Extraction and complexing of copper(II) with benzoic acid N,N-dihexylhydrazide

Article abstract of DOI:10.1134/S0036023606120217

The solubility and acid-base properties of benzoic acid N,N-dihexylhydrazide (BDHH) were studied. The extraction of copper(II), cobalt(II), nickel(II), zinc(II), iron(III), platinum(II), platinum(IV), chromium(III), chromium(VI), palladium(II), and molybdenum(VI) with this reagent was studied. It was shown that BDHH most efficiently extracts copper(II) from ammonia solutions and chromium(VI) from sulfuric acid solutions. In the extraction of copper(II), complexes with the [Cu(II)]: [BDHH] = 1: 1 and 1: 2 stoichiometries were found to form. The structure of the 1: 2 complex was suggested proceeding from its IR spectra. A copper(II) extraction isotherm was plotted. Nauka/Interperiodica 2006.

Full text of DOI:10.1134/S0036023606120217

ISSN 0036-0236, Russian Journal of Inorganic Chemistry, 2006, Vol. 51, No. 12, pp. 1973–1976. © Pleiades Publishing, Inc., 2006.
Original Russian Text © A.V. Radushev, V.Yu. Gusev, T.D. Batueva, G.S. Bogomazova, L.S. Shabalina,V.N. Tyryshkina, V.I. Karmanov, 2006, published in Zhurnal Neorgan-
icheskoi Khimii, 2006, Vol. 51, No. 12, pp. 2096–2099.
PHYSICAL CHEMISTRY
OF SOLUTIONS
Extraction and Complexing of Copper(II) with Benzoic Acid
N,N-Dihexylhydrazide
A. V. Radushev, V. Yu. Gusev, T. D. Batueva, G. S. Bogomazova, L. S. Shabalina,
V. N. Tyryshkina, and V. I. Karmanov
Institute of Technical Chemistry, Ural Division, Russian Academy of Sciences,
ul. Lenina 13, Perm, 614600 Russia
Received November 12, 2005
Abstract—The solubility and acid–base properties of benzoic acid N,N-dihexylhydrazide (BDHH) were stud-
ied. The extraction of copper(II), cobalt(II), nickel(II), zinc(II), iron(III), platinum(II), platinum(IV), chro-
mium(III), chromium(VI), palladium(II), and molybdenum(VI) with this reagent was studied. It was shown that
BDHH most efficiently extracts copper(II) from ammonia solutions and chromium(VI) from sulfuric acid solu-
tions. In the extraction of copper(II), complexes with the [Cu(II)] : [BDHH] = 1 : 1 and 1 : 2 stoichiometries
were found to form. The structure of the 1 : 2 complex was suggested proceeding from its IR spectra. A cop-
per(II) extraction isotherm was plotted.
DOI: 10.1134/S0036023606120217
A number of papers dealing with complexing of distilled off. The residue was recrystallized from an
nonprecious metals with aromatic hydrazides has been
published, e.g., [1–5]. These ligands form two types of
complexes (cationic or neutral) depending on pH [2–5].
The extraction of copper(II) and several nonprecious and
rare metals by aromatic [6] and naphthenic [7] hydrazides
has been studied. We have not found data regarding the
extraction of these metals with N,N-dialkylhydrazides.
Manganese(II), cobalt(II), nickel(II), copper(II), and
zinc(II) complexes with 2,4-dichloro-phenoxyacetic acid
and α-(2-methyl-4-chlorophenoxy)propionic acid
N,N-di-methylhydrazides having the general formula
[M(HL)2(H2O)2](NO3)2, where HL stands for a hydra-
zide molecule were prepared in [8]. Complexes of these
metals with 4-nitro-benzoic acid N,N-dimethylhy-
drazide were prepared in [9]. In addition, ML2 com-
plexes were isolated, where L is a deprotonated
hydrazide molecule. It was pertinent to elucidate how
the incorporation of two alkyl radicals into the func-
tional group would affect the extraction and complex-
ing of nonprecious metal ions. Benzoic acid
N,N-dihexylhydrazide PhCONHN(C6H13)2, BDHH)
was chosen for the study.
ethanol/water (2 : 1) mixture. Yield: 20 g (66%); mp =
77–78°ë; Rf = 0.74 (m-xylene : BuOH = 2 : 1). 1H NMR
and IR spectra verified the structure of the compound.
The main substance was 99.5% as determined with
nonaqueous potentiometric titration [10].
IR spectra were recorded on a Bruker IFS 66/S Fou-
rier transform spectrometer. UV spectra were recorded
on an SF 26 spectrophotometer. The solution pH was
measured on an EV-74 pH meter with glass and sil-
ver/silver chloride electrodes. Conductometric titration
was performed on a Radelkis OK-102/1 conductometer
equipped with an OK-0902P bell-shaped electrode. The
reagents used (CuSO4, NiCl2, ZnSO4, CoCl2, Fe2(SO4)3,
PdCl2, K2Cr2O7, CrCl3, and Na2MoO4) were analyti-
cally or chemically pure. Platinum(II, IV) sulfate was
prepared by dissolving metallic platinum in aqua regia,
concentrating the solution to wet salts, and treating the
precipitate with H2SO4 until SO3 vapor was expelled.
The concentration of the elements in standard solutions
and the aqueous phase after the extraction was deter-
mined as follows: zinc(II), cobalt(II), nickel(II),
iron(III), and copper(II) were determined complexo-
metrically [11]; low copper(II) concentrations were
determined photometrically with sodium diethyldithio-
carbamate [12]; molybdenum(VI), photometrically
with potassium rodanide [13]; palladium (II), plati-
num(II), and platinum(IV), spectrophotometrically
with diphenyldithiosemicarbazide [14]; chromium(III),
photometrically with K4[Fe(CN)6]; and chromium(VI),
EXPERIMENTAL
Synthesis of BDHH. Benzoic acid hydrazide (13.6 g,
0.1 mol) was dissolved in i-PrOH (150 ml), KOH (11.2 g,
0.2 mol) was added, and hexyl bromide (28 mL,
0.2 mol) was dropped under stirring. The reaction mix-
ture was heated under stirring until the pH was neutral
(for 5–6 h), and then filtered off; then, the solvent was photometrically with diphenylcarbazide [15].
1973

1974
RADUSHEV et al.
E
100
Cu(II), %
The Ka was determined spectrophotometrically
1
[16]. The measurement parameters were as follows:
λ = 270 nm, cBDHH = 5 × 10–4 mol/L, l = 1 cm, H2O :
EtOH = 1 : 1, and I = 0.1(NaNO3). The resulting value
80
60
40
20
was Ka = 2.83 0.04 (n = 5, ê = 0.95). The acid dis-
sociation of BDHH started when the alkali concentra-
1
tion was higher than 3 mol/L. The Ka value was not
2
determined because of the demixing of aqueous–ethan-
olic solutions of the reagent at high alkali concentra-
tions. For benzoic acid hydrazide, Ka = 3.27 0.03
1
and Ka = 12.2 0.1 [17]. Thus, the two hexyl radicals
2
introduced into the benzyl hydrazide molecule weaken
both the basic and the acid properties, which are char-
acterized by Ka and Ka , respectively.
1
2
Extraction properties of BDHH. The extraction of
the following metals was studied: 1 × 10−3 mol/L of cop-
per(II), cobalt(II), nickel(II), zinc(II), and iron(III) ions;
1.3 × 10–3 mol/L of chromium(III); and 0.66 × 10−3 mol/L
of chromium(VI) in sulfuric and ammoniac solutions
were extracted with a 0.05 M solution of BDHH in
m-xylene; 2.6 × 10−5 mol/L of platinum(II) and plati-
num(IV) in sulfuric acid solution and 5.2 × 10−5 mol/L
of palladium(II) in hydrochloric acid solutions were
extracted with a 5 × 10−3 M solution of BDHH in
m-xylene; and 1.46 × 10–4 mol/L molybdenum(VI) in
HCl was extracted with a 1.46 × 10−2 M solution of
BDHH in AmOH.
0
4
8
2 4
3
pHeq
cNH , mol/L
Fig. 1. Copper(II) extraction E
plot. The extractant was 0.05 mol/L BDHH in m-xylene.
vs. solution acidity
Cu(II)
–3
V
: V = 1 : 10. c
= 1 × 10 mol/L.
org
aq
Cu(II)
RESULTS AND DISCUSSION
Solubility and acid–base properties of BDHH.
The following solubility data were obtained:
Cobalt(II), nickel(II), zinc(II), iron(III), and chro-
mium(III) ions were practically not extracted into the
organic phase either from H2SO4 solutions or from NH3
solutions. Low percentage extraction was observed for
the following elements: for palladium(II), less than 16
(from 0.5–3 M HCl); for platinum(II) and plati-
num(IV), less than 7 (from 4–9 M H2SO4); and for
molybdenum(VI), 20–30 (pH 0–6). Of the ions consid-
Solvent:
H O, AmOH, Hexane, Toluene, m-Xylene.
2
Solubility, g/L:
0.2, 177.8,
1.9,
51.9,
48.6.
Thus, amyl alcohol and aromatic hydrocarbons are
the best solvents for BDHH. Unsubstituted benzoic
acid hydrazide is highly soluble in water and is practi-
cally insoluble in aromatic hydrocarbons. The incorpo-
ration of two hexyl radicals decreases the solubility of
the resulting compound in water and increases its solu-
bility in aromatic hydrocarbons, thus making it usable
in extraction processes.
ered, only Cr2O27– was 98–99% extracted in the form of
a positively charged orange complex from 0.3–0.9 M
H2SO4 and copper(II) ions were extracted to the same
degree in the form of a dark red complex from ammonia
solutions.
In BDHH solutions, the following equilibria exist
with their Ka and Ka :
1
2
+
+
Extraction and complexing of copper(II) with
BDHH. The copper(II) extraction increased from 3 to
95% at pHs from 2 to 4.5, remained unchanged until the
NH3 concentration reached 0.8 mol/L, and decreased
steadily to 71% as the NH3 concentration increased to
4.3 mol/L; the steady decrease was likely due to the
competing reaction of ammoniate formation (Fig. 1).
With the goal of elucidating how ammonium salts
affect the extraction, we studied the extraction of cop-
per(II) from solutions that contained 3.2 mol/L NH3
and various concentrations of (NH4)2SO4 (table). It is
clear that ammonium sulfate appreciably decreases the
copper(II) extraction.
–H ; pK
–H ; pK
a 2
a 1
H2L+
HL
L–.
(1)
Copper(II) extraction ECu(II) from an ammonia solution as a
function of (NH4)2SO4 concentration
c(NH ) SO
,
4
4
2
ECu(II), %
g L–1/mol L–1
0
84.0
31.8
17.3
13.5
86/0.65
172/1.30
376/2.85
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 51 No. 12 2006

EXTRACTION AND COMPLEXING OF COPPER(II) WITH BENZOIC ACID
1975
The molar ratio method was used to determine the
composition of copper(II) extraction complexes (Fig. 2).
The curve measured in the ammonia buffer had no well-
defined inflections (Fig. 2, curve 1). The slope method
[18] revealed the formation of two extraction complexes
with [Cu(II)] : [BDHH] = 1 : 1 and 1 : 2 stoichiometries
(Fig. 2, curve 2). In aqueous ammonia, the same curve
had a well-defined inflection at [Cu(II)] : [BDHH] = 1 : 2
(Fig. 2, curve 3). Figure 2 clearly demonstrates the
effect of the ammonium salt on the copper(II) extrac-
tion.
E
Cu(II), %
3
1
80
60
40
20
–logEx/(100 – Ex)
2
0
In the conductometric titration curve of an ethanolic–
aqueous–ammoniac solution of copper(II) with BDHH
(Fig. 3), there are two flex points at [Cu(II)] : [BDHH] =
1 : 1 and 1 : 2. Thus, conductometric titration also con-
firms the formation of these complexes.
tag b = 0.9
–1
tag a = 1.8
1.6
2.0
–logc
The extract of the copper(II) complex obtained in
the ammonia solution at [Cu(II)] : [BDHH] = 1 : 2 was
dark red. This color was conserved after passing
through cation-exchanger Ku-2-8rC in the Na-form,
which proves that the complex has no charge. The IR
spectrum of the extract did not display bands at 3314,
3420, and 3425 cm–1; these bands, which were in the
spectrum of the starting reagent, are intrinsic to the
stretching vibrations of the free and bound N–H group.
The C=O stretching vibrations at 1675 and 1695 cm–1
also did not appear. New bands appeared instead: the
band at 1550 cm–1 may be assigned to the C=N
stretches, and the band at 1350 cm–1 is due to the C–O
stretches [19]. This means that the reagent enters the
complex in the deprotonated form. There were no
absorptions bands of molecular ammonia in the IR
spectrum. Proceeding from the above data, we repre-
sent the configuration of the complex as follows:
0
4
8
[BDHH] : [Cu(II)]
Fig. 2. Saturation curves for the extraction of copper(II)
with BDHH in (1) an ammonia buffer solution and (3) aque-
ous ammonia. (2) Curve (1) processed using the slope
–3
method. For curve (1), Ò
= 4.5 × 10 mol/L, pH 10.0,
ëu(II)
V
: V = 1 : 1, and I = 0.2 (KC l). For curve (3), Ò
= 4 ×
org aq
−3
ëu(II)
10 mol/L, cNH = 0.14 mol/L, pH 10.4, V : V = 1 : 1, and
I = 0.2 (KCl).
org aq
3
∆σ, µS
44
R2N
Cu
N
O
40
36
32
28
O
N
NR2
The deprotonated hydrazide species does not exist
in the solution under the reaction conditions: its forma-
tion is observed when the alkali concentration is higher
than 3 mol/L. Therefore, the appearance of such a com-
plex in a less alkaline solution should be attributed to
the elimination of a proton from the inner-sphere
hydrazide complex. This process is likely due to the
fact that the alkyl substituents in the hydrazide group
create steric hindrances, and these hindrances induce an
increase in the energy of the copper(II) complex. The
deprotonation of the ligand molecule and the appear-
ance of a chemical bond between the O and N atoms
instead of a coordination link, likely, decrease the
energy of the complex.
0
4
8
VBDHH, mL
Fig. 3. Conductivity increment ∆G of the copper(II) solution
vs. titrant volume. cCuSO = 1 × 10 mol/L.
–2
=
V
CuSO4
4
–2
4 mL. c
= 1.01 × 10 mol/L. V
= 69 mL (EtOH :
BDHH
solution
H O = 2 : 1). c
= 0.14 mol/L.
2
NH3
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 51 No. 12 2006

1976
y(Cu) × 102, mol/L
RADUSHEV et al.
of the efficient copper(II) extraction is displaced to
higher pHs.
2.4
2.0
1.6
ACKNOWLEDGMENTS
This work was supported by the State Program for
Support of Leading Scientific Schools (project no.
NSh-5812.2006.3).
REFERENCES
1. A. A. Popel’ and V. A. Shchukin, Zh. Neorg. Khim. 20
1.2
0.8
0.4
(7), 1917 (1975).
2. P. N. Buev, Candidate Dissertation in Chemistry (Mos-
cow State Univ., Moscow, 1982).
3. P. V. Gogorishvili, M. V. Karkarashvili, and D. Z. Kalan-
darishvili, Zh. Neorg. Khim. 14 (6), 1516 (1964).
4. P. V. Gogorishvili, Yu. Ya. Kharitonov, M. V. Karkarash-
vili, and R. I. Machkhoshvili, Zh. Neorg. Khim. 14 (10),
2891 (1969).
5. R. I. Machkhoshvili, Doctoral Dissertation in Chemistry
(Kurnakov Inst. of General and Inorganic Chemistry,
Moscow, 1983).
0
0.5
1.0
1.5
2.0
2.5
x(Cu) × 103, mol/L
Fig. 4. Copper(II) extraction isotherm. c
= 0.05 mol/L.
BDHH
6. A. G. Ciba-Geigi, Patent FR 221327 (1974).
V
: V = 1 : 1. I = 0.2 (KCl). c
= 0.14 mol/L.
NH3
org
aq
7. A. V. Radushev, V. Yu. Gusev, G. S. Bogomazova, et al.,
Zh. Prikl. Khim. 69 (8), 1283 (1996).
8. V. F. Shul’gin, N. G. Zub, N. G. Strizhakova, et al.,
Proceeding from the above, the extraction may in
general be represented by the following scheme:
Koord. Khim. 26 (6), 446 (2000).
9. V. Ya. Zub, P. V. Bugaeva, N. G. Strizhakova, and
Yu. A. Maletin, Koord. Khim. 30 (10), 792 (2004).
[Cu(NH3) ]2+ + 2HL(org)
n
10. A. V. Radushev, V. Yu. Gusev, and G. S. Bogomazova,
(2)
Zh. Neorg. Khim. 37 (10), 2292 (1992).
+
CuL2(org) + (n – 2)NH3 + 2NH4 ,
11. Indicators, Ed. by E. Bishop (Pergamon, Oxford (U.K.),
1972; Mir, Moscow, 1976).
where HL is the neutral and L– is the deprotonated
BDHH molecule.
12. V. N. Podchainova and P. N. Simonova, The Analytical
Chemistry of Copper (Nauka, Moscow, 1990), p. 106 [in
Russian].
The extraction isotherm is plotted in Fig. 4. The cop-
per(II) capacity of the BDHH solution was 0.023 mol/L
or 1.5 g/L, which practically corresponds to the limiting
saturation of the organic phase with the complex at
[Cu(II)] : [BDHH] = 1 : 2.
13. A. I. Busev, The Analytical Chemistry of Molybdenum
(Akad. Nauk SSSR, Moscow, 1962), p. 217 [in Russian].
14. A. V. Radushev and L. A. Statina, Zh. Anal. Khim. 28
(12), 2360 (1973).
15. A. K. Lavrukhina and L. V. Yukina, The Analytical
Chemistry of Chromium (Nauka, Moscow, 1979) pp. 42,
43 [in Russian].
16. I. Ya. Bernshtein and Yu. L. Kaminskaya, Spectrophoto-
metric Analysis in Organic Chemistry (Khimiya, Lenin-
grad, 1975), p. 144 [in Russian].
In summary, the incorporation of two hexyl radicals
in the functional group of benzoic acid hydrazide
increases the solubility of the resulting compound in
aromatic hydrocarbons, decreases its solubility in
water, and weakens its acid and base properties relative
to the starting hydrazide. Benzoic acid N,N-dihexylhy-
drazide, unlike naphthenic acid hydrazides (which
extract copper(II) from low-acidity solutions in the form
of a charged complex with [Cu(II)] : [hydrazide] = 1 : 3),
BDHH extracts copper(II) in the form of an uncharged
complex with [Cu(II)] : [BDHH] = 1 : 2, and the range
17. A. A. Popel’ and V. A. Shchukin, Zh. Neorg. Khim. 20
(7), 1917 (1975).
18. M. I. Bulatov and I. P. Kalinkin, Manual on Photometric
Analysis (Khimiya, Leningrad, 1986) [in Russian].
19. Yu.Ya. Kharitonov, R. I. Machkhoshvili, and N. B. Gen-
eralova, Zh. Neorg. Khim. 19 (7), 1856 (1974).
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 51 No. 12 2006