Synthesis and application of an efficient calix[4]arene-based anion receptor bearing imidazole groups for Cr(VI) anionic species

Article abstract of DOI:10.1016/j.tet.2012.03.103

We synthesized the new calix[4]arene amines bearing two and four imidazole or tert-butylamine moieties (9a,b/10a,b) by the reaction of di- or tetra-tosylated calix[4]arene derivatives (7 and 8, respectively) with 1-(3-aminopropyl)imidazole and/or tert-butylamine, respectively. After the characterization of 9a,b/10a,b their extraction abilities toward Cr(VI) anionic species (CAS) was evaluated and compared by the liquid-liquid extraction method. The extraction results revealed that calix[4]arene amine having four imidazole groups (10a) was an efficient anion receptor for CAS. Moreover, the extraction of CAS by 10a in the presence of other anions such as Cl^-, NO ₃^-, and PO₄^3- showed that 10a could be a selective anion receptor for CAS in the presence of those anions.

Full text of DOI:10.1016/j.tet.2012.03.103

Tetrahedron 68 (2012) 4182e4186
Contents lists available at SciVerse ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthesis and application of an efficient calix[4]arene-based anion receptor
bearing imidazole groups for Cr(VI) anionic species
,
b
b
Mustafa Tabakci a , Begum Tabakci , A. Dincer Beduk
*
a Selc¸ uk University, Department of Chemical Engineering, 42075 Konya, Turkey
b Selc¸ uk University, Department of Chemistry, 42075 Konya, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
We synthesized the new calix[4]arene amines bearing two and four imidazole or tert-butylamine moi-
eties (9a,b/10a,b) by the reaction of di- or tetra-tosylated calix[4]arene derivatives (7 and 8, respectively)
with 1-(3-aminopropyl)imidazole and/or tert-butylamine, respectively. After the characterization of
9a,b/10a,b their extraction abilities toward Cr(VI) anionic species (CAS) was evaluated and compared by
the liquideliquid extraction method. The extraction results revealed that calix[4]arene amine having four
imidazole groups (10a) was an efficient anion receptor for CAS. Moreover, the extraction of CAS by 10a in
the presence of other anions such as Clꢀ, NO3ꢀ, and PO34ꢀ showed that 10a could be a selective anion
receptor for CAS in the presence of those anions.
Received 17 January 2012
Received in revised form 11 March 2012
Accepted 26 March 2012
Available online 30 March 2012
Keywords:
Calix[4]arene
Amine
Anion receptor
Cr(VI) anionic species
Extraction
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
Design of anion receptors for such applications remains a great
challenge for chemists because they have to take into consideration
Deterioration of water quality due to the presence of toxic heavy
metals in environmental water resources introduced by industrial
pollution is a serious matter of concern today.1 Chromium (Cr) is
one of the most commonly present heavy metal pollutants in in-
dustrial wastewater. In aqueous solution Cr is found in two stable
oxidation states; trivalent and hexavalent. Cr(VI) is widely used in
electroplating, leather tanning, metal finishing, photography, dye
and textile industries. The effluents from these industries often
contain elevated levels of Cr(VI). Cr(III) has been reported to be
biologically essential to mammals as it maintains effective glucose,
lipid, and protein metabolism. Cr(VI) can be toxic as it can diffuse as
Cr2O27ꢀ or HCr2Oꢀ7 through cell membranes and oxidize biological
molecules. So, human contact with Cr(VI) is known to cause severe
health problems such as skin irritation, liver damage, pulmonary
congestion, vomiting, and ulceration.2,3 As a result, the treatment of
wastewater containing Cr(VI) prior to discharge is essential. Several
methods, such as liquideliquid extraction, adsorption, chemical
precipitation, membrane separation, evaporation, and electro-
chemical treatment have been used to remove these Cr(VI) anionic
species (CAS) from aqueous solutions. Among them, liquideliquid
extraction is the most common system for the removal of these
anions. This needs efficient anion receptors.
the specific anion properties, such as a large range of shapes and
geometries, small electric charges versus sizes, high free energies of
solvation and, in some cases, multiple oxidation states of the cen-
tral atoms in anions or pH dependence.4 In many artificial anion
hosts, noncovalent interactions are responsible for hosteguest
recognition. They include electrostatic interactions, hydrogen
bonding, hydrophobic effects, and coordination to a metal ion or
combinations of these interactions. The hosts can be neutral, con-
taining urea,5e8 thiourea,9,10 or amide11 functions. They can also be
positively charged, containing pyridinium,12 polyammonium,13 or
quaternary ammonium14 binding sites.
Calixarenes15 are often used as scaffolds onto which these func-
tional groups can be attached. They are well-known macrocyclic
compounds that have been studied extensively for hosteguest
chemistry.15 Theycanbe readilyfunctionalized through the phenolic
groups or directly on the aromatic ring and this has resulted in the
design and synthesis of a variety of derivatives for a wide range of
functions. One of the more widely studied areas of calixarene
chemistry is their use as ionophores for both cations and anions.16e18
This has resulted in applications in ion selective electrodes,19,20
metal extraction,21e23 and catalysis.24,25 Recently, various amide,
amine, and pyridinium-functionalized calixarenes, which interact
with anions via electrostatic interactions or hydrogen bonding have
been reported as anion receptors.26ꢀ29 We anticipated that attach-
ing the appropriate groups to increase these interactions would be
* Corresponding author. Tel.: þ90 332 2232142; fax: þ90 332 2410635; e-mail
address: mtabakci@selcuk.edu.tr (M. Tabakci).
0040-4020/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2012.03.103

M. Tabakci et al. / Tetrahedron 68 (2012) 4182e4186
4183
goodstrategy for the synthesis of efficient calix[4]arene-based anion
receptors for CAS. As such, we decided to introduce ‘imidazole’ onto
an amino calix[4]areneframework as a substituent30 due to it having
two additional nitrogen atoms for these interactions. Consequently,
in thecurrentwork weconsidered thatcalix[4]arene aminesbearing
imidazole groups would be more effective ligands than the pre-
viously studied ones for the extraction of CAS. To evaluate this ap-
proach, we initially synthesized and characterized imidazole-
substituted calix[4]arene amines (Scheme 1) and then examined
their extraction abilities toward CAS.
butyl amine analogs (9b and 10b) were also synthesized to com-
pare their extraction properties for CAS with those of the
imidazole-substituted ones. The synthesis of 1e8 and 9a,be10a,b
was conducted as shown in Scheme 1.
Compounds 1e8 were synthesized according to previously lit-
erature methods15,31 and then their structures confirmed in this
study. After the preparation of 7 and 8, they were reacted with 2.05
or 4.1 equiv of 1-(3-aminopropyl)imidazole and tert-butylamine in
dry THF at room temperature for 5 h to obtain 9a, 9b, 10a, and 10b
in 68%, 52%, 64%, and 49% yields, respectively. The new compounds
have been characterized by a combination of 1H NMR, FTIR, FABMS,
and elemental analysis. The FTIR spectra of 9a,b and 10a,b show
2. Results and discussion
2.1. Synthesis
amine bands at 3148 cmꢀ1, 3142 cmꢀ1, 3147 cmꢀ1, and 3143 cmꢀ1
,
respectively. Following the ‘De Mendoza rule’,32 compounds 9a,b
and 10b were confirmed to be present in the cone conformation by
detailed study of their 1H NMR spectra (doublets at 3.32 ppm,
4.27 ppm, J¼13.1, at 3.32 ppm, 4.28 ppm, J¼13.1 Hz and at
3.00 ppm, 4.22 ppm, J¼12.8 Hz for ArCH2Ar protons, respectively).
The conformation of 10a could not be determined due to the peaks,
We were interested in the synthesis of calix[4]arene-based li-
gands having imidazole binding sites (9a and 10a) in order to
evaluate their complexation abilities toward CAS such as HCr2O7ꢀ
and Cr2O27ꢀ through the liquideliquid extraction system. The tert-
HO
OH
OH
OH
1
CH3I
CH3CN
BrCH2COOCH3 K2CO3/Acetone
R2O
OR1
R2O
OR1
HO
OR2
OR2
OH
OR
OR
O
1
1
O
LiAlH4
BrCH2COOCH3
K2CO3/Acetone
Diethylether
2
5 R1= CH3, R2= CH2CH2OH
6 R1,R2= CH2CH2OH
3 R1= CH3, R2= CH2COOCH3
4 R1,R2= CH2COOCH3
TosCl Pyridine
R2O
R2O
OR1
OR2
OR2
OR
OR
1
1
OR1
N
N
a:
b:
H2N
H2N
THF
CH CH NHCH CH CH
N
N
9a R1= CH3, R2=
9b R1= CH3, R2=
N
7 R1= CH3, R2= CH2CH2OTs
8 R1,R2= CH2CH2OTs
2
2
2
2
2
CH CH NHC(CH )
2
2
3
3
CH CH NHCH CH CH
2
N
10a R1,R2=
10b R ,R =
2
2
2
2
CH2CH2NHC(CH3)3
2
1
Scheme 1. The synthetic steps for the preparation of calix[4]arene amines 9a,b/10a,b.

4184
M. Tabakci et al. / Tetrahedron 68 (2012) 4182e4186
which belong to its ArCH2Ar protons overlapping with those of
other eCH2e protons. On the other hand, the singlets at 1.42, 1.18,
and 1.15 ppm for eNHe protons of 9a,b and 10a (it was overlapped
at the range of 1.45e1.15 for 10b), and the multiplets in the range of
7.40e7.18 and 7.80e6.50 ppm for imidazole protons of 9a and 10a,
respectively, in their 1H NMR spectra were some of the peaks
proving the substitution.
than 9b. It must be clarified that the combination of steric effects,
hydrogen binding, and electrostatic interactions between calix[4]
arene amines and CAS are major factors in the complexation pro-
cess. Consequently, it is revealed that our claim in the beginning of
this study to get more efficient ligands than those of the previously
published ones for the CAS extraction by calix[4]arene amines is
a good approach.
To gain a deeper insight into the complexation process, the
extraction data were also analyzed by using the classical slope
analysis method. Assuming the extraction of an anion (A) by the
anion receptor (L) according to the following equilibrium:
2.2. Extraction studies
In this study, liquideliquid extraction experiments were per-
formed to examine the extraction behavior of CAS such as HCr2O7ꢀ
and Cr2O27ꢀ from the aqueous phase into the organic phase
(dichloromethane) by using the new calix[4]arene amine de-
rivatives 9a,b and 10a,b at the range of pH 1.5e4.5. The equilibrium
concentration of CAS in aqueous phase was determined spectro-
photometrically. The extraction experiments with imidazole-
substituted calix[4]arenes (9a and 10a) at pH 1.5e2.5 could not
be performed because of their water solubility at those pH values.
From the results presented in Table 1, it has been observed that
the imidazole-substituted calix[4]arene amine derivatives 9a and
10a (especially 10a) are found to be effective extractants for the
phase transfer of CAS at pH 3.5e4.5. However, it has been clearly
demonstrated that an increase in the pH there is a decrease in
extraction ratios for all ligands. This can be explained by the fact
that the ligands contain ‘proton-switchable’ binding sites, appro-
priate for the achieving CAS at low pHs. That is, it has been in-
dicated that the partially protonated forms of ligands are effective
hosts for CAS. Upon addition of NaOH to the aqueous layer, the
deprotonated calixarenes in the dichloromethane are no longer an
effective host molecule for CAS, and the monoanion migrates back
into the aqueous layer in a reversible process (Scheme 2). This is in
agreement with the literature27 where the extraction of CAS with
a calix[4]arene derivative occurs when the aqueous phase is only
acidic especially at low pH values so that it leads to form the proton
ligands. This is a particularly important feature if it is desirable to
recover the metal in pure form and reuse the extractant by
changing the pH of aqueous solution.27
ꢀ
ꢁ
nðLÞorg þ nðAÞaq# ðLÞn; ðAÞn
(1)
org
The extraction constant Kex is then defined by:
ꢂꢀ
ꢁꢃ
ðLÞn; ðAÞn
org
Kex
¼
(2)
(3)
½Aꢁnaq½Lꢁnorg
Eq. 2 can be re-written as:
log DA ¼ log Kex þ n log½Lꢁorg
where DA is defined as ratio of the analytical concentration of the
anion (A) in both phases:
DA ¼ ½Aꢁorg=½Aꢁaq
(4)
A plot of the log DA versus log[L] may lead to a straight line
whose slope allows to access the stoichiometry of the extracted
species. Fig. 1 represents the extraction into dichloromethane at
different concentrations of 10a for CAS. A linear relationship be-
tween log D versus log[L] is observed with a slope for CAS by 10a,
which equals 0.94 at pH 3.5 suggesting that 10a form 1:1 complex
with CAS (Scheme 2).
However, it is well-known that at more acidic conditions
Na2Cr2O7 is converted into H2Cr2O7, and after ionization in an
aqueous solution it exists in the HCr2Oꢀ7 /Cr2O27ꢀ form.27 This
allowed us to consider these simultaneous extractions of 1:1
complexes according to the following equilibria (Eq. 5). According
to these assumptions, the extraction constant (Kex) has been cal-
culated from the experimental data. The calculation of this constant
value lead to log Kex (ꢂ0.2)¼3.60 for 10a.
Table 1
The extraction percentages (ꢂ0.1) of CAS by the calix[4]arene aminesa
Ligand
pH
h
ꢄ
ꢅi
LHnnðþorgÞ þ HCr2Oꢀ7 =Cr2O72ꢀðagÞ# LHnnþ; HCr2O7ꢀ=Cr2O27ꢀ
ðL ¼ 10aÞ
1.5
2.5
3.5
4.5
org
9a
db
db
8.36
db
0
64.2
2.14
90.2
0
23.1
0
84.8
0
9b
10a
10b
15.1
db
(5)
Moreover, in order to understand the selectivity of CAS extrac-
tion by 10a in the presence of competitive anions the extraction
studies were also carried out using the sodium salts of different
anions such as Clꢀ, NO3ꢀ and PO34ꢀ, and their mixtures. The results
summarized in Table 2 indicate that the extraction of CAS by 10a is
not affected by the presence of these anions. This implied that the
removal of CAS in liquideliquid extraction system by 10a can be
almost selective in the presence of these selected anions.
14.0
a
Aqueous phase, [Na2Cr2O7]¼1.0ꢃ10ꢀ4 M; organic phase, dichloromethane,
[ligand]¼1.0ꢃ10ꢀ3 M, at 25 ꢄC, for 1 h.
b
Could not be performed due to water solubility in this pH.
Importantly, according to the best of our knowledge, the ex-
traction results by 10a indicate that CAS can be extracted for the
first time in this study in quite high yields (approximately 90%)
even at pH 3.5. This can be attributed to calix[4]arene amine
bearing tetra-imidazole parts has more proton-switchable units
when it is compared to previously reported calix[4]arene amine-
based CAS receptors although some of them was not used as a li-
gand under same extraction conditions.27ꢀ29 On the other hand,
from the extraction results it is also observed that the tert-butyl-
amine-bonded calix[4]arenes are less effective ligands than their
imidazole-bonded analogs even at low pHs. This can be described
by steric hindrance of the flexible and bulky tert-butyl groups of 9b
and 10b. Besides, the lower CAS extraction of 10b than that of 9b
supports this explanation due to the 10b has more tert-butyl groups
3. Conclusions
In this study, new calix[4]arene amine derivatives bearing im-
idazole and tert-butyl amine groups were synthesized and char-
acterized, and their extraction behavior was evaluated and
compared by the liquideliquid extraction method for CAS. The re-
sults showed that the extraction of CAS by tetraamine-derivatized
calix[4]arene 10a having imidazole moieties mostly took place in
quite high yield (90%) and was greater than its corresponding tert-
butyl amine-derivatized analogs 9b and 10b (negligible extraction
for both of them) and also diimidazole-substituted derivative 9a

M. Tabakci et al. / Tetrahedron 68 (2012) 4182e4186
4185
N
N
+
N
N
+
N
H
H
N
N
N
A
H
H
H
N
H
N
N
N
+
+
H
H
-
OH
H+
A
+
O
O
O
O
O
O
O
O
Scheme 2. The proposed interactions of compound 10a with CAS (A: HCr2Oꢀ7, Cr2O27ꢀ, only two imidazole binding sites are represented for clarity).
4. Experimental section
4.1. General
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
Melting points were determined using an Electrothermal 9100
apparatus in a sealed capillary and were uncorrected. 1H NMR
spectra were recorded on a Bruker 400 MHz spectrometer in CDCl3
with TMS as the internal standard. FTIR spectra were obtained on
a PerkineElmer Spectrum 100 FTIR spectrometer. UVevisible
spectra were obtained on PG Instruments T80þ UVevisible re-
cording spectrophotometer. Elemental analyses were performed
using a Leco CHNS-932 analyzer. FABMS spectra were taken on
a Varian MAT 312 spectrometer. An Orion 420A pH meter was used
for the pH measurements. Analytical TLC was performed using
Merck prepared plates (silica gel 60 F254 on aluminum). The
chromatographic separations were performed on a Merck Silica Gel
60 (230e400 mesh). All reactions were conducted under nitrogen
atmosphere. All starting materials and reagents used were of
standard analytical grade from Fluka, Merck and SigmaeAldrich,
and used without further purification. The commercial grade sol-
vents were distilled and stored over molecular sieves. The drying
agent employed was anhydrous sodium sulfate. Anions were used
as their sodium salts in the extraction studies. All aqueous solutions
were prepared with deionized water that had been passed through
a Millipore milli-Q Plus water purification system.
-3.65
-3.5
-3.35
log[L]
-3.2
-3.05
Fig. 1. Log D versus log[L] for the extraction of CAS by the ligand 10a from an aqueous
phase into dichloromethane at 25 ꢄC and pH 3.5.
Table 2
The CAS extraction results (ꢂ0.1) by 10a in the presence of competitive anions (Clꢀ
,
NOꢀ3 , and PO34ꢀ) and their mixturesa
Ligand
Added anionb
Extracted CAS (%)
10a
d
Clꢀ
90.2
85.4
89.8
87.7
84.6
4.2. Synthesis of anion receptors
PO34ꢀ
NOꢀ3
Scheme 1 illustrates the successive synthetic steps of the several
amino calix[4]arenes and their precursors (1e8, 9a, 9b, 10a, and
10b). Compounds 1e8 were prepared following or by adapting to
previously published procedures.15,31 In current work, compounds
9a,b and 10a,b were firstly synthesized according to our knowledge.
The preparation of compounds 9a,b and 10a,b is carried out as
following the general procedure: 1-(3-aminopropyl)imidazole or
tert-butylamine (2.05 or 4.10 mmol) was added to a solution of 7/8
(1.00 mmol) dissolved in dry THF (20 mL), respectively. After the
mixture was stirred at room temperature for 5 h, distilled water
(10 mL) was added to the solution. The mixture was extracted with
dichloromethane, washed with distilled water (2ꢃ50 mL), brine
(2ꢃ50 mL), and then dried over anhydrous sodium sulfate. The
Clꢀ, PO43ꢀ, and NO3ꢀ
a
[Na2Cr2O7]¼1.0ꢃ10ꢀ4 M; [10a]¼1.0ꢃ10ꢀ3 M, at 25 ꢄC, pH 3.5.
b
The concentration of competitive anions¼1.0ꢃ10ꢀ3 M.
(64%) at pH 3.5. Additionally, the selectivity experiments demon-
strated the extraction of CAS by 10a was not affected by the pres-
ence of some selected anions such as Clꢀ, NO3ꢀ, and PO43ꢀ and their
mixtures even they used more concentrated than the concentration
of CAS. Consequently, we reported that an efficient and selective
calix[4]arene-based anion receptor (10a) bearing proton-
switchable units for CAS.

4186
M. Tabakci et al. / Tetrahedron 68 (2012) 4182e4186
solvent was evaporated under vacuo, and recrystallized from
where Ao and A are the initial and final concentrations of the CAS
dichloromethane to give 9a,b/10a,b as white crystals.
before and after the extraction, respectively.
4.2.1. 5,11,17,23-Tetra-tert-butyl-25,27-di-[1-(3-aminopropylethoxy)
Acknowledgements
imidazolyl]-26,28-dimethoxycalix[4]arene (9a). Yield: 68%; mp:
158 ꢄC. FTIR: 3148 cmꢀ1 (NH). 1H NMR (400 MHz, CDCl3):
d (ppm)
We thank the Research Foundation of Selc¸ uk University (SUBAP-
7.40e7.18 (m, 6H, Himidazole); 7.06 (s, 4H, ArH); 6.75 (s, 4H, ArH);
4.27 (d, J¼13.1 Hz, 4H, ArCH2Ar); 3.94 (br s, 8H, OCH2CH2N);
3.90e3.60 (m, 10H, OCH3, NHCH2CH2CH2N); 3.32 (d, J¼13.1 Hz, 4H,
ArCH2Ar); 2.43 (br s, 4H, NHCH2CH2CH2N); 1.84 (m, 4H,
NHCH2CH2CH2N); 1.42 (s, 2H, NH); 1.29 (s, 18H, (CH3)3C); 0.92 (s,
18H, (CH3)3C). FABMS m/z: 1002.21 (MþNa)þ. Anal. calcd for
C62H86N6O4 (979.38): C, 76.03; H, 8.85; N, 8.58. Found: C, 75.98; H,
8.80; N, 8.56.
08401058), Konya-Turkey for their financial support to this work.
References and notes
1. Fu, F.; Wang, Q. J. Environ. Manage. 2011, 92, 407e418.
2. Costa, M. Toxicol. Appl. Pharmacol. 2003, 188, 1e5.
3. Tabakci, M. J. Incl. Phenom. Macrocycl. Chem. 2008, 61, 53e60.
4. For recent reviews/books on anion-recognition, see: (a) Amendola, V.; Fab-
brizzi, L. Chem. Commun. 2009, 513e531; (b) Anion Sensing Topics in Current
Chemistry; Stibor, I., Ed.; Springer: Berlin, 2005; Vol. 255; (c) Gale, PA.; Garcia
Garrido, S. E.; Garric, J. Chem. Soc. Rev. 2008, 37, 151e190; (d) Cametti, M.;
Rissanen, K. Chem. Commun. 2009, 2809e2829; (e) Sessler, J. L.; Gale, P. A.; Cho,
W. S. Anion Receptor Chemistry; The Royal Society of Chemistry: Cambridge,
2006; (f) Recognition of Anions; Vilar, R., Ed.; Springer GmbH: Berlin, 2008; (g)
Gale, P. A.; Beer, P. D. Angew. Chem., Int. Ed. 2001, 40, 486e516; (h) Supramo-
lecular Chemistry of Anions; Bianchi, A., Bowman-James, K., Garcia-Espana, E.,
Eds.; Wiley-VCH: New York, NY, 1997.
4.2.2. 5,11,17,23-Tetra-tert-butyl-25,27-di-(tert-butylaminoethoxy)-
26,28-dimethoxycalix[4]-arene (9b). Yield: 52%; mp: 142 ꢄC. FTIR:
3142 cmꢀ1 (NH). 1H NMR (400 MHz, CDCl3):
d (ppm) 7.06 (s, 4H,
ArH); 6.75 (s, 4H, ArH); 4.28 (d, J¼13.1 Hz, 4H, ArCH2Ar); 3.94 (br s,
8H, OCH2CH2N); 3.85e3.65 (m, 6H, OCH3); 3.32 (d, J¼13.0 Hz, 4H,
ArCH2Ar); 1.30 (br s, 36H, (CH3)3C-NH, (CH3)3C-Ar); 1.18 (br s, 2H,
NH); 0.92 (s, 18H, (CH3)3C-Ar). FABMS m/z: 898.12 (MþNa)þ. Anal.
calcd for C58H86N2O4 (875.31): C, 79.59; H, 9.90; N, 3.20. Found: C,
79.58; H, 9.88; N, 3.19.
5. Bondy, C. R.; Gale, P. A.; Loeb, S. J. J. Am. Chem. Soc. 2004, 126, 5030e5031.
6. Amendola, V.; Boiocchi, M.; Esteban-Gomez, D.; Fabbrizzi, L.; Monzani, E. Org.
Biomol. Chem. 2005, 3, 2632e2639.
7. Brooks, S. J.; Edwards, P. R.; Gale, P. A.; Light, M. E. New J. Chem. 2006, 30, 65e70.
8. Turner, D. R.; Paterson, M. J.; Steed, J. W. J. Org. Chem. 2006, 71, 1598e1608.
9. Boerrigter, H.; Grave, L.; Nissink, J. W. M.; Chrisstoffels, L. A. J.; van der Maas, J.
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511e519.
4.2.3. 5,11,17,23-Tetra-tert-butyl-25,26,27,28-tetra-[1-(3-
aminopropylethoxy)imꢀid1azolyl]-calix[4]arene (10a). Yield: 64%; mp:
169 ꢄC. FTIR: 3147 cm (NH). 1H NMR (400 MHz, CDCl3):
d (ppm)
7.80e6.50 (m, 20H, ArH, Himidazole); 4.40e3.30 (m, 32H, ArCH2Ar,
NHCH2CH2CH2N, OCH2CH2N); 2.90 (br s, 8H, NHCH2CH2CH2N);
1.94 (br s, 8H, NHCH2CH2CH2N); 1.15 (s, 4H, NH); 1.05 (s, 36H,
(CH3)3C). FABMS m/z: 1276.55 (MþNa)þ. Anal. calcd for
C76H108N12O4 (1253.74): C, 72.81; H, 8.68; N, 13.41. Found: C,
72.88; H, 8.72; N, 13.42.
13. Dietrich, B. Pure Appl. Chem. 1993, 65, 1457e1464.
14. Egorov, V. V.; Rakhman’ko, E. M.; Okaev, E. B.; Pomelenok, E. V.; Nazarov, V. A.
Talanta 2004, 63, 119e130.
15. For books on calixarenes, see: (a) Gutsche, C. D. Calixarenes: An Introduction, 2nd
ed.; The Royal Society of Chemistry, Thomas Graham House: Cambridge, 2008;
(b) Calixarenes in the Nanoworld; Vicens, J., Harrowfield, J., Backlouti, L., Eds.;
€
Springer: Dordrecht, 2007; (c) Calixarenes 2001; Asfari, Z., Bohmer, V., Harrow-
field, J., Vicens, J., Eds.; Kluwer Academic: Dordrecht, 2001; (d) Mandolini, L.;
Ungaro, R. Calixarenes in Action; Imperial College: London, 2000; (e) Vicens, J.;
Asfari, Z.; Harrowfield, J. M. In Calixarenes 50th Anniversary: Commemorative Is-
4.2.4. 5,11,17,23-Tetra-tert-butyl-25,26,27,28-tetra-(tert-butylami-
noethoxy)calix[4]arene (10b). Yield: 49%; mp: 157 ꢄC. FTIR:
€
sue; Kluwer Academic: Dordrecht,1994; (f) Vicens, J.; Bohmer, V. In Calixarenes: A
3143 cmꢀ1 (NH).1H NMR (400 MHz, CDCl3):
d (ppm) 6.70 (s, 8H, ArH);
Versatile Class of Macrocyclic Compounds; Kluwer Academic: Dordrecht, 1991.
16. Creaven, B. S.; Donlon, D. F.; McGinley, J. Coord. Chem. Rev. 2009, 253, 893e962.
17. Wolf, N. J.; Georgiev, E. M.; Yordanov, A. T.; Whittlesey, B. R.; Koch, H. F.;
Roundhill, D. M. Polyhedron 1999, 18, 885e896.
18. Shokova, E.; Kovalev, V. Russ. J. Org. Chem. 2009, 45, 1275e1314.
19. El Nashar, R. M.; Wagdy, H. A. A.; Aboul-Enein, H. Y. Curr. Anal. Chem. 2009, 5,
249e270.
20. Kimura, K.; Tatsumi, K.; Yokoyama, M.; Ouchi, M.; Mocerino, M. Anal. Commun.
1999, 36, 229e230.
21. Harrowfield, J. M.; Mocerino, M.; Peachey, B. J.; Skelton, B. W.; White, A. H. J.
Chem. Soc., Dalton Trans. 1996, 1687e1699.
4.39 (br s, 8H, OCH2CH2N); 4.22 (d, J¼12.8 Hz, 4H, ArCH2Ar); 4.09 (br s,
8H, OCH2CH2N); 3.00 (d, J¼12.8 Hz, 4H, ArCH2Ar); 2.43 (s, 18H,
(CH3)3C-NH); 1.45e1.15 (m, 22H, NH, (CH3)3C-NH); 1.05 (s, 36H,
(CH3)3C-Ar). FABMS m/z: 1068.40 (MþNa)þ. Anal. calcd for
C68H108N4O4 (1045.61): C, 78.11; H, 10.41; N, 5.36. Found: C, 78.18; H,
10.45; N, 5.37.
22. Ohto, K. Solvent Extr. Res. Dev. Jpn. 2010, 17, 1e18.
23. Mokhtari, B.; Pourabdollah, K.; Dallali, N. J. Radioanal. Nucl. Chem. 2011, 287,
921e934.
4.3. Liquideliquid extraction studies
24. Li, Z. Y.; Chen, J. W.; Liu, Y.; Xia, W.; Wang, L. Y. Curr. Org. Chem. 2011, 15, 39e61.
25. Homden, D. M.; Redshaw, C. Chem. Rev. 2008, 108, 5086e5130.
26. For review on calixarene-based anion receptors see: (a) Kalchenko, V. I. Pure Appl.
Chem. 2008, 80,1449e1458; (b) Matthews, S. E.; Beer, P. D. Supramol. Chem. 2005,
The anion extraction experiments by the calix[4]arene amine de-
rivatives (9a,b and 10a,b) were performed following Pedersen’s pro-
cedure.33 An aqueous solution of sodium salt of anion (10 mL of
a 1.0ꢃ10ꢀ4 M; 0.01 M KOH/HCl solution was used in order to obtain
the desired pH at equilibrium) and calixarene ligand (10 mL of
1.0ꢃ10ꢀ3 M) in dichloromethane were shaken vigorously in a stop-
pered glass tube with a mechanical shaker for 2 min and then mag-
netically stirred in a thermostated water bath at 25 ꢄC for 1 h, and
finally left standing for an additional 30 min. The concentration of
anion remaining in the aqueous phase was then determined as de-
scribed previously for CAS.26 Blank experiments showed that no CAS
extraction occurred in the absence of calix[4]arene derivatives. The
percent extraction (E%) was calculated from the absorbance A of the
aqueous phase measured at 350 nm (for pH 1.5e4.5) using the fol-
lowing expression:
ꢀ
17, 411e435; (c) Lhotak, P. Top. Curr. Chem. 2005, 255, 65e96 see Ref 4b; (d)
Calixarenes 2001; Matthews, S. E., Beer, P. D., Eds.; Academic: Dordrecht, 2001;
pp 421e439; See Ref. 15c.
27. For some recent examples of calixarene-based receptors for CAS from our group
see: (a) Yilmaz, A.; Tabakci, B.; Tabakci, M. Supramol. Chem. 2009, 21, 435e441; (b)
Tabakci, M.; Memon, S.; Yilmaz, M. Tetrahedron 2007, 63, 6861e6865; (c) Yilmaz,
A.; Tabakci, B.; Akceylan, E.; Yilmaz, M. Tetrahedron 2007, 63, 5000e5005; (d)
Tabakci, M.; Memon, S.; Sap, B.; Roundhill, D. M.; Yilmaz, M. J. Macromol. Sci., Pure
Appl. Chem. 2004, 41, 811e825; (e) Ediz, O.; Tabakci, M.; Memon, S.; Yilmaz, M.;
Roundhill, D. M. Supramol. Chem. 2004, 16, 199e204; (f) Tabakci, M.; Memon, S.;
Yilmaz, M. J. Incl. Phenom. Macrocycl. Chem. 2003, 45, 265e270.
28. Georgiev, E. M.; Wolf, N.; Roundhill, D. M. Polyhedron 1997, 16, 1581e1584.
29. Aeungmaitrepirom, W.; Hagege, A.; Asfari, Z.; Vicens, J.; Leroy, M. J. Incl. Phe-
nom. Macrocycl. Chem. 2001, 40, 225e229.
ꢁ
ꢀ
30. Seneque, O.; Campion, M.; Giorgi, M.; Mest, Y. L.; Reinaud, O. Eur. J. Inorg. Chem.
2004, 1817e1826.
31. Tabakci, M.; Tabakci, B.; Yilmaz, M. J. Incl.Phenom. Macrocycl. Chem.2005, 53, 51e56.
32. De Mendoza, J.; Prados, P.; Nieto, P.; Sanchez, C. J. Org. Chem. 1991, 56,
3372e3376.
E% ¼ ½ðA0 ꢀ A=A0Þꢁ ꢃ 100
(6)
33. Pedersen, C. J. J. Fed. Proc. Fed. Am. Soc. Exp. Biol. 1968, 27, 1305e1309.