Extraction behavior of copper(II) with salicylidene aniline and salicylidene toluidine isomers in chloroform from sulfate medium

Article abstract of DOI:10.1080/15533174.2014.988229

The solvent extraction of copper(II) from aqueous sulfate solutions was studied using salicylideneaniline and the three isomeric salicylidenetoluidine diluted with chloroform at 25°C. The molecules of these extractants are studied theoretically using ab i

Full text of DOI:10.1080/15533174.2014.988229

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Extraction Behavior of Copper(II) with Salicylidene
Aniline and Salicylidene Toluidine Isomers in
Chloroform from Sulfate Medium
Sana Almia, Rachid Benakchaa & Djamel Barkata
a Laboratory of Molecular Chemistry and Environment, University of Biskra, Biskra, BP 145,
ALGERIA
Accepted author version posted online: 27 Apr 2015.
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To cite this article: Sana Almi, Rachid Benakcha & Djamel Barkat (2015): Extraction Behavior of Copper(II) with Salicylidene
Aniline and Salicylidene Toluidine Isomers in Chloroform from Sulfate Medium, Synthesis and Reactivity in Inorganic, Metal-
Organic, and Nano-Metal Chemistry, DOI: 10.1080/15533174.2014.988229
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Extraction Behavior of Copper(II) with Salicylidene Aniline and Salicylidene
Toluidine Isomers in Chloroform from Sulfate Medium
Sana Almi*, Rachid Benakcha and Djamel Barkat
Laboratory of Molecular Chemistry and Environment, University of Biskra, Biskra, BP 145,
ALGERIA
*Corresponding author. E-mail: sbenakcha@yahoo.fr
Abstract:
The solvent extraction of copper (II) from aqueous sulfate solutions was studied using
salicylideneaniline and the three isomeric salicylidenetoluidine diluted with chloroform at 25°C.
The molecules of these extractants are studied theoretically using ab initio methods at the HF/6-
31G(d) level, with theirs parameters optimized to reproduce geometries of these compounds. By
a statistical analysis of the extraction data, it was concluded that the extracted species are CuL2
with CuL2(HL). This tendency is confirmed from numerical extraction constants for metal
cations. The best extraction was according to the following order: HSOT  HSMT HSPT >
HSA.
Key Words: solvent extraction; copper(II); salicylideneaniline; salicylidene toluidine, ab initio
methods .
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1. Introduction
Investigation on metal organic complexes represents one of the most active areas of material
science and chemical research. Major advances have been made in these materials due to their
interesting properties and potential in various applications, e.g., electrical conductivity,
magnetism, host guest chemistry, ion exchange, catalysis, nonlinear optics, etc (1,2). Synthesis of
new Schiff bases and their metal complexes still the aim of many recent investigations. Schiff
bases have played an important role in the development of coordination chemistry as they readily
form stable complexes with most of the transition metals (3-6). Because of their diverse uses in
science, the solvent extraction of metals by such compounds is of interest. Although there are a
number of publications on the determination of the extraction constants of metals by the various
Schiff’s bases (7-16), a literature survey reveals that the extraction of metals by Schiff’s bases
prepared from substituted anilines and salicylaldehyde have not been studied extensively.
salicylidene o-, m-, and p-toluidine act mainly as bidentate ligands and their chemical formula are
illustrated in Figure 1. This article, therefore, deals with the solvent extraction of copper (II) with
salicylideneaniline and salicylidene o-, m-, and p-toluidine in chloroform.
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In the present work, we study the solvent extraction of Copper (II) ions, which is a highly
toxic metal ion that is readily encountered in the environment and represents a waste of resources.
Moreover, this work reports an investigation aimed at gaining information about the specific
effects of position of the substituent on the extraction of copper(II) with salicylidene o- toluidine,
salicylidene m- toluidine and salicylidene p-toluidine. The object of the work was the
determination of the stoichiometries of the extracted complexes and their extraction constants.
2. Experimental
2.1. Reagents and solutions
The salicylideneaniline (HSA), Salicyli-dene o-toluidine (HSOT), salicylidene m-toluidine
(HSMT) and salicylidene p-toluidine (HSPT) were prepared by refluxing salicylaldehyde with the
corresponding amine and were purified by recrystallisation from ethanol(17). Some physical and
IR spectroscopy data of the Schiff bases are shown in Table 1.
Chloroform was pre-equilibrated with aqueous solution which did not contain metal. The initial
compositions of the phases were as follows:
[Cu2+] =1.57×10-3 M; [Na2SO4] =0.33M
3. Results and discussion
3.1. Theoretical structural analysis of salicylideneaniline and salicylidene o-, m-, p-toluidine
The geometries of all Schif bases were optimized using Hartree-Fock (HF) approximations at
6-31G bases set, using the Gaussian 03 programs. The aim of these calculations was to determine
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the atomic charge values to describe the reactivity of the molecules and to reproduce the
geometries of these compounds.
The mulliken atomic charges are listed in Table 2, and a distinct trend is apparent. Not
unexpectedly, as the nitrogen atom becomes more electronegative, the negative charge on N
becomes greater according to the following order: HSA< HSMT<HSPT <HSOT. This can be
attributed the fact that the methyl substituent have a positive mesomeric effects on the benzene
ring.
The Table 2 presents also the O-H, C-N and N-H bond lengths which are almost the same one
for the four extractants. The optimized collector geometries with the numbering schema at HF/6-
31G basis set are shown in Figure 2. The N-H bond length indicates the presence of the
hydrogen bond in the geometry of the molecules; this intermolecular H-bond is responsible for
the stabilization of these compounds.
The values of dihedral angles indicating that, HSA is planar, whereas HSOT, HSMT and
HSPT have a distortion in their geometry.
3.2. Extraction and analytical procedure
Extractions were performed on thermostated vessels at 25 °C. Equal volumes, 40 ml each of
aqueous and organic phases, were shaken with a magnetic stirrer for 30 min, a period found to be
adequate to reach equilibrium. After phase separation by gravity, the metal concentration in the
aqueous phases was determined photometrically at 820 nm using a Philips UV-VIS SP6-36. The
pH of the aqueous phase was measured by a pH-meter with an accuracy of 0.02 pH unit. The pH
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was adjusted to the desired level by the addition of sodium hydroxide NaOH. The ionic strength
was maintained at 1 with Na2SO4.
3.3. Solvent extraction of copper(II) with chelating extractant
The overall reaction in the extraction of copper (II) with chelating extractant (HSA, HSOT,
HSMT and HSPT) in chloroform from sulphate aqueous medium of ionic strength (I=1.0 mol kg-
1), may be expressed as
Kex
(
)
(
)
The distribution ratio of copper is defined as follows (Eq.1)
Eq.1
[
]
[
]
The extraction constant, Kex, is defined using equation (2) and it can be rewritten as equation
(3) by using the distribution ratio, DCu, of the metals.
[
]
[
]
( )
Eq.2
[
][ ]
(
)
[
]
Eq.3
A study of the variation of log D as a function of pH to constant [HL]org was performed in
chloroform. Figures 3 represents the curves of extraction log D = f(pH) at 25°C of copper from
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sulfuric medium for various concentration of HSA, HSOT, HSMT and HSPT. The curves
obtained show that the extraction of Cu(II) increases with the concentration of the extractants.
The slopes equal to 2 in all cases, this suggesting exchange of two protons between the metal
cation and the extractant by his phenolate group.
Likewise, in the extraction of the metal with HSA, HSOT, HSMT and HSPT, plots of logDCu
versus log [HL]org at constant pH values are also linear with slopes equal to 2.3, 2.16, 2.23 and
2.25, respectively (as shown in Figure 4), this explains the number of molecules of HL
coordinated to the metal in the complex.
These results give n=2 and m= 0.3, 0.16, 0.23, 0.25 which are readily replaced in equation (3).
This means that two types of complexes are extracted; CuL2 with CuL2(HL) into chloroform.
This agrees with the published results for the extraction of nickel(II) (18) and zinc(II) (19) from
sulfate solutions by Bis(2-ethylhexyl) phosphoric acid dissolved in kerosene and for the solvent
extraction equilibrium of copper(II) with Diisodecylphosphoric acid in heptane and dodecane.
(20)
Next, considering two species to be formed in the organic phase, CuL2 with extraction
constant K20 and CuL2(HL) with extraction constant K21,
The distribution ratio of metal could be expressed as follows (Eq.4)
[
] [ )]
(
Eq.4
[
]
Using equation (2), Eq. 4 becomes
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Eq.5
Eq.6
[
]
[
]
[
]
or
[
]
[
]
[
]
Now, a plot of D[H+]2/[HL]2 versus [HL] would give a straight line with a slope equal to K21 and
intercept equal to K20 (Figure 5).
The extraction constants obtained are shown in Table 3. The structures of the extracted
species may be proposed as follows (Figure 6).
The Schiff base and its complexes were subjected to Infrared spectra were obtained by KBr
disc technique by using FTIR-8400S Spectrometer (SHIMADZU) in the range of 1100-400 cm-1.
Electronic absorption spectra were measured using SHIMADZU spectrophotometer.
Infrared spectral data of the Schiff base shows several bands at 3440 and 1613-1618cm-1 due
to OH and C=N of the free Schiff base (21, 22). These bands are shifted to lower frequency on
complexation with Cu(II) ions (Table 1) (Figure 7) (23, 24). New vibrations at 580 and 757cm-1
which are not present in the free Schiff base are attributed to the existence of (M-N) and (M-O),
respectively (25, 26). The appearance of these vibrations confirmed the involvement of nitrogen
and oxygen atoms in coordination to the metal ions (27, 28).
The electronic absorption spectral of the ligand show two bands at 271 and 340 nm which are
due to π → π* (phenyl ring) and n→π* (-C=N), respectively. The electronic spectra of Cu(II)
complexes display a broad band in the 600-700 nm region which is due to d-d and charge transfer
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transitions. A distorted octahedral geometry was suggested for this complex (29). So the
suggested structure of the extracted species mast be CuL2(H2O)2 and CuL2(HL)(H2O).
3.4. Comparison of the liquid-liquid extraction of Copper(II) by salicylidene o-, m-, and p-
toluidine
The various curves in Figure 8 allow us, as a result, to evaluate the effect of the methyl
substituent on solvent extraction of copper(II) and to compare them between each other. The best
extraction was according to the following order : HSOT  HSMT HSPT > HSA. A similar
conclusion has also been pointed out in theoritical analysis. Judging from the present results, it
seems reasonable to assume that the positive mesomeric effect of the methyl group on the
conjugated system in salicylideneanilines has enabled the increases of the negative charge on the
nitrogen atom, its basicity increases by improving its extractive capacity.
The obtained logKnm values of salicylideneanilines substituted are lower than that in
unsubstituted salicylideneanilines might be attributed to its high hydrophobicity and to an
increase in the affinity of their copper(II) complexes for chloroforme by the introduction of the
methyl substituent.
Conclusions
We have reported the results of ab initio calculation on the salicylideneaniline and the three
isomeric salicylidenetoluidine using Hartree-Fock (HF) approximations at 6-31G bases set. On
the basis of our calculations, the following conclusions can be drawn: (a) the methyl substituent
has positive mesomeric effects on the benzene ring and the substituted molecules have better
activity then the unsubstituted. (b) The presence of the hydrogen bond in the geometry of the
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molecules is responsible for the stabilization of these compounds. (c) HSA is planar, whereas
HSOT, HMOT and HPOT have a distortion in their geometry.
The extraction of copper(II) by salicylideneaniline and the three isomeric salicylidenetoluidine
in chloroform was studied. The extraction of Cu2+ ions increased with increasing the pH of the
medium and with the concentration of the four extractants. The stoichiometry of the extracted
species was determined by using the method of slope analysis. The extracted copper(II) species
were both CuL2 with CuL2(HL). The Infrared spectral data confirmed the involvement of nitrogen
and oxygen atoms in chelation. The electronic absorption spectral indicated that the geometry of
the complexes is octahedral and thay mast be CuL2(H2O)2 and CuL(HL)(H2O). Comparison with
graphical analysis and the basis set results show that the best extraction was according to the
following order: HSOT  HSMT HSPT > HSA.
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Table 1. Some physical and IR spectroscopy data of the Schiff bases.
Spectroscopie IRµ(cm-1)
Schiff Yield
Bases (%)
colour
m.p (°C)
C=N
1613
1618
1618
1618
OH
SA
80
66
76
78
Yellow
crystals
Yellow
powder
Yellow
crystals
Yellow
crystals
50
51
51
51
3440
3440
3440
3440
SOT
SPT
SMT
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Table 2. HF optimized bond distances (Å), bond angles (º), dihedral angles (º) and Mulliken
atomic charges obtained using 6-31G (d) basis set.
Central Bond distances
Dihedral angles
Mulliken atomic
charges
O-H
C(8)-
N(9)
N(9)-
C(8)-N(9)-
C(8)-N(9)- oxygen
nitrogen
H(21) C(10)-C(11) C(10)-C(15)
HSA 0.9633 1.2727 1.8805
180.0
0.0
-
-0.750656
-0.709631
-0.711728
-0.710371
0.811358
HSOT 0.9633 1.2724 1.8843 -140.9242
HSMT 0.9636 1.2723 1.8843 -142.8901
HSPT 0.9635 1.2723 1.8838 -145.2112
41.0854
38.6974
36.4966
-
0.813621
-
0.810389
-
0.810850
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Table 3. Extracted constants of solvent
extraction of copper(II) with substituted
salicylideneanilines in chloroform.
Extractant
HSA
logK20
-7.80
-7.68
-7.40
-7.51
logK21
-5.57
-5.54
-5.52
-5.52
HSOT
HSMT
HSPT
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CH3
CH
N
OH
Figure 1: Scheme of the chemical formula of salicylidene o-, m-, and p-toluidine
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HSOT
HSA
HSMT
HSPT
Figure 2. The optimized geometries of HSA, HSOT, HSMT and HSPT molecules at 6-31G(d) basis set.
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1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
-0.2
-0.4
-0.6
1.2
1.0
1,4
1,2
1.4
1.2
0.8
1,0
1.0
0,8
0.6
0.8
0,6
0.4
0.6
0,4
0.2
0.4
0,2
0.0
0.2
0,0
0.0
-0.2
-0.4
-0.6
-0.8
-1.0
-1.2
-1.4
-0,2
-0,4
-0,6
-0,8
-1,0
-1,2
-1,4
-0.2
-0.4
-0.6
-0.8
-1.0
-1.2
-1.4
[HSA]= 0.02M
[HSA]= 0.01M
[HSA]= 0.005M
[HSOT]=0.02M
[HSMT]=0.02M
[HSMT]=0.01M
[HSMT]=0.005M
[HSPT]=0.02M
[HSPT]=0.01M
[HSPT]=0.005M
-0.8
[HSOT]=0.01M
-1.0
[HSOT]=0.005M
-1.2
-1.4
4.6
4.8
5.0
5.2
5.4
5.6
pH
5.8
6.0
6.2
6.4
6.6
4.6
4.8
5.0
5.2
5.4
5.6
5.8
6.0
6.2
6.4
6.6
6.8
4,6
4,8
5,0
5,2
5,4
5,6
pH
5,8
6,0
6,2
6,4
6,6
4.6
4.8
5.0
5.2
5.4
5.6
pH
5.8
6.0
6.2
6.4
6.6
pH
Figure 3. pH effect on the Cu2+ extraction
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1.2
1.0
1,2
1,0
1.2
1.0
1.2
1.0
▪ pH=5.48
• pH=5.76
 pH = 5.7
pH = 5.59
▪ pH=5.46
• PH=5.66
0,8
0.8
0.6
▪ pH=5.42
• PH=5.68
0.8
0.8
0,6
0.6
0.6
0,4
0.4
0.4
0.4
0,2
0.2
0.2
0.2
0,0
0.0
0.0
0.0
-0,2
-0,4
-0,6
-0,8
-1,0
-0.2
-0.4
-0.6
-0.8
-1.0
-0.2
-0.4
-0.6
-0.8
-1.0
-0.2
-0.4
-0.6
-0.8
-1.0
-2,4
-2,3
-2,2
-2,1
-2,0
-1,9
-1,8
-1,7
-1,6
-2.4
-2.3
-2.2
-2.1
-2.0
-1.9
-1.8
-1.7
-1.6
log ([HSA)]
-2.4
-2.3
-2.2
-2.1
-2.0
-1.9
-1.8
-1.7
-1.6
-2.4
-2.3
-2.2
-2.1
-2.0
-1.9
-1.8
-1.7
-1.6
log([HSOT])
log ([HSMT])
log((HSPT))
Figure 4. Effect of extractant concentration
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1,00E-007
9,00E-008
8,00E-008
7,00E-008
6,00E-008
5,00E-008
4,00E-008
3,00E-008
HSA
HSOT
HSMT
HSPT
0,004 0,006 0,008 0,010 0,012 0,014 0,016 0,018 0,020 0,022
[HL]
Figure 5. Effect of HSA, HSOT, HSPT and HSMT concentration on the extraction equilibrium
of copper (II) in chloroform at 25°C
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CH3
OH
CH3
CH
N
H3C
CH N
O
O
CH N
O
Cu
Cu
N
CH
O
CH
N
H3C
CH3
CuL2
CuL2(HL)
Figure 6. Structures of the Cu-complexes of HSA, HSOT, HSMT, and HSPT
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22.5
20
17.5
15
12.5
10
580
7.5
5
1
757
6
2.5
1
0
2900-3000
0
4000
400
2000
800
600
3600 3200 2800 2400
1800 1600
1200 1000
1400
Wavenumber (cm-1)
Figure 7. IR Spectrum of the Copper complex
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1,4
1,2
1,0
0,8
0,6
0,4
0,2
0,0
-0,2
-0,4
-0,6
-0,8
-1,0
-1,2
HSOT
HSPT
HSMT
HSA
4,6
4,8
5,0
5,2
5,4
5,6
5,8
pH
Figure 8. pH effect on the extraction of Cu2+ with HSA, HSOT, HSMT and HSPT 0.04M in
chloroform; 0.33M
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