Di-substituted azocalix[4]arenes containing chromogenic groups: Synthesis, characterization, extraction, and thermal behavior

Article abstract of DOI:10.1016/j.tet.2013.06.018

In this study, the synthesis of chromogenic di-substituted azocalix[4]arene derivatives is described. Six novel azocalix[4]arenes (4a-f)were prepared by linking 4-methoxy, 4-methyl, 4-ethyl, 4-chloro, 4-bromo, and 4-nitroaniline to 25,26,27,28-tetrahydrox

Full text of DOI:10.1016/j.tet.2013.06.018

Tetrahedron 69 (2013) 6832e6838
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journal homepage: www.elsevier.com/locate/tet
Di-substituted azocalix[4]arenes containing chromogenic groups:
synthesis, characterization, extraction, and thermal behavior
*
€
Serkan Elc¸ in , Hasalettin Deligoz
Pamukkale University, Faculty of Science, Department of Chemistry, 20017 Denizli, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
In this study, the synthesis of chromogenic di-substituted azocalix[4]arene derivatives is described. Six
novel azocalix[4]arenes (4aef)were prepared by linking 4-methoxy, 4-methyl, 4-ethyl, 4-chloro, 4-
bromo, and 4-nitroaniline to 25,26,27,28-tetrahydroxy-11,23-di-(tert-butyl)calix[4]arene through a di-
azo-coupling reaction, and were characterized by elemental analysis, FTIR, 1H NMR spectra and ther-
mogravimetric analysis (TGA). The complexing properties of these compounds were studied by the
Received 28 January 2013
Received in revised form 15 May 2013
Accepted 4 June 2013
Available online 11 June 2013
liquideliquid extraction of selected metal cations (Sr2þ, Agþ, Hgþ, Hg2þ, Co2þ, Ni2þ, Cu2þ, Pb2þ, Cr3þ
,
Keywords:
Calixarene
Azocalix[4]arenes
Di-substituted
Liquideliquid extraction
pH effect
Al3þ). It has been observed that di-substituted azocalix[4]arenes showed a high affinity for Agþ, Hgþ, and
Hg2þ ions, but almost no affinity to other metals. The colors of these azocalix[4]arenes were compared
with respect to effect of varying pH on the absorption ability. Thermal behaviors of these compounds
were also reported by means of thermogravimetry (TG) and thermal analysis (DTA).
Ó 2013 Elsevier Ltd. All rights reserved.
Thermal analysis
1. Introduction
complexation9. These color changes as signals for chemical species
can be detected by ‘naked eye’ with inexpensive equipment or in-
Calix[n]arenes (n¼4e20) are phenolic [1]n-metacyclophanes
and are synthetic cyclic tetramers composed of four phenolic and
four methylene moieties. They can be easily synthesized through
acid or base catalyzed condensation of p-substituted phenols with
formaldehyde or paraformaldehyde.1 They possess easily functio-
nalizable hydrophobic upper rim and hydrophilic lower rim to en-
compass a hollow cavity, the dimensions of which depend upon
their conformation and appended functional groups.2 Introduction
of azo groups into the calix[n]arene framework confers chromo-
genicity that can be employed for the development of molecular
diagnostics and sensor materials for metal ions and organic mole-
cules3. The observed diversity of calix[n]arenes essentially lies in
their conformational isomerism due to rotation of AreCH2eAr
bonds or molecular rotation through the annulus.6 These kinds of
azocalix[n]arenes are found to be exceptionally selective macro-
cycles for various targets for possible applications binding cations,
deed no equipment at all. Furthermore, phenol-, azo-, and nitro-
phenyl- groups in derivatives of azophenol were all
electrochemically active and can be studied by electrochemical
methods14. Electrochemical signal transduction also gained a lot of
interest due to its low operational cost and the considerable re-
liability of the results17. To facilitate the monitoring of the binding
process upon complexation with metal ions, in many cases azo-
phenol groups were introduced into the calixarene derivatives at
the upper rim11.
Different studies on the synthesis of azocalix[n]arenes for related
applications have appeared in the literature 20. In our laboratory,
azocalix[4]arene derivatives have been synthesized for liquid-
23
eliquid extraction of transition metal ions (Agþ, Hg2þ and Hgþ)
.
Lu et al.26 have obtained calix[4]arene carboxyphenylazo derivative
as a diagnostic for lead. Potassium and cesium selective azocalix[4]
crown derivatives have been reported by Kim et al.27 and Chawla
et al.28 while a nickel selective azocalix[4]arene derivative has been
reported by Ma and co-workers.29
7
anions, neutral molecules, and nuclear-waste remediation .
By converting molecular recognition into an optical or chemical
signal, one can easily and analytically detect various kinds of
chemical species. Azophenol derivatized chromophores were re-
During recent years, several reports have appeared in the liter-
ature wherein the synthesis and characterization of partially
substituted azo calixarenes have been utilized to elicit a photo-
response to ionic or molecular recognition events30. Differential
observations and the outcome of the coupling reaction of calix[n]
arenes with diazonium salts derived from different aryl amine
structures have not been explained.
ported to give
a color change upon specific metal ion
* Corresponding author. Tel.: þ90 258 296 3613; fax: þ90 258 296 3535; e-mail
address: serel20@mynet.com (S. Elc¸ in).
0040-4020/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2013.06.018

€
S. Elc¸ in, H. Deligoz / Tetrahedron 69 (2013) 6832e6838
6833
Nowadays, high importance is given a control of the levels of
toxic heavy metals, like lead, cadmium, copper, silver, mercury,
chromium or arsenic in natural waters, which may cause great risk
to human health33. In this respect, our aim in this work was to
design di-substituted azocalix[4]arene possessing the ability to
bind these metal cations. Moreover, present study was aimed to
been designed to enable derivatization. To achieve the desired goal,
we synthesized p-tert-butylcalix[4]arene as a starting material
through the base catalyzed condensation reaction.36 This com-
pound was obtained quantitatively by basic condensation of p-tert-
butylphenol and formaldehyde, but we found it better to synthesize
via the microwave synthesis route. In this way, p-tert-butylcalix[4]
arene was obtained in a yield of 86% the calix[4]arene platform,
instead of 57% with isolation of calix[4]arene.
The synthetic strategy developed for the di-substituted azocalix
[4]arene was similar from 4a to 4f, and involved a selective double
deterbutylation of the di-p-tert-butylcalix[4]arene 3, followed by
a double benzoylation applied on the unprotected calixarene plat-
form. The resulting di-p-tert-butylcalix[4]arene 3 was then treated
in alcoholic basic conditions with THF/EtOH/Water and NaOH to
give the corresponding di-benzoyl calix[4]arene 2, which was di-
rectly catalytically hydrolyzed into the desired armed calixarene.
The synthesis of di-benzoyl-tetra-p-tert-butylcalix[4]arene 1
was based on previously reported procedures37. The selective in-
troduction of two chelates at the 5th and 17th positions of the di-
improve
25,26,27,28-tetrahydroxy-11,23-di-(tert-butyl)calix[4]
arene by using selective di-substituted azo-coupling reaction
(Fig. 1). These synthesized compounds were characterized by
R
R
R:
4a:
-OCH3
4b:
4c:
4d:
4e:
4f:
-CH3
-C2H5
-Cl
N
N
N
N
-Br
OH
OH
-NO2
HO
OH
benzoyl-di-p-tert-butylcalix[4]arene
2 involved a preliminary
retro-FriedeleCrafts di-deterbutylation step developed by Gutsche
et al. via a selective protective di-benzoylation of two hydroxyl
groups in diametric positions. The resulting benzoyl diester was
obtained in different acylation media, namely di-benzoyl chloride/
pyridine systems.39 More recently, we found that di-benzoyl-tetra-
p-tert-butylcalix[4]arene 1 could easily be synthesized from p-tert-
butylcalix[4]arene and benzoyl chloride using pyridine, with a good
yield of 74%.
Fig. 1. Diazo-coupled di-substituted azocalix[4]arene derivatives 4aef.
spectral analysis, studied for the complexing properties toward
selected metal cations, and characterized by means of thermal
behaviors.
2. Results and discussion
Then, the diester derivative of p-tert-butylcalix[4]arene was
treated with anhydrous AlCl3 in toluene in the presence of phenol
to yield calix[4]arene 2.39 The retro-FriedeleCrafts deterbutylation
step was carried out in toluene using only 5 equiv of AlCl3 relative
2.1. Synthesis and characterizations
The desired azocalix[n]arenes were easily synthesized, using the
synthetic route was shown in Fig. 2. The synthetic approach has
O
C
O
+
Pyridine
+
NaOH
+
C
Cl
H
O
H
Reflux
Ice bath
HO
O
OH
OH
O
HO
OH
OH
OH
O
C
O C
1
AlCl
3
Phenol
Toluene
rt
R
R
NaOH
N
NaNO2 / HCl
N
N
N
DMF / THF
THF / Water / EtOH
Reflux
H2N
R
+
HO
O
O
OH
Ice bath
O
C
O C
HO
OH
OH
OH
HO
OH
OH
OH
3
4
2
a)
-OCH3
b)
e)
d)
R=
-CH3
c)
-Cl
-Br
f)
-NO2
-C2H5
Fig. 2. Synthesis of di-substituted azocalix[4]arene derivatives.

€
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S. Elc¸ in, H. Deligoz / Tetrahedron 69 (2013) 6832e6838
Table 1
to di-benzoyl-di-p-tert-butylcalix[4]arene 2. The reaction was ini-
tiated by a gentle warming and was completed in ca. 1e2 h, giving 2
with a yield of 65%. Based on the recent work of Magrans et al.,
dedicated to the conformational study of 1,3-di-O-benzoylated
calix[4]arenes.40, the 13C NMR analyses of these compounds
showed that they should not be in a pure cone conformation. The
resonance signals of the AreCH2eAr groups appeared at dH 3.53
and 4.00, respectively, and between the standard dH 3.50 and 4.50
values observed for the pure syn and anti conformations. This
suggested that a rapid exchange between the cone and the 1,3-al-
ternate conformations takes place in solution. Nevertheless, for
legibility, 1 and 2 are drawn in the cone conformation.
Extraction of metal picrates with azocalix[4]arene derivatives 4aefa
Ligands Picrate salt extracted (%)
Sr2þ Agþ
Hgþ
Hg2þ Co2þ Ni2þ Cu2þ Pb2þ
Cr3þ Al3þ
4a
4b
4c
4d
4e
4f
<3
<3
<3
<3
<3
<3
11.10 19.75 19.68 <3
10.75 19.59 19.88 <3
9.71 20.96 21.04 <3
11.20 20.61 19.71 <3
11.76 20.39 26.74 <3
12.93 21.62 27.67 <3
<3
<3
<3
<3
<3
<3
<3
<3
<3
3.76
<3
<3
<3
<3
<3
4.63 3.04
8.94 5.07
7.75 5.69
4.31 6.04 4.46
<3
<3
6.17 3.26
5.92 4.03
a
H2O/CHCl3¼10/10 mL (v/v): [picric acid]¼2ꢀ10ꢁ5 M, [ligand]¼1ꢀ10ꢁ3 M,
[metal nitrate]¼1ꢀ10ꢁ2 M; 298 K, 1 h contact time.
ꢃꢄ2%.
a
The benzoate groups were then removed in alcoholic NaOH at
reflux. The 11,23-di-p-tert-butylcalix[4]arene 3 was obtained in an
almost quantitative yield.
The diazo-coupling reaction is known to be a very effective
derivatization tool at the para position (upper rim) of the calix[4]
arene41. Therefore, calix[4]arenes were treated with NaNO2 and
HCl/H2O in the presence of various carbocyclic amine derivatives
DMF/THF to yield azocalix[4]arenes.
measured three times. The equilibrium concentration of picrate
in aqueous phase has been determined as 354 nm
spectrophotometrically.
(lmax)
The ionophoric properties of azocalix[4]arene derivatives 4aef
toward the alkaline-earth and the transition metal cations were first
investigated by the picrate extraction method.19 The results
expressed as a percentage of cation extracted (E%) are given in Fig. 3.
In this study, six novel azocalix[4]arene derivatives 4aef were
synthesized from 4-methoxy, 4-methylaniline, 4-ethylaniline, 4-
chloroaniline, 4-bromoaniline, and 4-nitroaniline. Six new azoca-
lix[4]arenes (4aef) were thus achieved, according to previous pa-
pers.14, by diazo functional sodium nitrite using concentrate
a hydrochloric acid in DMF at room temperature for 30 min under
nitrogen. The purification of these azocalix[4]arenes for charac-
terization without column chromatography on silica gel obtained
crystals yield (65e86%).
All new azocalix[4]arenes were characterized by the combina-
tion of UVevis, IR, 1H NMR spectroscopic techniques, and elemental
analyses. The conformational characteristics of azocalix[4]arenes
were conveniently estimated by the splitting pattern of the
ArCH2Ar methylene protons in 1H NMR spectroscopy.1 1H NMR data
showed that these azocalix[4]arenes 4aef have a cone conforma-
tion, a typical AB pattern for the methylene bridge protons
(ArCH2Ar) of the calix[4]arene moiety appeared in two sets of
Fig. 3. Extraction percentages of azocalix[4]arene derivatives 4aef.
2.3. Thermal behaviors
doublets covering a range of
d
3.6 and 4.3 ppm in the 1H NMR
Thermal stability of calix[n]arenes is important due to the po-
tential industrial usage of them as sensors and receptors. According
to the literature, the thermal analysis was used to investigate p-tert-
butylcalix[4, 6, 8]arenes and their derivatives43. In this study we
focused on thermal behavior of new azocalix[4]arenes 4aef and
their starting materials 1, 2, 3.
The TG and DTA curves of the starting materials 1, 2, 3 are given
in Fig. 4.1 and 2 compounds showed similar thermal characteristics
and decompose with two stages. First stage belongs to degradation
of tert-butyl and benzoyl groups. The experimental mass loss per-
centages (47.85, 41.08) were compatible with the theoretical (50.53,
43.12) values. The entire structure was decomposed exothermically
in the second stage.
The thermal decomposition of compound 3 was slightly differ-
ent from 1 and 2 compounds. This compound decomposed in three
stages, which were identified as removal of ethyl alcohol groups,
removal of tert-butyl groups, and decomposition of the rest of
structure. The decomposition of tert-butyl groups occurred in two
consecutive sub-stages but the reaction boundaries could not be
separated so it was evaluated as a single-stage reaction.
The TG and DTA curves of 4aee compounds, which were taken
with using 10 ꢂC/min heating rate are given in Fig. 5. It was con-
cluded that the degradation of 4a compound starts at a lower
temperature (120 ꢂC) compared to other compounds (270 ꢂC). The
ethyl alcohol molecules could not be fully removed from the 4a
structure after the synthesis stage. Due to this situation de-
composition starts sooner than other compounds. Decomposition
of 4a completes in three stages, which belongs to removal of ethyl
alcohol, removal of tert-butyl groups and decomposition of the rest
(JAB¼13.2 Hz).
The molecular structures of azocalix[4]arene dyes (4aef) are
supported by the data obtained from micro analysis, where the
percentage of C, H, and N from the analysis conforms to the cal-
culated values. The structures of these novel compounds were fully
characterized using spectroscopic methods (FTIR and 1H NMR) and
elemental analysis.
2.2. Liquideliquid extractions
Previously, to increase the affinity of azocalix[4]arenes toward
metal ions and anions, two main strategies have been followed.
Firstly, different ionophoric groups including benzoyl esters have
been incorporated onto the calixplatform. Secondly, the azocalix[4]
arene units have been fixed to azo groups.
The present study is focused on identifying the strategic re-
quirements for the optimization of ionophoric properties of the
upper rim functionalized azocalix[4]arene derivatives 4aef toward
selected alkaline-earth and transition metal ions, such as Sr2þ, Agþ,
Hgþ, Hg2þ, Co2þ, Ni2þ, Cu2þ, Pb2þ, Cr3þ, and Al3þ. The extraction
properties of azocalix[4]arene derivatives 4aef have been evalu-
ated by solvent extraction of selected metal picrates (Table 1).
These data were obtained by using chloroform solutions of the
ligands to extract metal picrates from aqueous solution. Equal
volumes (10 mL) of aqueous solutions of metal picrates (2ꢀ10ꢁ5 M)
and solutions of azocalix[4]arene derivatives 4aef (1ꢀ10ꢁ3 M) in
chloroform were vigorously shaken at 25 ꢂC for an hour. After the
completion of phase separation, absorbance values have been

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S. Elc¸ in, H. Deligoz / Tetrahedron 69 (2013) 6832e6838
6835
1
2
3
1
-1.73mg
540.7C
568.0C
-47.85%
-1.83mg
429.4C
-50.41%
2
-1.46mg
-41.08%
-2.13mg
-60.12%
576.9C
384.2C
3
-0.30mg
-7.88%
-0.76mg
-19.71%
-2.96mg
-76.26%
301.4C
417.8C
Fig. 4. The TG and DTA curves of 1e3 compounds.
DTA
uV
TGA
%
343.4C
353.0C
-0.15mg
-4.86%
-0.40mg
-12.90%
513.6C
4a
4a
-2.68mg
-85.25%
-0.58mg
-15.89%
4b
4c
514.6C
-3.08mg
4b
-0.22mg
-11.32%
-84.62%
332.2C
342.0C
-1.87mg
4c
519.2C
517.1C
-93.68%
4d
4e
4d
-0.49mg
-3.04mg
-13.95%
-86.27%
345.7C
541.9C
-2.72mg
-0.38mg
-12.51%
4e
-88.85%
0.00
200.0
400.0
Temp[C]
600.0
800.0
0.00
200.0
400.0
600.0
800.0
Temp[C]
Fig. 5. The TG and DTA curves of 4aee compounds.
of structure in consecutive order. Theoretical and experimental
mass loss values were compatible with each other. Removal of ethyl
alcohol shows endothermic character but the other two reactions
show exothermic character.
Compounds 4bee showed similar thermal behavior and de-
compose with two exothermic stages. The first stage corresponded
to removal of tert-butyl groups and occurred in the 270e347 ꢂC
temperature range. The second stage corresponded to de-
composition of all the structure and completed with 88.36% ex-
perimental mass loss. Average exothermic peak temperatures of
these reactions were 342.37 and 548.25 ꢂC, respectively.
rest of structure decomposition and peak temperature was 512.87 ꢂC.
The TG and DTA curves of this compound are given in Fig. 6.
Reaction initial-final and peak temperatures, experimental and
theoretical mass loss values and removed groups values are sum-
marized in Table 2.
We titrated 0.01 g of 4f in CHCl3/CH3OH/H2O (200 mL, 1:1:8 v/
v)] with dilute aqueous NaOH (1.25ꢀ10ꢁ4 M) at room temperature
(Fig. 7). The observed color change was reversible and may be as-
cribed to the protonation or deprotonation of the phenol, eN]Ne,
NO2 moiety49 (Fig. 8).
The decomposition route of compound 4f was very different from
other compounds. Decomposition did not start from tert-butyl
groups but instead from the nitro groups. This reaction occurred
explosively at 381.64 ꢂC. The second reaction stage corresponded to
3. Conclusions
In conclusion, we have synthesized and characterized six new
chromogenic azocalix[4]arenes for application in ionic and non-
Fig. 6. The TG and DTA curves of 4f compound.

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S. Elc¸ in, H. Deligoz / Tetrahedron 69 (2013) 6832e6838
6836
uncorrected. 1H NMR spectra were referenced to tetramethylsilane
(TMS) at 0.00 ppm as internal standard solution and recorded on
a Bruker 400 MHz spectrometer at room temperature (25ꢄ1 ꢂC). IR
spectra were recorded by a Mattson 1000 FTIR spectrometer as KBr
pellets. UVevis spectra were obtained by a Shimadzu 1601
UVeVisible spectrophotometer. TG, DTG, and DTA curves were
obtained simultaneously using a Shimadzu DTG-60H thermal an-
alyzer. The measurements were carried out in an air atmosphere
and the temperature range of 25e800 ꢂC in a platinum crucible
heating at 10 ꢂC/min and using highly sintered Al2O3 as the refer-
ence material. Microwave assisted synthesis was performed using
a CEM Discover synthesis unit (monomode system). The elemental
analyses were performed in the TUBITAK (The Scientific and
Technological Research Council of Turkey) Laboratory.
Table 2
The thermoanalytical results obtained from TG and DTA curves
Compound TiꢁTf/ꢂC
Tpeak/ꢂC % Mass
loss(exp.) loss(theo.)
% Mass
Removed groups
1
290e460 429.45
47.85
50.51
41.08
60.13
50.53
49.47
43.12
56.88
2-tert-Butylþbenzoyl
groups
Rest of structure
decomposes
460e595 540.79
290e450 384.29
450e610 568.01
2
2-tert-Butylþbenzoyl
groups
Rest of structure
decomposes
1 mol C2H5OH
2-tert-Butyl
Rest of structure
decomposes
1 mol C2H5OH
2-tert-Butyl
Rest of structure
decomposes
2-tert-Butyl
Rest of structure
decomposes
2-tert-Butyl
Rest of structure
decomposes
2-tert-Butyl
Rest of structure
decomposes
2-tert-Butyl
Rest of structure
decomposes
Nitro groups
Rest of structure
decomposes
3
82e150
129.10
150e375 301.49
372e550 576.96
7.89
19.71
76.27
7.89
19.55
72.56
4a
120e170 151.90
270e346 343.44
346e582 513.66
4.86
12.91
85.25
5.41
13.25
81.34
Crystallization solvent was retained in some of the analytical
samples and affected the elemental analysis. In such cases, best fits
between the analytical values and appropriate fractional in-
crements of solvents were used.
4b
4c
4d
4e
4f
270e354 353.00
354e589 514.65
15.90
84.62
14.61
84.01
4.2. Preparation of the ligands
270e345 332.28
345e612 519.21
11.32
93.69
14.11
85.89
p-tert-Butylcalix[4]arene was synthesized as described
previously.36
270e344 342.03
344e567 517.18
13.95
86.27
14.00
86.00
4.3. Preparation of 25,27-di-benzoyl-26,28-dihydroxy-5,11,17,23-
tetra-(tert-butyl) calix[4]arene (1)
270e346 345.79
346e578 541.96
12.52
88.85
12.51
87.49
270e381 381.64
381e590 512.87
10.37
89.05
10.78
89.22
13.0 g (0.02 mol) of p-tert-butylcalix[4]arene in 100 mL of pyr-
idine was stirred in an ice bath for 60 min. After cooling, 18.8 mL
(0.16 mol) benzoyl chloride was added dropwise into the clear
solution. This solution was stirred in an ice bath for 90 min. The
Fig. 7. Color changes corresponding to different pH values [0.01 g of 4f in CHCl3/CH3OH/H2O (200 mL, 1:1:8 v/v)].
linear optical (NLO) sensors. Based on the presented evidence, the
potential use of these new azocalix[4]arenes for extractions of
cations, anions, and neutral molecules warrants further in-
vestigation. Compounds (4aef) contain conjugated chromophore
azo (eN]Ne) groups, which prefers soft metal (Hg2þ) cation. It can
be explained by the (hardesoft) acidebase (HSAB) principle. The
thermal analysis of azocalix[4]arene demonstrated that the stabil-
ity of the calix[4]arene depends on substituted groups and their
position in the calix[n]arene structure.
In addition, we have attempted to understand this reaction of
calix[n]arenes to rationally obtain molecular filters that may be
selective for metal ions and organic substrates. By this way, mod-
ified azocalix[n]arene can be used as a calix[n]arene dye, providing
color with different absorption characteristics.
resulting solution was poured into ice-water (300 mL). The residue
was precipitated to give a gel consistency. The precipitated residue
was decanted and dried. After removal of solvents, the crude
mixture was crystallized with CHCl3/C2H5OH (80 mL, 3:5 v/v) to
give 12.7 g of 1 (74%), white precipitate, mp 343e344 ꢂC.
(320e330 ꢂC (dec) was found.37) [Found: C: 81.47%; H: 7.43%];
C58H64O6 requires C: 81.27%; H: 7.53%. IR (KBr) n
: 1758 cmꢁ1 (eC]
O). 1H NMR (CDCl3, 25 ꢂC) dH: 1.04 (s, 18H, t-Bu), 1.19 (s, 18H, t-Bu),
3.53 (d, J¼14.21 Hz, 4H, ArCH2Ar), 4.00 (d, J¼14.17 Hz, 4H, ArCH2Ar),
5.18 (s, 2H, ArOH), 6.94 (s, 4H, ArH (ebenz)), 7.05 (s, 4H, ArH(eOH))
7.57 (t, J¼7.80 Hz, 4H m-ArH), 7.74 (t, J¼7.47 Hz, 2H p-ArH), 8.37 (d,
J¼7.08 Hz, 4H o-ArH).
4.4. Preparation of 25,27-di-benzoyl-26,28-dihydroxy-11,23-di-
(tert-butyl)calix[4]arene(2)
4. Experimental
4.1. General
A mixture of compound 1 (17.14 g, 0.02 mol), phenol (9.4 g,
0.10 mol), and AlCl3 (14.0 g, 0.11 mol) in 125 mL of toluene was
stirred at room temperature for 10 h. HCl (100 mL, 0.2 M) was
added dropwise into the toluene solution. The toluene phase was
separated and washed with water (3ꢀ50 mL), and the combined
organic phases evaporated to dryness. The beige residue was pre-
cipitated with MeOH (250 mL). After removal of solvents, the crude
All solvents and compounds were commercial grade reagents
and have been used without further purification. Melting points
were measured using an Electrothermal IA9100 digital melting
point apparatus in capillaries sealed under nitrogen and were

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S. Elc¸ in, H. Deligoz / Tetrahedron 69 (2013) 6832e6838
6837
O2N
NO2
O2N
NO2
N
NH
N
N
HN
N
N
N
HO
O
OH
OH
O
OH
O
O
azo-enol
keto-hydrazo
OH-
H+
OH-
H+
O2N
NO2
O2N
NO2
N-
N-
N
N
N
N
N
N
-O
O-
O-
O
O-
O
O
O
anionic form
anionic form
Fig. 8. The azo-enol and keto-hydrazo tautomer form of azocalix[4]arene dye 4f.
mixture was crystallized with CHCl3/CH3OH (100 mL, 2:3 v/v) to
give 9.68 g of compound 2 (65%), white precipitate, mp 322e324 ꢂC
(320 ꢂC (dec) was found.37) [Found: C: 80.77%; H: 6.39%]; C50H48O6
calix[4]arene (4f) were obtained using the same method in 65e86%
yield. The obtained compounds were purified by crystallization using
CHCl3eC2H5OH and analyzed, consecutively.
All of the azocalix[4]arenes 4aef were soluble in diethyl ether,
benzene, acetonitrile, DMF, THF, acetone, CH2Cl2, CHCl3, DMSO, but
insoluble in water, 10% HCl, and 10% NaOH.
requires C: 80.62%; H: 6.49%. IR (KBr)
n
: 1758 cmꢁ1 (eC]O). 1H
NMR (CDCl3, 25 ꢂC) dH: 1.09 (s, 18H, t-Bu), 3.57 (d, J¼14.42 Hz, 4H,
ArCH2Ar), 3.88 (d, J¼14.42 Hz, 4H, ArCH2Ar), 5.08 (s, 2H, ArOH), 6.59
(t, J¼7.46 Hz, 2H, ArH(eOH)), 6.93 (d, J¼7.49 Hz, 4H, ArH(eOH)),
9.99 (s, 4H, ArH(ebenz)), 7.54 (t, J¼7.85 Hz, 4H m-ArH), 7.72 (t,
J¼7.43 Hz, 2H p-ArH), 8.22 (d, J¼6.91 Hz, 4H o-ArH).
4.6.1. The synthesis of 25,26,27,28-tetrahydroxy-11,23-di-(tert-butyl)-
5,17-(4-methoxy phenylazo)calix[4]arene (4a). A solution of 4-
methoxyphenyldiazonium chloride, which was prepared from 4-
methoxyaniline (0.48 g, 3.90 mmol), sodium nitrite (0.54 g,
7.83 mmol) and conc. HCl (0.85 mL) in water (3 mL). Thus was mixed
in a shaker for 2 h, was added slowly to a cold (0 ꢂC) solution of
25,26,27,28-tetrahydroxy-11,23-di-(tert-butyl)calix[4]arene (1.0 g,
1.86 mmol) and sodium acetate trihydrate (1 g, 7.35 mmol) in DMF/
THF (50 mL, 3:2, v/v) to give a pale orange suspension. After keeping
the suspension at (0 ꢂC) temperature for 10 h, it was acidified with
aqueous HCl (5 mL, 0.25%). The resulting mixture was then warmed
to 60 ꢂC, and kept at that temperature for 30 min to give 4a, which
was filtered, washed with water and MeOH, and dried. Re-
crystallization from CHCl3/C2H5OH (50 mL, 3:2, v/v) mixture gave
a pale orange product (yield, 1.21 g (81%), mp (333e334 ꢂC)). [Found:
C: 74.53%; H: 6.42%; N: 7.05%]; C50H52N4O6 requires C: 74.60%; H:
4.5. Preparation of 25,26,27,28-tetrahydroxy-11,23-di-(tert-bu-
tyl)calix[4]arene (3)
A mixture of compound 2 (1.0 g, 0.0013 mol) and NaOH (7 g,
0.175 mol) in a mixture of EtOH (35 mL) and H2O (15 mL) was
stirred into 50 mL THF at room temperature for 24 h. After, the
solution was acidified by 0.2 M HCl. THF was then evaporated, to
give a white precipitate, which was collected by filtration. The
crude mixture was crystallized from CHCl3/C2H5OH (60 mL, 1:2 v/
v), and after was dried in oven to give 0.62 g of 3 (86%), white
precipitate, mp 302 ꢂC. (300 ꢂC was found.37) [Found: C: 80.84%; H:
7.39%]; C36H40O4 requires C: 80.56%; H: 7.51%. IR (KBr) n
: 3175 cmꢁ1
(eOH). 1H NMR (CDCl3, 25 ꢂC) dH: 1.22 (s, 18H, t-Bu), 3.51 (s, 4H,
ArCH2Ar), 4.25 (s, 4H, ArCH2Ar), 6.70 (t, 2H, ArH(eOH)), 7.02 (d, 4H,
ArH(eOH)), 7.06 (s, 4H, ArH(ebenz)), 10.26 (s, 4H, ArOH).
6.51%; N: 6.96%. IR (KBr) n
: 1458 cmꢁ1 (eN]N), 1H NMR (CDCl3,
25 ꢂC) dH: 1.24 (s, 18H, t-Bu), 3.65 (s, 4H, ArCH2Ar), 3.84 (s, 6H, OCH3),
4.31 (s, 4H, ArCH2Ar), 6.95 (d, J¼9.04 Hz, 4H, AreH), 7.17 (s, 4H, AreH),
7.61 (s, 4H, ArH), 7.77 (d, J¼9.02 Hz, 4H, AreH), 10.28 (s, 4H, ArOH).
4.6. Preparation of di-phenylazocalix[4]arenes (4aef)
Diazotization of the various carbocyclic amines was affected with
sodiumnitrite andconc. HCl. Atypicalprocedurethatdescribedbelow
was used for 4-methoxyaniline. 25,26,27,28-Tetrahydroxy-11,23-di-
(tert-butyl)-5,17-(4-methylphenylazo)calix[4]arene(4b), 25,26,27,28-
tetrahydroxy-11,23-di-(tert-butyl)-5,17-(4-ethylphenylazo)calix[4]
arene (4c), 25,26,27,28-tetrahydroxy-11,23-di-(tert-butyl)-5,17-(4-
chlorophenylazo)calix[4]arene (4d), 25,26,27,28-tetrahydroxy-11,23-
di-(tert-butyl)-5,17-(4-bromophenylazo)calix[4]arene (4e), and 25,
26,27,28-tetrahydroxy-11,23-di-(tert-butyl)-5,17-(4-nitrophenylazo)
4.6.2. The synthesis of 25,26,27,28-tetrahydroxy-11,23-di-(tert-bu-
tyl)-5,17-(4-methylphenylazo)calix[4]arene (4b). Azocalix[4]arene
4b was prepared as described for 4a using 4-methylaniline in wa-
ter/HCl and obtained, which was filtered, washed with water and
MeOH, and dried. The resulting solid was recrystallized from CHCl3/
C2H5OH (50 mL, 3:2, v/v) mixture that gave us a light-beige product
(76%), mp (340 ꢂC (dec)). [Found: C: 77.87%; H: 6.83%; N: 7.13%];
C50H52N4O4 requires C: 77.69%; H: 6.78%; N: 7.25%. IR (KBr)
n:
1458 cmꢁ1 (eN]N), 1H NMR (CDCl3, 25 ꢂC) dH: 1.23 (s, 18H, t-Bu),

€
S. Elc¸ in, H. Deligoz / Tetrahedron 69 (2013) 6832e6838
6838
2.38 (s, 6H, CH3), 3.65 (s, 4H, ArCH2Ar), 4.32 (s, 4H, ArCH2Ar), 7.17 (s,
4H, AreH), 7.24 (d, J¼8.14 Hz, 4H, AreH), 7.63 (s, 4H, ArH), 7.67 (d,
J¼8.21 Hz, 4H, AreH), 10.29 (s, 4H, ArOH).
reading of draft manuscript and making many helpful suggestions
and corrections.
Supplementary data
4.6.3. The synthesis of 25,26,27,28-tetrahydroxy-11,23-di-(tert-bu-
tyl)-5,17-(4-ethylphenylazo)calix[4]arene (4c). Azocalix[4]arene 4c
was prepared as described for 4a using 4-ethylaniline in water/HCl
and obtained, which was filtered, washed with water and MeOH,
and dried. The resulting solid was recrystallized from CHCl3/
C2H5OH (50 mL, 3:2, v/v) mixture that gave us an orange product
(yield, 1.28 g (86%), mp 321e323 ꢂC). [Found: C: 77.88%; H: 7.15%; N:
7.15%]; C50H56N4O4 requires C: 77.97%; H: 7.05%; N: 6.99%. IR (KBr)
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.tet.2013.06.018.
References and notes
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n
: 1458 cmꢁ1 (eN]N), 1H NMR (CDCl3, 25 ꢂC) dH: 1.23 (s, 18H, t-Bu),
1.24 (t, J¼7.58 Hz, 6H, CH2eCH3), 2.69 (q, J¼7.56 Hz, 4H, CH2eCH3),
3.64 (d, J¼13.18 Hz, 4H, ArCH2Ar), 4.31 (d, J¼13.16 Hz, 4H, ArCH2Ar),
7.17 (s, 4H, AreH), 7.27 (d, J¼8.19 Hz, 4H, AreH), 7.64 (s, 4H, ArH),
7.69 (d, J¼8.24 Hz, 4H, AreH), 10.27 (s, 4H, ArOH).
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4.6.4. The synthesis of 25,26,27,28-tetrahydroxy-11,23-di-(tert-bu-
tyl)-5,17-(4-chlorophenylazo)calix[4]arene (4d). Azocalix[4]arene
4d was prepared as described for 4a using 4-chloroaniline in water/
HCl and obtained, which was filtered, washed with water and
MeOH, and dried. The resulting solid was recrystallized from CHCl3/
C2H5OH (80 mL, 3:2, v/v) mixture that gave us a yellow-orange
product (67%), mp 338e339 ꢂC. [Found: C: 70.97%; H: 5.77%; Cl:
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€
8.71%; N: 6.88%. IR (KBr) n
: 1458 cmꢁ1 (eN]N), 1H NMR (CDCl3,
25 ꢂC) dH: 1.25 (s, 18H, t-Bu), 3.67 (s, 4H, ArCH2Ar), 4.32 (s 4H,
ArCH2Ar), 7.18 (s, 4H, AreH), 7.42 (d, J¼8.86 Hz, 4H, AreH), 7.66 (s,
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4.6.5. The synthesis of 25,26,27,28-tetrahydroxy-11,23-di-(tert-butyl)-
5,17-(4-bromophenylazo)calix[4]arene (4e). Azocalix[4]arene 4e was
prepared as described for 4a using 4-bromoaniline in water/HCl and
obtained, which was filtered, washed with water and MeOH, and
dried. The resulting solid was recrystallized from CHCl3/C2H5OH
(80 mL, 3:2, v/v) mixture that gave us a yellow-orange product (69%),
mp 342 ꢂC. [Found: C: 64.11; H: 5.02; Br: 17.83; N: 6.13];
C48H46Br2N4O4 requires C: 63.86; H: 5.14; Br: 17.70; N: 6.21. IR (KBr)
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and obtained, which was filtered, washed with water and MeOH,
and dried. The resulting solid was recrystallized from CHCl3/
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ArCH2Ar), 4.33 (s 4H, ArCH2Ar), 7.17 (s, 4H, AreH), 7.71 (s, 4H, ArH),
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This work was supported in part by a grant from the Scientific
Research Projects Council of Pamukkale University (BAP,
2012FBE003). The authors would like to express their thanks to
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€
Dr. Sevki ASLAN and Dr. Gulbanu Koyundereli Cılgı for their critical