The synthesis of (N2O2S2)-Schiff base ligands and investigation of their ion extraction capability from aqueous media

Article abstract of DOI:10.1016/j.saa.2011.05.087

Two new Schiff bases (I) and (II) containing nitrogen-sulfur-oxygen donor atoms were designed and synthesized in a multi-step reaction sequence. The Schiff base (I) was used in solvent extraction of metal chlorides such as Cu²⁺ and Cr³⁺ as well as metal picrates such as Hg ²⁺ and UO₂²⁺ from aqueous phase to the organic phase. The influences of the parameter functions, such as pH, solvent, ionic strength of aqueous phase, aqueous to organic phase and concentration of the extractant were investigated to shed light on their chemical extracting properties upon the extractability of metal ions. The effect of chloroform, dichloromethane and nitrobenzene as organic solvents over the metal chlorides extraction was investigated at 25 ± 0.1 °C by using flame atomic absorption and the result is that the ability of extraction in solvents as follows: C₆H₅NO₂ > CHCl₃ > CH₂Cl₂ and the compositions of the extracted species have been determined. The metal picrate extraction was investigated at 25 ± 0.1 °C by using UV-visible spectrometry. As well that the extraction of picrates metal such as UO₂²⁺ and Hg²⁺ with Schiff base(I) in absence and presence of 2-(2-aminoethyl) pyridine was investigated in chloroform. The extraction results revealed the presence of neutral donors 2-(2-aminoethyl) pyridine shifts the extraction percentage curves towards higher pH region, indicating a synergistic effect of this donors on extraction of UO₂²⁺ and Hg²⁺ by the studied Schiff base (I).

Full text of DOI:10.1016/j.saa.2011.05.087

Spectrochimica Acta Part A 79 (2011) 1909–1914
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
The synthesis of (N2O2S2)-Schiff base ligands and investigation of their ion
extraction capability from aqueous media
Wail A.L. Zoubi∗, Farouk Kandil, Mohamad Khaled Chebani
Department of Chemistry, Faculty of Science, University of Damascus, Syria
a r t i c l e i n f o
a b s t r a c t
Article history:
Two new Schiff bases (I) and (II) containing nitrogen–sulfur–oxygen donor atoms were designed and
synthesized in a multi-step reaction sequence. The Schiff base (I) was used in solvent extraction of metal
Received 28 February 2011
Received in revised form 21 May 2011
Accepted 25 May 2011
chlorides such as Cu2+ and Cr3+ as well as metal picrates such as Hg2+ and UO2 from aqueous phase to
2+
the organic phase. The influences of the parameter functions, such as pH, solvent, ionic strength of aque-
ous phase, aqueous to organic phase and concentration of the extractant were investigated to shed light
on their chemical extracting properties upon the extractability of metal ions. The effect of chloroform,
dichloromethane and nitrobenzene as organic solvents over the metal chlorides extraction was inves-
tigated at 25 0.1 ◦C by using flame atomic absorption and the result is that the ability of extraction in
solvents as follows: C6H5NO2 > CHCl3 > CH2Cl2 and the compositions of the extracted species have been
determined. The metal picrate extraction was investigated at 25 0.1 ◦C by using UV–visible spectrome-
try. As well that the extraction of picrates metal such as UO22+ and Hg2+ with Schiff base(I) in absence and
presence of 2-(2-aminoethyl) pyridine was investigated in chloroform. The extraction results revealed
the presence of neutral donors 2-(2-aminoethyl) pyridine shifts the extraction percentage curves towards
Keywords:
Schiff bases
Solvent extraction
Transition metal cation
Crown ether
higher pH region, indicating a synergistic effect of this donors on extraction of UO2 and Hg2+ by the
2+
studied Schiff base (I).
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
measurement of lithium in biological samples has been reported
[5]. Metal ions have enormous importance in many biological pro-
The field of solvent extraction, commonly called liquid–liquid
extraction, has grown extensively in the past half century to
become an economically significant family of techniques in indus-
try, analytical chemistry and research. Moreover, liquid–liquid
extraction has important applications in the removal of toxic metal
ions from the environment and pollution prevention.
In addition, the Key to an efficient separation process is the
development of extractant with a strong preference for relevant
chemical species. Examples of such extractants include macrocyclic
ligands, called crown ethers that bind metal ions such as sodium,
potassium, lithium, cesium, strontium and barium [1–4]. An appro-
priate macrocyclic ligand exhibits good extraction selectivity for
desired metal ion species. Recently, a crown extractant was used in
the solvent extraction process for separating radioactive 137Cs from
the high-level wastes. Technetium is another element removed
from alkaline nuclear-waste solution by the use of crown ethers.
Crown ethers were also used as spectrophotometric analyti-
cal reagents. For example, the use of some crown ethers for the
cesses. Especially, heavy metal ions are effective enzyme inhibitors
exerting toxic effects on living systems [6]. Therefore, separation
and determination of toxic metal ions such as mercury, lead and
cadmium in environmental sources play an important role for
healthy life. Although the using of crown ethers in determination
and separation of alkali metals has been thoroughly investigated,
their usage as extractant for the mentioned toxic metals has rela-
tively received little attention [7,8].
Moreover, lariat crown ethers which bear side-chain containing
donor atoms possess unique cation binding properties compared
with the parent crown ether containing no extra donor sites [9,10].
Also, as efficient organic ligands lariat crown ethers meet the
requirement of rapid, strong and three-dimensional cation binding
and mimic the properties of natural ionophores [11].
Furthermore, during the last decades considerable attention has
been devoted to the chemistry of biscrown ethers for their applica-
tions in various area especially in ion-selective electrodes [12–15].
Most of the consideration has focused on macrocyclic receptors
that tend to bind with more than one transition metal ion [16–22].
Especially, in the early 1990s, due to the soft donor functional-
ity of sulphur atom, several research groups such as Robson [23],
Schrode [24] and Brooker and co-workers [25], in 2000, achieved
∗
Corresponding author. Tel.: +963 1133924949.
E-mail address: wwailalzoubi@yahoo.com (W.A.L. Zoubi).
1386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2011.05.087

1910
W.A.L. Zoubi et al. / Spectrochimica Acta Part A 79 (2011) 1909–1914
similar researches aimed at introducing thiophenolate head units
into Schiff base macrocycles. In all actions, the thiophenolate ana-
logues are expected to reveal very different properties (e.g. redox
and magnetic) due to the presence of the very polarisable thio-
phenolate donors and their interest in thiolatebridged metal active
sites in biology.
water. It was dried in air and recrystalized from EtOH and filtered
under vacuum. Yield: 85%.
2.4. Synthesis of ligand
[N,Nꢀ-bis(2-aminothiophenol)-˛,˛ꢀ-bis(5-bromocarboxylidene
phenoxy)-1,4-xylene] [H2L]
Moreover, biscrown ethers show extra binding properties than
the monocrown ethers, where by the cooperatives action of two
adjacent crown units, bis(crown ethers) tend to form stronger
complexes with particular metal ion than the corresponding
monocrown ethers, where it forms complexes with two crown moi-
eties per cation: ‘sandwich complexes’ that improve the stability of
the complex especially when the cation is too large to fit the cavity
of the crown ethers [26,27].
A solution of ␣,␣ꢀ-bis(5-bromo-2-carboxyaldehyde phenoxy)-
1,4-xylene (10.0 mmol, 4.98 g) in 50 ml absolute ethanol was added
dropwise over 2 h to a stirred solution of 2-aminothiophenol
(20.0 mmol, 2.50 g) dissolved in 50 ml hot absolute ethanol. A solid
mass separated out on cooling, which was kept in a refrigerator for
better crystallization. It was then filtered and recrystallized from a
mixture of absolute ethanol–DMF, yield 50%, m.p. 234–236. Anal.
Calc. C, 56.98; H, 3.64; N, 3.91; S, 8.93. Found: C, 57.95; H, 4.06; N,
4.1; S, 9.5%.
Kantekin others have reported the use of N2O2S2 Schiff base con-
taining aromatic moieties for the transfer of various metal ions from
the aqueous phase into the organic phase in liquid–liquid extrac-
tion system [28–30]. In this work, we have been interested in the
design and synthesis of N2O2S2–crown ether extractants for the
selected metal ions, which have bigger cavity size. The aim of this
investigation is design and synthesis of two novel ligands, and also
2.5. Synthesis of ligand
[N,Nꢀ-bis(2-aminothiophenol)-1,7-bis(5-bromocarboxylidene
phenyl)-1,4,7-trioxaheptane [H2L]
solvent extraction properties for the metal cations such as Cu2+
,
A
solution
of
1,7-bis(5-bromo-2-formylphenyl)-1,4,7-
Cr3+, Hg2+, and UO2 have been investigated.
2+
trioxaheptane (10.0 mmol, 4.7 g) in 50 ml absolute ethanol was
added dropwise over 2 h to a stirred solution of 5-amino-1,3,4-
thia-diazole-2-thiol (20.0 mmol, 2.66 g) dissolved in 50 ml hot
absolute ethanol. A solid mass separated out on cooling, which was
kept in a refrigerator for better crystallization. It was then filtered
and recrystallized from a mixture of absolute ethanol–DMF, yield
60%, m.p. 238–240. Anal. Calc. C, 37.39; H, 3.39; N, 11.89; S, 18.2.
Found: C, 35.2; H, 2.2; N, 11.9; S, 18.13%.
2. Experimental
2.1. Reagents and apparatus
All the used chemicals were purchased from Aldrich or Merck
unless otherwise cited. The C, H and N were analyzed on a Carlo-
Erba 1106 elemental analyzer. The IR spectra of the ligands were
recorded with a Midac 1700 instrument in KBr pellets. 1H and
13C NMR spectra of ligands in CDCl3 and C2D5OD solution were
recorded on a Bruker 400 MHz spectrometer and chemical shifts
are indicated in ppm relative to tetramethylsilane. Mass spec-
tra were recorded using a KRATOS MS50TC spectrometer. AA 929
Unicam Spectrometer was used for FAAS measurements with an
air-acetylene flame. The UV–vis measurements were recorded on a
PerkinElmer ␭ 20UV–vis Spectrometer. A pH meter (Metrohm 691
pH Meter) was also used. All extractions were performed by using
a mechanical flask agitator in 50 cm3 stoppered glass flasks.
2.6. Extraction procedure
Aqueous solutions containing 1.5 × 10−3 mol l−1 metal chloride
or metal picrate (aqueous solution (10 ml) containing 1.25 × 10−5 M
picric acid and 1 × 10−2 M metal nitrate were placed in stop-
pered flask and shaken for 2 h at 25.0 0.1 ◦C) in appropriate
buffer were equilibrated with equal volumes of the chloroform,
dichloromethane and nitrobenzene solutions of the Schiff base (I)
4×10−4 mol l−1 by shaking in a mechanical shaker at 25 ◦C. Opti-
mum equilibration time was determined for this system. In most
cases distribution equilibrium was attained in less than 30 min and
a shaking time of 120 min. The ionic strength of the aqueous was
0.1 M KCl in all experiments except those in which the effect of ionic
strength was studied. After agitation, the solutions were allowed
to stand for 120 min. The copper and chrome concentrations of the
aqueous phase were determined by FAAS, and that of the organic
phase from the difference by considering the mass balance. But the
concentration of picrate ion remaining in the aqueous phase was
then determined spectrophotometrically at 355 nm. Blank experi-
ments showed that no picrate extraction The PH of aqueous phase
was recorded as equilibrium PH.
2.2. Synthesis of ˛,˛ꢀ-bis(5-bromo-2-carboxyaldehyde
phenoxy)-1,4-xylene
To
a
stirred solution of 5-bromosalicylaldehyde (40 g,
200 mmol) and K2CO3 (13.8 g, 100 mmol) in DMF (100 ml)
was added dropwise ␣,␣ꢀ-dibromo-p-xylene. (17.5 g, 100 mmol)
in DMF (40 ml). The reaction was continued for 4 h at 150–155 ◦C
and then for 4 h at room temperature. Then, 200 ml distilled
water was added and the mixture kept in refrigerator. After 1 h,
the precipitate was filtered and washed with 500 ml water. It
was dried in air and recrystalized from EtOH and filtered under
vacuum. Yield: 80%, m.p. 228–230.
The extractability of picrate (E%) was determined based on the
absorbance of picrate ion in the aqueous from Eq. (1)
ꢀ
ꢁ
(A0 − A)
E% =
× 100
(1)
A0
2.3. Synthesis of
1,7-bis(5-bromo-2-formylphenyl)-1,4,7-trioxaheptane
where A0 is the absorbance in the absence of ligand and A denotes
the absorbance in the aqueous phase after extraction.
To
a
stirred solution of 5-bromosalicylaldehyde (40 g,
200 mmol) and K2CO3 (13.8 g, 100 mmol) in DMF (100 ml),
was added dropwise 1-chloro-2-(2-chloroethoxy)ethane (14.3 g,
100 mmol) in DMF (40 ml). The reaction was continued for 4 h at
150–155 ◦C and then for 4 h at room temperature. Then, 200 ml
distilled water was added and the mixture kept in refrigerator.
After 1 h, the precipitate was filtered and washed with 500 ml
3. Results and discussion
3.1. Synthesis of Schiff bases
The synthetic experiments of new two Schiff bases (I) and (II)
are shown in Scheme 1. The structure of novel compounds were

W.A.L. Zoubi et al. / Spectrochimica Acta Part A 79 (2011) 1909–1914
1911
at 1607 cm−1 attributable to characteristic stretching frequencies
of the imino linkage ꢁ(C N) [32,33] provides strong evidence for
the presence of product. The absorption in IR spectrum of Schiff
base (II) at 2728 cm−1 is due to the presence of SH. A broad medium
intense band was at 3075 cm−1 due to for aromatic protons.
3.1.2. Mass spectrum
The electron impact mass spectrum of the Schiff bases (I) and
(II) confirm the probable formula by showing a peak at 716 amu,
corresponding to the Schiff base (I) and 700 amu, corresponding to
the Schiff base (II).
3.1.3. 1H NMR spectra
The Schiff base (I) [Fig. 1(b)] exhibits signal at 5.38 ppm due to
SH protons. It also exhibits resonance due to –CH2– protons around
1.57 ppm. The other characteristic resonance due to azomethine
proton in Schiff base (I) appears at 8.73 ppm. Signals in the region
7–8.12 ppm due to aromatic protons [29–31].
The Schiff base (II) [Fig. 2(b)] exhibits signal at 5.3 ppm due to SH
protons. It also exhibits resonance due to –CH2– protons around 3.8
and 1.1 ppm. The other characteristic resonance due to azomethine
proton in Schiff base (II) appears at 8.86 ppm. Signals in the region
6.9–7.9 ppm due to aromatic protons [29–31].
3.1.4. 13C NMR spectrum
The 13C NMR (75 MHz, CHCl3-d1 75 MHz) d (ppm) spectrum
[Fig. 1(a)] of Schiff base (I) indicated new resonances are Arom:
114.19, 114.73, 121.31, 123.00, 124.53, 125, 126.18, 128.25, 132.20,
134, 135.93, 136.15, 151.96, 155.09. CH N: 161.32. CH2: 70.99.
The 13C NMR (75 MHz, C2H5OH-d6 75 MHz) d (ppm) spec-
trum [Fig. 2(a)] of Schiff base (II) indicated new resonances are
CH2: 79.92, Arom:110.57, 111.16, 11687.31, 118.90, 120.97, 127.72,
129.28, 131.56, 133.44, 137.55, 154.13, 159.82, 162.58, CH N:
166.21.
3.2. Extraction of metal ions with Schiff bases
3.2.1. Effect of PH and solvents on the extraction of Cu(II) and
Cr(III)
The stability of a transition metal complex with a polydentate
chelate ligand depends on a range of factors including: number
and type of the donor atoms present, the number and size of the
chelate rings formed on complexation. In addition, the stability and
selectivity of complexations strongly depend on the donor ability
and dielectric constant of the solvent [34] and shape and size of the
solvent molecules [35].
Generally, it is expected that in solvents with a high donor ability
and dielectric constant, the stability constant of the complex should
decrease due to the competition between the ligand and the solvent
molecules for the metal ion. The donor ability of the solvent plays
the most important role in the behavior of complexes reaction in
nonaqueous solvents.
Scheme 1. Synthesis of Schiff bases (I) and (II).
characterized by a combination of elemental, IR, MS, 1H NMR, 13
NMR spectral analyses data. The preparation of the Schiff bases
illustrated in Scheme 1.
C
Fig. 3(C and D) shows the effect of PH on the extraction of Cu2+
and Cr3+ into chloroform, dichloromethane and nitrobenzene with
Schiff base (I). As shown in figure the copper and chrome extraction
is quantitative within the PH range of 6.1–7, 7.3–8.3 respectively.
Besides, figure shows that the ability of extraction is better in the
case of nitrobenzene solvent and this accords with what has been
reported above.
3.1.1. IR spectra
The spectrum showed a strong band at 1672 cm−1 in the spec-
trum of the Schiff base (I) are assigned to ꢀ(C N) of azomethine.
A broad medium intense band was at 2930 cm−1 due to methylene
groups. The IR spectrum of the thio Schiff-base (I) exhibited a strong
sharp band at 3400 cm−1. This band was assigned to the stretching
frequency of the N+H group, due to the presence of the intramolec-
ular hydrogen bond (N–SH) in the molecule [29–31] (Scheme 1).
In the IR spectrum of Schiff base (II) the absence of band in
the region ∼3400 cm−1 corresponding to free primary amine and
hydroxyl group suggests that complete condensation of amino
group with aldehyde. Appearance of a new strong absorption band
3.2.2. Extraction of UO2 and Hg2+ ions by H2L in the presence of
2+
neutral donor ligand
The synergistic extraction (Fig. 4) of metal chelates has been
mostly explained by an increase in hydrophobicity of extracted
chelates by a replacement reaction of water molecules bound

1912
W.A.L. Zoubi et al. / Spectrochimica Acta Part A 79 (2011) 1909–1914
Fig. 1. (a) 13C NMR(B) and (b) 1H NMR spectra of Schiff base (I) in CDCl3.
Fig. 2. (a) 13C NMR (B) and (d) 1H NMR (A) spectra of Schiff base (II).
to the central metal ion by basic neutral organic molecules (2-
(2-aminoethyl)pyridine). Keep in mind the presence of water
molecules in the structure of extracted species (Eq. (2)), one can
consider an enhancement of extraction efficiency in the presence
of a synergistic agent. To examine this suggestion, the effect of
neutral donor on the extraction of uranium and mercury ions by
Schiff base (I) was investigated (Fig. 4). The neutral donor was 2-
(2-aminoethyl)pyridine. Considering the participation of a neutral
Fig. 3. Effect of pH and Solvents on the extraction of Cu2+ (C), Cr3+ (D), [ ] nterbenzene, [ ] chloroform, [ ] dichloromethane, Schiff base (I).

W.A.L. Zoubi et al. / Spectrochimica Acta Part A 79 (2011) 1909–1914
1913
Fig. 4. Effect of pH on the extraction of UO22+, Hg2+, S = (2-(2-aminooethyl)pyridine),
organic solvent: chloroform, Schiff base (I).
Fig. 5. Effect of A/O on the extraction of Cu2+, organic solvent; chloroform, Schiff
base.
donor molecule (S) in the extracted species of synergistic extrac-
tion process, the corresponding equilibrium reaction can be shown
as: Considering the participation of a neutral donor molecule (S) in
extracted species of synergistic extraction process, the correspond-
ing equilibrium reaction can be shown as:
M2aq+ + H2L + Sorg + PIC2− ↔ MLPICS•2H2Oorg + 2Ha+q
its equilibrium constant is defined as Eq. (6):
MLPicS•2H O org[H+]aq
(2)
[
]
2
Ksyn
=
(3)
[M2+ aq[H2L]org[S]org[Pic−]aq
]
3.2.3. Effect of ionic strength of aqueous phase
The influence of KCl in the concentration range of 0.1–1.0 M on
the extraction efficiency of Cu2+ and Cr3+ were studied in solu-
tions containing 1.5 × 10−3 M Cu2+ and Cr3+ with 4 × 10−4 M Schiff
base (H2L) in organic phase. The extraction efficiency decreases
with increase in ionic strength of the aqueous medium. Taking into
account Eq. (4), the extraction constant (Ke0xt) at zero ionic strength
for this reaction can be correlated with the ionic strength (I) by
Fig. 6. Effect of time on the extraction of Cu2+, organic solvent: chloroform, Schiff
base.
The activity coefficient (ꢂ ) decreases with increase in ionic
strength. At the constant PH, the activity coefficient of Cu2+ and
Cr3+ decreases as the ionic strength increase, hence Kext decreases.
Cu
+ H2L(o) ꢀ CuL(o) + 2H+
(4)
(5)
(6)
2+
(w)
ꢂH2
+
Ke0xt = Kext
Kext = Ke0xt
3.2.4. Effect of aqueous to organic phase
Phase ratio (A/O) is one of the factors that affect the extraction
efficiency. The extraction efficiency, E% can be represented by [36].
ꢂCu
2+
ꢂCu
ꢂH2
2+
D
+
E% =
× 100
(8)
D + A/O
According to the Debye–Huckel limiting law given
√
where D is the distribution ratio, A and O are the volumes of the
aqueous and organic phases, respectively. Equation indicates that
log ꢂ = −0.5Zi2
I
(7)
Fig. 7. The plot of log D vs. pH at Constant Schiff base (I) ( ) chloroform ( ) dichloromethane ( ) nterbenzene.

1914
W.A.L. Zoubi et al. / Spectrochimica Acta Part A 79 (2011) 1909–1914
4. Conclusion
In the first stage, substituted Schiff Base analogues are obtained
from condensation of bis-aldehyde and aminothio in dry ethno.
Then, Schiff bases are synthesized from a 2:1 mixture of 1 and 2
expected pcs. The high transfer of Cu2+ and Cr3+ ions from the aque-
ous phase to the chloroform, dichloromethane and nitrobenzene
were observed with compound (H2L) and results showed that the
best order of solvents is as follows: C6H5NO2 > CHCl3 > CH2Cl2. The
results indicate that H2L in organic phase extracts efficiently Cu2+
and Cr3+ in aqueous phase containing 0.1 mol KCl in the pH range of
approximately 6–7 and 7–8.5 respectively at 25 ◦C. And the results
also show that this ligand is decomposing during extraction. The
compositions of extracted Cu-complexes and Cr-complexes were
1:1 (L:M) for the ligand in dichloromethane.
Fig. 8. Log D versus Log[Ligand(I)] for the extraction of Cu2+ and for Cr3+,organic
solvent: dichloromethane.
The synergic extraction with the mixtures is due to formation of
adduct ML(S). The synergic coefficient has high value in presence
of 2-(2-aminoethyl) pyridine, since has the high basicity.
the extraction efficiency decrease with increasing A/O ratio. Fig. 5
shown the effect of A/O on percentage extraction which was satis-
fied by Eq. (8).
References
[1] Y. Takeda, C. Takagi, S. Nakai, K. Endo, S. Katsuta, Talanta 48 (1999) 559–569.
[2] A.J. Tong, Y.S. Song, L.D. Li, Anal. Chim. Acta 420 (2000) 57–64.
[3] S. Tsurubous, M. Mizutani, Y. Kadota, Anal. Chem. 67 (1995) 1465–1469.
[4] W. Walkowiak, P.R. Brown, J.P. Shukla, R.A. Bartsch, J. Membrane Sci. 32 (1987)
59.
[5] G.D. Christian, J. Pharm. Biomed. Anal. 14 (1996) 881–889.
[6] E. Bacon, M. Kirch, J. Membrane Sci. 32 (1987) 159–173.
[7] E. Sekido, A. Nakabayashi, Anal. Chim. Acta 221 (1989) 99–108.
[8] J.C. Aguilar, E.R. San Miguel, J. Gyves, Talanta 54 (2001) 1195–1204.
[9] K.B. Chung, M. Tomoi, J. Polym. Sci. 30 (1992) 1089.
[10] E. Weber, F. Vogtle, Crown-type Compounds: An Introductory Overview. Host
Guest Complex Chemistry, 14, Springer, New York, 1981.
[11] G.W. Gokel, J.E. Trafton, Cation Binding by Lariat Ethers. Cation Binding by
Macrocycles, vol. 253, New York, 1990.
[12] P. Oggenfuss, W.E. Morf, U. Oesch, D. Ammann, E. pretsch, W. Slimon, Anal.
Chim. Acta 180 (1986) 299–311.
3.2.5. A kinetic criterion of reagent stability
Fig. 6 shows that percentage of extraction decreases with shak-
ing time and it also confirms that this Schiff base is decomposing
during extraction.
3.2.6. Composition of the extracted species
The extraction constant of the species CuL is given by
[CuL]o[H+]nw
[Cu2+
]w[HnL]o
Kext
=
(9)
When CuL is the only extractable species and the metal is
present in the aqueous phase predominantly as the cation Cu2+, the
metal distribution ratio (D) and the extraction constant are related
by
[13] K. Kimura, T. Shono, Anal. Chem. Symp. Ser. 22 (1984) 155.
[14] U. Oesch, P. Anker, D. Ammann, W. Simon, Anal. Chem. Symp. Ser. 22 (1985)
81.
[15] D. Ammann, W.E. Morf, P. Anker, P.C. Merier, E. Pretsch, W. Simon, Ion-Sel.
Electrode Rev. 5 (1983) 3–92.
[16] P.K. Coughin, S.J. lippard, Inorg. Chem. 23 (1984) 1588–1591.
[17] R.J. Motekaitis, A.E. Martell, B. Dietrich, J.M. Lehn, Inorg. Chem. 23 (1984)
1588–1591.
[18] Y. Agnus, R. Louis, J.P. Gisselbrecht, J. Am. Chem. Soc. 106 (1984) 93–102.
[19] A.E. Martin, L.E. Bulkowski, J. Org. Chem. 47 (1982) 412–415.
[20] J.M. Lehn, Pure Appl. Chem. 52 (1980) 2441–2459.
[21] A. Riesen, M. Zehnder, T.A. Kaden, Chem. Acta 69 (1986) 2074–2080.
[22] K. Travis, D.H. Busch, J. Chem. Soc. Chem. Commum. 2 (1970) 1041–1042.
[23] R. Robson, Inorg. Chim. Acta 85 (1984) 195.
[24] A.J. Downard, V. Mckee, Inorg. Chim. Acta 173 (1990) 181–185.
[25] S. Broker, P.D. Croucher, T.C. Davidson, P.D. Smith, Polyhedron 19 (2000)
1887–1894.
[26] K.H. Wong, M. Bourgoin, J. Smid, J. Chem. Soc. Chem. Commun. (1974) 715.
[27] M. Bourgoin, K.H. Wong, J.Y. Hui, J. Smid, J. Am. Chem. Soc. 97 (1975) 3462–3467.
[28] H. Kanttekin, U. Ocak, Y. Gok, I. Acar, J. Inc. Phenom. 48 (2004) 95–101.
[29] I. Yilmaz, H. Temel, H. Alp, Polyhedron 27 (2008) 125–132.
[30] A. Asharf, Tetrahedron 60 (2004) 1541–1548.
[31] E. Pretsch, P. Buhlmann, C. Affolter, Structure Determination of Organic Com-
pounds, New York, 2000.
[32] S. Chandra, L.K. Gupta, Trans. Met. Chem. 27 (2002) 732.
[33] S. Chandra, L.K. Gupta, Spectrochim. Acta A 80 (2004) 1563.
[34] B.O. Strasser, A.I. Propov, J. Am. Chem. Soc. 107 (1985) 7921–7922.
[35] A.I. Popov, Pure Appl. Chem. 51 (1979) 101–110.
log D = log Kext + npH + log [H2L]o
(10)
The effect of pH on the extraction of Cu2+ and Cr3+ ions from KCl
media of ionic strength (I = 0.1 M) has been studied, the logarithm
of the D values obtained were plotted against the corresponding pH
values (according to Eq. (10) a plot of log D against pH at constant
4 × 10−4 M of [HnL]). A straight lines with a slopes of about (0.94,
0.7, 1.83) and (0.716, 0.757, 0.85) were obtained at I = 0.1 of Cu2+ and
Cr3+ respectively, as shown Fig. 7. The values represent the number
of hydrogen ions released during the formation of metal–ligand
complex and intercept log[HnL] + log Kext
.
Fig. 8 shows the evolution of log D when increasing the
concentration of H2L at constant chloride concentration with
dichloromethane as organic solvent. As seen from the plots, there
is a linear relationship between log D and log[L]org, and the slope
should be equal to the number of ligand molecules per cation
in the extracted species. The slopes of lines are equal to 1.1 for
dichloromethane. Therefore, ligand forms a 1:1 (L:M) complex with
Cu2+ and Cr3+
.
[36] C. Pazos, J.P. Curieses, J. Coca 9 (4) (1991) 569–591.