Palladium(II) extraction by sulfur-containing calix[4,6]arenes from hydrochloric acid solutions

Article abstract of DOI:10.1134/S0036023608110235

The comparison of the extraction properties of calixarenes, thiacalixarenes, and calix[4,6]arene thioethers showed that methyl(thiamethyl) calix[4,6]arenes 3a and 4a have the highest extraction abilities. These extractants rapidly and completely extract p

Full text of DOI:10.1134/S0036023608110235

ISSN 0036-0236, Russian Journal of Inorganic Chemistry, 2008, Vol. 53, No. 11, pp. 1809–1815. © Pleiades Publishing, Ltd., 2008.
Original Russian Text © V.G. Torgov, G.A. Kostin, V.I. Mashukov, T.M. Korda, A.B. Drapailo, O.V. Kas’yan, V.I. Kal’chenko, 2008, published in Zhurnal Neorganicheskoi
Khimii, 2008, Vol. 53, No. 11, pp. 1932–1939.
PHYSICAL CHEMISTRY
OF SOLUTIONS
Palladium(II) Extraction
by Sulfur-Containing Calix[4,6]arenes
from Hydrochloric Acid Solutions
a
a
a
a
b
V. G. Torgov , G. A. Kostin , V. I. Mashukov , T. M. Korda , A. B. Drapailo ,
b
b
O. V. Kas’yan , and V. I. Kal’chenko
a
Nikolaev Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences, pr. Akademika Lavrent’eva 3,
Novosibirsk, 630090 Russia
b
Institute of Organic Chemistry, National Academy of Sciences of Ukraine, Kiev, Ukraine
Received August 14, 2007
Abstract—The comparison of the extraction properties of calixarenes, thiacalixarenes, and
calix[4,6]arene thioethers showed that methyl(thiamethyl)calix[4,6]arenes 3a and 4a have the highest
extraction abilities. These extractants rapidly and completely extract palladium from hydrochloric acid
solutions; regarding distribution factors achieved in the kinetic mode, they three to four orders of mag-
nitude exceed their monodentate analogue, octylbenzyl sulfide (OBnS). Approaches are considered to
enhance palladium extraction via generating mixed palladium species in low-acidity solutions and via
intramolecular catalysis by the protonated oxygen atoms of alkoxy groups in the lower rim. For 1 M HCl,
the kinetic order of diluent effects on palladium extraction was established. The substitution of sulfur
atoms for bridging CH groups was discovered to enhance palladium extraction by calix[4]arene thioet-
2
her 3c.
DOI: 10.1134/S0036023608110235
Extraction of palladium by organic sulfides (dialkyl tions with cHCl > 0.5 mol/L. Available data [9–11]
sulfides and petroleum sulfides) from hydrochloric
solutions is widely used in technologies for processing
of platinum-metal concentrates [1, 2]; in the analytical
chemistry of palladium, silver, and gold [2, 3]; and in
refer to low-acidity solutions (pH 1–3), in which pal-
ladium exists as labile aquachloro complexes.
Compared to monodentate R S, polydentate
2
refining palladium chips for deep decontamination calix[n]arene thioethers acquire new possibilities due
from silver radionuclides [4] in chloride systems. to the chelation and dimensional effects resulting from
The main limitation for use of these extractants is the complex formation: these effects improve the efficiency
low rates of palladium extraction from hydrochloric
solutions. This is due to the low surface-active prop-
erties of organic sulfides and the inertness of the
and selectivity of extraction of precious metals (palla-
dium, silver, and gold) [9–14]. In addition, substitution
of sulfur atoms for bridging CH groups in the macro-
2
2
–
PdCl major species in the substitution of the cyclic platform in calix[n]arene ethers (thiacalix[n]are-
4
extractant for chloride ion. It is known from [5–8] nes) and calix[n]arene thioethers (thiacalix[n]arene
that the zone of the chemical reaction between palla- thioethers) considerably widens the range of potential
dium and R S in heterogeneous systems can be either extractants. Thiacalix[n]arenes have recently generated
2
in one of the conjugate phases or at their interface. great interest in the context of the participation of
Possible approaches to enhancing palladium extrac-
bridging sulfur atoms in chelation during cation-
exchange extraction of many metals, including palla-
dium, silver, and gold, from low-acidity solutions and
also in the context of the feasibility of substitution of
RO group in the upper rim and inhibition of classical
reactions in the upper rim of the thiacalix[n]arene
tion are increasing R S concentration in the starting
2
aqueous phase [5], improving the surface-active
properties of R S [6] and palladium complex species
2
[
7], and introducing anion-exchange additives into
the organic phase to catalyze interfacial transfer of
2
–
PdCl [8]. These ideas were used to study palla- [15−18]. We have not found any data on the extraction
4
dium extraction by macrocyclic calix[4,6]arene thio- properties of thiacalix[n]arene thioethers in the litera-
ethers, which was described for hydrochloric solu- ture.
1
809

1
810
TORGOV et al.
‹
n
R
Y
X
1
1
2
ab
4
4
4
4
4
4
4
6
6
4
C H
H
CH2
S
S
3
7
Y
O
b
·
H
CH3
t-C H
H
H
4
9
a
a
2
3a
·c
n-C H
S
CH2
4
9
[
]n
b
X
n-C H CH SCH
3
3
7
2
b
3·
n-C H CH SC H -n
CH2
3
7
2
4
9
R
b
a
3
4
4
‚
a
n-C H CH SC H CH -p CH
3 7 2 6 4 3
2
CH3
CH SCH
CH2
2
3
·a
CH3
H
CH SC H -n
CH2
2
4
9
5b
CH SC H CH -p S
2
6
4
3
‡
b
c
conformationally mobile; cone; 1,3-alternate
Scheme 1.
In this work, we compare the extraction characteris- absorption (Hitachi Z-800 spectrophotometer) with
tics of calix[4]arenes (1‡), calix[4,6]arene thioethers Zeeman background correction in air–acetylene flame
3‡–3c, 4‡, and 4b), and their thia derivatives (1b, 2‡, or in an electrothermal atomizer, with a blank carried
(
2
b, and 5) (Scheme 1); we also substantiate the choice out at low palladium concentrations (on the level of
of the most efficient extraction system for rapid recov- 0.02 µg/mL).
ery of palladium from hydrochloric acid solutions.
In calculating observed rate constants from k =
Ì
0
2
.3log(c /c ) , Excel 97 and Origin 7.0 standard pro-
Pd τ
EXPERIMENTAL
gram packages were used for data processing.
The chemicals used were dibenzyl sulfide (DBnS),
octylbensyl sulfide (OBnS) (pure grade), HNO and
3
RESULTS AND DISCUSSION
HCl (both of high-purity grade), and organic solvents
(toluene, CCl , and dichloroethane of chemically pure
4
The test sulfur-containing calix[4,6]arenes contain
three types of sulfur atoms (one bridging atom and two
grade) after distillation.
Calixarene thioethers 3a–3c, 4a, 4b [13], and 5 [26]; in CH Së H CH and ëç SÄlk groups), which differ
2
6
4
3
2
and thiacalixarenes 1b and 2‡–2c [19, 20] were pre- in their charge states. Presumably, the inductive and
pared as described elsewhere.
steric effects of substituents at sulfur atoms in polyden-
tate macrocyclic ligands and their monodentate ana-
logues vary symbatically. If so, diphenyl sulfide (DPS)
is an analogue of thiacalixarenes; for calixarene thioet-
hers 3c and 5, the analogue is DBnS; and for 3‡, 3b and
–
5
Solutions of extractants L in diluents (10 to
–
3
–
10 mol/L) were prepared from exactly weighed ali-
quots of calixarenes. The stock palladium solution was
prepared by dissolving K PdCl , which was synthesized
2
4
4
‡, 4b, the analogue is OBnS. It was demonstrated in
5, 22] that the reaction of palladium with dialkyl sul-
fides is located in the aqueous phase (which is chloride
from metallic palladium (99.9%) as described in [21].
[
–4
–3
Working palladium solutions (10 to 10 mol/L) were
prepared by diluting the stock solution to the required
HCl concentration (0.01–6 mol/L).
[
5] or nitrate—nitrite [22] solution). With account for
the hydrophobicity of R S molecules, the general order
2
Solutions of trioctylammonium chloride (QCl) in
toluene were prepared by stirring solutions of triocty-
lamine in diluents with equal volumes of 1 M HCl for
of the influence of organic sulfides on the rate con-
stants, complex-formation equilibrium constants, and
extraction constants was experimentally established as
2
0–30 min and then used for preparing mixtures with L.
Extraction was performed by vigorously stirring (at
00 rpm) of equal volumes of organic and aqueous
follows: DPS ꢀ DBnS < OBnS < R S (propyl > hexyl)
2
[
23, 24]. As applied to sulfur-containing calix[4,6]are-
1
nes, this order can be transformed as follows: 1b, 2‡,
phases at 298 K for 2–180 min. Palladium extraction
being a non-steady-state process, effective distribution
2
b ꢀ 3c, 5 < 3b, 4b < 3‡, 4‡. The experimental data
below, in general, support this tendency.
0
0
ratios were determined: D = (c – c )/c , where c
τ
Pd
τ
τ
Pd
and c are, respectively, the initial and current palla-
τ
Palladium Extraction by Thiacalix[4]arenes
dium concentrations in hydrochloric acid solutions for
a fixed moment. The palladium concentration in aque-
For palladium, unlike for gold [13] and other metals,
ous solutions after extraction was determined by atomic 7–8% recovery (DPd = 0.07–0.08) is observed in extrac-
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 53 No. 11 2008

PALLADIUM(II) EXTRACTION BY SULFUR-CONTAINING CALIX[4,6]ARENES
1811
Table 1. Palladium extraction by tolyl(thiomethyl)calix[4]arene (3c) and its thia analogue 5 from hydrochloric solutions to toluene
3
0
Pd
× 104,
c × 10 ,
c
L
kobs, s–1
L
HCl
τ, min
Dτ
mol/L (cQCl
)
mol/L
3
c
c
c
c
c
c
c
c
c
c
c
c
6.65
6.65
6.65
6.65
6.65
6.8
0.01
0.1
1.0
3.0
6.2
1.0
1.0
1.0
3.0
3.0
3.0
3.0
1.0
0.1
1.0
6.2
10–60
10–60
10–60
10–60
10–60
30–180
10–60
10–60
10–45
10–45
10–45
5–1300
5–30
130–800
80–2400
0.15–3.1
0.2–5.8
(8.0 ± 2.0) × 10–3
3.7 × 10–
3∗ ∗
3
3
3
3
3
3
3
3
3
3
3
5
9.1
7.2–8.4
7.1
(3.7 ± 0.7) × 10–4
(5.0 ± 0.9) × 10–4
(6.9 ± 0.6) × 10–4
(6.9 ± 0.6) × 10–4
(3.5 ± 1.0) × 10–4
(3.0 ± 0.5) × 10–4
(0.7 ± 0.1) × 10–3
(3.8 ± 0.5) × 10–3
(7.0 ± 0.1) × 10–3
(1.4 × 0.2) × 10–4
(1.8 ± 0.8) × 10–3
7.4
0.5–12.8
2.2–3250
0.15–3.70
0.15–2.21
0.52–35.4
12.5–1820
134–1820
0.3–519
0.7–3.1
5.4 (0.19)
4.43
7.7
8.4
3.33
7.2–8.4
3.4
3.32 (0.14)
3.32 (0.7)
3.32 (1.4)
5.5
∗
∗
3.4
3.4
3.4
2.83
7.2
3.7 × 10–
(3.9 ± 0.6) × 10–4
4∗ ∗
4∗ ∗
2
6.5
9.1
60
30
DBnS
26.5
6.5
6.8
10–60
10–60
0.28–0.94
0.92
2
7.4
1.8 × 10–
*
Palladium concentration in the aqueous phase is below the detection limit.
*
* kobs was estimated from two points.
tion from chloride solutions by conventional calixarene arise from the reduction of electron density on the sul-
‡ (from 1 M HCl) and p-methoxycalix[4]arene (from
.1 M HCl). In transfer from 1a to thia-substituted 1b,
the extraction efficiency almost does not change (D =
1
fur atom in the −SC H CH group because of p-π inter-
6
5
3
0
actions with the aromatic rings of the macrocycle. For
palladium, in contrast, a rise in the π-donor ability of
the aromatic system of the macrocycle enhances extrac-
tion. Thus, the above opposite effects on palladium and
gold extraction generate the fundamental possibility of
separating these metals with dominant palladium
recovery, which is atypical of known S,N,O-coordinat-
ing extractants. For palladium and gold in the ratio
Pd
0
.05–0.1). This means that bridging sulfur atoms do not
participate in coordination to palladium during extrac-
tion; the donor ability of sulfur in 1b only insignifi-
2
4
–
cantly differs from that in DPS, for which the PdCl
extraction constant is 12 orders of magnitude lower
than for (ë H ) S [24]. Palladium extraction by
calix[4]- and thiacalix[4]arenes is due to the π-binding
of the palladium complex species with the fused aro-
matic system of the macrocycle; the existence of this
binding was verified by EXAFS spectroscopy in ben-
zene solutions of PdCl (R S) [25]. This interaction
6
13 2
1
: 1, palladium refining from gold is 3–10 times.
Palladium Extraction by p-
Tolyl(thiamethyl)calix[4]arene 3c
2
2
2
enhances both outer-sphere coordination of palladium
to benzene rings and its inclusion into the macrocyclic
cavity. Therefore, calix[4]arenes 2‡ and 2b in the
Palladium extraction by solutions of 3c in toluene
rises with acidity (1–6 M HCl), despite the increasing
concentrations of competing chloride ions (Fig. 1a), but
almost does not change for monodentate DBnS and
1
,3-alternate and partial cone conformations almost do
not extract palladium (D < 0.01).
The influence of the bridging sulfur atom on the
gold [26] and palladium extraction properties of OBnS when cHCl > 1 mol/L (Fig. 1b). This difference
calix[4]arene thioethers functionalized in the upper rim
was discovered in comparing the properties of 3c and 3.
In going from 3c to 5, gold extraction is reduced by two
orders of magnitude [26]; palladium extraction is, in
can arise from the presence of a propoxy group in the
lower rim; as a result of protonation, the propoxy oxy-
gen atom acts as an intramolecular catalyst of anion-
2
–
contrast, enhanced (Table 1). For gold, the effect can exchange PdCl transfer
4
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 53 No. 11 2008

1
812
TORGOV et al.
logD
4
(a)
(b)
logD
1
3
2
1
0
0
.5
0
1
6
0
–
0.5
3
0
2
3
2
0
–
1
1
0 τ, min
6
m
3
m
–1
1
m
0
.01
0.1
1
3
6
cHCl, mol/L
–
3
Fig. 1. Effect of HCl concentration on palladium extraction by solutions of 3c, DBnS, and OBnS in toluene. Panel(a): 6 × 10 mol/L
–
4
–4
−3
–3
3
c and 7 × 10 mol/L Pd. Panel (b): (1) 6 × 10 mol/L 3c, (2) 2.65 × 10 mol/L OBnS, and (3) 7 × 10 mol/L Pd. τ = 60 min.
2
4
–
(aq)
7000–28000 cm–1 is close to that in the spectra of
PdCl (R S) [27]. The protonation of the propoxy group
2
PdCl
+ LH Cl
2 2(org)
(
1)
2
2
2
rapidly
–
LH PdCl
+ 2Cl ,
(aq)
in 3c enhances the surface-active properties of the
2
4(org)
extractant. Therefore, the independence of the palla-
which is followed by the replacement of chloride ions dium extraction rate from 1 M HCl from the concentra-
in the coordination surrounding of palladium:
tion of 3c in the bulk of the organic phase (Table 1)
results from the interaction between palladium and 3c
LH PdCl PdCl L + 2HCl(aq)
.
(2)
2
(org)
2
(org)
near or at the interface. The sulfur atom in R S having
2
a far lower basicity than the oxygen atom in R O
Indeed, this species is absent in the electronic absorp-
tion spectra of extracts with 3c because of the substitu-
tion of the extractant for chloride ion in the organic
phase, and the position of the absorption band at
2
(
pK = –2.42 for Et O and –6.8 for Et S [28]), the HCl
a 2 2
concentration has no effect on palladium extraction by
monodentate R S (Fig. 1b).
2
The catalytic effect can be enhanced by introduction
of trioctylammonium chloride QCl (an anion-exchange
additive) (Fig. 2). The enhancement rises with increas-
ing additive concentration: with increasing QCl con-
centration from 20 to 100% relative to the QCl/Pd = 2
c(eq) /c(org)
Pd Pd
1
0
0
0
0
.0
.8
.6
.4
.2
0
stoichiometry, E > 95%, respectively, after 45 and 15
1
2
Pd
min (without additive, after 180 min) (Table 1). We
should note that anion-exchange palladium extraction
3
4
2
4
–
(eq)
–
(eq)
PdCl
+ 2QCl(org) = Q PdCl4(org)+2Cl
,
2
(
3)
5
K‡0 = 6.3 × 10 [24]
is insignificant in the range of ÒQCl tested (calculated
D = 0.0014–0.14); therefore, the additive has a cata-
Pd
lytic effect.
For lower acidities (0.01–0.1 M HCl), high extrac-
tion efficiencies (Table 1) must be due to the presence,
in the starting solution, of a nonsymmetrical complex
0
50
100
150
200
τ, min
–
species (possibly, Pd(H O)Cl [5]) with its surface
2
3
Fig. 2. Aqueous palladium concentration vs. time in extrac-
2–
4
activity increased relative to PdCl . Likely, it is for
–
4
tion by solutions of 3c in toluene. cPd = 7 × 10 mol/L,
cL = 3.3 × × 10− mol/L and (4) 5.3 × 10–3 mol/L. cQCl = (4) 0,
this reason that calix[4]arenes functionalized with SMe
and S–C(S)NMe in the lower rim rapidly extracted pal-
3
2
(
1
3) 1.4 × 10 mol/L, (2) 7.0 × 10–4 mol/L, and (1) 1.4 ×
0
−
4
2
–
−3
ladium introduced in the form of PdCl in nitrate
mol/L. W : O = 1 : 1.
4
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 53 No. 11 2008

PALLADIUM(II) EXTRACTION BY SULFUR-CONTAINING CALIX[4,6]ARENES
1813
Table 2. Palladium extraction from HCl by alkyl(thiamethyl)calix[4,6]arenes in diluents
3
0
Pd
× 104,
c × 10 ,
cHCl
,
c
L
kobs, s–1
L
Diluent
Toluene
τ, min
Dτ
mol/L
mol/L
mol/L
∗
∗
3
a
a
2.32
3.5
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
0.1
1.0
6.2
7.8
7.8
7.7
7.2
7.2
7.8
7.8
7.8
7.8
7.2
7.8
7.2
7.8
7.2
7.2
9.1
6.9
7.4
40–90
40–90
2–15
5–30
60
4100
4100
–
–
«
«
«
«
«
«
«
«
∗
7.2
135–4100
0.03 ± 0.01
∗
∗ ∗
4
8.1
3800
0.03
∗
0.74
0.33
0.64
1.2
3800
–
3
b
40–90
40–90
40–90
2–60
2–60
5–10
2–60
5–10
2–30
60
2.0–7.3
(4.2 ± 0.3) × 10–4
(6.6 ± 1.3) × 10–4
(9.2 ± 1.6) × 10–3
(5.6 ± 0.3) × 10–3
0.055 ± 0.023
–
3.6–14
∗
∗
∗
8.1–4100
1.3–4100
7.0
CCl4
2.68
6.52
3.17
6.52
7.3
760–3800
∗
«
4100
∗
∗
(1.03 ± 0.4) × 10–3
Dichloroethane
0.57–3800
∗
«
4100
–
4
b
Toluene
1.2–3800
4.6
(4.9 ± 0.7) × 10–3
4.7 × 10–
3.0 × 10–
4∗ ∗
«
«
«
«
0.66
26.8
26.8
26.8
3∗ ∗
OBnS
10–60
10–300
10–60
7.5–2400
0.33–3600
0.37–1.8
(5.4 ± 1.5) × 10–4
4∗ ∗
3.5 × 10–
*
Palladium concentration in the aqueous phase is below the detection limit.
*
* kobs was estimated from two points.
solutions with pH 1–3 [9–12]. The trend in D in this
region for 3c and DBnS is the same and caused by equi-
libria between palladium phases in the aqueous phase
Palladium Extraction
τ
by Alkyl(thiamethyl)calix[4,6]arenes
Palladium extraction by calix[4,6]arene thioethers,
as by monodentate thioethers, depends on the phase
contact time (Table 2, Fig. 3). With an excess of the
(
Fig. 1b). These data supplement the increasing order
of the kinetic efficiency of palladium species estab-
2
–
–
lished for R S [22]: PdCl < Pd(H O)Cl , and extractant, the variation of the current palladium con-
2
4
2
3
centration in the aqueous phase with time is quite well
fitted by the first-order rate equation
+
2
2–
4
+
2
2+
Pd < Pd(NO ) < PdNO . For PdCl and PdNO ,
2
2
all other conditions being equal, the complete palla-
dium extraction is achieved after 30 min and 10 s,
respectively. Therefore, the minimum (Fig. 1b) in the
acidity range 0.1 M < 1 M < 3 M, likely, appears
logD
4
3
2
1
0
2
–
because palladium exists as the inert species PdCl4
exclusively and because of the low degree of protona-
tion of the oxygen atom of the propoxy group; that is,
under these conditions, the concentration of 3c in the
aqueous phase can control the extraction efficiency.
–
1
30
Thus, due to the low donor ability of the sulfur atom
and low extraction rates, tolylmethylcalix[4]arene is
not efficient enough for concentrating palladium from
hydrochloric acid solutions, although its thia deriva-
tives are of interest for palladium separation from gold.
In addition, with the identical concentrations of the sul-
fur atoms, 3c only insignificantly exceeds DBnS in
extraction from 1 M HCl because of complex formation
sterically hindered by the bulky benzene ring.
3
a
5
4
a
3b
2
4
b
5
3c
τ, min
Fig. 3. Effect of the phase contact time on palladium extrac-
tion from 1 M HCl to solutions of calix[4,6]arene thioethers
in toluene. cPd = 7 × 10 mol/L. c = 6.6 × 10 mol/L for
–
4
−3
L
–3
3
a, 3b, 4a, and 4b and c = 3.3 × 10 mol/L for 3b and 5.
L
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 53 No. 11 2008

1
814
TORGOV et al.
–
7
log[Pd]
.0
R, %
1
2
3
4
90
6
5
4
.0
.0
.0
7
5
3
1
0
0
0
0
1
2
3
4
0
2
4
6
8
10
τ, min
3
.0
0
20
40
60
80
100
τ, min
Fig. 5. Palladium(II) extraction from 1 M HCl to solutions of
−
3
3
b in diluents: (1) ëël (1, c = 2.68 × 10 mol/L; (2) toluene,
Fig. 4. Effect of the concentration of 3b in toluene on palla-
dium extraction from 1 M HCl. cL = (1) 7.0 × 10 , (2)
4 L
–
3
cL = 7.0 × 10–3 mol/L; (3) DCE, c = 3.17 × 10 mol/L; and
–3
L
–3
–4
–4
–3
1
.2 × 10 , (3) 6.4 × 10 , and (4) 3.3 × 10 mol/L. cPd
.8 × 10–4 mol/L. The blank is shown by a dashed line.
=
(4) toluene, estimated for c = 3.17 × 10 mol/L. c = 3.3 ×
L
L
7
10–3 mol/L.
0
Pd
The limiting ratio Pd : L in the organic phase is two,
corresponding to the generation of the complex
[
Pd] = c exp(–k · τ).
(4)
aq
obs
In view of the fact that kobs for extraction from 1 M (PdCl ) L, in which there are two thioether groups per
2 2
HCl for methyl-substituted 3a and 4a is higher than for palladium atom, as in palladium nitrate complexes with
more hydrophobic butyl-functionalized 3b and 4b 3a–3b [14].
(
Table 2) and with reference to data for 3c (for 1 M
We could expect that transfer from conformation-
ally rigid calix[4]arenes to labile calix[6]arenes would
reduce steric hindrances due to conformational alter-
HCl), we have enough reasons to think that palladium
extraction by calix[4,6]arene thioethers under these
conditions is controlled by the concentration of L in the
aqueous phase according to
ation. However, our data show that D changes only
Pd
insignificantly in going from 3a and 3b to 4a and 4b
(Table 2). Thus, changes in the cavity volume and con-
formational rigidity of calixarenes are not the key fac-
(
L
org) (aq)
L(aq)
L(org)
,
K = c /cL
.
(5)
L
In the same way, the rate-controlling reaction for tors for the palladium extraction efficiency.
R S is the substitution reaction
2
Alkyl(thiamethyl)calix[4]arenes in toluene provide
the complete (>99.9%) palladium extraction in shorter
times (2–5 min for 3a and 30 min for 3b) than mono-
2
4
–
(aq)
k1
–
(aq)
PdCl
+ L(aq)
PdCl L + 2Cl
,
(6)
2
(aq)
dentate R S with the same concentration of donor
(
aq)
2
whose rate (w = k × c cPd ) depends on kobs and KL.
ç
L
atoms (Table 2); for short times, D for 3a and 3b is
Pd
With increasing alkyl radical volume at the S atom, the
hydrophobicity of the molecule rises, the equilibrium
aqueous concentration of L decreases, and the extrac-
tion efficiency is reduced in going from methyl- to
butylcalix[4]arene thioethers (Table 2).
three to four orders of magnitudes the respective values
for OBnS and DBnS (Tables 1, 2).
The effect of the nature of the diluent on the extraction
efficiency is determined by the distribution of L on
account of different solvating abilities of diluents. In
gold(III) extraction by calixarene thioethers [13, 26] and
For 3b, unlike for tolyl-functionalized 3c, an
increase in the concentration in the bulk of the organic
phase enhances palladium extraction (Fig. 4). When
c > c , the extraction efficiency increases with rising
monodentate R S [2], it was demonstrated that the increas-
2
ing polarity in the order ëCl < toluene, benzene < dichlo-
4
L
Pd
roethane in equilibrium increases extraction constants due
excess extractant concentration, and the residual aque-
to the preferred solvation of AuCl L. In the case of palla-
3
ous palladium concentration (log[Pd] ) acquires, with
t
dium (Fig. 5), the highest extraction by 3b for small
time, the level of the blank. Under these conditions, D
is on the level of (3–4) × 10 for two- to fourfold molar tions of 3b in dichloroethane and toluene for commen-
excess of L (Table 2).
extraction times is observed for CCl , and R for solu-
Pd
4
Pd
3
surate c are close (estimation for toluene solutions with
L
When c : c ≥ 1, the extraction efficiency decreases
c = 33 mmol/L was carried out on the assumption of a lin-
L
Pd
L
as the extractant is saturated with palladium (Table 2). ear dependence of the extraction efficiency on c
).
L
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 53 No. 11 2008

PALLADIUM(II) EXTRACTION BY SULFUR-CONTAINING CALIX[4,6]ARENES
1815
The increasing order of R(D) (dichloroethane ≤ tolu-
5. S. J. Al Bazi and H. Freizer, Solvent Extr. Ion Exch. 5
2), 265 (1987).
Pd
(
ene < CCl ) corresponds to the decreasing order of R S
4
2
6
. Yu. I. Murinov, V. N. Maistrenko, and N. G. Afzaletdi-
nova, Solvent Extraction of Metals by S,N-Organic Com-
pounds (Nauka, Moscow, 1993) [in Russian].
solvating abilities [29]. The highest palladium extrac-
tion by 3b with ëël as diluent is due to the lowest KL
4
and, thus, the highest aqueous concentration of L
7
8
. D. Bauer and G. Cote, Proceedings of ISEC 88, Vol. 2,
according to equilibrium (5). The rapid acquisition (in
3
p. 79.
2
–5 min) of high D (up to 4 × 10 ; Table 2) and D
Pd
Au
. G. Cote, D. Bauer, and S. Daamach, Proceedings of
ISEC 88, Vol. 2, p. 83.
values [13, 16] from chloride solutions (1–3 M HCl)
with the use of a three- to fourfold excess of 3‡ in tolu-
ene provides a more than 99% overall extraction of
these metals. Thus, the use of calixarene thioethers
9
. A. T. Yordanov, O. M. Falana, H. F. Koch, and D. M. Rou-
dhill, Inorg. Chem. 36, 6468 (1997).
releases the main limitation inherent to monodentate 10. A. Yordanov, B. Whittlesey, and D. Roundhill, Inorg.
Chem. 37, 3526 (1998).
R S and opens a possibility for organizing palladium
2
extraction together with gold in a continuous mode, in 11. A. Yordanov and D. Roundhill, Inorg. Chim. Acta 270,
2
16 (1998).
particular, with the use of solid extractants. The non-
steady-state character of palladium extraction by 12. A. Yordanov, B. Whittlesey, and D. Roundhill,
calix[4]arene thioethers and the extremely low palla-
Supramol. Chem. 9, 13 (1998).
dium concentrations in raffinates kept us from calculat- 13. V. Torgov, G. Kostin, V. Mashukov, et al., Solvent. Extr.
ing extraction constants; they were determined using
conjugate equilibria [27].
Ion Exch. 23 (2), 171 (2005).
4. V. Torgov, G. Kostin, T. Korda, et al., Solvent Extr. Ion
Exch. 23 (6), 781 (2005).
1
To conclude, we list the main strengths of
calix[4,6]arene thioethers over monodentate R S:
15. N. Iki and S. Miyano, J. Inclusion Phenom. Macrocyclic
2
Chem. 44, 99 (2001).
(i) The possibility of chelation increases DPd by
1
1
1
1
2
2
6. R. Lamartine, C. Bavoux, F. Vocanson, et al., Tetrahe-
dron Lett. 42, 1021 (2001).
three to four orders of magnitude compared to palla-
dium extraction with R S from chloride and nitrate–
2
7. P. Lhotak, M. Himl, I. Stibor, et al., Tetrahedron Lett. 42,
nitrite solutions [4, 14] and shortens the time of com-
plete palladium recovery from 40–60 min to 2–5 min;
7
107 (2001).
8. N. Morohashi, N. Iki, M. Aono, and S. Miyano, Chem.
Lett., 494 (2002).
9. H. Kumagai, M. Hasegawa, S. Miyanari, et al., Tetrahe-
dron Lett. 38, 3971 (1997).
(ii) Additional enhancement of palladium extraction
is possible due to intermolecular catalysis by the proto-
nated oxygen atoms of alkoxy groups in the lower rim
of calix[4,6]-arene thioethers for HCl concentrations
higher than 2–3 mol/L;
0. P. Lhotak, M. Himl, S. Pakhomova, and I. Stibor, Tetra-
hedron Lett. 39, 8915 (1998).
(iii) The presence of bridging sulfur atoms in thia-
1. Synthesis of Platinum-Group Metal Complexes, Ed. by I.
I. Chernyaev (Nauka, Moscow, 1964), p. 173 [in Rus-
sian].
calix[4,6]arene thioethers differently affects their reac-
tivity to palladium and gold, creating prerequisites for
the extraction separation of these metals.
2
2
2
2. V. V. Tatarchuk, I. A. Druzhinina, T. M. Korda, and
V. G. Torgov, Zh. Neorg. Khim. 47 (12), 2082 (2002)
[Russ. J. Inorg. Chem. 47 (12), 1917 (2002)].
ACKNOWLEDGMENTS
3. V. V. Tatarchuk, G. A. Kostin, and V. G. Torgov, Zh.
Neorg. Khim. 45 (9), 1588 (2000) [Russ. J. Inorg. Chem.
45 (9), 1453 (2000)].
This work was in part supported by the National Sci-
ence Foundation of the Russian Federation and the
Integration project of the Siberian Branch of the Rus-
sian Academy of Sciences and the National Academy
of Sciences of Ukraine (project no. 4-12).
4. V. G. Torgov and V. V. Tatarchuk, Zh. Neorg. Khim. 41
(
8), 1402 (1996) [Russ. J. Inorg. Chem. 41 (8), 1342
(1996)].
2
2
5. S. Erenburg, N. Bausk, L. Masalov, et al., Inorg. React.
Mech. 2, 1 (2000).
6. G. A. Kostin, V. I. Mashukov, T. M. Korda, et al., Zh.
Neorg. Khim. 51 (10), 1786 (2006) [Russ. J. Inorg.
Chem. 51 (10), 1682 (2006)].
REFERENCES
1
. M. A. Meretukov and A. M. Orlov, The Metallurgy of
Precious Metals (World’s Experience) (Metallurgiya,
Moscow, 1991) [in Russian].
2
7. G. A. Kostin, V. I. Mashukov, T. M. Korda, et al., Zh.
Neorg. Khim. 52 (11) (2007) [Russ. J. Inorg. Chem. 52
2
3
. V. G. Torgov, Isotopenpraxis 20, 352 (1984).
(11), 1697 (2007)].
. V. G. Torgov, T. M. Korda, and L. A. Terent’eva, The
Precious Metals: Chemistry and Analyses. Collected 28. E. M. Arnett, E. J. Mitchell, and T. S. Murty, J. Am.
Works, Ed. byV. G. Torgov and F.A. Kuznetsov (Novosi-
birsk, 1989) [in Russian].
Chem. Soc. 96 (12), 3875 (1974).
2
9. V. A. Mikhailov, S. S. Shatskaya, D. D. Bogdanova, and
V. G. Torgov, Izv. Sib. Otd. Russ. Akad. Nuak, Ser.
Khim., No 3, 34 (1976).
4
. V. G. Torgov, V. V. Tatarchuk, I. A. Druzhinina, et al., At.
Energ. 88 (5), 358 (2000).
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