ФИЗИКОХИМИЯ РАСТВОРОВ
УДК 547
METAL-ION RECOGNITION-COMPETITIVE BULK LIQUID MEMBRANE TRANSPORT OF TRANSITION AND POST-TRANSITION METAL CATIONS USING A THIOETHER DONOR ACYCLIC IONOPHORE © 2010 G. H. Rounaghi1, M. H. Arbab-Zavar, E. Fahmideh-Rad, H. Sadeghian
Department of chemistry, Factulty of Sciences, Ferdowsi University ofMashhad, Mashhad, Iran
The competitive bulk liquid membrane transport of Cr3+, Co2+, Cu2+, Zn2+, Cd2+, Ag+ and Pb2+ metal cations with a new synthetic sulfur donor acyclic ligand (pseudo-cyclic ionophore), i.e.1-(2-[(2-hydroxy-3-phenoxypropyl)sulfanyl]ethylsulfanyl)-3-phenoxy-2-propanol; (C20H26O4S2), was examined using some organic solvents as membranes. The membrane solvents include: chloroform (CHCl3), 1,2-dichloroethane (1,2-DCE), dichloromethane (DCM), nitrobenzene (NB), chloroform-nitrobenzene (CHCl3-NB) and chloroform-dichloromethane (CHCl3-DCM) binary mixtures. The transport process was driven by a back flux of protons, maintained by the buffering the source and receiving phases with pH 5 and 3, respectively. The aqueous source phase consisted of a buffer solution (CH3COOH/CH3COONa) at pH = 5 and containing an equimolar mixture of these seven metal cations. The organic phase contained the acyclic ligand, as an ionophore and the receiving phase consisted of a buffer solution (HCOOH/HCOONa) at pH = 3. For these systems that displayed transport behaviour, sole selectivity for Ag+ cation was observed under the employed experimental conditions in this investigation. The amount of Ag+ transported follows the trend: 1,2-DCE > CHCl3 > DCM > NB in the bulk liquid membrane studies. The transport of the metal cations in CHCl3-NB and CHCl3-DCM binary solvents is sensitive to the solvent composition. The influence of the stearic acid, palmitic acid and oleic acid in the membrane phase on the ion transport was also investigated.
Keywords: Bulk liquid membrane transport; 1-(2-[(2-hydroxy-3-phenoxypropyl)sulfanyl] ethylsulfanyl)-3-phenoxy-2-propanol (C20H26O4S2); Cr3+, Co2+, Cu2+, Zn2+, Cd2+, Ag+ and Pb2+ metal cations.
INTRODUCTION
Acyclic polyether (podant) chemistry has received a great deal of attention for many years, and various types of compounds have been synthesized [1—3]. Selective transport of metal cations using acyclic polyethers (po-dants) has long been studied from the viewpoints of selective separation, recovery, volume reduction, and selective instrumental sensor applied in most industrial fields [4—6]. Several studies have focused on determination of the selectivity and efficiency of podant-mediated extraction and transport of metal ions through an organic medium into an aqueous receiving phase [7]. In particular, selective separation of silver ion from industrial waste has been remarkably focused [8, 9]. Sulfur-containing po-dands were reported to show a selective complexation with silver ion over other metal ions [10].
In this study, the transport of Cr3+, Co2+, Cu2+, Zn2+, Cd2+, Ag+ and Pb2+ metal cations with pseudo-cyclic conformation of the organic ligand, 1-(2-[(2-hydroxy-3-phenoxypropyl)sulfanyl] ethylsulfanyl)-3-phenoxy-2-propanol, (Scheme I), as an ion carrier was performed using chloroform (CHCl3), 1,2-dichloroethane (1,2-DCE), dichloromethane (DCM), nitrobenzene (NB), chloroform-nitrobenzene (CHCl3-NB) and chloro-
1 Corresponding author. E-mail: ghrounaghi@yahoo.com
form-dichloromethane (CHCl3-DCM) binary mixtures as liquid membranes. The net result is the transport ofAg+ cation from the aqueous source phase into the aqueous receiving phase across the bulk organic membrane phase. It is well known that sulfur ligands coordinate with transition metal cations as exclusive donor atoms. In this respect, macrocyclic and noncyclic thio compounds have attracted widespread attention owing to the unique properties of these compounds [11].
Scheme I. Structure of C20H26O4S2.
Compared with the solvent extraction, liquid membrane transport for the selective removal, concentration or purification of given metal cations from their mixtures have the advantage that the amount of organic solvents and metal ion complexing agents are markedly reduced. However, despite the biological and industrial importance of silver cation, information about its transport across liquid membranes, in comparison with other transition metal cations is sparse [12—14].
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EXPERIMENTAL
Reagents and solvents: chromium(III) nitrate (BDH), cobalt(II) nitrate (BDH), copper(II) nitrate (BDH), zink(II) nitrate (Merck), cadmium(II) nitrate (Riedel), silver(I) nitrate (Merck), lead(II) nitrate (BDH), sodium acetate (Riedel), sodium hydroxide (Riedel), stearic acid (BDH), palmitic acid (Riedel) and oleic acid (Merck) were used without further purification. Formic acid (Riedel), chloroform (BDH ), 1,2-dichloroethane, dichloromethane, nitrobenzene, acetic acid and nitric acid, potassium carbonate, dimercaptoet-hane, epoxide, benzene, ethylacetate, silica gel 60 F254 (all from Merck) were used with the highest purity. All aqueous solutions were prepared using deionized double distilled water.
Synthesis of 1-(2-[(2-hydroxy-3-phenoxypropyl) sul-fanyl]-3-phenoxy-2-propanol. Synthetic route for the preparation of acyclic polyethers is described in Scheme II. The P,P'-dihydroxydithioethers were prepared by the action of two mole equivalents of epoxides with deporotonated dimercaptoethane which was formed by proton abstracting of carbonate anion under reflux condition and vigorous stirring. The method used
B
B A
C ( D )
Fig. 1. Representation of the bulk type liquid membrane cell used:
A, source phase; B, receiving phase; C, membrane phase; D, magnetic stirrer.
here is a simple, efficient and environmentally friendly procedure with excellent yields, high regioselectivity and need not any organic solvents either for reaction medium or extracting the products. Therefore, the work follows the basic aims which are important to green chemistry [15].
R
47
O
K2CO3 (aq)
HS
SH
R
OH
R
HO
O
O
K2CO3 (aq)
^ / HS
SH
о-
S S O OH HO O
^ //
Scheme II. Synthetic route for preparation of acyclic polyethers.
General procedure for ring opening of epoxides with dimercaptoethane. To a solution of potassium carbonate (50 g, 350 mmol) in water (65 ml) was added dimercaptoethane (13.5 ml, 160 mmol) followed by epoxide (300 mmol). The mixture was refluxed in oil bath while stirring vigorously. The completion of reaction was checked by TLC (silica gel 60 F254, benzene-ethylacetate 50 : 50). After completion, the mixture was cooled and the precipitated products, were filtered, washed with water (3 x 50 ml) and dried in an oven at 50—55° for 4h. White solid (Found: C, 61.13; H, 6.72; S, 16.07. C20H26O4S2 requires C, 60.88; H, 6.64; S, 16.25%); mp 79°C (from carbon tetrachloride); SH 2.39 (2H, br, 2 x OH), 2.71 (2H, dd, J7.2 and 15.5, 2 x CH2S), 2.79 (2H, dd, J4.2 and 17.8, 2 x CH2S), 2.85 (4H, s, SCH2CH2S), 4.04 (2H, dd, J6.2 and 15.8, 2 x CH2O), 4.12 (2H, m, 2 x x CH), 4.15 (2H, dd, J4.1 and 13.7, 2 x CH2O), 6.847.38 (10 H, m, 2 x Ph); 8C 33.10 (2 x t), 35.80 (2 x t), 69.91 (2 x t), 70.92 (2 x d), 114.90 (2 x d), 121.09 (d), 120.74 (2 x d), 159.23 (d); m/z EI 394 (M+), 287 (85%)
C13H19O3S2, 243 (86) C11H15O2S2, 211 (90) C11H15O2S, 75 (100) C6H5 [16].
Apparatus: A Shimadzu AA-670 atomic absorption spectrometer (AAS) was used for measurement of metal ions concentration. The pH measurements were made with a Metrohm 692 pH/ ion meter using a combined glass electrode. A bulk type liquid membrane cell was used in all transport experiments.
Procedure: Bulk liquid membrane(BLM) transport measurements were performed at ambient temperature in a cylindrical glass cell (inside diameter 5 cm) holding a glass tube (inside diameter 2 cm), thus separating the two aqueous phases (Fig. 1). The aqueous source phase (10 ml) and receiving phase (30 ml) were separated by an organic phase (50 ml). The two aqueous i.e. source and receiving phases were floating on the organic membrane phase, respectively. The membrane phase was constantly stirred using a Teflon-coated magnetic bar at 20 rpm. The aqueous source phase consisted of a buffer solution (CH3COOH/CH3COONa) at pH = 5 containing an equimolar mixture of the metal cations (0.01 M). The or-
+
Table 1. Data for seven metal cations competitive transport across organic solvents as bulk liquid membrane with C20H26O4S2 as ligand
Solvent Cr(III) Co(II) Cu(II) Zn(II) Cd(II) Ag(I) Pb(II)
CHCl3
% (Receiving )a _d - - - - 6.05 -
% (membrane )b — 8.32 - - 3.03 13.42 6.01
JM (mol m-2 s-1 )c — - - - - 14.68 -
1,2-DCE
% (Receiving )a - - - - - 6.90 -
% (membrane )b 2.95 4.20 - - - 23.47 4.61
JM (mol m-2 s-1 )c - - - - - 16.74 -
DCM
% (Receiving )a - - - - - 5.86 -
% (membrane )b - 3.21 6.10 - - 22.42 7.45
JM (mol m-2 s-1 )c - - - - - 14.20 -
NB
% (Receiving )a - - - - - 5.64 -
% (membrane )b - 6.06 0.94 - - 19.03 6.07
JM (mol m-2 s-1 )c - - - - - 13.68 -
a Percent of total metal cations in the receiving phase after 24h. b Percent of total metal cations in the membrane phase after 24h. c All flux values are x 10-8.
d The hyphenated symbols mean that the values are about zero or they are with high uncertainties.
ganic phase (liquid membrane) contained the synthetic pseudo-cyclic (acyclic) ionophore (0.001 M) and the receiving phase consisted of a buffer solution (HCOOH/HCOONa) at pH = 3. The pH gradient was used in order to facilitate the transport of the metal ions across the organic membrane by counter transport ofpro-tons. The organic solvents: CHCl3, 1,2-DCE, DCM, NB, CHCl3-NB and CHCl3-DMC binary mixtures were used as membrane phase.
All transport runs were terminated after 24h and the samples were withdrawn from the receiving phase and analyzed for the amount of cation transported measurements using atomic absorption spectroscopy along with a series of standard solutions which were made similarly, in order to convert the ato
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