Extraction and complexation of copper(II) with para-tert-butylbenzhydrazide and its N',N'-dimethyl derivative

Article abstract of DOI:10.1134/S1070363212040135

The extraction of copper(II) with the para-tert-butylbenzoic acid hydrazide and related N',N'dimethyl derivative was studied. The composition and structure of the extracted complexes were determined, the mechanism of extraction of copper(II) in different

Full text of DOI:10.1134/S1070363212040135

ISSN 1070-3632, Russian Journal of General Chemistry, 2012, Vol. 82, No. 4, pp. 679–684. © Pleiades Publishing, Ltd., 2012.
Original Russian Text © V.Yu. Gusev, D.A. Muksinova, A.V. Radushev, 2012, published in Zhurnal Obshchei Khimii, 2012, Vol. 82, No. 4, pp. 593–598.
Extraction and Complexation of Copper(II)
with para-tert-Butylbenzhydrazide
and Its N',N'-Dimethyl Derivative
V. Yu. Gusev, D. A. Muksinova, and A. V. Radushev
Institute of Technical Chemistry, Ural Branch, Russian Academy of Sciences,
ul. Akad. Koroleva 3, Perm, 614013, Russia
e-mail: info@itch.perm.ru
Received February 21, 2011
Abstract—The extraction of copper(II) with the para-tert-butylbenzoic acid hydrazide and related N',N'-
dimethyl derivative was studied. The composition and structure of the extracted complexes were determined,
the mechanism of extraction of copper(II) in different media was suggested, the extraction constant was
calculated. The copper(II) complex compounds with these reagents were isolated.
DOI: 10.1134/S1070363212040135
The hydrazide group is specific with respect to the
copper(II) cation. A lot of copper complexes with
aliphatic and aromatic acids hydrazides were obtained
[1–6]. Complexes of copper(II) with the N',N'-dialkyl
hydrazides derivatives with long hydrocarbon radicals
are soluble in organic solvents, which allows using
these compounds for copper extraction. The extraction
of copper(II) with octanoic acid hydrazide (HL) was
investigated [7] and it was shown that this compound
extracted copper from slightly acidic media as the
cationic complex [Cu(HL)3]2+. The benzoic acid N',N'-
dialkylhydrazides (HL) extract copper(II) from the
ammonia medium as the electrically neutral inner-
complexes of the general formula CuL2, where L is
deprotonated form of the reagent [8, 9]. The extraction
of copper(II) with substituted benzoic acid hydrazides
containing a hydrocarbon substituent in the benzene
ring, and their N',N'-dialkyl derivatives has not been
studied. Such moiety exhibits the +I-effect and can
affect the extraction properties of the reagents, as well
as the composition and structure of the formed copper(II)
complex. Therefore it is interesting to investigate the
extraction of copper(II) with these compounds, to
compare the results with the properties of compounds
containing no substituent in the benzene ring, and to
determine its effect on the copper(II) extraction, the
composition and structure of extracted complexes, and
to isolate the copper(II) complexes with these com-
pounds. For the study we selected para-tert-butyl-
benzoic acid hydrazide (I) and its N',N'-dimethyl
derivative (II).
O
t-Bu
NH N(R)2
R = H (I), CH3 (II).
Table 1 lists the solubility of the reagents. As seen,
the solubility of compounds in organic media increases
with increasing dielectric constant (ε) of the solvent.
Water falls out from this series: its dipole moment μ =
1.84, [10], which slightly increases the solubility of
these compounds; the latter are also polar substances.
Figure 1 illustrates the extraction properties of
compounds I and II toward copper(II). The character
of the copper extraction with these substances is
Table 1. Solubility of reagents at t = 20±1°C
Solubility, g l–1 (M)
Solvent (ε) [10]
compound I
compound II
Water (1.01)
1.0 (0.005)
0.85 (0.0039)
Hexane (1.90)
o-Xylene (2.51)
i-AmOH (14.7)
0.2 (0.001)
8.6 (0.045)
52.0 (0.270)
0.18 (0.0008)
0.85 (0.0039)
157.1 (0.7141)
679

680
GUSEV et al.
Е, %
–log D
c(NH3), M
рН
Fig. 1. Dependence of extraction of copper(II) with 0.05 M
solutions of compounds I and II in i-AmOH on pH and
concentrations of NH3. cCu(II) = 0.005 M, Vo:Vw = 1:2, τ =
3 min. (1) compound I, (2) compound II.
–log cr
different. Compound I reacts with copper(II) in acidic
medium to form a blue extractable complex. In the pH
range of 0.8–6 the degree of extraction increases from
35 to 95%. It reaches 98% at pH 7 and remains
constant up to pH 9. The color of the extract changes
to a dirty green. With a further increase of pH the degree
of extraction decreases rapidly, and at the NH3
concentration 1 M falls to 60%. The organic phase
becomes brown. Change in the color of the extract
suggests that at different pH values different
complexes are extracted.
Fig. 2. Dependence of the partition coefficient logarithm
(log D) of copper(II) vs. the reagent concentration
logarithm (log cR) at Vo:Vw = 1:1. (1) compound I, cCu(II)
0.002 M, pH = 1.22–1.30, τ = 3 min. (2) compound I, cCu(II)
=
=
0.005 M, pH = 10.3 (ammonia buffer), τ = 5 min., (3)
compound II, cCu(II) = 0.005 M, pH = 10.3 (ammonia
buffer), τ = 5 min.
hydrazide molecule, and neutral chelate compounds of
the general formula MLn, where L is the deprotonated
form of the hydrazide [11]. To determine the types of
extractable complexes we used the method of ion
exchange. By passing colored extracts of the
complexes through the cationite KU-2-8rC in Na+
form we established that compound I formed a charged
complex at pH < 6 while at pH > 6 the complex was
not charged. Compound II forms only an uncharged
complex in the entire investigated range of pH and
NH3 concentrations.
Compound II with copper(II) forms a violet
extractable complex over the entire studied range of
pH values and NH3 concentrations. It begins to extract
copper(II) at higher pH values than compound I. In the
pH range 4.8–6.7 the degree of extraction increases
from 32% to 98% and remains the same until c(NH3)
~1 M. At an increase in the ammonia concentration to
5 M it falls to 60%. Thus, the introduction of two
N',N'-methyl radicals to the molecule I shifts the region
of maximum extraction of copper(II) to higher pH
values and ammonia concentration. The presence of
para-tert-butyl radical in the benzene ring has no
effect on the region of maximum of the copper(II)
extraction with compound II compared with the
benzoic acid N',N'-dialkylhydrazides [8, 9].
Compound I was established by the method of the
shifting equilibrium to form at pH < 6 the extractable
complex with a ratio of [Cu(II)]:[reagent] = 1:3 (Fig. 2,
curve 1) we used the method of shifting the
equilibrium. At pH > 6 a complex is formed with a
component ratio [Cu(II)]:[ligand] = 1:2 (Fig. 2, curve
2). Compound II forms an extractable complex with a
ratio of components [Cu(II)]:[ligand] = 1:2 (Fig. 2,
curve 3).
It is known from the literature that hydrazides form
two types of complexes: positively charged complexes
of the general formula [M(HL)m]n+, where HL is the
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 82 No. 4 2012

EXTRACTION AND COMPLEXATION OF COPPER(II)
681
X
Based on these data, the process of copper(II)
extraction with these compounds from weakly acidic
medium can be represented by the following
equations:
Compound I: Cu2+ + 3HL(o) →← [Cu(HL)3]2+,
(1)
(2)
(w)
(o)
2+
Compound II: Cu + 2HL(o) →← CuL2(o)
.
(w)
Here HL are the molecules of the corresponding
reagents. Subscripts (w) and (o) denote the aqueous
and the organic phases respectively.
The comparison of extraction properties of
compound I and octanoic acid hydrazide (the data for
the benzoic acid hydrazide are absent due to its poor
solubility in organic solvents) shows that these
compounds form the extractable copper complexes of
the same composition and structure. They extract cop-
per(II) more efficiently from the slightly acidic media.
Y
Fig. 3. The Cu(II) extraction isotherm from ammonium
media with solution of compound II in i-AmOH. Vo:Vw =
1:1, cHL = 0.025 M, c(NH3) = 0.2 M, τ1 = 25 min. X is cCu(II)
in the organic phase (mM); Y is cCu(II) in the aqueous phase
(mM).
Compound II forms with copper(II) the extractable
complex, which is similar to the complexes formed with
the benzoic acid N',N'-dialkylhydrazides. Compound
II, like these reagents, which are its structural analogs,
extracts copper(II) from ammonia rather more
efficiently than from acidic medium.
release of protons, in the ammonium medium they will
interact with ammonia to form ammonium cations.
Therefore, the process of extraction of copper(II) with
compound II in this medium can be described by the
following equation:
The IR spectrum of the Cu(II) complex with
compound II extracted from ammonia medium does
not contain the absorption bands of ammonia in the
region 3200–3400 cm–1 (Table 5), that is, ammonia is
not included in its composition. Thus, the structure of
the extracted complex can be represented by the
general formula CuL2. These findings are consistent
with the results of [8] that in the IR spectra of the
copper(II) extract obtained with the benzoic acid N',N'-
dihexylhydrazide from the ammonia medium these
bands are also absent. Since the formation of chelate
compounds according to Eq. (2) proceeds with the
[Cu(NH3)4]2+ + 2HLorg ⇆ CuL2org + 2NH3(w) + 2NH4+(w). (3)
(w)
Hence, the expression for the extraction constant is:
[CuL2][NH4+]2[NH3]2
.
Kex
=
(4)
[Cu(NH23+)4][HL]2
Table 2. The calculation of the extraction constant of copper(II) with compound IIa
[Cu(NH3)42+]×10 3, M
[CuL2]×103, M
[HL]2×104, M
0.85
[NH4+]2×103, M
Kex×103
0.63
log Kex
2.80
2.67
0.1
0.9
1.3
1.9
2.9
7.9
10.0
10.7
10.9
11.2
0.7
0.9
1.2
1.4
1.2
0.25
0.47
0.13
0.76
2.88
0.10
0.80
2.90
0.07
0.68
2.83
a log Kex 2.82±0.06 (P = 0.95, n = 5).
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682
GUSEV et al.
The constant was calculated using the data of the
[Cu]:[I] = 1:2 was isolated. A similar difference in the
complexes of copper(II) in solution and in solid state
was also observed for ther hydrazides [5]. Shman’ko et
al. attributed this difference to the Jahn–Teller effect.
In the crystal the copper complex loses its degenerated
state due to the change in its geometry at the removal
of one ligand molecule. In solution, the stabiliza-
tion occurs due to its solvation by the solvent
molecules.
extraction isotherm of copper(II) (Fig. 3) in accordance
with [12]. Table 2 shows the calculation of the con-
stants of copper(II) extraction.
In the case of I, in ammonia medium a complex of
unknown structure is formed.
Thus, tert-butyl radical in the para position of
benzene ring has no effect on the extraction properties
towards copper(II) of both substituted benzoic acid
hydrazide and its N',N'-dimethyl derivative. This can
be attributed to its remoteness from the functional
group. The factor that dramatically changes the extrac-
tion properties of hydrazides is N',N'-alkylation of the
molecules, because in this case the alkyl groups are
directly attached to the hydrazide group and affect its
coordination-chemical behavior.
The uncharged complex with compound II is
readily soluble in aliphatic hydrocarbons and
chloroform, poorly in acetone, and is virtually
insoluble in water. The cationic complexes of both
compounds are soluble in alcohol, acetone, slightly
soluble in chloroform, o-xylene, and insoluble in water
and hydrocarbon solvents.
It is known that hydrazides and N',N'-dialkyl-
hydrazides coordinate metals by the oxygen and
terminal nitrogen atoms, forming a five-membered
metallocycle [13, 14]. The structure of the resulting
charged and uncharged complexes can be represented
by the following general formulas:
Table 3 shows the results of elemental analysis of
the obtained copper(II) complexes. Although the
compound I forms with copper(II) the positively charged
extractable complex of the composition [Cu]:[I] = 1:3,
in the crystalline state the complex of the composition
n+
M
M
O
O
N
R
Xn
R
C
C
NH NH2
NH2
n
m
Table 4 shows the frequencies of stretching vibra-
tions of these groups in the obtained complex com-
pounds of copper(II) and the studied reagents. In the
spectrum of the complex [Cu(HL)2]SO4·2H2O with
compound I the vibration frequency of NH2 group is
shifted by about ~100 cm–1 to the low-frequency region
compared to the original reagent. The C=O vibration
frequency (amide I) is shifted by 13 cm–1 to the low-
frequency region compared with the position of this
band in the solution of I in CCl4 (1678 cm–1). This
indicates the participation of these groups in the coordina-
tion with the copper atom. The amide-I band of
compound I in vaselibe oil (~1624 cm–1) is shifted to
the low frequency compared to the usual position in
compounds of this type (~1640–1660 cm–1) [15, 16].
This is due to the formation of stronger hydrogen bonds.
Table 3. Elemental analysis of the copper(II) complexes
Found, %
Calculated %
Formula
Complexes
Complex color
C
H
N
Cu(II)
C
H
N
Cu(II)
[Cu(HL)2]SO4·2H2O Blue
[Cu(HR)]Cl2 Green
[Cu(HR)2]SO4·2H2O Bright blue
CuR2 Pink
45.75
45.02
51.18
62.30
6.43
5.55
6.93
9.27 10.90
7.69 17.97
C22H36N4O8SCu
C13H20Cl2N2OCu
C26H44N4O8SCu
C26H38N4O2Cu
45.56
44.01
49.10
62.21
6.21
5.64
6.92
7.58
9.66 10.96
7.89 17.91
9.03
9.71
8.81
9.99
7.68 11.12 12.70
11.17 12.66
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EXTRACTION AND COMPLEXATION OF COPPER(II)
683
Table 4. Stretching vibration frequencies (cm–1) in the IR
spectra of compounds I and II and their complexes with
copper(II)
In the spectra of the charged complexes of compound
II the frequency of the amide-I band is reduced by 40–
50 cm–1 compared with the original reagent. Although
the N–H group is not involved directly in the complex
formation, its stretching vibration frequency is also
reduced by ~20–60 cm–1, due to the influence of the
neighboring nitrogen atom coordinated to the metal.
Compound
I (HL)
ν(N–H) ν(C=O) ν(C=N) ν(C–O)
3348,
3252
3147
1624,
1678a
1665
–
–
[Cu(HL)2]SO4·2H2O
II (HR)
−
–
−
–
The IR spectrum of the uncharged complex of
general formula CuL2 with compound II also does not
contain the bands of stretching vibrations of ν(N–H) and
ν(C=O), and there are bands of stretching vibrations of
ν(C–O) and ν(C=N) at 1361 and 1538 cm–1,
respectively. This confirms the fact that the ligand has
undergone structural changes and is involved in the
complex in the deprotonated form.
3198
3141
3178
–
1644
1595
1605
–
[Cu(HR)]Cl2
–
–
[Cu(HR)2]SO4·2H2O
−
−
CuR2
1538
1361
a Solution in CCl4.
EXPERIMENTAL
1
(amide II). H NMR spectrum, δ, ppm (J, Hz): 1.38 s
(9H, t-C4H9), 2.68 s (6H, 2NCH3), 7.04–7.10 s (1H,
NH, Z- and E-isomers), 7.40 d (J 8.4) (2H, C6H4), 7.67
d (J 8.1) (2H, C6H4). Purity 99%. Found, %: C 70.82,
70.76, H 9.03, 9.07; N 12.70, 12.69. C13H20N2O.
Calculated, %: C 70.87; H 9.15; N 12.72.
1H NMR spectra were recorded on
a
MERCURYplus300 spectrometer (Varian, USA) in
CDCl3, internal standard HMDS. The IR spectra were
obtained on a Fourier spectrometer IFS-66 (Bruker,
Germany) from pastes in vaseline oil. The pH values
were measured on an I-160M ionomer (ANTEH,
Belarus) with glass and silver chloride electrodes. The
main compound content was deter-mined by
conductometric titration with a conductivity meter OK-
102/1 (Radelkis, Hungary). Elemental analysis was
Method of studying the extraction equilibria.
The copper(II) solution was placed, then H2SO4 or
NH3 solution In a 50 ml separating funnel was added
for obtaining the necessary pH-value, and water to 10 ml
volume. 5 ml of 0.05 M reagent solution in i-AmOH
was added, and the mixture was shaken for 3 min.
Phase separation took about 10 minutes. After the
complete phase separation, the aqueous layer was
separated and the pHeq was measured. The residual
content of Cu(II) was determined photometrically [18].
The concentration of metal ions in the organic phase
was calculated from the material balance.
performed on
a
CHNS-932 analyzer (LECO
Corporation, USA). Reagents i-AmOH, H2SO4,
CuSO4·5H2O, CuCl2·2H2O are of analytical grade,
aqueous ammonia corresponds to GOST 3760-79 “2.”
para-tert-Butylbenzoic acid hydrazide I was ob-
tained by reacting n-propyl tert-butylbenzoate with
hydrazine hydrate, mp 127.5–129.5°C (lit. 126–128°C
[17]).
Method of obtaining the copper(II) complex
compounds. To obtain the cationic complexes with
copper(II), the aqueous solutions of metal salt and
ethanol solutions of hydrazide equals (molar ratio
metal salt:hydrazide 1:1 or 1:2) were mixed and stirred
with a magnetic stirrer for 20 min, the precipitate
formed was filtered off and washed with cold ethanol
and water.
p-tert-Butylbenzoic acid N',N'-dimethylhydrazide
(II). 45.5 ml (0.6 mol) of 1,1-dimethylhydrazine was
dissolved in 250 ml of hexane and cooled with a
mixture of snow and salt. A cooled solution of 58 ml
(0.29 mol) of para-tert-butylbenzoyl chloride in
100 ml of hexane was added dropwise while cooling to
this solution. The reaction mixture was left overnight.
Next day the formed precipitate was filtered off,
dissolved in 200 ml of chloroform, and the insoluble
part was filtered out. After distilling off chloroform
the residue was recrystallized from a mixture of
water–i-PrOH (3:1). Yield 57%, mp 143–144°C. IR
spectrum, ν, cm–1: 3209 (NH); 1644 (amide I); 1550
The neutral complex was prepared by mixing
solutions of copper(II) ammoniate and compound II in
ethanol (a molar ratio metal salt: hydrazide = 1:2),
followed by stirring for 30 min. The precipitate
formed was filtered off, washed with water and cold
ethanol.
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GUSEV et al.
9. Gusev, V.Yu., Baigacheva, E.V., Radushev, A.V., and
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This work was supported by Russian Foundation
for Basic Research (grant no. 09-03-00 281-a).
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11. Machkhoshvili, R.I., Doctorate (Chem.) Dissertation,
Moscow, 1983.
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