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Acta Chim. Slov. 2008, 55, 430–433
Short communication
Solvent Extraction of Ba2+, Pb2+ and Cd2+ into Nitrobenzene by Using Strontium Dicarbollylcobaltate in the Presence of Tetraethyl p-tert-Butylcalix[4]arene
Tetraacetate
Emanuel Makrlík,a,* Petr Vanˇurab and Pavel Seluckýc
a Faculty of Applied Sciences, University of West Bohemia, Husova 11, 306 14 Pilsen, Czech Republic. b Institute of Chemical Technology, Technická 5, 166 28 Prague 6, Czech Republic
c Nuclear Research Institute, 250 68 Re`, Czech Republic
ˇ
* Corresponding author: E-mail: makrlik@centrum.cz Received: 02-10-2007
Abstract
From extraction experiments and y-activity measurements, the exchange extraction constants corresponding to the general equilibrium M2+(aq) + SrL2+(nb) <s=> ML2+(nb) + Sr2+(aq) taking place in the two-phase water-nitrobenzene system (M2+ = Ba2+, Pb2+, Cd2+; L = tetraethyl p-tert-butylcalix[4]arene tetraacetate; aq = aqueous phase, nb = nitrobenzene phase) were evaluated. Further, the stability constants of the ML2+ complexes in water saturated nitrobenzene were calculated; they were found to increase in the order Ba2+ < Cd2+ < Pb2+.
Keywords: Barium, lead, cadmium, strontium dicarbollylcobaltate, nitrobenzene, calix[4]arene, extraction and stability constants
1. Introduction
Calixarenes (products of the base condensation reaction between p – substituted phenols and formaldehyde) and their lower rim as well as upper rim derivatives have found widespread applications.1,2
The presence of a hydrophobic cavity (able to host neutral species) besides the hydrophilic one (able to interact with ionic species) confers outstanding properties to ca-lix[4]arene derivatives in their “cone” conformation relative to macrocycles such as crown ethers and cryptands. Calix[4]arenes containing ester and ketone functional groups at the lower rim have shown pronounced selectivity for alkali – metal cations in different media, particularly in acetonitrile.3,4
In the present work, stability constants of Ba2+, Pb2+ and Cd2+ complexes of tetraethyl p-tert-butylcalix[4]arene tetraacetate (see Scheme 1) in the organic phase of the water – nitrobenzene extraction system were determined.
2. Experimental
Tetraethyl p-tert-butylcalix[4]arene tetraacetate, called
also sodium ionophore X, was purchased from Fluka,
Buchs, Switzerland. Cesium dicarbollylcobaltate, Cs-ˇ DCC, was supplied by Katchem, Re`, Czech Republic. A
nitrobenzene solution of hydrogen dicarbollylcobaltate (HDCC) was prepared from CsDCC by the method described in Reference 5. The other chemicals used (Lache-ma, Brno, Czech Republic) were of reagent grade purity. The equilibration of the nitrobenzene solution of HDCC with stoichiometric Sr(OH)2, which was dissolved in an aqueous solution of Sr(NO3)2 (0.2 mol L–1), yielded the corresponding Sr(DCC)2 solution in nitrobenzene. The ra-dionuclide 85Sr2+ (DuPont, Belgium) was of standard ra-diochemical purity.
The extraction experiments were carried out in 10 mL glass test-tubes covered with polyethylene stoppers: 2 mL of an aqueous solution of M(NO3)2 (M2+ = Ba2+, Pb2+, Cd2+) of the concentration in the range from 1 × 10–4 to 1
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are given by definitions
Scheme 1. Structural formula of tetraethyl p-tert-butylcalix[4]arene tetraacetate.
× 10–3 mol L-1 and microamounts of 85Sr2+ were added to 2 mL of a nitrobenzene solution of tetraethyl p-tert-butyl-calix[4]arene tetraacetate and Sr(DCC)2, whose initial concentrations varied also from 1 × 10–4 to 1 × 10–3 mol L-1 (in all experiments, the initial concentration of tetraethyl p-tert-butylcalix[4]arene tetraacetate in nitrobenzene, CL, was always equal to the initial concentration of Sr(DCC)2 in this medium, CiSnr,(nDbCC)2). The test-tubes filled with the solutions were shaken for 12 hours at 25 ± 1 °C, using a laboratory shaker. Then the phases were separated by centrifugation. Afterwards, 1 mL samples were taken from each phase and their y-activities were measured using a well-type NaI(Tl) scintillation detector connected to a y-analyzer NK/350 (Gamma, Budapest, Hungary).
The equilibrium distribution ratio of strontium, DSr, was determined as the ratio of the measured radioactivities of 85Sr2+ in the nitrobenzene and aqueous samples.
3. Results and Discussion
Regarding the results of previous papers,6–10 the two-phase water- M(NO3)2 (M2+ = Ba2+, Pb2+, Cd2+)-nitroben-zene-Sr(DCC)2 extraction system can be described by the following general equilibrium
(1)
with the corresponding exchange extraction constant Kex(M2+, Sr2+); aq and nb denote the presence of the species in the aqueous and nitrobenzene phases, respectively. The changes of the standard Gibbs energies corresponding to the transfer of the ions M2+ (M2+ = Ba2+, Pb2+, Cd2+) and Sr2+ from the aqueous into the nitrobenzene phase, expressed by
(2)
(3)
(4)
(5)
Here µ0 – s are the standard chemical potentials of the ions M2+ and Sr2+ in the two phases concerned.
The individual extraction constants KiM2+ (M2+ = Ba2+, Pb2+, Cd2+) and KiS r2+ for the divalent metal cations in the water-nitrobenzene extraction system are defined by6
(6)
(7)
Combination of the relation
(8)
corresponding to Equilibrium (1) with Eqs (4)-(7) yields
logK^M"1, Sr~' ) = logK' :, -logK' ,.         (9)
Knowing the values log KiBa2+ = -10.5,9 log KPb2+ = -10.6,10 log KiCd2+ = -11.5,10 and log KiSr2+ = -10.7, which was inferred from References 6 and 8, the single exchange extraction constants K (M2+, Sr2+) were simply calculated
ex
on the basis of Eq. (9). The corresponding data are given in Table 1.
Table 1. Equilibrium data for the M2+ and ML2+ cations in the two-phase water- nitrobenzene extraction system at 25 °C (M2+ = Sr2+, Ba2+, Pb2+, Cd2+; L = tetraethyl p-tert-butylcalix[4]arene tetraacetate; for the meaning of the constants see text).
Quantity	Sr2+	Ba2+	Pb2+	Cd2+
log KMi 2+	-10.7a	-10.5b	-10.6c	–11.5c
log Kex(M2+, Sr2+)d	-	0.2	0.1	-0.8
log Kex(M2+, SrL2+)e	-	0.6	1.6	-1.2
log ßnb(ML2+)f	6.2g	6.6	7.7	5.8
a Inferred from Refs 6 and 8. b Ref. 9. c Ref. 10.
d
Calculated from Eq. (9) using data from Refs 6 and 8–10. e Calculated from Eq. (17).
f Calculated from Eq. (18) using data from Refs 6, 8–10 and 14. g Ref. 14.
With respect to previous results,11–13 the two-phase wa-ter-M(NO3)2 (M2+ = Ba2+, Pb2+ Cd2+)-nitrobenzene-L (L = tetraethyl      p-tert-butylcalix[4]arene      tetraacetate)-
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Acta Chim. Slov. 2008, 55, 430–433
Sr(DCC)2 extraction systems (see Experimental), chosen for determination of stability of the ML2+ complexes in nitrobenzene saturated with water, can be characterized by the main chemical equilibrium
K„(M\SrL2') with the general equilibrium constant Kex(M2+, SrL2+): [ML2l]„b[Sr2']aq
(10)
Ke(MJ-.SrLJ-):
[M^]aq[SrL:+]nb
(11)
It is necessary to emphasize that tetraethyl p-tert-butyl-calix[4]arene tetraacetate is a considerably hydrophobic ligand, practically present in the nitrobenzene phase only, where it forms the very stable complexes ML2+ with the mentioned divalent cations.
Taking into account the conditions of electroneutrality in the organic and aqueous phases of the system under study
(12)
(13)
the mass balances of the divalent cations studied at equal volumes of the nitrobenzene and aqueous phases
(14) (15)
as well as the measured equilibrium distribution ratio of strontium
(16)
then combination of Relations (11) – (16) gives the final expression for the exchange extraction constant Kex(M2+, SrL2+):
(17)
where CMin,(aNp O3)2 is the initial concentration of M(NO3)2 in the aqueous phase of the system under consideration.
In this study, from the extraction experiments and ?-activity measurements (see Experimental) by means of Eq.
(17), the logarithms of the constants Kex(M2+, SrL2+) were determined as reviewed in Table 1.
Moreover, with regard to References 11 and 13, for the extraction constants Kex(M2+, SrL2+) and Kex(M2+, SrL2+) defined above, as well as for the stability constants of the complexes ML2+ and SrL2+ in nitrobenzene saturated with water, denoted by ßnb(ML2+)and ßnb(SrL2+), respectively, one gets
Using the constants log K (M2+, Sr2+) and log K (M2+,
 ex                                                   ex
SrL2+) given in Table 1, the value log ßnb(SrL2+) = 6.2, determined from the distribution of strontium picrate in the water-nitrobenzene system containing also tetraethyl p-tert-butylcalix[4]arene tetraacetate,14 and applying Eq. (18), we obtain the stability constants of the complexes ML2+ (M2+ = Ba2+, Pb2+, Cd2+) in nitrobenzene saturated with water. These data are also summarized in Table 1. Thus, the ßnb(ML2+) values from this table indicate that the stability of the complex cation ML2+ in water saturated nitrobenzene increases in the Cd2+ < Sr2+ < Ba2+ < Pb2+ order. On the other hand, in the acetonitrile medium Danil de Namor et al.4 found that the stability of the mentioned complex species increases in the series Cd2+ < Ba2+ < Sr2+ < Pb2+ as follows from Table 2.
Table 2. Stability constants of the ML2+ cations (M2+ = Sr2+, Ba2+, Pb2+, Cd2+; L = tetraethyl p-tert-butylcalix[4]arene tetraacetate) in acetonitrile at 25 °C (taken from Ref. 4).
M2+	Sr2+	Ba2+	Pb2+	Cd2+
log ßnb(ML2+)	5.35	4.34	7.39	4.08
4. Acknowledgement
The present work was supported by the Czech Ministry of Education, Youth and Sports, Projects MSM 4977751303 and MSM 6076137307.
5. References
1. V. Böhmer, Angew. Chem., Int. Ed. Engl. 1995, 34, 713–745.
2. C. D. Gutsche, Calixarenes Revisited. The Royal Society of Chemistry, Cambridge, 1998.
3. A. F. Danil de Namor, R. M. Cleverly, M. L. Zapata – Or-machea, Chem. Rev. 1998, 98, 2495–2525.
4. A. F. Danil de Namor, S. Chahine, D. Kowalska, E. E. Castellano, O. E. Piro, J. Am. Chem. Soc. 2002, 124, 12824– 12836.
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5. E. Makrlík, Collect. Czech. Chem. Commun. 1992, 57, 289– 295.
6. J. Rais, Collect. Czech. Chem. Commun. 1971, 36, 3253– 3262.
7. J. Rais, P. Selucký, M. Kyr{, J. Inorg. Nucl. Chem. 1976, 38, 1376–1378.
8. P. Vanˇura, E. Makrlík, J. Rais, M. Kyr{, Collect. Czech. Chem. Commun. 1982, 47, 1444–1464.
9. I. Podzimek, M. Kyr{ , J. Rais, J. Inorg. Nucl. Chem. 1980, 42, 1481–1486.
10. E. Makrlík, P. Vanˇura, unpublished results.
11. E. Makrlík, J. Hálová, M. Kyr{, Collect. Czech. Chem. Commun. 1984, 49, 39–44.
12. E. Makrlík, P. Vanˇura, J. Radioanal. Nucl. Chem. 2006, 268, 155–157.
13. E. Makrlík, P. Vanˇura, J. Radioanal. Nucl. Chem. 1996, 214, 339–346.
14. P. Vanˇura, E. Makrlík, P. Selucký, unpublished results..
Povzetek
 Z ekstrakcijo in meritvami y-aktivnosti smo dolo~ili konstante ekstrakcije v sistemu dveh faz (voda/nitrobenzen), ki jo ponazorimo z ravnote`jem M2+(aq) + SrL2+(nb) <s=> ML2+(nb) + Sr2+(aq); (M2+ = Ba2+, Pb2+, Cd2+; L = tetraetil-p-tert-bu-til-kaliks[4]aren tetraacetat; aq = vodna faza, nb = nitrobenzen). Ocenili smo tudi konstante stabilnosti kompleksov ML2+ v nitrobenzenu nasi~enem z vodo in ugotovili nasledenje zaporedje konstant stabilnosti kompleksov: Ba2+ < Cd2+ < Pb2+.
Makrlík et al.:   Solvent Extraction of Ba2+, Pb2+ and Cd2+ ...