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Liquid ion-exchange extraction study of hexacyanoferrate(III) with trioctylmethylammonium chloride (aliquat-336)
Chimica Acta, 105 (1979) 383-390 0 Elsevier Scientific Publishing Company, Amsterdam
Analytica
-
Printed in The Netherlands
LIQUID ION-EXCHANGE EXTRACTION STUDY OF HEXACYANOFERRATE(II1) WITH TRIOCTYLMETHYLAMMONIUM CHLORIDE (ALIQUAT-336)t
JUN’ICHI Department
ITOH**,
HIROSHI
of Organic
KOBAYASHI***
Synthesis,
Faculty
and KEIHEI UENO*
of Engineering,
Kyushu
University,
Fukuoka
8 I2
(Japan) (Received 4th July 1978)
SUMMARY Liquid-liquid ion-exchange extraction of various anions including hexacyanoferrate( III) with a chlorobenzene solution of trioctylmethylammonium chloride (TOMA-CI; Aliquat-336 chloride) is described. The ion-pair extraction constant of TOMA-Cl (Kzicl = 104) and the ion-exchange extraction constants of TOMA-Cl for each anion (K$kx) are reported_ The order of selectivity of anion extraction is Fe(CN),3-(log Kzix = 22.41) > ClO,- (8.47) > PAR-(7.80) > I-(7.32) > NO,-(5.81) > Br-(5.34) > Cl-(4.00).
Liquid ion-exchange extractions of anions with long-chain tertiary amines and quatemary ammonium salts have been widely used as separation processes in industry as well as in analytical chemistry [ 1,2]. Irving and Damodaran [ 31 were unable to extract hexacyanoferrate( III) and hexacyanoferrate( II) ions in their ion-exchange extraction study on various metal cyanides with tetrahexylammonium salts in MIBK. However, in their later work [4] on the ion-exchange extraction of anionic EDTA complexes with Aliquat-336 in dichloroethane, they successfully extracted multivalent anionic complexes such as FeY(OH)23- and V02Y3-. Qualitatively, the extraction of anions should be favoured by decrease of hydrophilicity, i.e. by increase in size and decrease in charge of the anions, but these results could not be explained on this basis. The extraction of hexacyanoferrate(II1) with Aliquat-336 in chlorobenzene is successful [ 51, though this would not be expected from the results with the tetrahexylammonium salt-MIBK system. This paper reports on the liquid ion-exchange extraction of anions of various charges with Aliquat-336 chloride (trioctylmethylammonium chloride; TOMA-Cl) in chlorobenzene, and describes an attempt to elucidate the factors governing the selectivity of the anion extraction.
tcontribution No. 495 from the Department of Organic Synthesis, Kyushu University. **Present address: Kitami Institute of Technology, Kitami 090. ***Present address: Research Institute for Industrial Science, Kyushu University, Fukuoka 812.
334 EXPERIMENTAL
Reagents TOMA-Cl solution was prepared by dissolving a suitable amount of Aliquat336 chloride (kindly donated by General Mills Inc.) in chlorobenzene to make a 0.5% (v/v) solution, which was shaken with an equal volume of 0.1 M hydrochloric acid, and then with five successive equal volumes of water. Although about 20% of TOMA-Cl was lost by this treatment, trace impurities and excess of chloride were eliminated, so that the errors in the equilibrium study could be reduced markedly_ The concentration of TOMA-Cl was determined by extractive photometric titration (395 nm) at pH 10 with a standard solution of PAR (4-( 2-pyridylazo)resorcinol). PAR solution was prepared from the purified (recrystallized from DMF) commercial product (Dojindo Labs., Kumamoto) and was standardized against a standard nickel(I1) solution by photometric titration at pH 9.2. TOMA-HR (hereafter, a neutral PAR molecule is abbreviated as HzR) solution in chlorobenzene was prepared by shaking equal volumes of solutions of 5 X lo4 M TOMA-Cl iii chlorobenzene and 5 X 10s3 M PAR in water (pH 10 adjusted with ammonia solution), followed by repeated washing with water (pH 10) until the absorbance of the aqueous phase at 410 nm became less than 0.02. The concentration of the TOMA-HR was determined photometrically by using the molar absorptivity of TOMA-HR in chlorobenzene (E = 3.00 X 10’ 1 mol-’ cm-’ at 395 nm). All the anions investigated were used as their potassium salts (analytical grade). The twice&stilled water used for the equilibrium study was presaturated with chIorobenzene_ Extraction procedure Extractions were done in glass-stoppered 50-ml centrifuge tubes. Portions (ZO-ml each) of TOMA-HR solution in chlorobenzene and of aqueous anion solution (buffered to pH lo), were shaken for 20 min on a mechanical shaker equipped with a constant-temperature (20 +- 0.5%) water circulation device. The tube was then centrifuged for 15 min at 2000 r-pm for phase separation, followed by spectrophotometric measurement of the PAR in the organic and aqueous phases at 395 nm and 410 nm, respectively, to determine the extraction constants. Similar experiments were done to determine the distribution ratio, D, of TOMA-Cl between chlorobenzene and water; known concentrations of TOMA-Cl in chlorobenzene were used. The total concentration of the TOMA species in the aqueous phase after equilibration, was determined on 5-ml aliquots by ion-pair extraction photometry, after treatment with 5 ml of 1 X low3 M PAR solution and 5 ml of chlorobenzene at pH 10. A Hitachi Model 200 recording spectrophotometer equipped with standard l-cm quartz cells was used.
335
Analyses of extraction equilibria The ion-exchange extraction constants between TOMA-Cl and various anions, etx, were determined indirectly by the method of Irving and Damodaran 131, to avoid undue errors in the complicated analysis for each anion. Thus, the ionexchange extraction constants between TOMA-HR and anions, and between TOMA-Cl and HR-, were determined separately, and the values of K$k”were then computed from the two values. This modified method is more convenient than the direct determination, because the concentrations of the distributed species can easily be determined by spectrophotometry. The use of PAR as the indicator anion is advantageous because the dye is readily purified, giving a stable univalent anion with a high molar absorptivity over a wide pH range, and its concentration can be determined accurately by photometric titration with standard metal ion solutions. The ion-exchange extraction constants between TOMA-HR and various anions can be defined as follows; nQHR,
+ X”-,
K::-X
=
= Q,,X, + nHR-,
I&,X1, [HR-l”,/[QHRl”,
lx”-lw
(1)
where Q’ represents the TOMA cation. It can be assumed that the distributions of the ion pairs, QHR and QX, into the aqueous phase, and the distributions of the anions, X- and HR-, into the organic phase, are negligible, and so eqn. (1) can be rewritten:
(l/n) ([QHRL - [QHRI,)” f1
K,H,Rax = CQHRI”, {lx-I, - (l/n) ([QHRI, - [QHRI, 1
(2)
where [QHR], and [X-IT represent the initial concentrations of Q-HR in the organic phase and of the anion in the aqueous phase, respectively. Thus Kr$-x can be obtained from eqn. (2) by determining the concentration of Q-HR in the organic phase photometrically_ However, in order to attain the above stoichiometry, clear phase separation is essential, and this can be attained only by adequate centrifugation. Distribution of TOMA-Cl between chlorobenzene and water The distribution ratio for Q’, + Cl-, = Q-Cl,, can be defined as D =
IQCWUQ’I,
+ [QW,)
(3)
and the ion-pair extraction constant of TOMA-Cl can be defined as K$‘Cl
=
IQCll, [Q’l, [Cl-l,
(4)
Equation (4) can be rewritten by introducing the distribution coefficient, p = [QWAQW,, to give D = l/
(
1
K$$c’_ [Cl-],
1 +p 1
(5)
386
where [CI-1, can be expressed by ([Cl-], - [QCI], - [QCl],). The value of IQCl], is not known, but is very small so that [Cl-], = [Cl-]r - [&Cl],. The plot of log D vs. log [Cl-], should give a straight line with a slope of 1 over the range where the term l/P can beneglected. The value of K$!Zclcan be evaluated from the intercept of this line at log D = 0. RESULTS
AND
Ion-exchange
DISCUSSION
extraction
with TOMA-HR
Tables 1 and 2 show the results obtained in the ion-exchange extraction study with TOMA-HR and various anions in the water-chlorobenzene system. Equation (2) was used to evaluate KpxR-x, and the values were in good agreement over the concentration range investigated. In the case of hexacyanoferrate(III), analysis of the results indicated the value n = 3 in eqn_ (2), i-e. a stoichiometry of TOMA+: Fe( CN),3- = 3:l in the complex extracted. TABLE
1
Equilibrium data for the extraction of chloride, bromide and nitrate ions (X-) by TOMA-PAR
[Q-HR IT
in chlorobenzenesolution
= [x-l,
log
t Q-HRI,
i/;;lw
0.877 1.35 2.45 3.11 3.73 0.283
4.12 3.65 2.55 1.89 1.27 0.717
-3.71 -3.70 -3.88 -3.94 -4.06 -3.74
4.99
0.402
0.598
-3.75
1
2.00 0.998
0.563 0.686
0.437
-3.77 -3.84
1
0.499
O-770
0.314 0.230.
Bromide 5 5 5 5 5
2.00 O-99 0.50 -0.200 0.099
1.57 2.15 2.78 3.47 3.92
3.43 2.85 2.22 1.53 1.08
x lo5
Chloride 5
5 5 5 5 1 1 1
[X-IT x 10’ 99.8
49.9 20.0 9.98 4.99 9.98
x10’
= [QXI,
-3.86 Average -3.80 -2.42 -2.42 -2.45
-2.47 -2.53 Average -2-46
Nitrate 5 5 5 5 3
9.98 4.99 2.00 O-998 O-499
1.20 1.91 2.59 3.24 3.73
3.80 3.09 2.41 1.76 1.27
-1.92 -2.00 -1.95 -2.02 -2.06
Average -1.99
KgyX
387 TABLE
2
Equilibrium data for the extraction of perchlorate, hexacyanoferrate(II1) (X-) by TOMA-PAR in chlorobenzene solution
CQHR x 105
IT
[X-IT x 105
w-1, x lo5
[QHRI,
[HR-I,
= [QXI,
and iodide ions
log K:$x
x lo5
x lo5
0.32 O-71 0.96 1.58 2.87
4.68 4.29 4.04 3.42 2.13
0.66 0.66 0.70 0.68 0.64 Average 0.67
0.30 0.68 0.92 1.53 2.81
4.70 4.32 4.08 3.47 2.19
0.68 0.68 0.72 0.72 0.74
Perchlorateat20"C 5
19.9
5 5 5
9.95 7-46
5
2.49
4.98
Perchlorateat50"C 5 19.9 5 9.95 5 7.46 5 4.98 5 2.49
15.2
5.66 3.42 1.56 0.36
15.2 5.63 3.38 1.51 0.30
Average 0.7 1
Hexacyanoferrate(ZZZ)a 18.82 5 20 5 10 9.01 5 4.18 5.0 5 1.37 2.0 5 0.471 1.0
2.18 2-40 2.72 3-18 3.45
2.82 2.60 2.28 1.82 1.55
Zodideb 5 5 5 5 5
1.01 1.80 2.51 3.19 3.93
3.99
5.00 2.00 1.00 0.50 0.20
46.0 16.8 7.51 3.19 0.93
3.20 2.49 1.81 1.07
-0.97 -0.91 -0.97 -1.08 -1.00 Average -0.99
-0.47 -0.47 -0.48 -0.49 -0.50 Average -0.48
aIn this case [HR-1, = 3[QX],. bFor iodide, [I-IT was 10’ M instead of lo-
M.
The ion pair, TOMA - Fe(CN), showed an absorption maximum at 420 nm (e = lo3 1 mol-’ cm-‘) in chlorobenzene. However, the photometric error for TOMA - HR caused by this species did not exceed 1% under the experimental conditions shown in Table 2, so that corrections were not made in the analysis of the results. Distribution of TOMA-Cl between water and chlorobenzene The ion-pair extraction constant of TOMA-Cl, K!SSol>was evaluated as described under Experimental, by plotting log D vs. log [Cl-],. Though the plots showed some scatter (Fig. l), a nearly straight line of slope 1 was obtained
388
Fig. 1. log D vs. log [Cl-] plots for the distribution of TOMA-Cl.
in the log [Cl-], range -2.3 to -3.8. The plots deviated considerably from the straight line at lower concentrations, probably because the amount of species concentrated at the liquid-liquid interface cannot be neglected, as [Q]r is also small at low concentrations. The value of lo4 for KEGS’is slightly lower than that obtained for tetradecyldimethylbenzylammonium chloride (TDBA-Cl) in a water-chloroform system (Kzgcl = lo’-’ * ) [ 6] . Selectivity
for ion-exchange
extraction
Table 3 summarises the results of Tables 1 and 2. The values of Kgkx are the ion-exchange extraction constant of TOMA-Cl for various anions, and were calculated from the equation K$$X = [QX],
[Cl-],/[QCl],
The values of K$$rare TABLE
IX-],
= K::-X
(K::-c’)-l
(6)
the ion-pair extraction constant of TOMA’
and various
3
Equilibrium constants for the extraction of anions from aqueous solution by TOMA in chlorobenzene at 20°C X ClBrNO,IHRc10,Fe(CN),‘-
log KF:-x -3-80 -2.46 -1.99 -0.48
aData for TDBA-chlorofotm
log K$!kx
log K$$
(TDBA)a
0 1.34 1.81 3.32 3.80 4.47 10.41
4.00 5.34 5.81 7.32 7.80 8.47 22.41
(5.11) (5.93)
system [ 7 ] _
(7.27) (7.31) (7.40)
salts
389
anions (X-), and were calculated from the following equation with the observed value of K$$l= 104.00:
K$__X= [QX],/[Q+],
[X-l,
= K:kx K$$’
(7)
The corresponding values for TDBA-Cl in the water-chloroform system [ ‘71 are included in Table 3 for comparison_ The order of anion selectivity of TOMA is ClO, > I- > NO3- > Br- > Cl% so*2- which is similar to that of TDBA. This order, except for the nitrate ion, is also found in ion-pair extraction with tris (l,lO-phenanthroline)iron( II) in nitrobenzene [ 81 or with tris(8-quinolinol)zinc(II) in chloroform [9] . These orders are readily interpreted by the well known working hypothesis that the extraction of anions is favoured by increase in size and decrease in charge. This hypothesis cannot be extended to the hexacyanoferrate(II1) ion, because the selectivity order is Fe(CN),3- > ClO,- in the TOMA-Cl--chlorobenzene system. However, in a similar experiment with the tetrahexylammonium (THA’) salt in MIBK, Irving and Damodaran [3] found that the order of selectivity was M(CN)2- > C104- % M(CN)42- % Fe(CN),3-, and were unable to extract Fe(CN),3- with Erdman’s salt of THA. This order accords well with the above hypothesis. Irving and Damodaran also found, in their experiments on the extraction of EDTA complexes of iron(II1) and vanadium(V) with TOMA-Cl in dichloroethane, that the selectivity order was FeY(OH)23> FeY(OH)*-> Fey-and V02Y3-> V02HY2-. Thus, they were able to extract relatively large and highly charged anions with TOMA-Cl in dichloroethane. Reviewing these results, it seems likely that anion selectivity in ion-exchange extraction is strongly dependent on the kind of the quaternary ammonium ion and the solvent used. It is interesting to note that the Kf&Xvahe of TOMA-Cl is an order of magnitude smaller than that of TDBA-Cl, whereas Ks2x of TOMA-CIOa is one order larger than that of TDBA-ClO,. This means that the anion selectivity of TOMA is much greater than that of TDBA, indicating that the order of K$ix depends not only on the difference in free energy among anions in the aqueous phase, but also on the structural difference between TOMA and TDBA. Any difference between the free energies of TOMA’ and TDBA’ in the aqueous phase would not affect the selectivity order, because it would contribute equally to the K$cx values for each anion. Accordingly, KFcx should be mainly governed by the relative extent of interaction between the solvent molecules and the respective ion pair in both the aqueous and organic phases. One of us (J. I.) acknowledges receipt of a Grant-in-Aid for Encouragement of Scientists (275415) from the Ministry of Education. We also thank Prof. T. Yotsuyanagi of Tohoku University for valuable advice on the TDBAchloroform system.
390 REFERENCES 1 2 3 4 5 6 7 8 9
R. Kunin and A_ G_ Winger, Angew. Chem. Intern. Ed. Engl., 1 (1962) 149. H. Green, Talanta, 20 (1973) 139_ H. M. N. H. Irving and A. D. Damodaran, Anal. Chim. Acta, 53 (1971) 267. H. M. N. H. Irving and R. H. Al-Jarrah, Anal. Chim. Acta, 74 (1975) 321. J. Itoh, T. Yano, H. Kobayashi and K. Ueno, Bunseki Kagaku, 27 (1978) 602. H_ Hoshino, T. Yotsuyanagi and K. Aomura, Anal. Chim. Acta, 83 (1976) 743. T. Yotsuyanagi and H. Hoshino, Bunseki, (1976) 743. Y. Yarnamoto, Bunseki Kagaku, 21 (1972) 418. E. Sekido, Y. Yoshimura and Y. Masuda, J. Inorg. Nucl. Chem., 38 (1976) 1183,
1187.
Analytica
-
Printed in The Netherlands
LIQUID ION-EXCHANGE EXTRACTION STUDY OF HEXACYANOFERRATE(II1) WITH TRIOCTYLMETHYLAMMONIUM CHLORIDE (ALIQUAT-336)t
JUN’ICHI Department
ITOH**,
HIROSHI
of Organic
KOBAYASHI***
Synthesis,
Faculty
and KEIHEI UENO*
of Engineering,
Kyushu
University,
Fukuoka
8 I2
(Japan) (Received 4th July 1978)
SUMMARY Liquid-liquid ion-exchange extraction of various anions including hexacyanoferrate( III) with a chlorobenzene solution of trioctylmethylammonium chloride (TOMA-CI; Aliquat-336 chloride) is described. The ion-pair extraction constant of TOMA-Cl (Kzicl = 104) and the ion-exchange extraction constants of TOMA-Cl for each anion (K$kx) are reported_ The order of selectivity of anion extraction is Fe(CN),3-(log Kzix = 22.41) > ClO,- (8.47) > PAR-(7.80) > I-(7.32) > NO,-(5.81) > Br-(5.34) > Cl-(4.00).
Liquid ion-exchange extractions of anions with long-chain tertiary amines and quatemary ammonium salts have been widely used as separation processes in industry as well as in analytical chemistry [ 1,2]. Irving and Damodaran [ 31 were unable to extract hexacyanoferrate( III) and hexacyanoferrate( II) ions in their ion-exchange extraction study on various metal cyanides with tetrahexylammonium salts in MIBK. However, in their later work [4] on the ion-exchange extraction of anionic EDTA complexes with Aliquat-336 in dichloroethane, they successfully extracted multivalent anionic complexes such as FeY(OH)23- and V02Y3-. Qualitatively, the extraction of anions should be favoured by decrease of hydrophilicity, i.e. by increase in size and decrease in charge of the anions, but these results could not be explained on this basis. The extraction of hexacyanoferrate(II1) with Aliquat-336 in chlorobenzene is successful [ 51, though this would not be expected from the results with the tetrahexylammonium salt-MIBK system. This paper reports on the liquid ion-exchange extraction of anions of various charges with Aliquat-336 chloride (trioctylmethylammonium chloride; TOMA-Cl) in chlorobenzene, and describes an attempt to elucidate the factors governing the selectivity of the anion extraction.
tcontribution No. 495 from the Department of Organic Synthesis, Kyushu University. **Present address: Kitami Institute of Technology, Kitami 090. ***Present address: Research Institute for Industrial Science, Kyushu University, Fukuoka 812.
334 EXPERIMENTAL
Reagents TOMA-Cl solution was prepared by dissolving a suitable amount of Aliquat336 chloride (kindly donated by General Mills Inc.) in chlorobenzene to make a 0.5% (v/v) solution, which was shaken with an equal volume of 0.1 M hydrochloric acid, and then with five successive equal volumes of water. Although about 20% of TOMA-Cl was lost by this treatment, trace impurities and excess of chloride were eliminated, so that the errors in the equilibrium study could be reduced markedly_ The concentration of TOMA-Cl was determined by extractive photometric titration (395 nm) at pH 10 with a standard solution of PAR (4-( 2-pyridylazo)resorcinol). PAR solution was prepared from the purified (recrystallized from DMF) commercial product (Dojindo Labs., Kumamoto) and was standardized against a standard nickel(I1) solution by photometric titration at pH 9.2. TOMA-HR (hereafter, a neutral PAR molecule is abbreviated as HzR) solution in chlorobenzene was prepared by shaking equal volumes of solutions of 5 X lo4 M TOMA-Cl iii chlorobenzene and 5 X 10s3 M PAR in water (pH 10 adjusted with ammonia solution), followed by repeated washing with water (pH 10) until the absorbance of the aqueous phase at 410 nm became less than 0.02. The concentration of the TOMA-HR was determined photometrically by using the molar absorptivity of TOMA-HR in chlorobenzene (E = 3.00 X 10’ 1 mol-’ cm-’ at 395 nm). All the anions investigated were used as their potassium salts (analytical grade). The twice&stilled water used for the equilibrium study was presaturated with chIorobenzene_ Extraction procedure Extractions were done in glass-stoppered 50-ml centrifuge tubes. Portions (ZO-ml each) of TOMA-HR solution in chlorobenzene and of aqueous anion solution (buffered to pH lo), were shaken for 20 min on a mechanical shaker equipped with a constant-temperature (20 +- 0.5%) water circulation device. The tube was then centrifuged for 15 min at 2000 r-pm for phase separation, followed by spectrophotometric measurement of the PAR in the organic and aqueous phases at 395 nm and 410 nm, respectively, to determine the extraction constants. Similar experiments were done to determine the distribution ratio, D, of TOMA-Cl between chlorobenzene and water; known concentrations of TOMA-Cl in chlorobenzene were used. The total concentration of the TOMA species in the aqueous phase after equilibration, was determined on 5-ml aliquots by ion-pair extraction photometry, after treatment with 5 ml of 1 X low3 M PAR solution and 5 ml of chlorobenzene at pH 10. A Hitachi Model 200 recording spectrophotometer equipped with standard l-cm quartz cells was used.
335
Analyses of extraction equilibria The ion-exchange extraction constants between TOMA-Cl and various anions, etx, were determined indirectly by the method of Irving and Damodaran 131, to avoid undue errors in the complicated analysis for each anion. Thus, the ionexchange extraction constants between TOMA-HR and anions, and between TOMA-Cl and HR-, were determined separately, and the values of K$k”were then computed from the two values. This modified method is more convenient than the direct determination, because the concentrations of the distributed species can easily be determined by spectrophotometry. The use of PAR as the indicator anion is advantageous because the dye is readily purified, giving a stable univalent anion with a high molar absorptivity over a wide pH range, and its concentration can be determined accurately by photometric titration with standard metal ion solutions. The ion-exchange extraction constants between TOMA-HR and various anions can be defined as follows; nQHR,
+ X”-,
K::-X
=
= Q,,X, + nHR-,
I&,X1, [HR-l”,/[QHRl”,
lx”-lw
(1)
where Q’ represents the TOMA cation. It can be assumed that the distributions of the ion pairs, QHR and QX, into the aqueous phase, and the distributions of the anions, X- and HR-, into the organic phase, are negligible, and so eqn. (1) can be rewritten:
(l/n) ([QHRL - [QHRI,)” f1
K,H,Rax = CQHRI”, {lx-I, - (l/n) ([QHRI, - [QHRI, 1
(2)
where [QHR], and [X-IT represent the initial concentrations of Q-HR in the organic phase and of the anion in the aqueous phase, respectively. Thus Kr$-x can be obtained from eqn. (2) by determining the concentration of Q-HR in the organic phase photometrically_ However, in order to attain the above stoichiometry, clear phase separation is essential, and this can be attained only by adequate centrifugation. Distribution of TOMA-Cl between chlorobenzene and water The distribution ratio for Q’, + Cl-, = Q-Cl,, can be defined as D =
IQCWUQ’I,
+ [QW,)
(3)
and the ion-pair extraction constant of TOMA-Cl can be defined as K$‘Cl
=
IQCll, [Q’l, [Cl-l,
(4)
Equation (4) can be rewritten by introducing the distribution coefficient, p = [QWAQW,, to give D = l/
(
1
K$$c’_ [Cl-],
1 +p 1
(5)
386
where [CI-1, can be expressed by ([Cl-], - [QCI], - [QCl],). The value of IQCl], is not known, but is very small so that [Cl-], = [Cl-]r - [&Cl],. The plot of log D vs. log [Cl-], should give a straight line with a slope of 1 over the range where the term l/P can beneglected. The value of K$!Zclcan be evaluated from the intercept of this line at log D = 0. RESULTS
AND
Ion-exchange
DISCUSSION
extraction
with TOMA-HR
Tables 1 and 2 show the results obtained in the ion-exchange extraction study with TOMA-HR and various anions in the water-chlorobenzene system. Equation (2) was used to evaluate KpxR-x, and the values were in good agreement over the concentration range investigated. In the case of hexacyanoferrate(III), analysis of the results indicated the value n = 3 in eqn_ (2), i-e. a stoichiometry of TOMA+: Fe( CN),3- = 3:l in the complex extracted. TABLE
1
Equilibrium data for the extraction of chloride, bromide and nitrate ions (X-) by TOMA-PAR
[Q-HR IT
in chlorobenzenesolution
= [x-l,
log
t Q-HRI,
i/;;lw
0.877 1.35 2.45 3.11 3.73 0.283
4.12 3.65 2.55 1.89 1.27 0.717
-3.71 -3.70 -3.88 -3.94 -4.06 -3.74
4.99
0.402
0.598
-3.75
1
2.00 0.998
0.563 0.686
0.437
-3.77 -3.84
1
0.499
O-770
0.314 0.230.
Bromide 5 5 5 5 5
2.00 O-99 0.50 -0.200 0.099
1.57 2.15 2.78 3.47 3.92
3.43 2.85 2.22 1.53 1.08
x lo5
Chloride 5
5 5 5 5 1 1 1
[X-IT x 10’ 99.8
49.9 20.0 9.98 4.99 9.98
x10’
= [QXI,
-3.86 Average -3.80 -2.42 -2.42 -2.45
-2.47 -2.53 Average -2-46
Nitrate 5 5 5 5 3
9.98 4.99 2.00 O-998 O-499
1.20 1.91 2.59 3.24 3.73
3.80 3.09 2.41 1.76 1.27
-1.92 -2.00 -1.95 -2.02 -2.06
Average -1.99
KgyX
387 TABLE
2
Equilibrium data for the extraction of perchlorate, hexacyanoferrate(II1) (X-) by TOMA-PAR in chlorobenzene solution
CQHR x 105
IT
[X-IT x 105
w-1, x lo5
[QHRI,
[HR-I,
= [QXI,
and iodide ions
log K:$x
x lo5
x lo5
0.32 O-71 0.96 1.58 2.87
4.68 4.29 4.04 3.42 2.13
0.66 0.66 0.70 0.68 0.64 Average 0.67
0.30 0.68 0.92 1.53 2.81
4.70 4.32 4.08 3.47 2.19
0.68 0.68 0.72 0.72 0.74
Perchlorateat20"C 5
19.9
5 5 5
9.95 7-46
5
2.49
4.98
Perchlorateat50"C 5 19.9 5 9.95 5 7.46 5 4.98 5 2.49
15.2
5.66 3.42 1.56 0.36
15.2 5.63 3.38 1.51 0.30
Average 0.7 1
Hexacyanoferrate(ZZZ)a 18.82 5 20 5 10 9.01 5 4.18 5.0 5 1.37 2.0 5 0.471 1.0
2.18 2-40 2.72 3-18 3.45
2.82 2.60 2.28 1.82 1.55
Zodideb 5 5 5 5 5
1.01 1.80 2.51 3.19 3.93
3.99
5.00 2.00 1.00 0.50 0.20
46.0 16.8 7.51 3.19 0.93
3.20 2.49 1.81 1.07
-0.97 -0.91 -0.97 -1.08 -1.00 Average -0.99
-0.47 -0.47 -0.48 -0.49 -0.50 Average -0.48
aIn this case [HR-1, = 3[QX],. bFor iodide, [I-IT was 10’ M instead of lo-
M.
The ion pair, TOMA - Fe(CN), showed an absorption maximum at 420 nm (e = lo3 1 mol-’ cm-‘) in chlorobenzene. However, the photometric error for TOMA - HR caused by this species did not exceed 1% under the experimental conditions shown in Table 2, so that corrections were not made in the analysis of the results. Distribution of TOMA-Cl between water and chlorobenzene The ion-pair extraction constant of TOMA-Cl, K!SSol>was evaluated as described under Experimental, by plotting log D vs. log [Cl-],. Though the plots showed some scatter (Fig. l), a nearly straight line of slope 1 was obtained
388
Fig. 1. log D vs. log [Cl-] plots for the distribution of TOMA-Cl.
in the log [Cl-], range -2.3 to -3.8. The plots deviated considerably from the straight line at lower concentrations, probably because the amount of species concentrated at the liquid-liquid interface cannot be neglected, as [Q]r is also small at low concentrations. The value of lo4 for KEGS’is slightly lower than that obtained for tetradecyldimethylbenzylammonium chloride (TDBA-Cl) in a water-chloroform system (Kzgcl = lo’-’ * ) [ 6] . Selectivity
for ion-exchange
extraction
Table 3 summarises the results of Tables 1 and 2. The values of Kgkx are the ion-exchange extraction constant of TOMA-Cl for various anions, and were calculated from the equation K$$X = [QX],
[Cl-],/[QCl],
The values of K$$rare TABLE
IX-],
= K::-X
(K::-c’)-l
(6)
the ion-pair extraction constant of TOMA’
and various
3
Equilibrium constants for the extraction of anions from aqueous solution by TOMA in chlorobenzene at 20°C X ClBrNO,IHRc10,Fe(CN),‘-
log KF:-x -3-80 -2.46 -1.99 -0.48
aData for TDBA-chlorofotm
log K$!kx
log K$$
(TDBA)a
0 1.34 1.81 3.32 3.80 4.47 10.41
4.00 5.34 5.81 7.32 7.80 8.47 22.41
(5.11) (5.93)
system [ 7 ] _
(7.27) (7.31) (7.40)
salts
389
anions (X-), and were calculated from the following equation with the observed value of K$$l= 104.00:
K$__X= [QX],/[Q+],
[X-l,
= K:kx K$$’
(7)
The corresponding values for TDBA-Cl in the water-chloroform system [ ‘71 are included in Table 3 for comparison_ The order of anion selectivity of TOMA is ClO, > I- > NO3- > Br- > Cl% so*2- which is similar to that of TDBA. This order, except for the nitrate ion, is also found in ion-pair extraction with tris (l,lO-phenanthroline)iron( II) in nitrobenzene [ 81 or with tris(8-quinolinol)zinc(II) in chloroform [9] . These orders are readily interpreted by the well known working hypothesis that the extraction of anions is favoured by increase in size and decrease in charge. This hypothesis cannot be extended to the hexacyanoferrate(II1) ion, because the selectivity order is Fe(CN),3- > ClO,- in the TOMA-Cl--chlorobenzene system. However, in a similar experiment with the tetrahexylammonium (THA’) salt in MIBK, Irving and Damodaran [3] found that the order of selectivity was M(CN)2- > C104- % M(CN)42- % Fe(CN),3-, and were unable to extract Fe(CN),3- with Erdman’s salt of THA. This order accords well with the above hypothesis. Irving and Damodaran also found, in their experiments on the extraction of EDTA complexes of iron(II1) and vanadium(V) with TOMA-Cl in dichloroethane, that the selectivity order was FeY(OH)23> FeY(OH)*-> Fey-and V02Y3-> V02HY2-. Thus, they were able to extract relatively large and highly charged anions with TOMA-Cl in dichloroethane. Reviewing these results, it seems likely that anion selectivity in ion-exchange extraction is strongly dependent on the kind of the quaternary ammonium ion and the solvent used. It is interesting to note that the Kf&Xvahe of TOMA-Cl is an order of magnitude smaller than that of TDBA-Cl, whereas Ks2x of TOMA-CIOa is one order larger than that of TDBA-ClO,. This means that the anion selectivity of TOMA is much greater than that of TDBA, indicating that the order of K$ix depends not only on the difference in free energy among anions in the aqueous phase, but also on the structural difference between TOMA and TDBA. Any difference between the free energies of TOMA’ and TDBA’ in the aqueous phase would not affect the selectivity order, because it would contribute equally to the K$cx values for each anion. Accordingly, KFcx should be mainly governed by the relative extent of interaction between the solvent molecules and the respective ion pair in both the aqueous and organic phases. One of us (J. I.) acknowledges receipt of a Grant-in-Aid for Encouragement of Scientists (275415) from the Ministry of Education. We also thank Prof. T. Yotsuyanagi of Tohoku University for valuable advice on the TDBAchloroform system.
390 REFERENCES 1 2 3 4 5 6 7 8 9
R. Kunin and A_ G_ Winger, Angew. Chem. Intern. Ed. Engl., 1 (1962) 149. H. Green, Talanta, 20 (1973) 139_ H. M. N. H. Irving and A. D. Damodaran, Anal. Chim. Acta, 53 (1971) 267. H. M. N. H. Irving and R. H. Al-Jarrah, Anal. Chim. Acta, 74 (1975) 321. J. Itoh, T. Yano, H. Kobayashi and K. Ueno, Bunseki Kagaku, 27 (1978) 602. H_ Hoshino, T. Yotsuyanagi and K. Aomura, Anal. Chim. Acta, 83 (1976) 743. T. Yotsuyanagi and H. Hoshino, Bunseki, (1976) 743. Y. Yarnamoto, Bunseki Kagaku, 21 (1972) 418. E. Sekido, Y. Yoshimura and Y. Masuda, J. Inorg. Nucl. Chem., 38 (1976) 1183,
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