An approach to the synthesis of chemically modified bisazocalix[4] arenes and their extraction properties

Article abstract of DOI:10.1016/j.tet.2005.07.078

Bisazocalix[4]arenas [N,N′-bis(5-azo-25,26,27-tribenzoyloxy-28- hydroxycalix[4]arene)benzene (1), N,N′-bis(5-azo-25,26,27-tribenzoyloxy- 28-hydroxycalix [4]arene)biphenyl (2) and N,N′-bis(5-azo-25,26,27- tribenzoyloxy-28-hydroxycalix[4]arene)-2,2′-dinitro

Full text of DOI:10.1016/j.tet.2005.07.078

Tetrahedron 61 (2005) 9624–9629
An approach to the synthesis of chemically modified bisazocalix[4]
arenes and their extraction properties
b
Tahir Tilki, Izzet S¸ener, Fikret Karcı, Ahmet Gulce and Hasalettin Deligoz
a
a
b
a,
˙
*
¨
¨
aDepartment of Chemistry, Faculty of Science-Arts, Pamukkale University, 20017 Denizli, Turkey
¨
Department of Chemistry, Faculty of Science-Arts, Suleyman Demirel University, 32200 Isparta, Turkey
b
Received 8 November 2004; revised 21 June 2005; accepted 21 July 2005
Available online 10 August 2005
Abstract—Bisazocalix[4]arenes [N,N0-bis(5-azo-25,26,27-tribenzoyloxy-28-hydroxycalix[4]arene)benzene (1), N,N0-bis(5-azo-25,26,27-
tribenzoyloxy-28-hydroxycalix[4]arene)biphenyl (2) and N,N0-bis(5-azo-25,26,27-tribenzoyloxy-28-hydroxycalix[4]arene)-2,20-dinitro
biphenyl (3)] have been synthesized from 25,26,27-tribenzoyloxy-28-hydroxycalix[4]arene by diazocoupling with the corresponding
aromatic diamines (p-phenylenediamine, 4,40-diamino biphenyl and 4,40-diamino-2,20-dinitrobiphenyl). Extraction studies of bisazoca-
lix[4]arenes 1, 2, and 3 show no difference in their extraction behavior and selectivity, whereas azocalix[4]arenes are a poor extractant for
heavy metal cations. The absorption spectra of the prepared bisazocalix[4]arenes are discussed, both the effect of varying pH and solvent
upon the absorption ability of bisazocalix[4]arenes.
q 2005 Elsevier Ltd. All rights reserved.
1. Introduction
solvents. The presence of azo-chromophores in these
compounds allow detection of changes of optical absorption
in the visible range, which is resulting from the interaction
of the heterocyclic ring with the p-electrons of the azo-
chromophores.13–16
Recent developments in calixarene chemistry1 have led to
remarkable advances in which these developments have
been used as building blocks for host molecules with various
applications in supramolecular chemistry.2 Functionalized
calixarenes are fascinating objects for the study of various
aspects of their supramolecular chemistry, from simple
host–guest interactions3 to applications as artificial sensors,4
as synthetic receptors for biological agents,5 as antibody
mimetics6 or as building blocks for molecular boxes.7 The
synthesis, structures and cation-binding properties of
calixarene derivatives as a new class of macrocyclic
molecular receptors have been reviewed.8 Calixarene esters
have shown unusual ionophoric properties toward alkali
metal ions such as sodium and cesium ions.9
The functionalization of the lower rim, including with
phenyl groups such as benzoyl esters,17 has frequently been
used to create calixarenes with solubility in various
solvents; but mainly with the focus on increasing solubility
in basic solvents. We set out to introduce benzoyl
substituents of the lower rim (–OH) selectively for the
cone conformation18 with the aim of obtaining a transition
metal complex at the bottom of a molecular cavity. We
examined the introduction of diazo substituents by
diazocoupling reaction: 25,26,27-tribenzoyloxy-28-hydro-
xycalix[4]arene was treated with an excess of p-phenylene-
diamine, 4,40-diamino biphenyl and 4,40-diamino-2,20-
dinitrobiphenyl in the presence of an excess of sodium
nitrite and concd HCl under neat conditions at lower
temperatures. As part of our work on this bisazocalix[4]-
arenes, we report herein the synthesis and solid-state
structures of N,N0-bis(5-azo-25,26,27-tribenzoyloxy-28-
hydroxycalix[4]arene) benzene (1), N,N0-bis(5-azo-
25,26,27-tribenzoyloxy-28-hydroxycalix[4]arene)biphenyl
(2) and N,N0-bis(5-azo-25,26,27-tribenzoyloxy-28-hydro-
xycalix[4]arene)-2,20-dinitrobiphenyl (3) having two sym-
metric ligating sites on the calixarene framework.
In our recent work, we have reported the synthesis of
azocalix[n]arene in which a p-position is substituted by a
nitrogen atom10,11 and discussed their selective extraction of
transition metal cations.12 Chromogenic calix[n]arenes (nZ
4, 6) substituted by phenylazo and hetarylazo groups have
been previously characterized and their absorption spectra
have been investigated with a variation in pH and different
Keywords: Calix[n]arenes; Bisazocalix[4]arenes; Diazocoupling reaction;
Solvent extraction; Absorption properties.
Corresponding author. Tel.: C90 258 213 4030x1452; fax: C90 258 212
5546; e-mail: hdeligoz@pamukkale.edu.tr
*
0040–4020/$ - see front matter q 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2005.07.078

T. Tilki et al. / Tetrahedron 61 (2005) 9624–9629
9625
2. Results and discussion
properties of such compounds have been published
hitherto.
In recent years, various attempts have been undertaken to
incorporate calixarenes into different polymers, including
self-assembled systems.19 There are two general strategies
to prepare covalently linked calixarene-based polymers: the
fırst is the attachment of the calixarene by reaction with a
suitably functionalized polymer or oligomer and the second
is the preparation of calixarene monomer and its poly-
merization or copolymerization with typical monomers.20,21
The former approach gives better defined products since
there is no risk of incomplete substitution of the
functionalized polymer. Thus, calixarene monomers have
been incorporated into dimer backbones by utilizing
functional groups at the wide as well as at the narrow rim.
The target bisazocalix[4]arenes were prepared according to
the synthetic route shown in Scheme 1. The effects of the
bis-structure on the color and the selectivity of the
bisazocalix[4]arenes are discussed. Their dyeing behavior
and performance on solvent and framework effects are
assessed.
In this study, the synthesis of three new bisazocalix[4]arene
derivatives is reported. Firstly, p-tert-butylcalix[4]arene
was prepared by reaction of p-tert-butylphenol with
formaldehyde according to the method of Gutsche.19
Treatment of p-tert-butylcalix[4]arene with anhydrous
aluminium chloride gave calix[4]arene according to the
method described by Gutsche.23 Then the reaction of
25,26,27-tribenzoyloxy lower-rim substituted calix[4]arene
with 9 equiv of the appropriate benzoyl chloride in the
presence of pyridine gave the calix[4]arene ester in yield of
78%.23 The diazonium salts were excellent electrophiles
and would attack any available position on the calixarenes
to yield complex mixtures. The diazonium salt derivatives
were synthesized from aromatic diamines in sodium nitrite
and concd HCl, finally we employed 1 equiv of these salts
Previously, we reported the synthesis of azocalix[n]arene
derivatives in which a hydrogen atom is replaced by a
nitrogen atom10 and their selective metal extraction12 or dye
absorption properties.13–16 As part of our work, some
bisazocalix[4]arenes include two ligating sites (benzoyl
ester and diazo moieties) on the calix[4]arene framework.
The synthesis of some bisazocalix[4]arene derivatives is
now reported. No details of the synthesis and physical
Scheme 1. The synthetic route for three novel bisazocalix[4]arene derivatives (iZAlCl3/toluene, iiZPhCOCl, pyridine, iiiZNaNO2/concd HCl, NH2-R0-
NH2).

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T. Tilki et al. / Tetrahedron 61 (2005) 9624–9629
Table 1. Extraction of metal picrates with ligandsa
Picrate salt extracted (%)
Pb2C
Ligand
AgC
HgC
Hg2C
Cd2C
Al3C
Cr3C
La3C
1
2
6.3
10.1
15.0
54.0
29.9
30.9
35.2
37.0
28.0
29.1
27.8
77.0
3.2
9.2
%1.0
20.0
5.7
12.0
2.6
3.5
14.7
10.3
28.0
4.7
2.0
16.0
%1.0
41.0
15.2
%1.0
16.0
3
425
—
a Aqueous phase (H2O/CHCl3Z10 mL v/v), [metal picrate]Z2.0!10K5 M; organic phase, chloroform, [ligand]Z1.0!10K3 M, at 25 8C, for 1 h contact
time. Experimental error was G2%.
in DMF with 2 equiv of calix[4]arene to obtain the
corresponding bisazocalix[4]arenes (1–3). Work up of the
reaction mixture afforded the corresponding three new
bisazocalix[4]arenes 1, 2, and 3 in yields of 66, 77 and 73%,
respectively.
arenes are summarized in Table 1 for comparison purposes.
These data have been obtained by using chloroform
solutions of these compounds 1–3 to extract metal picrates
from an aqueous phase. Then, the equilibrium concen-
trations of picrates in the aqueous phase were determined
spectrophotometrically.
All newly synthesized bisazocalix[4]arenes (1, 2, and 3)
were identified by a combination of 1H NMR spectral data,
FT-IR, UV–vis and elemental analysis. Completion of the
reaction was followed by IR spectroscopy, which shows the
disappearence of the band due to the amino groups at
3383 cmK1, and the appearance of a new band at 1465–
1462 cmK1 for the diazo groups. The dimerization reaction
of the prepared compounds have been performed sequen-
tially with diazonium chloride salts of diamines in the
presence of DMF to give bisazocalix[4]arenes 1–3 in
quantitative yields after purification by reprecipitation from
DMF/H2O system.
From the data in Table 1 it can be seen that bisazocalix[4]-
arene 1, 2, and 3 are not effective in transferring heavy metal
ions into organic phase, whereas azocalix[4]arene deriva-
tive 4 is effective for all these heavy metal ions. Here we
should note that tetra substituted azocalix[4]arenes in cone
conformations show high extraction ability toward heavy
metal cations (Scheme 2).
We first checked the transferring ability of azocalix[4]
arenes 4 and compared the results with the data obtained for
three dimeric bisazocalix[4]arenes 1–3. As shown in
Table 1, neither soft (AgC, HgC, Hg2C) nor hard (Cd2C
,
The 1H NMR spectra of bisazocalix[4]arene 1–3 have
revealed singlet peaks at 3.01–3.86 ppm for methylene
protons (–CH2–), multiplets between 6.80–8.20 ppm for
aromatic protons (Ar–H) and broad peaks at 5.21–5.62 ppm
for hydroxyl groups (OH). A conformational study has been
Pb2C, Al3C, Cr3C, La3C) metal cations were significantly
extracted by bisazocalix[4]arene 1–3 from the aqueous to
the organic phase. However, with the introduction of
tribenzoyl ester groups to the cone conformation on the
lower rim of azocalix[4]arene 4, the characteristic soft
metals were transferred more effectively than bisazoca-
lix[4]arene 1–3, but the hard metal cations were extracted
very poorly.25
1
perfected by H NMR spectra, which is a versatile tool for
the identification of calixarene conformation.24 The 1H
NMR spectra of bisazocalix[4]arenes 1–3 exhibited an AB
system formed by the equatorial protons at 3.01–3.86 ppm
(JZ13 Hz) for the ArCH2–Ar bridges at room temperature.
For compounds 1, 2, and 3, 1H NMR data have revealed that
each calix[4]arene moiety of the biscalix[4]arene deriva-
tives exists in several conformational forms at room
temperature.
By comparing the solvent extraction results of bisazoca-
lix[4]arenes 1–3 and azocalix[4]arene 4, we observed that
compounds 1–3 almost did not extract any of the metal ions
used in the extraction studies, whereas compound 4 was
particularly selective for AgC, HgC and Hg2C. From these
observations, it was concluded that the size of the
macrocycle does not play a major role in the complexation
phenomenon alone, but the nature and the ionic diameter of
the metal ions, the calixarene conformation, and the
effectiveness and aggregation of functional groups are
important factors in complexation.26 In the case of
extractants 1–3, the decreased affinity in complexation
compared with the azocalix[4]arene 4 can be explained by
2.1. Extraction studies
The evaluation of the extraction efficiencies of the
compounds have been carried out by the two-phase solvent
extraction of heavy metal picrates (AgC, HgC, Hg2C
,
Cd2C, Pb2C, Al3C, Cr3C and La3C) into chloroform under
neutral conditions. The results obtained from bisazocalix[4]
Scheme 2. The structure of 25,26,27-tribenzoyloxy-p-(2-thiazolylazo)calix[4]arene.

T. Tilki et al. / Tetrahedron 61 (2005) 9624–9629
Table 2. Absorption maxima (nm) of bisazocalix[4]arenes 1–3
9627
Ligand
Chloroform
ChloroformC
piperidine
Methanol
MethanolCKOH
MethanolCHCl
Acetic acid
1
2
3
307
309
315, 440s
315
320s, 435s
311
311
310
399, 450s
309, 354s
393, 460s
310, 353s
436, 384s
308, 356s
308
307
308
306, 386s, 434s
s: Shoulder.
the fact that the bridge provides greater size between the
calixarene moieties due to the aromatic structure. On the
other hand, the hard soft acid and base principle27 seems not
to be an important factor in selectivity. As the molecule
triester functionalities are deeply hidden in the molecular
framework, the molecules are restricted from having a
pertinent conformation and do not participate in binding
metal ions. Moreover, in the two phase extraction system,
3. Conclusion
Three new calixarene-based receptors with three benzoyl
ester groups immersed in a large cavity have been
synthesized. The synthesis of all the diazo-coupled
compounds was been achieved using the method of
Morita.28 We have shown that bisazocalix[4]arene deriva-
tives as a starting point in the synthesis of double
calixarenes can be connected together with ‘classical’
calixarenes and polymeric calixarene building blocks. The
application of ionic interactions for the self-assembly of
supramolecular structures is a very interesting approach for
two reasons: these compounds represent a first step toward
calixarene-based diazo dye structures and exhibit interesting
dynamic behavior because of selective metal extraction.
azocalix[4]arene 4 showed a strong affinity toward Hg2C
.
In this study, another purpose was to synthesize a
conformationally stable form of the azocalix[4]arene,
which has led to the enhancement of AgC and HgC ion
selectivity by minimizing the side arm effect. However,
extraction results of bisazocalix[4]arenes 1–3 showed no
selectivity toward heavy metal ions. The increased affinity
of bisazocalix[4]arenes in the complexation can be
explained by the fact that there may be an important role
played by the azo bridges of the dimeric skeleton at the
water–chloroform interface, which is also in agreement with
our previous result.12
In conclusion, the dimeric cups combine a chemical
coupling control of assembly with desirable properties
such as a cone conformation. Finally, because the assembly
depends on encapsulation of a suitable guest, reversible
polymerization can be triggered by molecular recognition,
providing macroscopic structural changes in response to
chemical signals.
2.2. Absorption properties
UV–vis absorption spectra were recorded on the bisazoca-
lix[4]arenes 1–3 in various solvents. The spectral changes
clearly reflect the fact that the absorption spectra of compounds
in solvents generally change with respect to the absorption
spectra in chloroform: lmax of the bisazocalix[4]arenes 1–3
shifted considerably in chloroform (e.g., for compounds 1, 2,
and 3, lmax is 307, 309 and 306 nm, respectively).
4. Experimental section
General Remarks: All solvents and compounds were
commercial grade reagents that were used without further
purifications. Melting points (8C, uncorrected values) were
determined with a gallenkamp in a sealed capillary tubes.
The elemental analyses were performed in the TUBITAK
laboratory (Center of Science and Technology Research of
Turkey). IR spectra was recorded on a Mattson 1000 FT-IR
spectrometer as KBr pellets (n in cmK1). UV–vis spectra
were obtained on a Schimadzu 160A UV–vis recording
spectrophotometer (lmax in nm). 1H NMR spectra were
referenced to tetramethylsilane (TMS) at 0.00 ppm as
internal standard and were recorded on a Bruker 400 MHz
spectrometer at room temperature (25 8C G1).
It appears that the equilibrium depends on the basicity of the
solvents used in this study, and changes significantly upon
varying the solvent. For compound 2, however, a red or a
blue of shift increases in solvents with hydrogen bond donor
properties, for example, methanol and acetic acid. Shifts
were observed in both proton accepting solvents such as
methanol in which the lmax of the compounds displayed
slightly a red shift of the lmax, and in proton donating
solvents such as acetic acid in which the lmax of the
compounds displayed blue shift of lmax (Table 2).
The p-tert-butylcalix[4]arene, calix[4]arene and 25,26,27-
tribenzoyloxy-28-hydroxy calix[4]arene were synthesized
according to the literature procedures.19,22,23 The other
bisazocalix[4]arenes employed in this work as illustrated in
Scheme 1 have been synthesized follows.
The lmax values of the compounds showed bathochromic
effects when a small amount of piperidine was added to each
of the compounds in chloroform (Table 2). The lmax of the
compounds in methanol also showed bathochromic effects
when 0.1 M KOH was added. The lmax of the compounds in
methanol also showed slightly hypsochromic effects when
0.1 M HCl was added.
4.1. General procedure
4.1.1. N,N0-Bis(5-azo-25,26,27-tribenzoyloxy-28-hydro-
xycalix[4]arene)benzene (1). A solution of p-phenylene-
bisdiazonium chloride, prepared from p-phenylenediamine
(0.04 g, 0.37 mmol), sodium nitrite (0.05 g, 0.74 mmol) and
concd HCl (1 mL) in water (10 mL), was added slowly to a
It was shown that the mechanism of absorption shifting is
based on the interaction between additional protons or
hydroxyl and azo groups.

9628
T. Tilki et al. / Tetrahedron 61 (2005) 9624–9629
cold (5 8C) solution of calix[4]arene (0.54 g, 0.74 mmol)
and sodium acetate trihydrate (1.10 g, 8 mmol) in DMF
(15 mL) to give a yellow suspension. After standing for 2 h
at room temperature, the suspension was acidified with
aqueous HCl (150 mL, 0.1 M) and the mixture was then
warmed to 60 8C for 30 min to give 1 (yield, 0.40 g, 67%) as
a yellow solid, which was filtered and washed with water
and methanol. A representative analysis was obtained as
follows: 1 was dissolved in 100 mL of hot aqueous NaHCO3
(4.20 g) solution; activated charcoal was added to this
solution (1 g). After the charcoal was filtered, the filtrate
was cooled to room temperature and acidified with concd
HCl (1 or 2 mL). The solution was heated to 60 8C for
30 min and then cooled. The resulting solid was filtered,
washed with water, and dried. Recrystallization from DMF/
H2O mixture gave a light yellow product.
picric acid and 1.0!10K2 M metal nitrate and either 10 mL
of 1.0!10K3 M solution of bisazocalix[4]arene (1, 2, and
3) in CHCl3 were vigorously agitated in a stoppered glass
tube with a mechanical shaker for 2 min. The two phase
systems were then magnetically stirred in a thermostated
water-bath at 25 8C for 1 h, and finally left standing for an
additional 30 min. The concentration of picrate ion
remaining in the aqueous phase was then determined
spectrophotometrically. Blank experiments showed that no
picrate extraction occurred in the absence of calixarene. The
percent extraction (E%) has been calculated as:
(E%)Z(AoKA/Ao)!100,
where Ao and A are the initial and final concentrations of the
metal picrate before and after the extraction, respectively.
Yield: 0.40 g (66%); mp 265 8C. UV–vis (CHCl3): lmax
Z
307 nm. IR (KBr): nmaxZ3536 cmK1 (OH), 3060 cmK1
(arom. C–H), 2970 cmK1 (aliph. C–H), 1785 cmK1(C]O),
1572 cmK1 (C]C), 1464 cmK1(N]N) and 1178 cmK1(C–
Acknowledgements
The authors are gratefully to TUBITAK for financial
support the project number of TBAG-AY 351.
1
O). H NMR (400 MHz, DMSO-d6): dZ5.62 (s, 2H, OH),
6.80–8.20 (m, 56H, ArH), 3.82–3.58 (m, 16H, ArCH2Ar).
Elemental Anal. Calcd for C104H74N4O14 (1602): C 77.9%,
H 4.6%, N 3.49%. Found C 77.6%, H 4.5%, N 3.50%.
4.1.2. N,N0-Bis(5-azo-25,26,27-tribenzoyloxy-28-hydro-
xycalix[4]arene)biphenyl (2). Compound 2 was prepared
as described above, using 4,40-diaminobiphenyl and
obtained as pink solid, which was filtered and washed
with water and methanol, as a pale pink solid.
References and notes
1. Gutsche, C. D. Calixarenes; Royal Society of Chemistry:
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¨
cyclic Compounds; Vicens, J., Bohmer, V., Eds.; Kluwer
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2. Gutsche, C. D. Calixarenes Revisited; The Royal Society of
Yield: (77%); mp 272 8C. UV–vis (CHCl3): lmaxZ309 nm.
IR (KBr): nmaxZ3517 cmK1 (OH), 3055 cmK1(arom. C–H),
2892 cmK1(aliph. C–H), 1767 cmK1(C]O), 1607 cmK1
(C]C), 1462 cmK1 (N]N) and 1125 cmK1(C–O). 1H
NMR (400 MHz, DMSO-d6): dZ5.34 (s, 2H, OH), 6.55–
8.10 (m, 60H, ArH), 3.21–3.86 (m, 16H, ArCH2Ar).
Elemental Anal. Calcd for C110H78N4O14 (1678): C
78.66%, H 4.64%, N 3.37%. Found C 78.69%, H 4.62%,
N 3.35%.
¨
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IR (KBr): nmaxZ3518 cmK1(OH), 3032 cmK1(arom. C–H),
2960 cmK1 (aliph. C–H), 1686 cmK1 (C]O), 1554 cmK1
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¨
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¨
Picrate extraction experiments were performed as described
our in earlier procedure:29 A 10 mL aliquot of 2.0!10K5
M

T. Tilki et al. / Tetrahedron 61 (2005) 9624–9629
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