From 1-(2-Aminoethyl) piperazine and investigation of its analytical properties for the extraction and preconcentraton of some divalent cations

Article abstract of DOI:10.1007/bf03246203

The synthetic, structural, spectroscopic and analytical properties of steric hindered Schiff-base ligand [N-(3,5-di-tertbutylsalicylaldimine)- 1-(2-Aminoethyl) piperazine (HL)] and its mononuclear Cu(II), Co(II) and Ni(II) complexes are described. The new

Full text of DOI:10.1007/bf03246203

J. Iran. Chem. Soc., Vol. 8, No. 1, March 2011, pp. 68-77.
JOURNAL OF THE
Iranian
Chemical Society
Synthesis and Characterization of an Unsymmetric Salicylaldimine Ligand Derived
from 1-(2-Aminoethyl) piperazine and Investigation of Its Analytical Properties for the
Extraction and Preconcentratıon of some Divalent Cations
A. Kilica,*, I. Teginb, E. Tasb and R. Ziyadanogullarıb,*
aDepartment of Chemistry, Faculty of Arts and Sciences, Harran University, Sanliurfa 63510, Turkey
bDepartment of Chemistry, Faculty of Arts and Sciences, Siirt University, Siirt 56100, Turkey
(Received 16 November 2009, Accepted 8 April 2010)
The synthetic, structural, spectroscopic and analytical properties of steric hindered Schiff-base ligand [N-(3,5-di-tert-
butylsalicylaldimine)-1-(2-Aminoethyl) piperazine (HL)] and its mononuclear Cu(II), Co(II) and Ni(II) complexes are described.
The new unsymmetric steric hindered Schiff base ligand containing a donor set of NONO was prepared by the reaction of 1-(2-
Aminoethyl) piperazine with 3,5-di-tert-butylsalicylaldehyde. Certain metal complexes of this ligand were synthesized by treating
an ethanolic solution of the ligand with an equimolar amount of metal salts. The ligand and its metal complexes were
1
characterized by FT-IR, UV-Vis, H NMR, elemental analysis, molar conductivity and magnetic susceptibility techniques. The
reaction of this ligand in a 1:2 mole ratio with metal acetate afforded mononuclear metal complexes. The molar conductivity (Λ )
M
-1
values of the metal complexes of Ni(II), Co(II) and Cu(II) were in the range of 6.4 to 9.8 Ω cm2 mol-1 at room temperature.
Preconcentration and separation of Cu2+ from aqueous solution using N-(3,5-di-tert-butylsalicylaldimine)-1-(2-Aminoethyl)
piperazine (HL) as a new extractant were studied. The extraction experiments were carried out at various pHs. While Cu2+ showed
the highest extractability and selectivity at pH 7.0, extractions of Co2+ and Ni2+ were unsuccessful due to precipitate formation.
Keywords: Schiff base, 1-(2-Aminoethyl) piperazine, Cu(II) Preconcentration, Extraction of Cu2+, Co2+, Ni2+
INTRODUCTION
natural systems are unsymmetric [4]. Dissymmetric Schiff
base metal complexes as chiral analogues become more
effective and prevalent in asymmetric catalysis; an
inexpensive, large-scale production of these materials would
be highly desirable [4-7]. It has also been reported that
transition metal complexes of Schiff bases containing
tetradentate ligands are involved in anti-microbial activity [8].
Sterically hindered ligands bearing salicylaldimines are known
to be effective antioxidants and are widely used in
rancidification of fats and oils [9]. The Cu(II) ions play a
central role in biological redox metalbenzymes like
plastocyanin, hemocyanin, azurin, galactose oxidase and
others [10,11]. Transition metal complexes with redox active
ligands bearing sterically hindered salicylaldimines are also
Schiff base metal complexes containing different metal
ions such as Ni, Co and Cu have been studied in great detail
for their various crystallographic features, structure-redox
relationships
and
enzymatic
reactions,
mesogenic
characteristics and catalytic properties [1-3]. Recent interest in
the design, synthesis and characterization of dissymmetrical
Schiff base ligands derived from appropriate amines for
transition metal ion complexes is stimulated by the realization
that the coordinated ligands around central metal ions in
*Corresponding authors. E-mail: kilica63@harran.edu.tr
rektor@siirt.edu.tr
,

Kilic et al.
reported to undergo one- or two-electron transfer. Proton
Company, Taufkirchen, Germany). 3,5-Di-tert-butyl-2-
hidroxybenzaldehyde (3,5-DTB) was synthesized according to
the literature procedure [36]. The elemental analyses were
carried out in the Laboratory of the Scientific and Technical
Research Council of Turkey (TUBITAK). IR spectra were
recorded on a Perkin Elmer Spectrum RXI FT-IR spectrometer
transfer can occur both in solid and solution states, in basic
and excited states [12-16]. In most salicylaldimines, the proton
is localized at the oxygen atom and in some cases is attached
to the nitrogen atom [12,13].
Chelate extraction is a very effective analytical separation
method for the metal species in solution [17-22]. The most
widely used techniques for the separation and
preconcentration of trace amounts are extraction [23],
precipitation and chelating resins [24]. Very often, both
separation and preconcentration are required, and an
advantage of solvent extraction is that both can be obtained
simultaneously [25]. Recovery of metals from an aqueous
phase by solvent extraction is achieved by contacting the
aqueous phase with an organic phase that contains a metal
selective chelating agent dissolved in a diluent [26]. For the
extraction of metal ions, it is preferable to use a chelating
agent that has a high distribution coefficient and pH
dependence in the system chosen. Reagents such as crown
ethers, Schif bases, oximes, amines and several phosphine
oxides can be used as chelating agents [27-35].
1
as KBr pellets. H NMR spectra were recorded on a Bruker-
Avance 400 MHz spectrometer. Magnetic susceptibilities were
determined on a Sherwood Scientific Magnetic Susceptibility
Balance (Model MK1) at room temperature (20 °C) using
Hg[Co(SCN)4] as a calibrant; diamagnetic corrections were
calculated from Pascal’s constants [37,38]. UV-VIS spectra
were recorded on a Schimadzu 1601 PC. Molar conductivities
(Λ ) were recorded on a Inolab Terminal 740 WTW Series. A
M
Unicam model 929 atomic absorption spectrophotometer was
used for the determination of the concentration of metal ions
in aqueous solutions. Mettler Toledo digital pH-meter
equipped with a Toledo 413 combined glass electrode was
used to determine the pH values.
Preparation of Ligand (HL)
In the present work, we prepared a new Schiff base ligand
and its mononuclear Cu(II), Ni(II) and Co(II) complexes. The
synthesis, characterization, spectra and analysis of novel
Ni(II), Co(II) and Cu(II) metal complexes derived from N-
(3,5-di-tert-butylsalicylaldimine)-1-(2-Aminoethyl) piperazine
(HL) were investigated. The ligand and its Cu(II), Ni(II),
Co(II) complexes were identified by a combination of
The ligand (HL) was prepared by a literature method
[16,38]. N-(3,5-Di-tert-butylsalicylaldimine)-(2-Aminoethyl)
piperazine (HL) ligand was synthesized by the reactions of 10
mmol (1.29 g) 1-(2-Aminoethyl) piperazine in 40 ml absolute
methanol and 10 mmol (2.34 g) 3,5-di-tert–butyl-2-
hidroxybenzaldehyde for ligand (HL) in 25 ml absolute
methanol. Then, five drops of formic acid were added as
catalyst. The mixture was refluxed for 5 h, followed by
cooling to room temperature. The crystal was filtered in
vacuum. Then the product was recrystallized from methanol.
The product (Fig. 1) is soluble in common organic solvents
1
elemental analyses, H NMR spectra, FT-IR spectra, UV-Vis
spectra, magnetic susceptibility and molar conductivity
measurements. The first aim of this study is to prepare a new
highly soluble Schiff base ligand and its mononuclear Cu(II),
Ni(II), Co(II) complexes. The second aim is to find out if this
Schiff base can be used as a chelating agent. The third aim is
to explore preconcentration and separation with solvent
extraction of Cu2+ from aqueous solution using N-(3,5-di-tert-
butylsalicylaldimine)-1-(2-Aminoethyl) piperazine (HL).
1
such as CH3CH2OH, CHCl3, DMF and DMSO. H NMR (400
MHz, CDCl3, ppm): δ = 13.70 (s, 1H, -OH, D-exchangeable),
δ = 8.36 (s, 1H, HC=N), δ = 7.37 (m, 1H, Ar-CH), δ = 7.06
(m, 1H, Ar-CH), δ = 3.72 (t, 2H, N-4CH2), δ = 2.90 (s, 4H,
NH-CH2), δ = 2.75 (t, 2H, N-3CH2), δ = 2.52 (s, 4H, N-2CH2),
and δ = 1.42-1.25 (m, 18H, C-CH3). IR (KBr pellets, cm-1):
2785-3424 υ(N…OH), 3123 υ(Ar-H), 2953, 2816 υ(Aliph-H),
1632 υ(C=N), 1593 υ(C=C), 1319 υ(C-O). UV-Vis [in
C2H5OH λmax/nm (logε)]: 216 (5.82), 262 (4.08), 327 (3.27),
410 (2.32); [in CHCl3 λmax/nm (logε), (*:shoulder peak)]: 217
(5.11), 259 (4.34)*, 328 (3.23).
EXPERIMENTAL
Reagents and Apparatus
All reagents and solvents were of reagent-grade quality
and obtained from commercial suppliers (Fluka Chemical
69

Synthesis and Characterization of an Unsymmetric Salicylaldimine Ligand
(*:shoulder peak)]: 223 (5.21), 264* (4.16), 320 (3.30), 397
(2.84), 434 (2.12); [in CHCl3 max/nm (logε), (*:shoulder
λ
peak)]: 219 (4.89), 259 (4.13), 342 (3.57), 417* (2.43), 455
(1.96).
[Co(L)2]. IR (KBr pellets, cm-1): 3106 υ(Ar-H), 2953,
2867 υ(Aliph-H), 1622 υ(C=N), 1518 υ(C=C), 1362 υ(C-O),
550 υ(M-N), 469 υ(M-O). UV-Vis [in C2H5OH λmax/nm
(logε)]: 221 (5.17), 260 (4.05), 291 (3.78), 405 (2.75), 640
(1.92); [in CHCl3 λmax/nm (logε),]: 222 (4.73), 254 (4.45), 297
(3.24), 407 (2.36), 582 (1.76).
Extraction Procedure
Aqueous solutions containing 1.0 × 10-4 M of Cu(II) in
appropriate buffer were equilibrated with equal volumes of the
chloroform solution of 1.0 × 10-3 M of the ligand by shaking
with a mechanical shaker at 25 °C. Optimum equilibration
time was determined for this system. The ionic strength of the
aqueous solution was 1.0 × 10-1 M KCl in all experiments
except those in which the effects of ionic strength were
studied. After agitation, the solutions were allowed to stand
for 10 min. The Cu(II) concentration of the aqueous phase was
determined by AAS, and that of the organic phase was
obtained from the difference by considering the mass balance.
The pH of the aqueous phase was recorded as equilibrium pH.
Fig. 1. Synthesis of the ligand (HL).
Preparation of Metal Complexes
The metal(II) complexes were prepared by the same
general method: The ligand (HL) (0.52 g, 1.5 mmol) was
dissolved in 40 ml absolute ethanol at room temperature. A
solution of 0.75 mmol (0.15 g) of Cu(CH3COO)2.H2O, 0.75
mmol (0.19 g) of Ni(CH3COO)2.4H2O or 0.75 mmol (0.19 g)
of Co(CH3COO)2.4H2O in 20 ml of absolute ethanol was
added dropwise under a nitrogen atmosphere with continuous
stirring. The stirred mixtures were then heated to the reflux
temperature for 70 min and were maintained at this
temperature. Then, the mixtures were evaporated to a volume
of 10 ml in vacuum and left to cool to room temperature. The
compounds were precipitated after adding 5 ml methanol. The
products were filtered in vacuum and washed with a small
amount of methanol and water, successively. The products
were recrystallized from ethanol. Then they were dried at 100
°C.
Preconcentration Procedure
After the extraction of the aqueous phase (100 ml)
containing 63.5 µg of Cu(II) with 20 ml portion of the organic
phase (1 × 10-3 M HL), the organic phase was stripped with 10
ml of aqueous acid solutions, including HCl, HNO3 or H2SO4.
The highest recovery values (almost quantitative) were
obtained with 0.1 M H2SO4. The amount of Cu(II) in the
aqueous phase after stripping the organic phase was
determined by AAS, and then the recovery percentage (%R)
was calculated.
[Cu(L)2]. IR (KBr pellets, cm-1): 3091 υ(Ar-H), 2956,
2868 υ(Aliph-H), 1621 υ(C=N), 1523 υ(C=C), 1361 υ(C-O),
558 υ(M-N), 472 υ(M-O). UV-Vis [in C2H5OH λmax/nm (logε)
(*:shoulder peak)]: 217 (5.81), 262 (4.74), 283* (3.52), 321
RESULTS AND DISCUSSION
(3.05), 390 (2.23), 623 (1.73); [in CHCl3
λ
max/nm (logε),
Synthesis and Characterization
(*:shoulder peak)]: 221 (5.67), 264 (4.63), 281* (3.18), 326
(2.80), 401* (2.24), 632 (1.68).
The reaction steps for the synthesis of the ligand and its
mononuclear Cu(II), Ni(II) and Co(II) metal complexes are
given in Figs. 1 and 2. In the first step, the ligand (HL) was
prepared by the reaction of 1-(2-Aminoethyl) piperazine with
[Ni(L)2]. IR (KBr pellets, cm-1): 3093 υ(Ar-H), 2957, 2868
υ(Aliph-H), 1620 υ(C=N), 1526 υ(C=C), 1361 υ(C-O), 561
υ(M-N), 463 υ(M-O). UV-Vis [in C2H5OH λmax/nm (logε)
70

Kilic et al.
The analytical and spectral data for the ligand and its metal
complexes are presented in the experimental section and Table
1.
1
The H NMR spectral results obtained for ligand (HL) in
CDCl3, do not give any signal corresponding to 1-(2-
aminoethyl) piperazine and 3,5-di-tert-butylsalicylaldehyde
protons. The ligand gives well-defined 1H NMR spectra,
which permit unambiguous identification and assessment of
purity. The OH signal was found at 13.70 ppm as a singlet in
the spectrum of the salicyaldimine ligands due to
intramolecular OH….N hydrogen bonding. When D2O was
added to the ligand solution, a rapid loss of these signals was
observed as expected. The singlets corresponding to
azomethine group were observed at 8.36 ppm for the ligand.
The peaks at 7.37 and 7.06 ppm for ligand (HL) are assignable
to the protons of Ar-CH as multiplet peaks. Also, the protons
of the t-butyl groups of the ligands exhibit singlet peak in the
M: Cu(II), Ni(II) and Co(II)
Fig. 2. The structure of the Ni(II), Co(II) and Cu(II) metal
complexes.
1
3,5-di-tert-butylsalicylaldehyde. In the second step,
mononuclear metal complexes were synthesized by the
reaction of ligand (HL) with the corresponding metal salts.
The metal complexes were obtained in good yields and high
purity by the slow evaporation of the solvent mixture at
atmospheric pressure. The metal to ligand ratios in the
mononuclear metal complexes were found to be 1:2. The
ligand and its metal complexes were characterized by FT-IR,
UV-Vis, 1H NMR spectroscopy, elemental analysis, as well as
range of 1.42-1.25 ppm for the ligand (HL). The other H
NMR data of the ligand are given in the experimental section.
The free Schiff base ligand showed a strong peak at 1632
cm-1 in its IR spectrum, which is characteristic of the
azomethine υ(C=N) group [39,40]. Coordination of the
aldimine ligand to the metal through the nitrogen atom is
expected to reduce the electron density in the azomethine link
and lower the υ(C=N) absorption frequency. The peak
assigned to υ(C=N) is shifted to lower frequencies and appears
around 1620-1622 cm-1, indicating the coordination of the
through magnetic susceptibility and molar conductance (Λ ).
M
Table 1. The Formula, Formula Weight, Colors, Melting Points, Molar Conductivity Yields, Magnetic Susceptibilities,
and Elemental Analysis Results of the Compounds
Compounds
F.W.
Color
m.p.
(°C)
Λ
Yield
(%)
μ
Elemental analysis
%calculated (found)
H
M
eff
(g mol-1)
(Ω cm2 mol-1)
[B.M]
-1
C
N
Ligand (HL)
C21H35N3O
73.04
(72.94)
10.15
(10.02)
12.17
(12.46)
345
747
747
752
Yellow
Green
106
-
86
-
[Ni(L)2]
C42H68N6O2Ni
[Co(L)2]
C42H68N6O2Co
[Cu(L)2]
C42H68N6O2Cu
67.47
(67.13)
67.47
(67.26)
67.02
9.10
(8.98)
9.10
(9.03)
9.04
11.24
(11.08)
11.24
(11.12)
11.17
132
153
136
69
64
72
2.25
3.89
1.83
7.2
6.4
9.8
Brown
Dark
Green
(66.87)
(8.86)
(11.04)
71

Synthesis and Characterization of an Unsymmetric Salicylaldimine Ligand
azomethine nitrogen to nickel, cobalt or copper ions [41]. The
indicating their almost non-electrolytic nature. Due to the
absence of counter ions in M(II) metal complexes, the results
indicate that these complexes are very poor in molar
conductivity.
bonding of the metal ions to the ligands through the nitrogen
and oxygen atom is further supported by the presence of new
bands in the 561-550 and 472-463 cm-1 range due to the υ(M-
N) and υ(M-O), respectively. Thus, it is evident that the ligand
(HL) is bonded to the metal ion in a NONO fashion through
the deprotonated phenolate oxygen and salicylaldimine
nitrogen.
Extraction of Cu(II) from Aqueous Solutions into the
Organic Phase
Choice of agitation time. The effect of agitation time on
the degree of extraction was studied at pH 7.0 with HL = 1.0 ×
10-3 M in CHCl3 and [Cu2+] = 1.0 × 10-4 M. In all cases
equilibrium was reached in less than 30 min. However, as
shown in Fig. 3, a shaking period of 45 min was chosen for
assurance.
Effect of pH on the extraction of Cu(II) and other metal
ions. Figure 4. shows the effect of pH on the extraction of
Cu(II) into chloroform with HL. As shown in Fig. 4, the Cu(II)
extraction is quantitative at pH 7.0-9.0. After adjusting the pH
to the desired value, it was buffered with the tampon system.
Effect of ionic strength of the aqueous phase. The
influence of KCl in the concentration range of 0.1-1.0 M on
the extraction efficiency of Cu(II) was studied in solutions
containing 1.0 × 10-4 M Cu2+ with 1.0 × 10-3 M HL in the
organic phase. The extraction efficiency decreases with an
increase in ionic strength of the aqueous medium. Taking Eq.
(5) into account, the extraction constant (Koext) at zero ionic
strength for this reaction can be correlated with the ionic
strength (I) by
Each ligand (HL) with Cu(II), Ni(II) and Co(II) complexes
shows several intense absorptions in the visible and ultraviolet
regions. In the electronic spectra of the ligand and its metal
complexes, the wide range bands seem to be due to both the
π→π* and n→π* of benzene ring or azomethine (-C=N)
groups or charge-transfer transition arising from π electron
interactions between the metal and ligand which involves
either a metal-to-ligand or ligand-to-metal electron transfer
and d-d transitions [42-44]. The bands at the 216-297 nm
region are assigned to intraligand π→π* transitions and the
band at the 321-410 nm are attributed to n→π* transitions of
benzene ring or azomethine (-C=N) groups. In the spectra of
the complexes, the bands of the azomethine chromophore n-π*
transition are shifted to lower frequencies indicating that the
imine nitrogen atom is involved in coordination to the metal
ion. The spectra of the complexes show intense bands in the
high-energy region in the 455-417 nm range which can be
assigned to charge transfer L→M bands. The bands observed
in the 640-582 nm region can be attributed to d-d transitions of
the metal ions [45,46].
Magnetic susceptibility measurements provide sufficient
data to characterize the structure of the metal complexes. The
magnetic moment of the Cu(II) complex was found to be 1.83-
1 B.M., which indicates a mononuclear Cu(II) complex with a
spin state S = 1/2 not indicating antiferromagnetic coupling of
the spins at this condition. The magnetic moments of Co(II)
complex was found to be 3.89 B.M. which indicates a
mononuclear Co(II) complex with a spin state S = 3/2. The
magnetic moment of Ni(II) complex was found to be 2.25
B.M.
γ 2
H +
Koext = Kext
Kext = Ko
(1)
(2)
(3)
γ Cu2+
γCu24
ext γ 2
H 4
log
= - 0.5 zi2
I
γ
According to the Debye-Huckel limiting law given by
log
= - 0.5 zi2
I
γ
In order to study the electrolytic nature of the metal
complexes, their molar conductivities were measured in DMF
(dimethyl formamide) at 1 × 10-3 M. The molar conductivity
values of Cu(II), Ni(II) and Co(II) complexes were in the
the activity coefficient ( ) decreases with an increase in
γ
ionic strength. At the constant pH, the activity coefficient of
Cu2+ decreases as the ionic strength increases, hence Kext
decreases.
-1
range of 9.8 to 6.4 Ω cm2 mol-1 at room temperature [47],
Effect of aqueous on organic phase ratio. Phase ratio
72

Kilic et al.
80
70
60
50
100
90
80
70
60
50
40
0
15
30
45
60
75
90
0
2
4
6
8
Time (min)
A-O Ratio
Fig. 3. The plot of %E vs. time.
Fig. 5. Effect of the A/O ratio on the extraction of Cu(II) with
HL in chloroform.
80
60
40
20
0
2
4
6
8
10
12
pH
Fig. 4. Effect of pH on the extraction of Cu(II).
Fig. 6. The plot of logD vs. pH at constant [HL].
(A/O) is one of the factors that affect the extraction efficiency.
The extraction efficiency, %E can be given by Eq. (4) [48],
Extractability of the complex and composition of the
extracted species. The aqueous phase (15 ml) containing 1.0
× 10-4 M of Cu(II) in appropriate buffer and 0.1 M KCl was
extracted with successive 15 ml portions of 1.0 × 10-3 M HL in
chloroform. The percentage extraction (%E) of some divalent
metals into chloroform with Schiff base was plotted as a
function of the aqueous phase pH equilibrated with the organic
phase in Fig. 3.
D
%E =
(4)
×100
D + A/ O
where D is the distribution ratio, A and O are the volumes of
the aqueous and organic phases, respectively. This equation
indicates that the extraction efficiency decreases with
increasing A/O ratio. Figure 5 shows the effect of A/O on the
percentage extraction which was satisfied by Eq. (4).
The extraction process may be represented by the equation:
73

Synthesis and Characterization of an Unsymmetric Salicylaldimine Ligand
M2+(w) + 2HL(o) ↔ ML2(o) + 2H+
(5)
Preconcentration of Cu(II). The effect of various acids
(w)
on the stripping of the aqueous solution containing 5.2 ppm
Cu(II) has been given in Table 3 for the preconcentration
purpose. The highest recovery values (almost quantitative)
were obtained with 0.5 M HNO3 and 0.1 M H2SO4. The results
obtained by using 0.1 M H2SO4 and 0.5 M HNO3 for
preconcentration of 0.52 ppm Cu(II) solutions are shown in
Table 4, indicating that the recovery is 99.2%.
where HL represents the extractant reagent and subscripts(w)
and (o) denote the aqueous and organic phases, respectively.
The extraction constant of the species CuL is given by
2
[
ML2
[
]
[
H +
]
w
Kex
=
o
(6)
2
M 2+
]
[HL
]
w
o
CONCLUSIONS
The values of logKex can be calculated by using the following
equation.
The synthetic, structural, spectroscopic and analytical
properties of steric hindered Schiff-base ligand [N-(3,5-di-tert-
butylsalicylaldimine)-1-(2-Aminoethyl) piperazine (HL)] and
its mononuclear Cu(II), Co(II) and Ni(II) complexes are
described. The new unsymmetric steric hindered Schiff base
ligand containing a donor set of NONO was prepared by the
reaction of 1-(2-Aminoethyl) piperazine with 3,5-di-tert-
butylsalicylaldehyde. Certain metal complexes of this ligand
were synthesized by treating an ethanolic solution of the
ligand with an equimolar amount of metal salts. The ligand
and its metal complexes were characterized by FT-IR, UV-
Vis, 1H NMR, elemental analysis, molar conductivity and
magnetic susceptibility techniques. The molar conductivity
values of Cu(II), Ni(II) and Co(II) complexes were in the
logKex = logD- 2log[HL] - 2pH
where
D =
(7)
[
ML2
]
org
(8)
[
M 2+
]
aq
According to Eq. (7), a plot against pH at constant 1.0 × 10-3
M of [HL] will give a straight line with a slope of two and
intercept of 2log[HL] + logKex (Eq. 7). From the graph shown
in Fig. 6, the extraction constant (logKex) was calculated to be
-7.56.
Separation of Cu(II) from other metal ions. The
separation of the metal ions based on the pH adjustment was
assisted by the observation that some of the metals were
quantitatively extracted at certain pH values at which others
were extracted minimally or not at all. This means that it was
possible to predict the separation ability of Cu(II) from other
metal ions. The degree of separation was determined in terms
of ’’separation factor’’ Sf defined as the ratio of D1 for the
desired metal ion M1 to D2 for the contaminant metal ion M2.
-1
range of 9.8 to 6.4 Ω cm2 mol-1 at room temperature,
indicating their almost non-electrolytic nature. The extraction
mechanism corresponds to a cation exchange in which a
complex of stoichiometric formula (CuL2) is formed in the
organic phase liberating at the same time 2 mol of H+ ions in
the aqueous phase. The results indicate that HL in the organic
phase extracts Cu(II) efficiently in aqueous phase containing
0.1 M KCl at pH 7.0 and 25 °C. The extraction reaction is
exothermic with logKex = -7.56. The separation of Cu(II) from
other metal ions by an extraction process was investigated by
using N-(3,5-di-tert-butylsalicylaldimine)-1-(2-Aminoethyl)
piperazine (HL). A single extraction and stripping gave a good
separation and preconcentration of Cu(II) from other metal
ions in aqueous solutions. The analytical performance of the
developed method was examined in view of critical
parameters such as pH, agitation time, ionic strength, and
effect of the other ion on separation factor. The results showed
that it could be applied to samples which contain Cu(II) as
Sf = D1/D2
At certain pH values, Cu(II) is quantitatively extracted with
HL in chloroform alone from synthetic binary mixtures of
Cu(II) with other metal ions (Table 2). All of these separations
are based upon the magnitude of the separation factor (Sf). As
shown in Table 2, the separation of Cu(II) is possible from
Ni(II), Co(II), Pb(II), Fe(II) and Mn(II) at pH 7.0.
74

Kilic et al.
Table 2. The Separation Factor for the Separation of Cu(II) from other Metals
Metal ion
Ni(II)
pH = 3.2
pH = 4.7
19.8
pH = 5.7
12.3
13.4
∞
pH = 7.0
4.46
12.2
0
∞
∞
∞
∞
∞
Co(II)
Fe(II)
21.4
51.4
Pb(II)
0
∞
0.05
24.8
Mn(II)
0
113.3
Table 3. The Effect of Various Acids on the Stripping Aqueous Solution
HCl (M)
R (%)
RSD (%)a
HNO3 (M)
R (%)
RSD (%) H2SO4 (M)
R (%)
RSD (%)
0.5
1.0
1.5
86.44
87.74
87.64
0.065
0.062
0.059
0.1
0.3
0.5
85.93
87.43
98.25
0.084
0.071
0.048
0.1
0.5
1.0
100
99.98
98.95
0.026
0.025
0.032
aRelative standard deviation (RSD).
Table 4. The Recovery Values of Cu(II) on the Preconcentration Procedure by Using HNO3
and H2SO4
HNO3 (M)
0.5
R (%)
98.65
RSD (%)
0.042
H2SO4 (M)
0.1
R (%)
99.12
RSD (%)
0.038
well as Ni(II), Co(II), Pb(II), Fe(II), Mn(II) ions. The
separation of Cu(II) can be accomplished quantitatively from
other metal ions. From the loaded organic phase, Cu(II)
stripping efficiency was found to be quantitative. As a result, it
can be concluded that the proposed procedure can be
conveniently considered as an alternative method for the
preconcentration and separation of Cu(II) from other metals.
The proposed method has certain superior analytical
characteristics compared with the previous works. It affords
simple extraction procedure, short time, high efficiency, and
low relative standard deviation (RSD) values. There was no
considerable interference from the metal ions with the studied
pH. Thus, high separation factor and recovery could be
obtained for Cu(II).
ACKNOWLEDGEMENTS
This work has been partially supported by the Research
Fund of Harran University, Sanliurfa, Turkey.
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