
in Northern
Ireland
Cation-exchange separation and determination of silver in admixture with mercury(II) ACCORDINGto Scott and Furman* volumetric determination of silver by Volhard’s method cannot be carried out when mercury or highly coloured salts of copper, nickel and cobalt constitute more than 60% of the sample. Iodometric,**s complexometric* and colorimetrid procedures cannot be used under these conditions. Khopkar et uf.Ohave reported the separation of silver from a wide range of other metals, using different ion-exchange techniques, but were unable to separate it from mercury. Ion-exchange separation of silver from mercury(H) based on the differences in the stability constants of the complexes formed by these elements with EDTA has not been reported previously in the literature. Preliminary investigations showed that mercury(H) forms a stable anionic complex with EDTA at pH 4-5. This passes through a cation-exchange column unchanged. The silver-EDTA complex is not stable and is dissociated on the column, resulting in the retention of silver on the resin bed.
EXPERIMENTAL Reagents Ion-exchange column. A column 10 x 150 mm, containing the air-dried strongly acid cationexchange resin Dowex 5OW-X8 in the sodium form (SO-100 mesh) was prepared. Standard solutions. All metal solutions were prepared from the pure nitrates by dissolving them in about 25 ml of water containing 2 ml of concentrated nitric acid. These solutions were diluted to 250 ml to give 0.05M solutions. EDTA solution 0*05M. Eluent. Nitric acid 16% (v/v). Glacial acetic acid (60 ml) was added to sodium acetate trihydrate (13.70 g> Acetate buerpH4.6. and the mixture was diluted to 100 ml with distilled water.
Procedure The solution containing silver and mercury(H) as nitrates was diluted to about 30 ml. About 6-7 ml of the acetate buffer solution were added and the pH was adjusted to 4.6. To this solution a slight excess of the EDTA solution was added, and it was passed through the cation-exchange column at the rate of 5-6 ml/mm. The column was thoroughly washed with 300 ml of distilled water to remove EDTA and the mercury complex. The eluate was collected from the beginning of the sorption step. An ahquot of the effluent and the washmgs was analysed’ for its mercury content, by titrating the excess of EDTA. Silver was eluted by passing 250 ml of 16% nitric acid at the rate of 4 ml/min through the column. The eluate was boiled for a few minutes, cooled and titrated with standard ammonium thiocyanate solution, with iron(II1) nitrate as indicator.*
Per~amon Press. Printed in Northem
Ireland
SHORT COMMUNICATIONS
On the distribution coefficient of nickel dimethylglyoximate between an aqueous solution and organic solvents (Received 6 JuIy 1971. Accepted 1 August 1971) SUCCJZ.WVLapplications of the regular-solution theory to the distribution coefficients of chelating reagents such as B&ketones and oxine and their metal chelates have been made.‘-& ?n the present work, the theory is applied to the distribution of nickel dimethylglyoximate. EXPERIMENTAL Reagents The reagents and the solvents used were all of guaranteed reagent grade and were used without further purification. A **Ni radiotracer of 99.9 % purity was used. Distribution measurements of nickel-dimethylglyoxime
chelate
A (6-ml) volume of aqueous phase and an equal volume of an organic solvent were equilibrated by shaking in a glass-stoppered vial for 30 min. The aqueous phase contained nickel perchlorate labelled with O*Ni (2.0 x 10-sM) and dimethylglyoxime (DG) (2.8 x 10-BM). Its pH was maintained at about 10 with sodium hydroxide and its ionic strength was adjusted to be 0.1 with sodium perchlorate. The mixture was then centrifuged for 5 min. An aliquot (0.1 or 1 ml) of the organic phase was transferred to a stainless-steel planchet, heated at 300” to remove excess of DG and counted on a 2~ gas-flow counter. Part of the aqueous phase (2 ml) was transferred to another vial and the nickel in the solution was extracted into an equal volume of chloroform. The radioactivity of the organic extract, which was measured as described above, was taken as that of the aqueous phase. The distribution coefficients were obtained as the average of three independent runs. The experiments were all carried out in a temperature-controlled room at 20”. RESULTS The distribution
AND
DISCUSSION
ratio of nickel, DI. in terms of molarity is given by: D,“[A-]’ Dm = 1 + /%[A-1 + 8&4-l*
(1)
where DCo,p,, and [A-] represent the distribution coefficient of the nickel-DG chelate, the nth overall stability constant of the chelate and the concentration of the anion of DG, respectively. The preliminary experiments showed that the concentration of nickel (10-e-10-4M) did not affect the distribution ratio of nickel. The distribution ratio of nickel can be equated to the distribution coefficient of the chelate at pH 7-12 under the experimental conditions,’ and the pH of the aqueous phase was adjusted to about 10 for experimental convenience. The distribution coefficients of nickel-DG chelate for 6 inert solvents are given in Table I. The distribution coefficients of the chelate in terms of the mole fraction, PC”, are calculated from DC0by multiplying by the ratio of the molar volume of an organic solvent to that of water at 20”. The following formal relationship’ is given by the regular-solution theory:
(2) 1233
1234
Short communication
where V, is the molar volume of the chelate, S is the solubility parameter, and the subscripts aq, org and c refer to the aqueous phase, the organic phase and the chelate, respectively. The distribution data in Table I are successfully interpreted by equation (2). The numerical values obtained by the method of least squares are V, = 182 ml/mole, 6,, = 18.6 and 6, = 12.9. In this calculation, the 6 values for organic solvents at 25” were used, because the difference of the solubility parameters between 25” and 20” is so small as to be below 0.1 6 unit,O and the datum for TABLE~.-DI~TRI~UTION COEFPKXENTS OF Ni-DG CHELATEFORINERT ORGANICSOLVENTS
f%g Solvent 1 2 3 4 5 6
Chloroform Methylene chloride o-Dichlorobenzene Benzene Carbon tetrachloride n-Hexane
found 9.3
9.2 8.6 7.3
log DC0 calcd.
2.58 2.53 2.27 1.85 0.96 -0.79
1.92 2.39 2.39 1.78 1.08 -0.81
log P.0 found 3.23 3.08 3.07 2.54 l-69 0.07
chloroform was excluded, because the distribution coefficient of the chelate for chloroform was found to be much higher than that expected from the solubility parameter of chloroform. The empirical solubility parameter for an aqueous phase, daq, determined in this work is a little larger than those reported elsewhere. l** A study of the factors affecting the empirical solubility parameter for an aqueous phase is under way. The distribution coefficients of the chelate, calculated from equation (2) with the three values obtained above, are also given in Table I. These are seen to agree well with the observed values except in the case of chloroform. In a plot of log PCo/(& - CL,,,)against&r, practically all the experimental points fall on a single straight line, which is independent of the organic solvents used, as expected from equation (2). In the case of chloroform, a considerable deviation is observed, and a similar trend has also been found in b-diketone’ and oxineS systems with inert solvents. These facts suggest that chloroform has some specific interactions with these solutes and cannot be treated as a simple inert solvent. s. ORl Faculty of Engineering Shimoka University Hamamatsu, Japan Summary-The distribution coefficients of nickel dimethylglyoximate between an aqueous solution and 6 inert solvents were determined at 20”. The distribution coefficients of the nickel chelate were quantitatively interpreted in terms of solubility parameters. The solubility parameter for the nickel chelate was evaluated to be 12.9, that for the aqueous solution to be 18.6, and the molar volume of the chelate to be 182 ml/mol. Zusammenfassung-Die Verteilungskoeffizienten von Nickeldimethylglyoximat zwischen einer wmrigen LSsung und 6 inerten Liisungsmiteln wurden bei 20” bestimmt. Die Verteilungskoeffizienten des Nickelchelats wurden quantitativ an Hand von Loslichkeitsparametern interpretiert. Der Loslichkeitsparameter des Nickelchelats betrlgt 12.9, der der w%Wigen Liisung 18.6, das Molvolumen des Chelats 182 ml/mol. R&sum&-On a determine les coefficients de partage a 20” du dimethylglyoximate de nickel entre une solution aqueuse et 6 solvants inertes. On a interprete quantitativement les coefficients de partage du chelate du nickel en fonction de parametres de solubilite. Le parametre de solubilite pour le ch6late de nickel a 6te evaI& a 12,9, celui de la solution aqueuse a 18,6, et le volume molaire du chelate a 182 ml/mol.
Short communication
1235
REFERENCES T. Wakabayashi.
S. Oki, T. Omori and N. Suzuki, J. Inorg. Nucl. Chem., 1964,26,2255. S. Oki and N. Suzuki, ibid., 1964,26,2265. T. Wakabayashi, Bull. Chem. Sot. Japan, 1967,40,2836. i: N. Suzuki, K. Akiba and H. Asano, Anal. Chim. Acta, 1970,52,115, for reference. 5. D. Dyrssen, F. Krasovec and L. G. Sillen, Acta Chem. &and., 1959,13,50. 6. J. H. Hildebrand and R. L. Scott, The Solubility of Nonelecrrolytes, 3rd Ed., Dover, New York, 1964.
:: T. Omori, T. Wakabayashi,
Talattta,
1971 I Vol. 18, pp. 1235 to 1236.
Persamon
Press.
Printed
in Northern
Ireland
Cation-exchange separation and determination of silver in admixture with mercury(II) ACCORDINGto Scott and Furman* volumetric determination of silver by Volhard’s method cannot be carried out when mercury or highly coloured salts of copper, nickel and cobalt constitute more than 60% of the sample. Iodometric,**s complexometric* and colorimetrid procedures cannot be used under these conditions. Khopkar et uf.Ohave reported the separation of silver from a wide range of other metals, using different ion-exchange techniques, but were unable to separate it from mercury. Ion-exchange separation of silver from mercury(H) based on the differences in the stability constants of the complexes formed by these elements with EDTA has not been reported previously in the literature. Preliminary investigations showed that mercury(H) forms a stable anionic complex with EDTA at pH 4-5. This passes through a cation-exchange column unchanged. The silver-EDTA complex is not stable and is dissociated on the column, resulting in the retention of silver on the resin bed.
EXPERIMENTAL Reagents Ion-exchange column. A column 10 x 150 mm, containing the air-dried strongly acid cationexchange resin Dowex 5OW-X8 in the sodium form (SO-100 mesh) was prepared. Standard solutions. All metal solutions were prepared from the pure nitrates by dissolving them in about 25 ml of water containing 2 ml of concentrated nitric acid. These solutions were diluted to 250 ml to give 0.05M solutions. EDTA solution 0*05M. Eluent. Nitric acid 16% (v/v). Glacial acetic acid (60 ml) was added to sodium acetate trihydrate (13.70 g> Acetate buerpH4.6. and the mixture was diluted to 100 ml with distilled water.
Procedure The solution containing silver and mercury(H) as nitrates was diluted to about 30 ml. About 6-7 ml of the acetate buffer solution were added and the pH was adjusted to 4.6. To this solution a slight excess of the EDTA solution was added, and it was passed through the cation-exchange column at the rate of 5-6 ml/mm. The column was thoroughly washed with 300 ml of distilled water to remove EDTA and the mercury complex. The eluate was collected from the beginning of the sorption step. An ahquot of the effluent and the washmgs was analysed’ for its mercury content, by titrating the excess of EDTA. Silver was eluted by passing 250 ml of 16% nitric acid at the rate of 4 ml/min through the column. The eluate was boiled for a few minutes, cooled and titrated with standard ammonium thiocyanate solution, with iron(II1) nitrate as indicator.*