Synthesis and characterization of azocalix[4]arene ester and ketone derivatives incorporated in a polymeric backbone with bisphenol-A and their cation-binding properties

Article abstract of DOI:10.1007/s13738-012-0085-4

This study comprises synthesis and characterization of azocalix[4]arene compounds having copolymeric structures. The novel bisazocalixphenol-A and copolymer containing pendant azocalix[4]arene units with ester (5) and ketone (6) functionalities at their l

Full text of DOI:10.1007/s13738-012-0085-4

J IRAN CHEM SOC (2012) 9:729–735
DOI 10.1007/s13738-012-0085-4
ORIGINAL PAPER
Synthesis and characterization of azocalix[4]arene ester
and ketone derivatives incorporated in a polymeric backbone
with bisphenol-A and their cation-binding properties
¨
Mukaddes Meryem Tunc¸ Ozlem Ozen Karakus¸
¨
•
•
¨
Hasalettin Deligoz
Received: 13 September 2011 / Accepted: 15 February 2012 / Published online: 27 April 2012
Ó Iranian Chemical Society 2012
Abstract This study comprises synthesis and character-
ization of azocalix[4]arene compounds having copolymeric
structures. The novel bisazocalixphenol-A and copolymer
containing pendant azocalix[4]arene units with ester (5)
and ketone (6) functionalities at their lower rim have been
synthesized via diazo-coupling reaction. The phase transfer
study is performed by liquid–liquid extraction method. It
has been deduced from the observations that their precur-
sors 25,26,27-tribenzoyloxy-28-hydroxy-5-(4-aminophe-
nylazo)calix[4] arene (3), 25,27-diacetoniloxy-26,28-dihy
droxy-5,17-(4-aminophenylazo)calix[4]arene (4) and
bisazocalixphenol-A (5) show a good phase transfer
affinity towards selected transition metal cations, unlike
copolymer (6). These compounds are studied by the
selective extraction of Fe3? cation from the aqueous phase
into the organic phase and it is carried out using com-
pounds 1–6. It is observed that the reduced azoca-
lix[4]arene 4 is the most efficient (82.93 %) carrier of all
compounds (3–6) in the extraction of Fe3? at pH 5.4.
supramolecular chemistry, since it can be applied to many
useful and important chemical technologies. Calix[n]arenes
(n = 4–20, where n is the number of aromatic rings joined
by methylene bridges) are phenolic [1n]-metacyclophanes
that can be easily obtained by base catalysed condensation
of p-substituted phenols with formaldehyde or parafor-
maldehyde [1].
Calix[n]arenes, a class of macrocyclic compounds,
grows technical importance in various areas. Parent
calix[n]arenes have received intense attention over the past
25 years [2, 3]. Most of this interest has focused on the
calix[4]arene series containing four phenolic residues that
are the subject of our present contribution. They are known
to provide useful building blocks for hollow molecular
scaffolds with easily functionalizable hydrophilic and
hydrophobic groups at either the ‘‘lower rim’’ oxygens or
the ‘‘upper rim’’ carbons, respectively [4, 5].
Azocalix[n]arenes, which are generated by the insertion of
nitrogen atoms into the p-position units of the calix[n]arene
structures, have several isomers based on the position of
nitrogen atoms and ring size. The first reported calix[4]arene
diazo coupling process is the reaction of p-nitro-
benzenediazonium tetrafluoroborate with calix[4]arene [6].
Azocalixarenes, containing conjugated chromophore azo
(–N=N–) groups in p-positions, are synthesized via ‘‘one-
pot’’ procedures with satisfactory yields [5]. Introduction of
azo groups into the calix[n]arenes has been studied by var-
ious researchers recently for their use in ionic and molecular
recognition recently [7]. Despite such studies, predictive
information on the efficiency of coupling reaction between
calix[n]arene and substituted aromatic amines is very lim-
ited. For example, it has been reported that the reaction of
calix[4]arene with substituted benzene diazonium flourob-
orate in the presence of pyridine provides tetrakis(pheny-
lazo)calix[4]arene with higher yield, but the same reaction
Keywords Calix[n]arene ꢀ Azocalix[4]arene ꢀ
Copolymer ꢀ Liquid–liquid extraction ꢀ Phase transferring ꢀ
Transition metal cations
Introduction
There has been recent interest in the design of new stimuli
responsive host systems. The development of chromogenic
ionophores has been a very active research area in a
¨
¨
¨
M. M. Tunc¸ ꢀ O. O. Karakus¸ ꢀ H. Deligoz (&)
Department of Chemistry, Faculty of Science,
Pamukkale University, 20017 Denizli, Turkey
e-mail: hdeligoz@pamukkale.edu.tr
123

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J IRAN CHEM SOC (2012) 9:729–735
with benzene diazonium salt derived from aniline gives a
very poor yield of the related product [6, 8].
forms of chromatography. The drying agent employed is
anhydrous magnesium sulphate. Melting points are mea-
sured using an Electrothermal IA 9100 digital melting
point apparatus in capillaries sealed under nitrogen and
uncorrected. 1H-NMR spectra are referenced to tetra-
methylsilane (TMS) at 0.00 ppm as internal standard and
recorded on a Bruker 400-MHz spectrometer at room
temperature (25 1 °C) in CDCl3. IR spectra are recorded
on a Mattson 1000 FT-IR spectrometer using KBr pellets.
UV–vis spectra are obtained on a Shimadzu UV-1601 UV–
visible recording spectrophotometer. Osmometric molecu-
lar weight determination is carried out on a Knauer vapor
pressure osmometer at concentration of ca. 10-3 M CHCl3.
The elemental analyses are performed in TUBITAK (The
Scientific and Technological Research Council of Turkey)
Laboratories.
With these subjects in mind, we have synthesized sev-
eral azocalix[n]arene derivatives [9–12]. We have found
that these azocalix[n]arenes act as excellent host molecules
for the selective binding of metal ions [13–15]. They also
act as excellent enol–keto tautomers. This article briefly
discusses various molecular designs of azocalix[n]arene-
type macrocycles for metal ions, and gives examples on the
relationship among the structure, complexing, metal
selectivity and thermal behaviours of them [16].
Bisphenol-A (BPA, 2,20-bis(4-hydroxyphenyl)propane)
is widely used in manufacturing epoxy resins and poly-
carbonate, and detected in water and sediments everywhere
on the earth. BPA is listed as one of the so-called ‘‘envi-
ronmental estrogens (endocrine disrupters)’’, and its tox-
icity (BPA is sometimes used as a fungicide) [17] and
biological effects have been reported. Recently, a migra-
tion of BPA from epoxy coating into infant formula liquid
concentration has been observed [18–20].
All aqueous solutions are prepared with de-ionized
water that have been passed through a Human Power I Plus
I ? UV water purification system.
Following a recent communication from this laboratory
[12], we report here the synthesis of macromolecular
characterization of bisazocalixphenol-A (5) and copolymer
(6) in which mono- and di-amino azocalix[4]arene groups
are incorporated in the main chains (Scheme 1). In this
paper, diazo-coupling reactions between mono- or di-
amino azocalix[4]arene compounds and bisphenol-A are
described. Finally, the transition metal cation-binding
ability of the copolymers is illustrated through the picrate
extraction procedure and compared to those of nitro (1 and
2) and amino (3 and 4) azocalix[4]arene derivatives.
Preparation of the ligands
p-tert-Butylcalix[4]arene [21], calix[4]arene [22], 25,26,
27-tribenzoyloxy-28-hydroxy-5-(4-nitrophenylazo)calix[4]
arene (1) and 25,27-diacetoniloxy-26,28-dihydroxy-5,17-
(4-nitro phenylazo)calix[4]arene (2) are synthesized as
described by a previously reported method [23, 24].
Reduction of the ligands 1 and 2
25,26,27-Tribenzoyloxy-28-hydroxy-5-(4-
aminophenylazo)calix[4]arene (3)
Experimental
0.95 g (1.11 mmol) 25,26,27-tribenzoyloxy-28-hydroxy-5-
(4-nitrophenylazo) calix[4]arene (1) and 2.30 mL (47
mmol) hydrazine hydrate (80 %) were dissolved in 15 mL
THF. Then, 2.34 g (41 mmol) of dried Raney–Ni was
All reagents used are purchased from Merck or Carlo-Erba
and chemically pure. Merck PF254 silicagel is used for all
Scheme 1 Bisazocalixphenol-
A (5) and polymeric
azocalix[4]arene (6)
CH3
C
CH3
HO
OH
HO
C
OH
N
CH3
N
N
CH3
N
N
N
N
N
N
N
N
N
N
N
N
N
OR
OH
OH
OR
OR
OR
OR
OR
OH
OH
C7H5O-
R
OR
OR
C3H5O-
R
n
5
6
123

J IRAN CHEM SOC (2012) 9:729–735
731
added to solution. This mixture was stirred until the gases
depart from the solution. The mixture was allowed to warm
to room temperature and stirred for additional 2 h and set
aside throughout the day. It was filtered. The solution was
concentrated under vacuum to a volume of 5–8 mL and
treated with petroleum ether. The resulting pale brownish
powder was filtered, treated with petroleum ether and
yielded as 0.48 g (53 %). m.p. 192 °C [Found: C 77.03; H
4.97; N 4.66. C55H41N3O7 requires C 77.18; H 4.83; N
4.91]. kmax (e): 460 (7,920). mmax: 3,528, 1,726, 1,451,
reddish solid, and then filtered and washed with water and
MeOH, respectively. A sample for analysis was obtained as
follows: compound (5) was dissolved in 100 mL of a hot
NaHCO3 (4.2 g) solution. To this, solution was added
activated charcoal (1 g). After the charcoal was filtered, the
filtrate was cooled (room temperature) and acidified with
conc. HCl (1 or 2 mL). The solution was heated (60 °C)
again for 30 min and cooled. The resulting solid was fil-
tered, washed with water, and dried. Yield, 0.90 g (82 %),
m.p. 241 °C; osmometric molecular Mn (CHCl3, 37 °C),
1,950 (calculated: 1,962). [Found: C 76.34; H 4.87; N 5.56.
1,267 cm-1
.
1H-NMR (DMSO-d6, 25 °C): dH: 10.38
(broad, 2H, –NH2); 7.76 (s, 1H, OH); 6.96 (m, 4H, ArH–
NH2); 6.58 (m, 11H, ArH); 6.56 (m, 15H, ArH–CO);
3.55–4.15 (s, 8H, Ar–CH2–Ar).
C
125H92N8O16 requires C 76.52; H 4.73; N 5.71]. kmax (e):
426 (8,790). mmax: 3,529–3,435, 1,727, 1,451, 1,268 cm-1
.
1H-NMR (DMSO-d6, 25 °C): dH: 11.40 (s, 2H, bis-OH);
8.68 (s, 2H, OH); 7.92 (m, 6H, bis-ArH); 7.86 (m, 8H,
ArH–N=N); 7.64 (m, 30H, ArH–CO); 7.41 (m, 22H, ArH);
3.52–3.92 (s, 16H, Ar–CH2–Ar); 1.93 (s, 6H, –CH3).
This compound (5) was soluble in CHCl3, DMSO,
benzene, but insoluble in water, EtOH, diethyl ether, ace-
tone, acetic acid.
This compound (3) was soluble in diethyl ether, acetone,
acetic acid, CHCl3, DMSO, benzene, but insoluble in
water, EtOH.
25,27-Diacetoniloxy-26,28-dihydroxy-5,17-(4-
aminophenylazo)calix[4]arene (4)
The reduction reaction of 25,27-diacetoniloxy-26,28-
dihydroxy-5,17-(4-nitrophenyl azo)calix[4]arene (2) with
Raney–Ni was carried out according to the procedure
above [25]. Yield, 0.80 g (48 %), m.p. 285 °C [Found: C
71.08; H 5.63; N 10.39. C46H42N6O6 requires C 71.30; H
5.46; N 10.85]. kmax (e): 395 (5,610). mmax: 3,423, 1,736,
Copolymer 6 from 25,27-diacetoniloxy-26,28-dihydroxy-
5,17-(4-aminophenylazo) calix[4]arene (4)
with bisphenol-A
The diazo-coupling reaction of 25,27-diacetoniloxy-26,28-
dihydroxy-5,17-(4-amino phenylazo)calix[4]arene (1.0 g,
1.30 mmol) (4) with bisphenol-A (0.4 g, 1.80 mmol) was
carried with the above-described procedure. Usual workup
provided 6. Yield, 1.0 g (77 %), m.p. [ 360 °C (dec);
osmometric molecular Mn (CHCl3, 37 °C), 5,450 (calcu-
lated: 5,472) [Found: C 70.17; H 5.18; N 11.93.
(C61H52N8O8)n requires C 70.46; H 4.97; N 12.28]. kmax
1,466, 1,246 cm-1
.
1H-NMR (DMSO-d6, 25 °C): dH:
10.30 (s, 4H, –NH2); 7.96 (s, 2H, OH); 7.10 (m, 8H, ArH–
NH2); 6.60 (m, 10H, ArH); 3.47–4.15 (s, 8H, Ar–CH2–Ar);
2.10 (s, 4H, –CH2–); 1.16 (s, 6H, CO–CH3).
This compound (4) was soluble in EtOH, diethyl ether,
acetone, acetic acid, CHCl3, DMSO, benzene, but insoluble
in water.
(e): 410 (3,680). mmax
: 3,300–3,232, 1,728, 1,465,
1,243 cm-1. 1H-NMR (DMSO-d6, 25 °C): dH: 9.20 (s, 2H,
OH); 8.05 (s, 2H, OH); 7.20–7.00 (m, 14H, ArH); 6.70 (m,
10H, ArH); 3.35–4.05 (s, 8H, Ar–CH2–Ar); 2.30 (s, 4H,
–CH2–); 2.00 (s, 6H, Ar–CH3), 1.50 (s, 6H, CO–CH3).
Compound (6) was soluble in DMSO, and slightly sol-
uble in CHCl3, and insoluble in water, EtOH, acetone,
acetic acid, benzene, diethyl ether.
Copolymerization
Bisazocalixphenol-A 5 from 25,26,27-tribenzoyloxy-28-
hydroxy-5-(4-aminophenylazo) calix[4]arene (3)
with bisphenol-A
Diazonium chloride solution of 25,26,27-tribenzoyloxy-28-
hydroxy-5-(4-amino phenylazo)calix[4]arene, which was
prepared by 3 (1.00 g, 1.20 mmol), sodium nitrite (0.20 g,
2.90 mmol) and conc. HCl (2 mL) in acetic acid (5 mL),
was added slowly into a cold (*0 °C) solution of
bisphenol-A (0.12 g, 0.53 mmol) in aqueous NaOH and
sodium acetate trihydrate (4.08 g, 30 mmol) in DMF–
MeOH (26 mL, 8:3, v/v) to give a red suspension. After
standing for 2 h at room temperature, the suspension was
acidified with aqueous HCl (50 mL, 0.25 %). The resulting
mixture was first warmed to 60 °C and kept at that tem-
perature for 30 min to give 5 (yield 1,02 g, 93 %) as a
Liquid–liquid extraction [15]
A chloroform solution (10 mL) of ligand (1.10-3 M) and
an aqueous solution (10 mL) containing metal ions in
2.10-5 M picric acid were shaken together at 298 K for an
hour. An aliquot of the aqueous solution was taken and the
UV spectrum was recorded. A similar extraction was per-
formed in the absence of picrate ion in the aqueous solu-
tions. This extraction procedure was repeated three times.
The extractability (Ex %) of the metal cations is expressed
by means of the following equation:
123

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J IRAN CHEM SOC (2012) 9:729–735
and useful for multiple applications, such as laboratory,
clinical, environmental, and industrial analyses. To achieve
the desired goal, we have attempted to synthesize p-tert-
butylcalix[4] arene, calix[4]arene, 25,26,27-tribenzoyloxy-
28-hydroxy-5-(4-nitrophenylazo)calix [4]arene (1) and 25,
27-diacetoniloxy-26,28-dihydroxy-5,17-(4-nitrophenylazo)
calix[4]arene (2) according to the stated methods [21–24].
Recently, we have demonstrated the high selectivity of
azocalix[4]arene derivatives toward Ag?, Hg? and Hg2?
cations [15]. With the present work, we extended our
previous studies by coupling 5 and 6 with azocalix[4]arene
and bisphenol-A (Scheme 2).
Ex % ¼ ½ðA0 ꢁ AÞ = A0ꢂ ꢃ 100
where A0 and A are the absorbancies in the absence and
presence of ligands, respectively.
Extraction of Fe3? cation [26]
A
5 mL solution of chloroform containing 1–5
(5.3 9 10-4 M, 1.2 9 10-2 g 6) and a 25 mL aqueous
solution containing a metal salt (1.06 9 10-4 M) were
placed in a flask. The aqueous solution was adjusted to pH
2.2 (0.01 M NaNO3/HNO3, l = 0.1 with KCl), or buffered
to pH 3.8, 4.5 and 5.4 (0.01 M CH3COONa/CH3COOH,
l = 0.1 with KCl). The reported pH values are those of
corresponding buffers without individual pH measurement
in equilibrated solutions. The mixture was shaken for an
hour at room temperature. The extraction was not affected
by further shaking, indicating that the equilibrium has been
attained within an hour. The extractability (Ex %) was
determined by below formula:
The diazo-coupling reactions were carried out as descri-
bed in the experimental section. The synthesis of 25,26,27-
tribenzoyloxy-28-hydroxy-5-(4-aminophenylazo)calix [4]
arene (3) and 25,27-diacetoniloxy-26,28-dihydroxy-5,17-
(4-aminophenylazo)calix[4] arene (4), their conversion to
bisazocalixphenol-A (5) and copolymer (6) by the diazo
coupling reaction with bisphenol-A in DMF/MeOH with the
presence of NaNO2 and HCl/CH3COOH were performed
according to the literature methods [10]. The bisazocalix-
phenol-A 5 and copolymer 6 were obtained in 82 and 77 %
yield, respectively.
Â
Ã
Ex % ¼ ðmetalÞblankꢁðmetalÞwater= ðmetalÞblank ꢃ 100
where (metal)blank and (metal)water denote the metal con-
centrations in the aqueous phase, before and after extrac-
tion with pure chloroform solution containing extractants,
respectively.
The synthesis of azocalix[4]arene containing one free
phenolic group (5) was performed with moderate yields
(82 %) by reacting tribenzoylated calix[4]arene at 0–5 °C
with 1 equivalent of diazonium salt.
Polymeric azocalix[4]arene (6) containing two free
phenolic groups was synthesized by the diazonium cou-
pling reaction of diazotized aromatic amines and
calix[4]arene [23, 24]. The identities of purified products
were confirmed by spectral data (IR, NMR).
Results and discussion
Results and characterization of the products
In recent years, various attempts have been undertaken to
incorporate azocalix[n]arenes into different polymer
including self-assembled systems. There are two main
strategies to prepare diazo coupled calixarene-based
polymers. The first one is the attachment of the amino
calix[n]arene by diazotization reaction with a suitably
functionalized polymer or oligomer. The second one is the
reaction of calix[4]arene with the substituted benzene
diazonium flouroborate in the presence of pyridine. The
former approach gives better defined products since there
is no risk of incomplete substitution of the functionalized
polymer. Thus, azocalix[n]arene monomers have been
incorporated into dimer backbones by utilizing functional
groups [12].
The IR spectra of synthesized amino azocalix[4]arenes
(3 and 4) showed absorptions for OH as a broad band at a
considerable higher frequency (3,450–3,200 cm-1) than
parent calix[4]arenes [10] (*3,120 cm-1) indicating that
hydrogen bonds are comparatively weaker in amino
azocalix[4]arenes. An asymmetric stretching vibration for
the –N=N– group appeared in the 1,600–1,550 cm-1
range.
The synthesized azocalix[4]arenes (3 and 4) could be
1
characterized by analyses of their H-NMR spectra. The
position of NMR signals for methylene carbons in the d
3.47–4.15 ppm range for synthesized compounds allowed
us to conclude that these derivatives were present in their
cone conformation. This conclusion is in accordance with
the results reported in the literature [6]. The chemical shift
values and splitting pattern of synthesized bisazocalix-
phenol-A and copolymer are listed in the experimental
section.
Azocalix[n]arenes containing p-nitrophenylazo-chro-
mogen group with one or two free phenolic groups were
synthesized through the diazo-coupling reaction of corre-
sponding diazotized amines with calix[4]arene derivatives.
The main focus of this work is the design of new
calixarene-based polymers those are easily accessible, with
effective binding character for a particular set of cations,
Room temperature benzoylation of calix[4]arene with
benzoylchloride and pyridine yielded 1, in which methy-
1
lene protons appeared as a pair of doublets in its H-NMR
123

J IRAN CHEM SOC (2012) 9:729–735
733
Scheme 2 Synthesis diagram
of bisazocalixphenol-A (5) and
polymeric azocalix[4]arene (6)
C7H5OCl
K2CO3 / C3H5OCl
OH
4
OR
OH
OR
OH
3
2
C6H6O2N2
C6H6O2N2
NO2
NO2
N=N
OH
N=N
OH
2
1
OR
OR
3
2
Raney-Ni, H2NNH2
Raney-Ni, H2 NNH2
NH2
NH2
N=N
N=N
3
4
OR
OH
3
OR
OH
2
Bisphenol A
Bisphenol A
CH3
C
HO
N
OH
N
CH3
C
CH3
N
OH
N
HO
CH3
N
N
N
N
N
N
N
N
N
N
N
N
OH
OR
OH
OR
OR
OR
OR
OR
C7H5O-
R
OH
OH
OR
OR
C3H5O-
R
n
6
5
Extraction studies
spectrum. When azocalix[4]arenes with two free phenolic
groups present in the cone conformation (5) were sub-
jected to etherification in the presence of chloroacetone
and K2CO3 at room temperature, they gave 5 and 6 with
82–77 % yield, which exhibited a pair of doublet in the
1H-NMR spectrum.
Although numerous investigations have recently been
reported regarding the extraction of alkaline metals from
aqueous phase into organic phase by azocalix[n]arene,
information concerning the extraction of transition metals
123

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J IRAN CHEM SOC (2012) 9:729–735
Table 1 Extractions of metal picrates with ligands
Ligands
Picrate salt extracted (%)
Ag?
Hg?
Hg2?
Co2?
Ni2?
Cu2?
Cd2?
Zn2?
Al3?
Cr3?
La3?
3
4
5
6
66.7
67.0
73.0
–
79.0
68.5
81.2
8.6
91.0
57.1
65.7
9.3
11.7
7.7
23.4
–
10.9
10.1
16.7
–
6.5
5.7
8.9
–
9.0
6.9
11.4
–
6.0
2.6
38.7
–
4.0
1.2
3.2
–
11.2
17.8
21.8
–
6.0
5.3
7.9
–
H2O/CHCl3 = 10/10 (v/v): aqueous phase [metal nitrate] = 10-2
M
[picric acid] = 2 9 10-5 M; organic phase, chloroform
[ligand] = 1 9 10-3 M; 25 °C for 1 h contact time. Experimental error was 2 %
is very limited. In this work, we have investigated the
100.0
effectiveness of four diazo-coupling calix[4]arenes (3–6) in
transferring transition metals (Ag?, Hg?, Hg2?, Co2?
90.0
,
Ni2?, Cu2?, Cd2?, Zn2?, Al3?, Cr3?, La3?) from aqueous
80.0
70.0
60.0
50.0
40.0
30.0
20.0
10.0
0.0
phase into organic phase (Table 1).
6
5
4
3
We initially investigated the transferring ability of
dimeric bisazocalixphenol-A (5) and compared the results
with the data obtained for azocalix[4]arenes 3. As shown in
Table 1, both soft (Ag?, Hg?, Hg2?) and hard (Co2?, Ni2?
,
Cu2?, Cd2?, Zn2?, Al3?, Cr3?, La3?) metal cations were
not extracted by polymeric azocalix[4]arene (6) from the
aqueous phase to organic phase. However, with the intro-
duction of tribenzoyl ester groups at the cone conformation
on the lower rim of azocalix[4]arene (3), the soft Hg2? has
been transferred more effectively than that of bisazoca-
lix[4]arene 4, but both ligands for the hard metal cations
were extracted very poorly.
3
4
5
Cd2+
Cu2+
Ni2+
6
Co2+
Hg2+
Hg+
Ag+
Fig. 1 Extraction percentage of the metal picrates with azoca-
lix[4]arenes 3–6. Aqueous phase [metal nitrate] = 10-2 M [picric
acid] = 2 9 10-5 M; organic phase, chloroform [ligand] = 1 9
10-3 M; 25 °C for 1 h
From the data given in Table 1, it can be seen that
polymeric azocalix[4]arene (6) is not effective in trans-
ferring heavy metal ions into organic phase, whereas
bisazocalix phenol-A (5) and azocalix[4]arene derivatives
(3 and 4) are effective in transferring soft (Ag?, Hg?,
Hg2?) metal cations. Here, we should note that azoca-
lix[4]arenes (3) and bisazocalixphenol-A (5) in cone con-
formations show high extraction ability toward Hg2?
(91 %) and Hg? (81.2 %) metal cations, respectively. The
results expressed as percentage of cation extracted (E %)
are used to graph Fig. 1.
Ionophoric polymer-supported azocalixarenes in which
their upper rims are coupled via a single site on each
azocalix[n]arene were synthesized. The synthesized
dimeric azocalix[4]arene (5) and copolymeric azoca-
lix[4]arene (6) were subjected to comparative studies. The
results of two-phase extraction measurements of 1–6 with
Fe3? cations in a water–chloroform system at pH 2.2, 3.8,
4.5, and 5.4 are summarized in Table 2.
With all ligands substituted with more than one azoca-
lix[4]arene unit 10.47–25.90 % extraction was accom-
plished at pH 2.2. When the ketone substituted
azocalix[4]arene (4) was used, the extraction ratio was
increased significantly (Fig. 2).
In our previous work, two-phase solvent extraction of
Fe3? cation from aqueous phase into organic phase was
achieved with calix[4]arene and some of its derivatives. In
this work, we have synthesized new polymeric compounds
containing more than one azocalix[4]arene units by react-
ing azocalix[n]arene derivatives with bisphenol-A and
investigated the extraction abilities of these polymeric
azocalix[4]arenes in the water–chloroform system at vari-
ous pH levels.
These compounds are capable of extracting Fe3? even
at lower pH ranges. This shows that the n electrons on the
–N=N– groups are effective in neutral media and extrac-
tion depends on the hydrogen atom in acidic medium.
Furthermore, the compound 4 extracted 82.93 % of the
Fe3?, and this process is due to easy separation of
hydrogen atom easily from the compound 4. This phe-
nomenon has also been reported previously [26].
Polymeric calixarenes are potentially capable of forming
stable complexes with many metal ions. On the basis of the
previous experiences, bisazocalixphenol-A (5) and poly-
meric azocalix[4]arene (6) were constructed as shown in
Scheme 1.
The increase in pH is due to the number of liberated H?
cations, after the complex is formed between the
123

J IRAN CHEM SOC (2012) 9:729–735
735
Table 2 Extraction of Fe3? with ligands
The thermal stability of 6 is up to 320 °C. Both copolymers
show a good phase transfer affinities toward selected
transition metal cations. Their processability, successful
immobilization and special properties could open up a new
area of selective, polymer supported reagents for catalysis
and metal-ion separation, which enhance their utility in
phase transfer reactions, as absorbents, or as potential
candidate materials for fabricating membranes and sensors.
Ligand
Percentage of extraction
pH
2.2
3.8
4.5
5.4
1
2
3
4
5
6
25.90
24.67
20.57
25.40
15.02
10.47
35.50
35.60
37.53
63.17
39.58
26.95
55.33
39.09
51.85
75.03
59.92
66.50
69.87
48.38
69.39
82.93
64.86
74.16
Acknowledgments We thank to the Research Foundation of The
Pamukkale University of Turkey for the financial support (BAP
2005FBE019).
Aqueous phase [metal nitrate = 1.06 9 10-4 M]. Organic phase
[chloroform (ligand) = 5.3 9 10-4 M]. pH: 2.2 (0.01 M NaNO3/
HNO3, l = 0.1 with KCl), pH: 3.8; 4.5, and 5.4 (0.01 M CH3CO-
ONa/CH3COOH, l = 0.1 with KCl), at room temperature for 12 h
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ꢂ
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In this study, two new copolymers have been synthesized
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tion. The copolymers are amorphous and exhibit low Tg.
123