New diazo-containing phenolic oximes: Structural characterization, computational studies, and solvent extraction of Cu(II), Ni(II), and Zn(II) ions

Article abstract of DOI:10.3906/kim-1807-139

In the current study, four new phenolic oxime ligands (HL1ox–HL4ox) containing diazo groups (-N=N-) were synthesized and used for liquid-liquid extraction of heavy metal ions [Cu(II), Ni(II), and Zn(II)]. The new compounds were characterized by analytical and spectroscopic methods. Solid-state structures of HL1ox–HL3ox were determined by single-crystal X-ray diffraction studies. Hirshfeld surface analysis of the compounds was performed to determine the contribution of different intermolecular contacts to the stability of the structures. The HL1ox–HL4ox ligands showed higher extraction performance for Cu(II) ion than Ni(II) and Zn(II) ions. The effect of pH on extraction capacity was investigated and the oxime compounds showed high extraction capacity at low pH values. The effects of the substitute groups (at the meta position of the phenol ring) on the extraction were investigated. Within the oxime ligands, the HL3ox compound exhibited higher extraction capacity for Cu(II) ions. The better extraction value of HL3ox is attributed to the weak hydrogen bond type interactions, which result in more stable complexes.

Full text of DOI:10.3906/kim-1807-139

Turk J Chem
Turkish Journal of Chemistry
(2019) 43: 197 – 212
© TÜBİTAK
http://journals.tubitak.gov.tr/chem/
doi:10.3906/kim-1807-139
Research Article
New diazo-containing phenolic oximes: structural characterization, computational
studies, and solvent extraction of Cu(II), Ni(II), and Zn(II) ions
1
1
2
1,∗
Muharrem KARABÖRK ,, Hilal KIRPIK ,, Koray SAYIN ,, Muhammet KÖSE
,
1
Department of Chemistry, Kahramanmaraş Sütçü İmam University, Kahramanmaraş, Turkey
2
Department of Chemistry, Institute of Science, Cumhuriyet University, Sivas, Turkey
Received: 31.07.2018
•
Accepted/Published Online: 09.11.2018
•
Final Version: 05.02.2019
Abstract: In the current study, four new phenolic oxime ligands (HL1ox–HL4ox) containing diazo groups (-N=N-) were
synthesized and used for liquid-liquid extraction of heavy metal ions [Cu(II), Ni(II), and Zn(II)]. The new compounds
were characterized by analytical and spectroscopic methods. Solid-state structures of HL1ox–HL3ox were determined
by single-crystal X-ray diffraction studies. Hirshfeld surface analysis of the compounds was performed to determine the
contribution of different intermolecular contacts to the stability of the structures. The HL1ox–HL4ox ligands showed
higher extraction performance for Cu(II) ion than Ni(II) and Zn(II) ions. The effect of pH on extraction capacity was
investigated and the oxime compounds showed high extraction capacity at low pH values. The effects of the substitute
groups (at the meta position of the phenol ring) on the extraction were investigated. Within the oxime ligands, the
HL3ox compound exhibited higher extraction capacity for Cu(II) ions. The better extraction value of HL3ox is attributed
to the weak hydrogen bond type interactions, which result in more stable complexes.
Key words: Solvent extraction, Cu(II) ion, phenolic oxime, computational studies
1. Introduction
Hydrometallurgy is often preferred to conventional pyrometallurgy by industry since it usually results in excellent
1
materials and energy balances because of the reusability of the reagents. A hydrometallurgical process usually
involves three main operations: leaching, concentration and separation, and reduction. First of all, the metal
ore is solved in an aqueous medium (leaching), and then the metal to be recovered is separated and concentrated
2
using liquid-liquid extraction and the resulting high-purity aqueous solution is reduced to generate the metal.
3
Solvent extraction has been widely applied to extract valuable metals from ore processing. The solvent
extraction in extractive hydrometallurgy has commercial importance. Conventionally, to recover the base
4
metal, metal cations are transferred selectively to a water-immiscible phase by using ion-exchanger ligands,
5
which release an equivalent number of cations, usually protons, back to the aqueous feed solution. Among the
most commercially successful cation exchange reagents are phenolic oxime reagents, which are used for copper
6
recovery from sulfate streams. Copper production using phenolic oxime extractants accounts for approximately
7
25% of copper production in the world. The sensitivity and selectivity of phenolic oxime extractants for Cu(II)
compared to other base metal ions results from the more stable pseudomacrocyclic structure of the copper
complex (Figure 1).
∗Correspondence: muhammetkose@ksu.edu.tr
197
This work is licensed under a Creative Commons Attribution 4.0 International License.

KARABÖRK et al./Turk J Chem
H
O
H
O
H
O
H
O
N
H
N
O
H
N
O
Cl
CH3
H
C6
5
H
H
C9
H
C9
19
19
H
C9
19
Acorg K2000
LIX
SME 529
LIX 70
84-I
P50
Acorga
a)
R1
H
O
O
R1
H
O
R
N
O
R
O
N
Cu
N
R
Cu
H
O
N
R
O
R1
H
R1
O
c)
b)
Figure 1. a) Examples of commercially available phenolic oxime extractants, b) general sutructure of Cu(II) complexes,
and c) interligand buttress of hydrogen bonding.
Formation of the strong interligand hydrogen bonds between the oxime hydrogen and the phenolic oxygen
8−10
atoms provides a planar donor set and a suitable cavity for Cu(II).
There are also mixtures used for the
extraction of heavy metals. Moore et al., for example, employed HDNNS (dinonylnaphthalene sulfonic acid) and
8−10
Lix63 (5,8-diethyl-7-hydroxy-6-dodecanone oxime) for the extraction of copper(II) from iron(III).
Recently,
Zhu et al. used a mixture of dinonylnaphthalene sulfonic acid and n-hexyl 3-pyridinecarboxylate ester for the
8−10
extraction of Cu(II) from aqueous solution. The mixture showed synergistic solvent extraction for Cu(II).
Intermolecular interactions between extractants, such as hydrogen bonds, have a significant effect on the stability
of complexes that form in the water-immiscible phase, and buttressing of interligand hydrogen bonding control
11
cavity sizes consequently can be very effectively used to tune strengths of saliclylaldoxime extractants. The
usage of highly selective and stable extractants for a specific metal is critical for reducing production cost,
12
enhancing product quality, and minimizing the environmental impact.
In this work, four new azo-aldehyde compounds (HL1–HL4) and their oxime derivatives (HL1ox–HL4ox)
were synthesized and characterized. The HL1ox–HL4ox compounds were used for solvent extraction of metal
ions. The effects of time and pH on the extraction capacity were investigated in detail.
2. Results and discussion
In this work, four new azo-aldehyde compounds, HL1–HL4, and their oxime derivatives, HL1ox–HL4ox, were
synthesized and characterized by spectral and analytical methods. In the azo-aldehyde synthesis, the diazonium
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KARABÖRK et al./Turk J Chem
salts of the p-substituted aniline compounds were prepared using hydrochloric acid and sodium nitrite followed
by the coupling reaction with salicylaldehyde derivatives. The oxime compounds (HL1ox–HL4ox) were obtained
13
by the condensation reaction of the azo-aldehyde compounds with hydroxylamine in ethanol. The synthesis
reaction of the azo-aldehyde and their oxime derivatives is shown in Figure 2.
R1
R1
R1
iii
i ii
,
N
N
N
N
°
-
0 5 C
EtOH
N
N
R2
R2
H
O
O
H
N
O
H
O
Figure 2.
The synthesis of new HL1ox–HL4ox (i
=
NaOH (10%), ii
=
2-hydroxybenzaldehyde, 3-tert-
butyl-2-hydroxybenzaldehyde, 2-hydroxy-3-methoxybenzaldehyde, 2-hydroxy-3-methylbenzaldehyde, iii = NaOAc and
NH2 OH.HCl).
1
13
The synthesized aldehyde and oxime compounds were characterized by H and C NMR, FTIR spec-
troscopy, and elemental analysis (CHN). The CHN data are in good agreement with calculated values. Single
crystals of HL1ox–HL3ox compounds were grown from slow evaporation of MeOH solutions of the compounds.
The solid-state structures of these compounds were determined by single-crystal X-ray diffraction (XRD) stud-
ies.
2.1. NMR spectra
1
13
The characterization of the synthesized azo-aldehyde compounds (HL1–HL4) was carried out by H and
C
NMR spectra and obtained data are given in the experimental section. In the spectra of the compounds, signals
due to the phenolic-OH protons were observed in 11.33–12.15 ppm range. The singlet signals in the 10.01–10.05
ppm range are due to the protons of the aldehyde group (H-CO-). The aromatic protons of the compounds were
1
observed in the range between 7.13 and 8.23 ppm. In the H spectra of HL1 and HL2, the multiplet signals
due to the ethyl group (-CH2 CH3) protons were observed in the 1.32–1.33 and 2.76–2.77 ppm ranges. For
HL2, tert-butyl group (-C(CH3)3) protons were observed as a singlet peak at 1.53 ppm. The methoxy group
(-OCH3) protons of HL3 were observed at 1.53 ppm. The singlet peaks observed at 1.41 and 2.38 ppm in the
spectrum of HL4 are due to the protons of the tert-butyl (-C(CH3)3) and (-CH3) group protons, respectively.
1
The H NMR spectra of the four synthesized p-substituted phenolic oxime compounds (HL1ox–HL4ox)
were measured in CDCl3 . The integration values are in good agreement with the number of protons present
in the compounds and there are no organic impurities in the samples. The carbonyl group (-CH=O) proton
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KARABÖRK et al./Turk J Chem
signals observed in the spectrum of the azo-aldehyde compounds (HL1–HL4) in the range of 10.01–1.05 ppm
1
completely disappeared in the H NMR spectra of the oxime compounds. Instead, new singlet signals due to
the azomethine (-CH=N) group proton were seen in the 8.36–8.38 ppm range. The singlet signals observed at
10.28, 10.79, 10.35, and 10.52 ppm in the HL1ox–HL4ox spectra of the compounds, respectively, are due to the
phenolic proton (Ph-OH).
13
In the C NMR spectra of HL1–HL4, the characteristic carbonyl group (-CH=O) carbon signals were
observed at 196.60, 197.28, 196.35, and 196.73 ppm, respectively. The ethyl group (-CH2 CH3) carbon signals
in the spectra of HL1 and HL2 compounds were seen in the 15–29 ppm range. The peaks observed at 29.18
ppm and 35.20 ppm in the spectrum of HL2 confirmed the presence of the tert-butyl (-C(CH3)3) group in the
compound. The methoxy group carbon signal in the spectrum of HL3 was observed at 56.40 ppm. The carbon
atom of the methyl (-CH3) group in the HL4 compound was observed at 15.25 ppm and the presence of the
tert-butyl group (-C(CH3)3) in the compound was confirmed by the peaks observed at 31.29 and 35.04 ppm.
The carbon atom signals in the aromatic rings of the compounds (HL1–HL4) were observed in the range of
13
117.92–154.69 ppm. In the C NMR spectra of the oxime compounds (HL1ox–HL4ox), the carbonyl group
(-CH=O) carbon atom signal was completely absent and, instead, oxime group (-C = N-OH) carbon signals
in the range of 158 to 159 ppm were observed. The rest of the carbon atom signals are in good agreement with
their proposed structures.
2.2. FTIR spectra
FTIR spectra of the compounds were obtained to determine the characteristic vibration bands and the obtained
data are given in the experimental section. The carbonyl group í(C=O) vibrations in the spectra of HL1–HL4
were observed as sharp peaks at 1652, 1646, 1666, and 1651 cm−1 , respectively. The vibration band of the
N=N bond was observed in the 1426–1460 cm−1 range. The O-H stretching vibrations of the phenolic groups
in the compounds (HL1–HL4) were observed as a broad band between 3000 and 3200 cm−1 . In FTIR spectra
of the oxime compounds (HL1ox–HL4ox), the carbonyl group stretching (íC=O) completely disappeared and a
new sharp peak due to the imine bond (íC=N ) was observed in the 1610–1638 cm−1 range. The rest of the
stretching peaks of HL1ox–HL4ox are similar to those of the HL1–HL4 compounds.
2.3. X-ray structure of the HL1ox–HL3ox compounds
Single crystals of HL1ox were obtained from slow evaporation of an acetone solution of the compound. The
molecular structure of the compound in the solid state was determined by XRD study. The molecular structure
of the compound is solved in the monoclinic crystal system and P21 /c space group. The molecular structure
of the compound is given in Figure 3.
The bond lengths of diazo (N2=N3) and azomethine (C1=N1) groups in the compounds are 1.275(12)
and 1.234(11) Å, respectively. The phenyl and phenol rings in the molecule are translocated with respect to
the diazo group. There is a phenol-imine intramolecular (O1H· · · N1) hydrogen bond in the molecule. In
addition to the intramolecular phenol-imine hydrogen bond, the phenol-imine molecule forms a dimer with two
13,14
complementary hydrogen bonds of two azo-oxime molecules, as shown in Figure 4.
In the structure, dimeric
molecules are further linked by π − π interactions.
The HL2ox compound was recrystallized from EtOH solution. The structure of the compound was solved
in the monoclinic crystal system and P21 /n space group. The X-ray structure of HL2ox is given in Figure 3. The
200

KARABÖRK et al./Turk J Chem
HL1ox
HL2ox
HL3ox
Figure 3. X-ray structures of HL1ox–HL3ox compounds with atom numbering. Hydrogen bonds in HL3ox are shown
as dashed lines.
201

KARABÖRK et al./Turk J Chem
HL1ox
HL2ox
Figure 4. Hydrogen bonded dimers in HL1ox and HL2ox.
bond lengths of diazo (N2=N3) and azomethine (C=N) groups are 1.144(7) and 1.277(8) Å, respectively. As
expected, there is a phenol-imine intramolecular (O1H· · · N1) hydrogen bond. In the structure of the compound,
the ethyl group of the C8/C13 phenyl ring is disordered and this was modeled over two positions. The oxime
oxygen group (as hydrogen bond donor) makes a hydrogen bond with a phenolic oxygen atom of a neighboring
molecule (hydrogen bond acceptor), resulting in a hydrogen bonded dimer (Figure 4). The π − π interactions
between the phenol rings (centroid-centroid distance between phenol rings is 3.808 Å) of the dimeric molecules
were observed.
Single crystals of HL3ox suitable for single-crystal XRD study were obtained from slow evaporation of
MeOH solution of the compound. The X-ray structure of the compound is given in Figure 3. In the structure of
the compound, there were two molecules in the asymmetric unit. These two molecules in the asymmetric unit
exhibit small differences between the dihedral of the phenyl rings in the molecules with similar bond angles and
distances. The azomethine (C=N) and diazo (N=N) bond lengths in both molecules in the asymmetric unit are
within the expected limits. In the structure of the molecule, there is a phenol-imine hydrogen bond (OH· · · N).
In the structure, hydrogen bond chains are formed by hydrogen bonds between the oxime group (hydrogen
bond donor) and the phenolic and methoxy group oxygen atoms (hydrogen bond acceptor). The structure of
the compound is further stabilized by the π − π phenyl-phenyl interactions (centroid-centroid distance between
phenol and phenyl rings is 3.919 Å).
Hirshfeld surface analysis is a common tool to investigate the nature of intermolecular interactions within
crystal packing. The Hirshfeld surfaces for HL1ox–HL3ox were obtained for visualizing the van der Waals
15
distances and determining the interaction sites within the structures. The surfaces for the oxime compounds
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KARABÖRK et al./Turk J Chem
16
were obtained using Crystal Explorer software, which uses X-ray crystallographic data in CIF format. The
fingerprint plots of the compounds show two large spikes for the (H· · · O/O· · · H) contacts to the adjacent
molecules. The fingerprint plot of HL1ox is shown in Figure 5. The hydrogen bond contacts in the compounds
are seen as intense red spots on the dn surface. A cyclic hydrogen bond pattern is usually shown by a large
number of fused spots between the main spikes.
Figure 5. Fingerprint plots for HL1ox.
Relative contribution of the different contacts to the Hirshfeld surface of the HL1ox–HL3ox molecules
were calculated. For the compounds, the largest contribution comes from H· · · H contacts, followed by H· · ·
O/O· · · H and H· · · C/C· · · H contacts. The H· · · N/N· · · H contacts also play a role in the packing structure.
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KARABÖRK et al./Turk J Chem
2.4. Computational studies
The mentioned ligands, HL1ox–HL4ox, in dimeric form and their metal complexes are optimized at B3LYP/6–
1
2
31G(LANL2DZ) level in gas phase. Optimized structures of dimeric ligands and [Cu(L )2 ], [Cu(L )2 ],
3
4
3
3
[Cu(L )2 ], [Cu(L )2 ], [Ni(L )2 ], and [Zn(L )2 ] complex dimers were calculated. Dimeric ligand structures
are investigated at B3LYP/6-31G level. There is a cavity in each dimer structure. Thermodynamic parameters
of the mentioned complexes and the dimeric oxime ligands, which are total energy (ET otal), enthalpy energy
(H), and Gibbs free energy (G), are given in Table 1.
Table 1. Thermodynamic parameters of related complexes’ B3LYP/6-31G(LANL2DZ) levels in gas phase.
a
a
a
b
b
Complexes ET otal
H
G
∆E
∆H
1
[Cu(L )2]
–1984.474234 –1984.47329
–1984.58756
–2778.22 –2783.17
2
[Cu(L )2]
–2298.659375 –2298.658431 –2298.793701 –2746.81 –2751.77
–2975.426906 –2975.425962 –2975.544023 –2747.21 –2752.17
–2948.615301 –2948.614356 –2948.729978 –2989.34 –2994.3
–2844.884784 –2844.88384
–2220.124186 –2220.123241 –2220.254032 –2775.72 –2780.68
3
[Cu(L )2]
3
[Ni(L )2]
3
[Zn(L )2]
–2845.003789 –2475.27 –2480.23
4
[Cu(L )2]
3
1
According to Table 1, [Cu(L )2 ] is the most stable copper complex, while [Cu(L )2 ] is the best interacting
1
complex. Additionally, [Cu(L )2 ] has the highest formation stability. As for the other complexes, represented
as M(L )2 , the most stable complex is [Cu(L )2 ]. Additionally, [Ni(L )2 ] is the best interacting complex and
4
3
3
has the highest formation stability.
2.5. Investigation of absorption spectra of synthesized compounds
The absorption properties of the novel azo-aldehydes (HL1–HL4) and their oxime derivatives (HL1ox–HL4ox)
were studied in DMF solution (10−5 M). UV-Vis spectra of the compounds are given in Figure 6.
Two broad absorption bands are observed in the UV-Vis spectra of the synthesized azo-aldehyde com-
pounds (HL1–HL4). The broad and intense absorption bands observed in the range of 290–420 nm are assigned
to the π − π* transitions of the π electrons present in the compounds. The second band in the 410–520 nm
range can be due to the n-π* transitions. The n-π* electronic transitions in HL1–HL4 are absent in the UV-vis
spectra of HL1ox–HL4ox. A single absorption band in the UV-Vis spectra of HL1ox–HL4ox was seen as a
strong absorption band in the range of 306–420 nm. This absorption band is attributed to π − π* electronic
transitions. In oxime compounds, the absorption bands due to the π−π* electronic transitions shifted to longer
wavelengths (red shift) when compared to the same bands in the azo-aldehyde (HL1–HL4) compounds.
2.6. Solvent extraction studies of oxime compounds
The solvent extraction capacities of the new oxime compounds for Cu(II), Ni(II), and Zn(II) ions were in-
vestigated. The solvent extraction procedure is shown in Figure 7. Liquid-liquid extraction processes were
investigated for Cu(II), Ni(II), and Zn(II) metal ions at a pH range of 0 to 5 (Figure 8). The synthesized oxime
compounds were found to have extraction capacity even at very low pH. As the pH increases from 0 to 5, the
extraction capacity of the oxime compounds increases. At pH 0, 30% of Cu(II) content was transferred from the
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KARABÖRK et al./Turk J Chem
3
3
2
1
0
HL2
HL2ox
HL1
HL1ox
2
1
0
270
320
370
420
470
520
570
270
2
320
370
420
470
520
570
Wavelength (nm)
Wavelength (nm)
HL3
HL3ox
HL4
HL4ox
3
2
1
0
1
0
270
370
470
570
267
317
367
417
467
517
567
Wavelength (nm)
Wavelength (nm)
Figure 6. UV-Vis spectra of the compounds in DMF.
aqueous phase to the organic phase (CHCl3). For the HL1ox compound, Ni(II) and Zn(II) ions showed very
close extraction capacities between pH 0 and 5. For all oxime compounds at all pH values, Cu(II) ion shows
higher extraction values than Ni(II) and Zn(II) ions. The vacancy formed by the dimerization of the oxime
ligands is thought to be more suitable for Cu(II) ion, thus resulting in better extraction values (Figure 8).
Figure 7. Schematic representation of liquid-liquid extraction.
Of the oxime ligands, the HL3ox compound was found to show the maximum extraction capacity for the
Cu(II) ion at all pH values. In the HL1ox–HL4ox compounds, there are -H, -t-But, -OCH3 , and -CH3 groups at
the meta positions with respect to the oxime group (C=N-OH). In HL1ox, HL2ox, and HL4ox, the -C=N-OH
group of oxime in the hydrogen bonded dimers does not interact with the groups at the meta positions, but the
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KARABÖRK et al./Turk J Chem
HL1ox
100
80
60
40
20
0
100
HL2ox
80
Cu(II)
Cu(II)
60
Zn(II)
Zn(II)
Ni(II)
40
Ni(II)
20
0
0
1
2
3
4
5
0
1
2
3
4
5
pH
pH
100
80
60
40
20
0
HL4ox
HL3ox
100
80
60
40
20
0
Cu(II)
Cu(II)
Zn(II)
Ni(II)
Zn(II)
Ni(II)
0
1
2
3
4
5
0
1
2
3
4
5
pH
pH
Figure 8. Cu/Ni/Zn(II) loading of chloroform solutions of HL1ox–HL4ox as a function of the equilibrium pH of the
aqueous phase.
methoxy group of HL3ox enters into weak hydrogen bond interaction with the oxime group of the neighboring
17,18
molecule.
These weak hydrogen bond interactions are thought to contribute to the overall stability of the
17,18
resulting complex.
When the extraction results are examined, it is found that HL1ox, HL2ox, and HL4ox
have about 30% extraction capacities at pH 0, while HL3ox has about 55% extraction capacity. In the Cu(II)
extraction for the HL3ox compound, 75% extraction was obtained at pH 3 and this did not show considerable
change at pH 4 and pH 5 (Figure 8). When the results of extraction studies are examined, 100% extraction
was not observed for Cu(II), Zn(II), or Ni(II) ions. The transfer of metal ions to the organic phase was due
to the coordination of the ligands to the metal ions. During the complexation, there are two possible 1:2 and
1:1 (metal:ligand) complexations. If only the 1:1 (metal:ligand) complex forms, then all of the metal ions will
have been extracted. If only the 1:2 (metal:ligand) complexations have formed, then 50% of the metal ions will
have been retained in aqueous solutions. In the solvent extraction study of Cu(II), more than 50% of Cu(II)
(pH 1–5) was transferred to the organic phase. This suggests that both 1:1 and 1:2 complexations formed in
the recovery process.
In order to compare the stability of the complexes with the extraction capacities, the thermodynamic
parameters [energy (ET otal), enthalpy energy (H), and Gibbs free energy (G)] for the possible structures
3
[M(Loxime)2 ] (M = Cu, Ni, or Zn) were calculated. According to the thermodynamic parameters, [Cu(L )2 ] is
3
the most stable complex among the studied compounds. The lower Gibbs free energy (G) of complex [Cu(L )2 ]
resulted in better extraction capacity for the complex.
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KARABÖRK et al./Turk J Chem
Time-dependent extraction study of Cu(II) was done for the HL3ox ligand at pH 5. In the end of the first
15 min, almost 30% of Cu(II) was removed from the aqueous solution and the extraction reached a maximum
at 60 min with over 70% extraction. After 60 min, the extraction capacity of HL3ox did not show considerable
change. To compare the selectivity of HL3ox, competing experiments were also carried out at pH 5 for 120
min. The Cu(II)/Ni(II), Cu(II)/Zn(II), and Cu(II)/Ni(II)/Zn(II) stock solutions were extracted with chloroform
solutions containing HL3ox (0.01 M). The extraction values are expressed as % extraction and shown in Figure
9. For all three competing experiments, Cu(II) showed better extraction values, confirming the selectivity of
HL3ox for Cu(II).
HL3ox
Cu(II)
HL3ox
Cu(II)
Zn(II)
70
60
50
40
30
20
10
0
Ni(II)
70
60
50
40
30
20
10
0
pH 5
pH 5
HL3ox
Cu(II) Ni(II)
Zn(II)
70
60
50
40
30
20
10
0
pH 5
Figure 9. Liquid-liquid extraction for Cu(II)/Ni(II), Cu(II)/Zn(II), and Cu(II)/Ni(II)/Zn(II) mixed solutions.
2.7. Conclusions
In this work, four new azo-aldehyde compounds (HL1–HL4) were synthesized by diazo coupling reactions.
Subsequently, p-substituted phenolic oxime compounds (HL1ox–HL4ox) were synthesized by reacting the syn-
thesized azo-aldehyde compounds with hydroxylamine. Solid-state structures of HL1ox–HL3ox were determined
by single-crystal XRD studies. Absorption properties of the synthesized azo-aldehyde and oxime compounds
were investigated in DMF. Finally, the HL1ox–HL4ox compounds were used for solvent extraction of metal
ions. The HL1ox–HL4ox ligands showed higher extraction performance for Cu(II) ion than Ni(II) and Zn(II)
ions. The effect of pH on extraction was investigated and it was found that the synthesized oxime compounds
could extract at even as low as pH as 1. When the results were examined, the -OMe group in the meta position
of the HL3ox compound increased its extraction capacity. For industrial applications, the HL3ox compound
can be used for the liquid-liquid extraction of Cu(II) from aqueous solutions. Computational studies of the
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KARABÖRK et al./Turk J Chem
mentioned compounds were performed by B3LYP method. Thermodynamic parameters of related complexes
were examined in detail. Formation enthalpy and interaction energy for each complex were calculated and
examined.
3. Experimental
3.1. Materials
4-Ethylaniline, 4-chloroaniline, 2-hydroxybenzaldehyde, 3-tert-butyl-2-hydroxybenzaldehyde, sodium nitrite,
CuSO4 .5H2 O, NiSO4 .6H2 O, and ZnSO4 .7H2 O were purchased from Aldrich Chemical Company and used
as received. 4-tert-Butylaniline, 2-hydroxy-3-methoxybenzaldehyde, 2-hydroxy-3-methylbenzaldehyde, and hy-
droxylamine hydrochloride were purchased from Acros Organics Chemical Company and used as received. All
other materials used were of reagent grade quality, provided from chemical companies and used as received
without further purification.
3.2. Physical measurements
NMR spectra were obtained using a Bruker Advance III 400 MHz spectrometer. The FTIR spectra were obtained
(4000–450 cm−1) using a PerkinElmer spectrum 400 FTIR spectrophotometer. The absorption spectra in the
200–800 nm range were obtained on a Shimadzu UV-160A UV-Vis spectrophotometer. Solid-state structures
of HL1ox, HL2ox, and HL3ox were determined using a Bruker D8 QUEST diffractometer. Efficacy of the new
p-substituted phenolic oxime ligands for recovery of metal ions was determined by PerkinElmer Optima 2100
DV ICP-OES.
3.3. Synthesis of azo-aldehyde ligands HL1–HL4
19,20
Azo-aldehyde compounds HL1–HL4 were synthesized according to the reported method.
4-Substituted
aniline derivatives (10 mmol) were mixed with 50 mL of water. To this solution, concentrated HCl (2.5 mL)
was added and the solution was filtered. The solution was then cooled on an ice bath (0–5 °C), followed by
slow addition of NaNO2 (13.9 mmol) in water (2 mL). The reaction solution was kept for 30 min in an ice
bath. To the ice-cold solution, corresponding salicylaldehyde derivatives (10 mmol) in 10% NaOH solution (10
mL) were added dropwise and the reaction mixture was stirred for 2 h at room temperature. Upon addition
of salicylaldehyde derivatives, the formed yellow precipitate was filtered under vacuum, washed with water (15
mL), and dried in air.
1
HL1: Yellow powder, yield: 1.261 g, 5 mmol (49.6%). Mp 116–120 °C. NMR (CDCl3 , ä ppm): H,
11.33 (s, 1H, OH), 10.02 (s, 1H, CH=O), 8.18 (s, 1H, aromatic CH), 8.17 (d, H, aromatic CH), 7.85 (d, 2H,
aromatic CH), 7.37 (d, 2H, aromatic CH), 7.13 (d, H, aromatic CH), 2.76 (q, 2H, ethyl group protons -CH2 -),
13
1.32 (t, 3H, ethyl group protons –CH3).
C, 196.60 (C=O), 163.52, 150.59, 147.94, 145.99, 130.67, 129.08,
128.64, 122.8, 120.3, 118.5 (aromatic C atoms), 28.86 and 15.40 (ethyl group C atoms). IR (ATR, cm−1):
3194((O−H)) , 2959((C−H)) , 1652((C=O)) , 1455((N=N))
.
1
HL2: Brown powder, yield: 1.0285 g, 3.3 mmol (66.4 %). Mp 92–96 °C. NMR (CDCl3 , äppm): H,
12.15 (s, 1H, OH), 10.01 (s, 1H, CH=O), 8.23 (s, 1H, aromatic CH), 8.04 (s, 1H, aromatic CH), 7.87 (d, 2H,
aromatic CH), 7.37 (d, 2H, aromatic CH), 1.53 (s, 9H, tert-butyl group protons –C(CH3)3), 2.77 (q, 2H, ethyl
13
group protons -CH2 -), 1.33 (t, 3H, ethyl group protons –CH3).
C, 197.28 (C=O), 163.28, 150.77, 147.66,
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KARABÖRK et al./Turk J Chem
145.31, 139.45, 128.61, 126.72, 122.80, 120.34 (aromatic C atoms), 35.20 and 29.18 (tert-butyl group C atoms),
28.86 and 15.42 (ethyl group C atoms). IR (ATR, cm−1): 2955((C−H)) , 1646((C=O) , 1426((N=N))
.
1
HL3: Brown powder, yield: 1.1000 g, 3.78 mmol (75.8 %). Mp 178–182 °C. NMR (CDCl3 , ä ppm): H,
10.05 (s, 1H, CH=O), 7.87 (d, 2H, aromatic CH), 7.73 (s, 1H, aromatic CH), 7.50 (d, 2H, aromatic CH), 7.29
13
(s, H, aromatic CH), 4.03 (s, 3H, methoxy group protons –OCH3). C, 196.35 (C=O), 154.69, 150.65, 149.31,
145.39, 136.92, 129.43, 124.55, 124.02, 123.94, 119.95, 119.58, 117.92 (aromatic C atoms), 56.40 (methoxy C
atom). IR (ATR, cm−1): 3088((O−H)) , 1666((C=O)) , 1426((N=N))
.
1
HL4: Yellow powder, yield: 2.2578 g, 7.6 mmol (76.2 %). Mp 102–106 °C. NMR (CDCl3 , ä ppm): H,
11.62 (s, 1H, OH), 10.01 (s, 1H, CH=O), 8.05 (s, 1H, aromatic CH), 7.86 (d, 2H, aromatic CH), 7.57 (d, 2H,
aromatic CH), 2.38 (s, 3H, methyl group protons -CH3), 1.41 (s, 9H, tert-butyl group protons –C(CH3)3).
13
C, 196.73 (C=O), 162.16, 154.53, 150.37, 145.49, 130.50, 128.09, 127.59, 126.09, 122.45, 119.66 (aromatic
C atoms), 35.04 and 31.29 (tert-butyl group C atoms), 15.25 (methyl group C atoms). IR (ATR, cm−1):
2957((C−H)) , 1651((C=O)) , 1442((N=N))
.
3.4. Synthesis of azo-oxime compounds HL1ox–HL4ox
The azo-aldehyde compounds (1.000 g, 3.9 mmol for HL1; 1.000 g, 3.2 mmol for HL2; 1.000 g, 3.4 mmol for
HL3 and HL4) were dissolved in EtOH (100 mL). Then NaOAc (0.8 g for HL1, 0.66 for HL2, 0.70 g for HL3
and HL4, excess amounts) and NH2 OH.HCI (0.68 g for HL1, 0.56 for HL2, 0.59 g for HL3 and HL4, excess
21,22
amounts) were added to the solutions
and refluxed for 2 h. The reaction mixture was then poured into
ice-cooled water (250 mL) and precipitates were collected by filtration and dried in air.
HL1ox: Yellow crystals, yield: 0.5163 g, 1.92 mmol (49.16%). Mp 130–140 °C. NMR (CDCl3 , ä ppm):
H, 10.28 (s, 1H, OH), 8.36 (s, 1H, CH=N-O), 7.96 (d, H, aromatic CH), 7.94 (s, 1H, aromatic CH), 7.84 (d,
1
2H, aromatic CH), 7.36 (d, 2H, aromatic CH), 7.13 (d, 1H), 2.76 (q, 2H, ethyl group protons -CH2 -), 1.31
13
(t, 3H, ethyl group protons –CH3).
C, 159.65 (C=N-OH), 152.70, 150.78, 147.56, 146.12, 128.61, 125.97,
125.81, 122.72, 117.51, 116.59 (aromatic C atoms), 28.84 and 15.41 (ethyl group carbon atoms). IR (ATR,
cm−1): 3411((O−H)) , 2965((C−H)) , 1612((C=N)) , 1448((N=N)
.
HL2ox: Orange crystals, yield: 0.3815 g, 1.17 mmol (36.64%). Mp 155–165 °C. NMR (CDCl3 , ä ppm):
H, 10.79 (s, 1H, OH), 8.37 (s, 1H, CH=N-O), 8.0 (s, 1H, aromatic CH), 7.84 (d, 2H, aromatic CH), 7.71 (s, 1H,
1
aromatic CH), 7.37 (d, 2H, aromatic CH), 1.52 (s, 9H, tert-butyl group protons –C(CH3)3), 2.75 (q, 2H, ethyl
13
group protons -CH2 -), 1.31 (t, 3H, ethyl group protons –CH3). C, 159.16 (C=N-OH), 153.42, 150.94, 147.22,
145.40, 138.22, 128.56, 124.16, 123.57, 122.61, 116.84 (aromatic C atoms), 35.21 and 29.31 (tert-butyl group
carbon atoms), 28.81 and 15.42 (ethyl group carbon atoms). IR (ATR, cm−1): 3438((O−H)) , 2968((C−H))
,
1638((C=N)) , 1454(((N=N))
.
HL3ox: Brown crystals, yield: 0.2904 g, 0.95 mmol (27.86%). Mp 213–223 °C. NMR (CDCl3 , ä ppm):
H, 10.35 (s, 1H, OH), 8.38 (s, 1H, CH=N-O), 7.87 (s, 1H, aromatic CH), 7.58 (d, 2H, aromatic CH), 7.51 (s,
1
1H, aromatic CH), 7.28 (d, 2H, aromatic CH), 4.03 (s, 3H, methoxy group protons –OCH3). IR (ATR, cm−1):
3416((O−H)) , 1610((C=N)) , 1434((N=N))
.
HL4ox: Yellow powder, yield: 0.4462 g, 1.43 mmol (42.15 %). Mp 133–143 °C. NMR (CDCl3 , ä ppm):
H, 10.52 (s, 1H, OH), 8.36 (s, 1H, CH=N-O), 7.85 (d, 2H, aromatic CH), 7.72 (s, H, aromatic CH), 7.56 (d,
1
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KARABÖRK et al./Turk J Chem
2H, aromatic CH), 2.39 (s, 3H, methyl group protons -CH3), 1.41 (s, 9H, tert-butyl group protons –C(CH3)3).
13
C, 158.09 (C=N-OH), 154.19, 152.86, 150.51, 145.68, 126.88, 126.08, 125.97, 124.62, 122.31, 115.90 (aromatic
C atoms), 35.01 and 31.30 (tert-butyl group C atoms), 15.96 (methyl group C atoms). IR (ATR, cm−1):
3400((O−H)) , 2953((C−H)) , 1632((C=N)) , 1427((N=N)).
3.5. X-ray structure solution and refinement
X-ray crystallographic data for oxime compounds HL1ox, HL2ox, and HL3ox were collected at 293(2) K on
a Bruker D8 QUEST diffractometer using Mo-Kα radiation (1 = 0.71073 Å). Data reduction was performed
23,24
25,26
using Bruker SAINT.
SHELXS97 was used to solve and SHELXL2014/6 to refine the structures.
The
structures were solved by direct methods and refined on F2 using all the reflections. All the nonhydrogen
atoms were refined using anisotropic atomic displacement parameters and hydrogen atoms bonded to carbon
and oxygen atoms were fixed at calculated positions using a riding model and refined with temperature factors.
The crystal data and refinement details for HL1ox, HL2ox, and HL3ox are given in Table 2.
3.6. Solvent extraction experiments of HL1ox–HL4ox compounds
Stock solutions (0.01 M) of the oxime ligands (HL1ox, HL2ox, HL3ox, and HL4ox) were prepared in chloroform.
Aqueous stock solutions (0.01 M) of Cu(II), Ni(II), and Zn(II) were prepared from their sulfate salts. To adjust
the pH of metal solutions, 0.1 M NaOH and 0.5 M H2 SO4 solutions were prepared. All extractions were
performed according to the same general procedure. Solutions of ligands (0.01 M) in chloroform (5 mL) were
added to 0.01 M metal aqueous solutions (5 mL), which were adjusted to different pH values and stirred for 24
11
h at room temperature. After the phase separations, aliquots of 0.1 mL of the aqueous phase were separated
for metal analysis by ICP-OES. From the results obtained, the content of metal transferred from the aqueous
phase to the organic phase (CHCl3) was calculated as % and graphically plotted against pH.
3.7. Computational method
GaussView 5.0.9 and Gaussian 09 AS64L-G09RevD.01 package programs were used to carry out quantum
27,28
chemical calculations.
B3LYP, which is one of the hybrid density functional theory functions, was selected
as the method for the investigated molecules. As basis sets, LANL2DZ was selected for metal atoms and 6–31G
was selected for the rest of the atoms in the complexes. No imaginary frequency was obtained from calculations.
Additionally, organic compounds were calculated at B3LYP/6-31G level in vacuum. Optimized structures of
29
related compounds were taken via the Chemcraft Version 1.8 software program. Interaction energies and
formation enthalpy of the complexes are calculated by using Eqs. (1) and (2), respectively.
∆E = EComplex − EMetal − ELigands
∆H = HComplex − HMetal − HLigands
(1)
(2)
210

KARABÖRK et al./Turk J Chem
211

KARABÖRK et al./Turk J Chem
Acknowledgments
The authors are grateful to the Kahramanmaraş Sütçü İmam University Science Projects Unit for the financial
support for this study (Project Number: 2017/1-49 YLS). The authors also acknowledge the Scientific and
Technological Research Application and Research Center, Sinop University, Turkey, for use of the Bruker D8
QUEST diffractometer.
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