Extraction of gold(III), palladium(II), and platinum(IV) by 1-[2-(2,4-dichlorophenyl)-4-propyl-1,3-dioxolan-2-ylmethyl]-1H-1,2,4-triazole from hydrochloric acid solutions

Article abstract of DOI:10.1134/S0036023607060253

The extraction of gold(III), palladium(II), and platinum(IV) with 1-[[2-(2,4-dichlorophenyl)-4-propyl-1,3-dioxolan-2-yl]methyl]-1H-1,2,4-triazole from hydrochloric acid solutions into toluene has been studied. The extraction follows the anion-exchange mec

Full text of DOI:10.1134/S0036023607060253

ISSN 0036-0236, Russian Journal of Inorganic Chemistry, 2007, Vol. 52, No. 6, pp. 969–978. © Pleiades Publishing, Inc., 2007.
Original Russian Text © R.A. Khisamutdinov, Yu.I. Murinov, O.V. Shitikova, 2007, published in Zhurnal Neorganicheskoi Khimii, 2007, Vol. 52, No. 6, pp. 1041–1050.
PHYSICAL CHEMISTRY
OF SOLUTIONS
Extraction of Gold(III), Palladium(II), and Platinum(IV)
by 1-[2-(2,4-dichlorophenyl)-4-propyl-1,3-dioxolan-
2-ylmethyl]-1H-1,2,4-triazole from Hydrochloric Acid Solutions
R. A. Khisamutdinov, Yu. I. Murinov, and O. V. Shitikova
Institute of Organic Chemistry, Ufa Scientific Center, Russian Academy of Sciences,
pr. Oktyabrya 71, Ufa, 450054 Bashkortostan, Russia
Received April 18, 2006
Abstract—The extraction of gold(III), palladium(II), and platinum(IV) with 1-[[2-(2,4-dichlorophenyl)-4-
propyl-1,3-dioxolan-2-yl]methyl]-1H-1,2,4-triazole from hydrochloric acid solutions into toluene has been
studied. The extraction follows the anion-exchange mechanism. The concentration constants and thermody-
namic parameters of the extraction reaction have been calculated. The reagent is proposed for use in the extrac-
tion of the sum of precious metals.
DOI: 10.1134/S0036023607060253
Recently, the attention of researchers has been
focused on the use of derivatives of 1,2,4-triazole with
substituents bearing extra donor atoms, such as nitro-
gen and sulfur, in complexing with transition metals.
For example, metal complexes with N-derivatives [1−6]
and S,N-derivatives of 1,2,4-triazole [7, 8] have been
studied. It was shown that sulfur- and nitrogen-contain-
ing substituents increase the stability of complexes on
account of the chelate effect. The coordination chemis-
try of 1,2,4-triazole and its derivatives is surveyed else-
where [9].
Reagent S is a yellow thick liquid; the main substance
is at least 98%. Its solubility in water is 110 mg/L, Tm =
58°C, and FW = 342.2. The individuality and purity of
the compound was verified by elemental and functional
analysis, thin-layer and gas--liquid chromatography,
and 1H and 13C NMR spectroscopy.
The stock solutions of the reagent were prepared
from exact weights; working solutions were prepared
by diluting the stock solutions. Chemically pure tolu-
ene was used as the diluent.
Although the complexing properties of 1,2,4-triaz-
ole derivatives relative to many metals, including palla-
dium, are well documented [10, 11], their extraction
properties remain almost unstudied.
The goal of this work is to study the extraction prop-
erties of 1-[2-(2,4-dichlorophenyl)-4-propyl-1,3-diox-
olan-2-ylmethyl]-1H-1,2,4-triazole with respect to
gold(III), palladium(II), and platinum(IV).
Gold(III) solutions were prepared from 99.99%
metal gold by dissolving it in aqua regia followed by
conversion to hydrochloric acid solutions. Palla-
dium(II) and platinum(IV) solutions were, respectively,
prepared from palladium chloride and hexachloropla-
tinic acid H2PtCl6 · 6H2O by dissolving them in hydro-
chloric acid. The metal ion concentration in the stock
and working solutions was determined spectrophoto-
metrically: gold(III) was determined by the color intrin-
sic to the AuCl–4 ion [12]; palladium(II) and plati-
num(IV) were determined with tin chloride [13]. In raf-
finates, the metals were determined by atomic-
absorption spectrophotometry on a Hitachi 508 instru-
ment. Aqueous solutions were burnt in acetylene--air
flame; lamps with a hollow cathode manufactured of
the analyte element served as the monochromatic radi-
ation source.
EXPERIMENTAL
The extractant in question, known as Propiconazole
since 1979, has been employed as a systemic means for
plant protection. This compound (hereafter, reagent S)
has the following structural formula:
Extraction experiments were carried out in temper-
ature-controlled glass separatory funnels. Stirring was
performed with a Universal shaker type 327. The ratio
between the aqueous and organic phases was main-
tained equal to 1 : 1. The dynamic phase contact time
required for extraction equilibrium to be acquired was
determined in preliminary experiments.
O
HC
C
H
N
C
C3H7 CH O
N
H
CH
HC
N
969

970
KHISAMUTDINOV et al.
Table 1. Parameters (chemical shifts δ and extra chemical shifts ∆δ, ppm) of a fragment of the 1H NMR spectrum for reagent S
6
1
2
CH
N
N
2
3
and its hydrochloric extracts with D-chloroform
CH
H5C
N
4
1 M HCl
2 M HCl
3 M HCl
4 M HCl
Proton
Isomer
S
δ
∆δ
δ
∆δ
δ
∆δ
δ
∆δ
3CH
cis
7.82
7.82
8.11
8.14
4.67
7.88
7.89
8.17
8.20
4.70
0.06
0.07
0.06
0.06
0.03
7.90
7.90
8.19
8.21
4.73
0.07
0.08
0.07
0.07
0.06
7.91
7.91
8.29
8.29
4.75
0.10
0.10
0.19
0.15
0.08
8.06
8.07
8.75
8.86
4.80
0.24
0.25
0.63
0.72
0.13
trans
cis
5CH
trans
6CH2
The electronic absorption spectra of the reagents, existence of two sets of signals from the carbon atoms with
aqueous solutions of metal ions, extracts, and complex different intensities. The strongest differences are observed
for signals from the atoms 5 C (1.6 ppm), 6ë (0.5 ppm), 12ë
(0.5 ppm), and 18ë (0.4 ppm); these atoms have differ-
ent 1,3 or 1,4 interactions in the two isomers. The sig-
nals from equivalent atoms coincide in their chemical
shift, but have the doubled intensity. The isomerization
of the reagent is probably a dynamic process.
From what we know about the extraction chemistry
of precious metals, we can expect the extraction of the
test metal ions to occur due to the nitrogen atom
(atoms) of the 1,2,4-triazole ring and not to oxygen
atoms. In this case, two extraction routes are possible:
anion-exchange extraction (in acid media) or coordina-
tive extraction with the incorporation of the donor
nitrogen atoms into the inner coordination sphere of the
metal ions (in neutral or weakly acidic media).
compounds were recorded on a Specord M40 spectro-
photometer using silica cells 0.2--5.0 mm thick. IR
spectra were recorded on a Specord M80 spectropho-
tometer in the range 4000--250 cm–1. When the spectra
were recorded as liquid films, KCl plates and polyeth-
ylene disks were used. NMR spectra were recorded on
a Bruker AM 300 spectrometer (300 MHz) in D-chlo-
roform.
RESULTS AND DISCUSSION
1
The test compound is a complex N-substituted
derivative of 1,2,4-triazole. In the structural formula of
the reagent below, the carbon atoms are enumerated
and the chemical shifts of their signals in the 13ë NMR
spectra (δ, ppm) are indicated.
Because the extraction was performed from hydro-
chloric acid solutions (which are the most common
environment for the test metals), we first studied the
behavior of reagent S in its reaction with hydrochloric
16
15
14
17
13
1
acid under the extraction conditions using H and 13C
12134.70
70.03
NMR spectroscopy. As a result of contacting (vigorous
stirring) of the reagent with 1, 2, 3, or 4 M acid solu-
tions, we obtained and separated extracts whose NMR
spectra were compared to the spectra of the reagent.
Table 1 displays the spectral parameters of the informa-
tive protons in the 1H NMR spectra of the reagent and
hydrochloric acid extracts. The extra chemical shifts of
proton signals from the other part of the molecule
almost do not differ from the chemical shifts of the sig-
nals from the reagent. For convenience, the numbering
of the molecule fragment is changed to correspond to
the numbering in the 1,2,4-triazole ring. In the 1H NMR
spectra of the hydrochloric extracts, there are extra
O
135.37
4
3
18.76
19
CH2
2
106.68
HC
C
C 6
53.79
54.26
CH O
5
1 H
CH3
N
N
CH2
H
20
76.46
7
8
18
78.11
13.75
CH
HC
34.30
34.73
9
144.5171
151.04
N
10
From the interpretation of the spectrum, the reagent
is a mixture of two spatial isomers: the cis-isomer
accounts for 55--65% and trans-isomer for 35--45%.
These isomers differ from each other by the opposite
arrangement of the triazole and aromatic rings relative
to the dioxane ring plane, which is indicated by the downfield chemical shifts of the proton signals from the
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 52 No. 6 2007

EXTRACTION OF GOLD(III), PALLADIUM(II), AND PLATINUM(IV)
971
Table 2. Parameters (chemical shifts δ and extra chemical shifts ∆δ, ppm) of a fragment of the 13C NMR spectrum for reagent S
1
N
2
N
6
CH
2
3
and its hydrochloric extracts with D-chloroform
CH
HC
5
N
4
1 M HCl
2 M HCl
∆δ
3 M HCl
4 M HCl
Proton
Isomer
S
δ
∆δ
δ
δ
∆δ
δ
∆δ
3CH
cis
151.15
151.04
144.57
144.46
54.26
151.14
151.24
144.66
144.49
54.41
–0.01
0.20
0.09
0.03
0.15
0.17
151.15
151.17
144.70
144.70
54.45
0
150.49
150.49
144.48
144.47
54.50
–0.66
–0.55
–0.09
0.01
148.31
147.91
144.30
144.30
54.96
–2.84
–3.13
–0.27
–0.16
0.70
trans
cis
0.13
0.13
0.24
0.19
0.20
5CH
trans
cis
6CH2
0.24
trans
53.79
53.96
53.99
54.04
0.25
54.47
0.68
6
tion for the corresponding atoms has the same ten-
dency. This means that the protonation of the atom 4N
under the extraction conditions occurs not only in
hydrochloric but also in nitric acid solutions.
1,2,4-triazole ring and the ëH2 groups relative to the
spectrum of reagent S; that is, the ∆δ values are posi-
tive (Table 1). The extra chemical shifts of the proton
signals tend to increase differently with increasing
aqueous acidity. When the HCl concentration is 1 or
2 mol/L, the extra chemical shifts for these protons are
insignificant and almost identical (0.6--0.8 ppm); with
increasing acid concentration to 3 and especially to
4 mol/L, the ∆δ increase, but the increase for the signals
To verify these suggestions, we recorded the 13ë
NMR spectra of the reagent and hydrochloric extracts
(Table 2). In the spectra of the extracts, as in the spec-
trum of the reagent, there is the nonequivalence of some
signals from the two isomers. Of the triazole carbon
atoms of interest, the difference between the chemical
shifts for the two isomers in the spectra of the extracts
is 0.5 ppm only for the atom 6C; for the atoms 3ë and
5ë, this difference does not exceed 0.1 ppm, or the dou-
ble-intensity signals are broaden. The extra chemical
shifts for the signals from carbon atoms are also slightly
different, but the tendency is retained. An extra chemi-
cal shift results from the fact that the shielding of both
5
3
from the CH protons is greater than for the CH pro-
tons. From these tendencies we can assume that the
atom N, which is in the α position to each of the
4
methine groups of the 1,2,4-triazole ring, is protonated
gradually; however, the effect on the proton of the 5CH
group (probably, on account of the delocalization of the
electron density through the π bond) is more significant
than the effect through the σ bond on the proton of the
3CH group. The fact that the extra chemical shift for the the nearest-neighboring (α) and the more distant (γ)
6
carbon atoms by the unprotonated nitrogen atom is
slightly lower in its absolute value than the shielding by
the protonated nitrogen atom.
signals from the protons of the ëç2 group does not
exceed 0.13 ppm and that it is almost nonexistent for
more distant groups, agrees with this assumption. If the
atom 1N or 2N were protonated, ∆δ(6ç) would be com-
Comparing the spectra of the reagent and hydro-
parable with ∆δ(5ç) and ∆δ(3ç). In addition, extra chloric extracts, we can trace the difference between
chemical shifts would have been observed for the sig- the shielding of the α- and γ-carbon atoms and protons
in the protonated and unprotonated forms of the mole-
cule. Increasing acid concentration (extent of protona-
tion of the nitrogen atom) affects the chemical shift of
the signals from the neighboring carbon atoms 3ë and
5ë (the α effect): the chemical shift decreases, this
nals from protons of the dioxane and aromatic rings that
are at a distance of three or four bonds from the proto-
nated nitrogen atom. While the extra chemical shifts of
proton signals (5ëç; 1.41; ëç and ëç2, 0.68 and
3
6
0.28 ppm) in the spectrum of the intentionally synthe-
sized compound S · HNO3 are higher than in the spec- decrease being more significant through the N–3C ordi-
trum of the hydrochloric acid analogue, the ∆δ varia- nary bond and less significant through the N=5C double
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 52 No. 6 2007

972
E, %
KHISAMUTDINOV et al.
1
the suggestions derived from ç NMR spectra; they
verify that the protonation under the extraction condi-
tions occurs at the atom 4N of the triazole ring, and the
extent of the protonation of this atom and, thus, of the
reagent increases with increasing aqueous acidity.
2 M HCl
3 M HCl
100
80
60
40
20
1 M HCl
(‡)
Preliminary experiments determined the time
required for extraction equilibrium to be acquired and
the optimal aqueous acidity. From the plots in Fig. 1,
the extraction of metal ions, especially platinum(IV),
increases with increasing aqueous acidity, which
matches the behavior of the reagent in hydrochloric
acid solutions. Based on the results of these preliminary
experiments, the phase contact time in all extraction
experiments was 10 min for all gold(III) and 20 min for
palladium(II) and platinum(IV). Because increasing
hydrochloric acid concentration in the aqueous phase
positively affects the extraction of metal ions, we stud-
ied extraction from 3 M HCl. High aqueous acidities
are rarely used in the analytical and synthetic chemistry
of precious metals, but they are ordinary at the dissolu-
tion and concentrate processing stages of affinage pro-
duction and in hydrometallurgy at electrolysis, extrac-
tion, and other stages.
0
5
3 M HCl
10
15
20
25
100
80
60
40
20
1 M HCl
(b)
2 M HCl
The isotherms of the extraction of metals by reagent
S recorded under the specified conditions are displayed
in Fig. 2. The slope of the initial portions of the iso-
therms signifies that the reagent has a fairly high extrac-
tion capacity. The solvation number q, determined by
the saturation method, is equal to unity for gold(III) and
two for palladium(II) and platinum(IV). The solvation
numbers determined by the slope method (Fig. 3) cor-
respond to these values; this means that compounds
with the ratios Au : S = 1 : 1, Pd : S = 1 : 2, and Pt : S =
1 : 2 are extracted along the whole isotherm. Thus, each
metal is extracted only in one form.
0
10
20
30
40
50
60
4 M HCl
3 M HCl
100
80
60
40
20
(c)
2 M HCl
1 M HCl
To study in more detail the composition and struc-
ture of the compounds extracted by the reagent, we
obtained extracts using the saturation technique. Table 3
0
10
20
30
40
t, min
1
lists the parameters of the H NMR spectra of the
extracts against the spectra of the reagent and its proto-
nated form. In the spectra of all extracts, the signals
from the protons of the triazole ring experience an
insignificant extra downfield chemical shift relative to
the spectrum of the protonated reagent; this indicates the
Fig. 1. Extraction vs. phase contact time and vs. aqueous
acidity at 25°ë for (a) gold(III) (c = 0.002 mol/L,
Au(III)
c = 0.006 mol/L), (b) palladium(II) (c
= 0.005 mol/L,
S
Pd(II)
c = 0.025 mol/L), and (c) platinum(IV) (c
= 0.005 mol/L,
S
Pt(IV)
c = 0.025 mol/L).
S
4
retained protonation of the atom N. In the 13ë NMR
spectra of the extracts, the extra chemical shift of the
signals from carbon atoms of the triazole ring practi-
cally does not change relative to the spectrum of the
hydrochloric extract. The electronic spectra of the
bond. In the 1ç NMR spectra, there is an inverse corre-
lation: with increasing HCl concentration, the chemical
shifts for the protons at the α-carbon atoms increase; in
addition, the α effect on the proton at the double bond
is stronger than on the proton at the ordinary bond.
extracts have absorption bands intrinsic to AuCl–4 ,
PdCl24– , and PtCl26– ions. Along with the absorption
bands of the reagent, the electronic absorption spectra
of the gold(III) extract contain a strong band at
30000 cm–1 intrinsic to the tetrachloroaurate(III) ion
Regarding the extra chemical shifts of signals from
the carbon atoms 6ëç, their positive values are natural:
the γ effects of the nitrogen atom have the sign opposite
to the α effect [14]. 13ë NMR spectra do not contradict and the spectra of the platinum(IV) extracts contain a
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 52 No. 6 2007

EXTRACTION OF GOLD(III), PALLADIUM(II), AND PLATINUM(IV)
973
yAu(III), mol/L
logDAu(III)
0.004 mol/L
1.6
(‡)
0.004
(‡)
1.4
1.2
1.0
0.8
0.6
0.003 mol/L
0.002 mol/L
0.003
0.002
0.001
0.001 mol/L
q = 1
0
0.001
0.002
0.003
0.004
xAu(III), mol/L
yPd(II), mol/L
0.025
(b)
–3.1 –3.0 –2.9 –2.8 –2.7 –2.6 –2.5 –2.4
logDPd(II)
0.04 mol/L
0.03 mol/L
0.020
0.015
1.5
1.3
1.0
(b)
0.02 mol/L
0.01 mol/L
0.010
0.005
0
0.8
0.5
0.3
0
q = 2
xPd(II), mol/L
yPt(IV), mol/L
0.025
(c)
0.04 mol/L
0.020
0.015
0.010
0.005
0.03 mol/L
0.02 mol/L
–2.00 –1.75
–1.50
logDPt(IV)
1.2
(c)
1.1
1.0
0.9
0.8
0.7
0.01 mol/L
0
0.01
0.02
0.03
0.04
0.05
xPt(IV), mol/L
q = 2
Fig. 2. Extraction isotherms for the extraction of (a)
gold(III), (b) palladium(II), and (c) platinum(IV) by reagent
S from 3 M HCl at 25°ë.
0.6
0.5
0.4
–2.9 –2.8 –2.7–2.6 –2.5–2.4
–2.3
band at 37200 cm–1 intrinsic to the PtCl26– ion. In the
IR spectra of the compounds precipitated with hexane
from the extracts, there are strong absorption bands in
the far-IR range associated with the halometal ions:
log[Sc‚]
Fig. 3. Effect of the free extractant concentration on the
extraction of (a) gold(III), (b) palladium(II), and (c) plati-
num(IV).
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 52 No. 6 2007

974
KHISAMUTDINOV et al.
Table 3. Parameters (chemical shifts δ and extra chemical shifts ∆δ, ppm) of a fragment of the 1H NMR spectrum for reagent S,
6
CH
1
N
2
N
2
3
CH
its protonated form, and extracts with D-chloroform
HC
5
N
4
S
S · HCl
Au(III)
Pd(II)
Pt(IV)
∆δ rel.
to
S · HCl
Proton Isomer
∆δ rel.
to S
∆δ rel. ∆δ rel. to
∆δ
∆δ rel. to
δ
δ
∆δ
δ
δ
δ
to S
S · HCl
rel. to S S · HCl
3CH
cis
7.82
7.82
8.11
8.14
8.48
8.46
9.62
9.57
0.66
0.64
1.50
1.42
8.61
8.57
9.30
9.28
0.79
0.75
1.19
1.13
0.12
0.11
0.32
0.29
8.39
8.37
8.51
8.47
0.57
0.55
0.40
0.33
0.11
0.09
0.40
0.29
8.35
8.35
9.61
9.46
0.53
0.53
1.49
1.31
0.13
0.13
0.01
0.11
trans
cis
5CH
trans
Table 4. Elemental analysis data for palladium(II) and platinum(IV) complexes with reagent S obtained by the direct and
extraction method
Found/calcd., %
Complex
Medium; set ratio
Color
composition
C
H
N
M
Cl
Extract
Extract
H2PdCl4 · 2S
37.7
38.5
3.8
4.1
8.7
9.0
10.7
11.4
23.5
22.8
Yellow
H2PtCl6 · 2S
PdCl2 · 2S
PtCl4 · 2S
33.3
32.9
3.2
3.5
8.0
7.7
15.0
17.8
30.2
32.8
Yellow
Neutral medium
1 : 1, 1 : 2
44.9
41.8
3.0
2.2
9.6
9.8
12.9
12.3
24.7
20.7
Light yellow
Orange
Neutral medium
1 : 1, 1 : 2
38.6
35.2
3.1
3.3
8.2
8.2
17.9
19.1
24.2
20.8
ν(Au–Cl) at 360 cm--1, ν(Pd–Cl) at 340 cm--1, and ν(Pt–
Cl) at 330 cm--1.
mental analysis (Table 4) verify the formation of com-
pounds in which the Pd : S and Pt : S ratios are 1 : 2 and
the Pd : Cl and Pt : Cl ratios are 1 : 6 and 1 : 8 with
account for the fact that the reagent itself contains two
chlorine atoms; namely, the complexes are H2PdCl4 · 2S
and H2PtCl6 · 2S.
Our results imply that the mechanism of the extrac-
tion of metals under the test conditions is interfacial
anion exchange. In this case, the insignificant extra
1
chemical shift of the proton signals in the H NMR
spectra of the extracts compared to the spectrum of the
protonated form can be explained by the noncoordina-
tion of the donor atom of the reagent to the metal ion
and by the effect of the substitution of bulkier chloro
complex anions for chloride ions.
Our results are consistent with the structure
described in work [15] for the ion associate of 1,2,4-tri-
azolo-[1,5α]-pyrimidine (L), a derivative of 1,2,4-triaz-
ole having the structural formula
Palladium(II) and platinum(IV) complexes were
isolated from extracts through the saturation of the
organic phase followed by deposition and washing with
hexane. After drying, the complexes were powders sol-
uble in ordinary organic solvents. The results of ele-
1
N
7
8
N
6
5
2
3‡
N
N
3
4
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 52 No. 6 2007

EXTRACTION OF GOLD(III), PALLADIUM(II), AND PLATINUM(IV)
975
3
logDPd(II)
0.7
with platinum(IV); the N atom in the formula corre-
sponds to the 4N atom in reagent S [15]. Single-crystal
X-ray diffraction showed that the compound synthe-
sized from 5 M HCl is an ion pair composed of two
3N-monoprotonated cations of the reagent and one
(‡)
0.6
0.5
0.4
0.3
0.2
0.1
0.0
PtCl26– anion. Each L cation is linked with the other
into a dimer through two hydrogen bonds N···4ç; in
3
the dimer the repulsion of the two positively charged
triazole--pyrimidine ions is weaker than their attraction
by hydrogen bonds. The octahedral hexachloroplati-
nate(IV) ion in the ion associate is distorted insignifi-
cantly: the Pt--Cl bond is elongated from 2.317 to
2.324 Å and the bond angle ClPtCl increases from 88.5°
to 91.5°. The protonation of the atom 3N was also judged
in [15] from the singlet at 11 ppm in the 1H NMR spec-
trum, which disappears upon addition of D−water.
–0.1
0
0.1 0.2
0.3 0.4 0.5
0.6 0.7
logDPt(IV)
1.2
(b)
Figure 4 displays the extent of extraction of palla-
dium(II) and platinum(IV) by reagent S vs. hydrogen
ion concentration. With increasing hydrogen ion con-
centration, the extraction increases, proving that the
metals are extracted in the form of ion associates [16].
1.0
0.8
To study the effect of the aqueous acidity on the rate
and mechanism of formation of palladium(II) and plat-
inum(IV) complexes with reagent S, we synthesized
their compounds from a neutral medium with the
metal : S ratio set equal to 1 : 1 or 1 : 2. The reaction
time required for the complexes to form in the reaction
of reagent S with Na2PdCl4 and Na2PtCl6 · 6H2O from
a neutral water--acetone solution was 30 min and 3 h,
respectively, which was dictated by the nature of the
metal ions. The time required for extraction equilib-
rium to be acquired in the case of interfacial anion
exchange is known to be not longer than several min-
utes. The slightly longer phase contact time required for
the extraction by the triazole derivative can probably be
explained by the set of steric factors, which arise from
the large size of the molecule, high acid concentration
required for the protonation of the nitrogen atom of the
reagent, and the gradual and consecutive protonation of
the reagent.
0.6
0
0.1
0.2
0.3
0.4
0.5
0.6
log cH
+
Fig. 4. Extraction of (a) palladium(II) and (b) platinum(IV)
with extractant S vs. hydrogen ion concentration at 25°ë
(c
= 0.005 mol/L, c = 0.015 mol/L, t = 20 min;
= 0.0049 mol/L, c = 0.02 mol/L).
S
Pd(II)
S
c
Pt(IV)
strong absorption band at 350 cm–1 and bands at 330
and 318 cm–1 are due to the stretching vibrations
ν(Pt−Cl) in a compound of the trans-PtCl4L2 type. The
formation of the coordination bonds Pt--N and Pd--N
can be judged from the appearance of broad medium-
intensity bands at 530--510 cm–1 in the spectra of the
complexes as distinct from the spectrum of the reagent.
It is pertinent to suggest that complexing occurs
through the formation of a metal--nitrogen coordina-
After complexing was over, the compounds were fil-
tered off, washed with water, and dried at room temper-
ature. From the results of chemical analysis (Table 4),
one can see that regardless of the set ratio, compounds
of one composition are only formed, namely PdCl2 · 2S
and PtCl4 · 2S. These compounds are powders and are
insoluble in ordinary organic solvents, unlike the
extraction complexes. For this reason NMR spectra
were not recorded for these compounds. In the far-IR
4
tion bond with the N triazole atom. The electronic
absorption spectra of the complexes did not display
resolved bands. The ability of the 4N heterocyclic atom
to coordinate to precious metal ions is indicated in the
literature: 15N and 195Pt NMR spectroscopy showed that
platinum(II) and platinum(IV) under neutral conditions
3
range, the palladium(II) complex shows a strong are complexed through the donor atom N and yield
absorption band at 360 cm–1, which is associated with
the stretching vibrations ν(Pd–Cl) in a complex of the
trans-PdCl2L2 type. In the platinum(IV) complex, the
trans-isomers [15]. Therefore, the acidity of the
medium directly influences the formation time, compo-
sition, and structure of the resulting compounds.
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 52 No. 6 2007

976
logDAu(III)
KHISAMUTDINOV et al.
4
nism with the initial protonation of the triazole N
atom:
1.95
(a)
(b)
(c)
H+ + AuCl–4 + S
concentration constant of extraction is
(S · H+)(AuCl–4 ). The relevant
1.90
[(SH+)AuCl–4]
1.85
1.80
1.75
1.70
y
˜
------------------------------------------------------
K = ---------------------------------------- =
[H+][AuCl–4][S]
(3 – y)(x0 – y)(S0 – y)
y
-------------------------
=
.
3x(S0 – y)
For palladium,
2H+ + PdCl24– + 2S
(S · H+)(PdCl24– ),
3.32 3.36 3.40 3.44
3.48
3.52 3.56
logDPd(II)
0.40
[(SH+)2PdCl2–]
4
˜
----------------------------------------------
K =
[H+]2[PdCl42–][S]2
0.38
0.36
0.34
0.32
0.30
0.28
0.26
y
y
-----------------------------------------------------------------
------------------------------
=
=
.
(3 – 2y)2(x0 – y)(S0 – 2y)2
9x(S0 – 2y)2
For platinum,
2H+ + PtCl26– + 2S
(S · H+)(PtCl26– ),
[(SH+)2PtCl2–]
6
˜
--------------------------------------------
K =
[H+]2[PtCl62–][S]2
103/T, K–1
y
y
-----------------------------------------------------------------
------------------------------
=
=
.
logDPt(IV)
1.6
(3 – 2y)2(x0 – y)(S0 – 2y)2
9x(S0 – 2y)2
Here, ı is the equilibrium metal ion concentration in the
aqueous phase, mol/L; y is the equilibrium metal ion
concentration in the organic phase, mol/L; x0 is the
starting metal ion concentration, mol/L; S0 is the start-
1.4
1.2
1.0
0.8
0.6
ing extractant concentration, mol/L; and H+ is the
hydrochloric acid concentration, equal to 3 mol/L.
The calculated concentration constants of extraction
are listed in Table 5.
With increasing temperature, the extraction of
gold(III), palladium(II), and platinum(IV) by reagent S
decreases (Fig. 5). Therefore, the extraction reactions
are exothermic. The thermodynamic parameters of the
extraction reactions were calculated from
0.4
3.25
3.30 3.35
3.40 3.45
3.50 3.55
1/T × 103, K–1
˜
∆G = –RTlnK ,
Fig. 5. Effect of temperature of the extraction of (a)
gold(III) (c = 0.0017 mol/L, c = 0.005 mol/L, t =
∆H – ∆G
----------------------
∆S =
,
Au(III)
S
T
10 min), (b) palladium(II) (c
0.015 mol/L, t = 20 min), and (c) platinum(IV) (c
= 0.0047 mol/L, c
=
=
Pd(II)
S
Pt(III)
RT1T2(logK2/K1)
Q = –∆H = -------------------------------------------- = 2.3Rtanα.
T2 – T1
0.0049 mol/L, c = 0.02 mol/L, t = 30 min) with reagent S
S
from 3.0 M HCl.
They are displayed in Table 6. The extraction is due to
the enthalpy factor.
The test metals can fully be stripped from the
organic phase by 5% aqueous solutions of thiourea fol-
lowed by the repeated use of the reagent in extraction
The body of the data obtained allows us to state that
the extraction of precious metals with reagent S under
the test conditions follows the ion-exchange mecha-
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 52 No. 6 2007

EXTRACTION OF GOLD(III), PALLADIUM(II), AND PLATINUM(IV)
977
Table 5. Concentration constants for the extraction of gold(III), palladium(II) and platinum(IV) with reagent S from 3.0 M
HCl to toluene at 25°C
Equilibrium concentration, mol/L
Concentration constants
Initial extractant
concentration, mol/L
˜
Kav
˜
of extraction K
x
y
Gold(III)
0.002
0.003
0.004
0.000010
0.000015
0.000020
0.000025
0.000113
0.000155
0.000190
0.000220
20.0 × 102
18.7 × 102
17.5 × 102
16.5 × 102
0.000010
0.000015
0.000020
0.000025
0.000230
0.000310
0.000370
0.000420
27.7 × 102
25.6 × 102
23.5 × 102
21.7 × 102
31.0 × 102
28.3 × 102
25.9 × 102
(23.3 4.0) × 102
0.000015
0.000020
0.000025
0.000490
0.000580
0.000650
Palladium(II)
0.01
0.02
0.03
0.04
0.000100
0.000150
0.000200
0.000250
0.000195
0.000280
0.000370
0.000440
23.5 × 102
23.3 × 102
24.0 × 102
23.5 × 102
0.000100
0.000150
0.000200
0.000250
0.000750
0.001050
0.001300
0.001550
24.4 × 102
24.3 × 102
23.9 × 102
24.1 × 102
24.4 × 102
24.9 × 102
24.8 × 102
24.3 × 102
24.5 × 102
24.8 × 102
24.2 × 102
24.7 × 102
(24.2 3.8) × 102
0.000100
0.000150
0.000200
0.000250
0.001580
0.002200
0.002700
0.003100
0.000100
0.000150
0.000200
0.000250
0.002650
0.003600
0.004300
0.005000
Platinum(IV)
0.01
0.02
0.03
0.04
0.0002
0.0003
0.0004
0.0005
0.0007
0.0009
34.29 × 102
35.05 × 102
37.18 × 102
0.0002
0.0003
0.0004
0.0015
0.0022
0.0023
28.84 × 102
33.48 × 102
28.86 × 102
(32.1 2.8) × 102
0.0002
0.0003
0.0004
0.0030
0.0046
0.0055
28.93 × 102
29.32 × 102
30.44 × 102
27.89 × 102
33.02 × 102
33.33 × 102
0.0002
0.0003
0.0004
0.0047
0.0065
0.0075
Table 6. Thermodynamic parameters of the extraction reac-
tion at 25°C
(the phase contact time during stripping extraction was
5 min). The reagent does not experience destruction
during extraction; redox processes do not occur. Lack-
ing selectivity, as most nitrogen-containing exractants,
thiourea can however extract the sum of precious met-
als from complex analytical and technological solu-
tions. Along with precious metals, the reagent can
extract several nonprecious and ferrous metals, such as
Metal
∆H, kJ/mol ∆G, kJ/mol ∆S, J/(mol K)
Gold(III)
–22.2
–10.6
–6.3
–19.2
–19.3
–20.0
–0.01
0.03
0.05
Palladium(II)
Platinum(IV)
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 52 No. 6 2007

978
KHISAMUTDINOV et al.
5. M. H. Palmer and D. Christen, J. Mol. Struct. 705 (1–3),
nickel(II), iron(III), and specifically zinc(II) and cop-
per(II). The problem of separating associated metals
can be solved both at the stripping stage and during fur-
ther hydrometallurgical conversion of the extracts.
177 (2004).
6. D. Bin, Y. Long, G. Hong-Ling, et al., Inorg. Chem.
Commun. 8 (1), 102 (2005).
7. C. M. Menzies and P. J. Squattrito, Inorg. Chim. Acta
From the above results, we can infer that the extrac-
tion and complexing properties of reagent S toward the
tested metals are due to the protonation and electron-
314, 194 (2001).
8. R. W. Clark, P. J. Squattrito, A. K. Sen, and S. N. Dubey,
Inorg. Chim. Acta 293, 61 (1999).
4
donating ability of the N triazole atom. The reagent
9. J. G. Haasnoot, Coord. Chem. Rev. 200–202, 131
can be recommended for use as a group extractant for
the precious metals, in particular, for their extraction
from strong acid solutions that contain only these met-
als. Other advantages of the reagent include its relative
availability and practical insolubility in aqueous
phases.
(2000).
10. A. I. Matesanz, J. Mosa, I. Garcia, et al., Inorg. Chem.
Commun. 7 (6), 756 (2004).
11. F. Dallavalle, F. Gaccioli, R. Franchi-Gazzola, et al.,
J. Inorg. Biochem. 92 (2), 95 (2002).
'
'
y
12. F. Vydra and J. elikovsk , Chem. Listy 51, 768 (1957).
C
13. S. I. Ginzburg, N. A. Ezerskaya, I. V. Prokof’eva, et al.,
The Analytical Chemistry of the Platinum Metals
(Nauka, Moscow, 1972) [in Russian].
REFERENCES
1. O. G. Shakirova, D.Yu. Naumov,Yu. G. Shvedenkov, et al.,
14. E. Pretsch, T. Clerc, J. Seibl, and W. Simon, Tables of
J. Struct. Chem. 44 (4), 642 (2003).
Spectral Data for Structure Determination of Organic
Compounds
(Springer,
Berlin/Heidelberg/New
2. M. Shakir, S. Parveen, N. Begum, and P. Chingsubam,
York/London/Paris/Tokyo/Hong Kong, 1998), p. 15.
Transition Met. Chem. 29, 196 (2004).
15. E. Szlyk, L. Pazderski, I. Lakomska, et al., Polyhedron
3. M. H. Klingele and S. Brooker, Coord. Chem. Rev. 241,
21, 343 (2002).
119 (2003).
16. Yu. A. Zolotov, B. Z. Iofa, and L. K. Chuchalin, Extrac-
tion of Metal Halide Complexes (Nauka, Moscow, 1973)
[in Russian].
4. P. J. van Koningsbruggen, K. Goubitz, J. G. Haasnoot,
and J. Reedijk, Inorg. Chim. Acta 268, 37 (1998).
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 52 No. 6 2007