Synthesis and metal extraction behavior of pyridine and 1,2,4-triazole substituted calix[4]arenes

Article abstract of DOI:10.1007/s10847-010-9796-2

Three series of heterocycle substituted calixarenes, derivatized at lower and upper rim, were synthesized and successfully evaluated for metal extraction towards alkali, alkaline, transition and heavy metal ions. The presence and placement of sulfur, heterocycle functionality at upper/lower rim played a crucial role toward the extractability and selectivity of metal ions. The lower rim substituted calixarenes have shown high extractability and poor selectivity. In contrast to this, upper rim substituted calixarenes exhibited good selectivity. Moreover, sulfur functionalized calixarenes have shown better selectivity for heavy metal ions than alkali and alkaline metal ions. Among upper rim substituted calixarenes, 17 and 18 were found to be suitable for Na⁺, K⁺ and Ag⁺, 19,13 for heavy metal ions i. e., Pb²⁺, Hg⁺, Hg²⁺ and Ag⁺, and 11,12 for Pb²⁺ and Ag⁺ only.

Full text of DOI:10.1007/s10847-010-9796-2

J Incl Phenom Macrocycl Chem (2010) 68:369–379
DOI 10.1007/s10847-010-9796-2
ORIGINAL ARTICLE
Synthesis and metal extraction behavior of pyridine
and 1,2,4-triazole substituted calix[4]arenes
•
Ashok Kumar Pratibha Sharma
•
•
Bhagwan Lal Kalal Lal Kumar Chandel
Received: 18 February 2010 / Accepted: 28 April 2010 / Published online: 16 May 2010
Ó Springer Science+Business Media B.V. 2010
Abstract Three series of heterocycle substituted calixa-
renes, derivatized at lower and upper rim, were synthesized
and successfully evaluated for metal extraction towards
alkali, alkaline, transition and heavy metal ions. The
presence and placement of sulfur, heterocycle functionality
at upper/lower rim played a crucial role toward the
extractability and selectivity of metal ions. The lower rim
substituted calixarenes have shown high extractability and
poor selectivity. In contrast to this, upper rim substituted
calixarenes exhibited good selectivity. Moreover, sulfur
functionalized calixarenes have shown better selectivity for
heavy metal ions than alkali and alkaline metal ions.
Among upper rim substituted calixarenes, 17 and 18 were
found to be suitable for Na?, K? and Ag?, 19,13 for heavy
metal ions i.e., Pb2?, Hg?, Hg2? and Ag?, and 11,12 for
Pb2? and Ag? only.
substituted calixarene derivative e.g. ester, amide and car-
bonyl in their cone conformation are selective ligands for
Na? cations [4], and are used in various sensors. Similarly,
1,3-calix crown ethers in 1,3-alternate conformation are
highly selective for K? ions [5], while calixcrown-6 shows
exceptionally high Cs? ion selectivity [6] and used for the
extraction of cesium ion from high-salinity nuclear waste
[7]. The literature clearly revealed that binding at lower rim
via oxygen or nitrogen provides selective extraction of
group I and II metal ions. On the other hand, little has been
published on the extractive ability of upper rim substituted
calixarenes, which comparatively possesses large cavity
size and could be effective extractant towards transition and
heavy metal ions. Moreover, the type of substituent on
calixarene moiety also plays a crucial role towards the metal
extraction, in particular, N and S containing heterocycles are
well known for metal ligation in coordination chemistry.
Bonnamour et al. have reported the extraction properties of
derivatized azocalix[4]arenes bearing ester [8], amide [9],
bipyridyl [10], and bithiazoyl [11] functionalities. They
have shown that the amide derivatives of calixarene are able
to complex alkali metal cations, whereas bipyridyl analogue
are able to complex soft cations such as zinc. In this per-
spective, pyridine and triazole heterocycles are quiet known
for their basicity and ligation [12–18] with metal ions.
Hence, it is possible that when sulfur, ester/amide, hetero-
cyclic functionalities are suitably placed on calixarene
skeleton, they would provide a well preorganized coordi-
nation sphere for metal binding and hence, enhanced
extractability may be attained. Keeping this in mind and in
continuation of our research devoted to heterocycles [19,
20] and calixarenes [21–23], we have synthesized upper and
lower rim substituted calixarenes by incorporating hetero-
cycles/sulfur/amide functionalities, and explored their
potential as metal extractant.
Keywords Calixarenes ꢀ Heterocycles ꢀ
Solvent extraction ꢀ Metal extraction
Introduction
Calix[n]arenes play an increasingly important role in host–
guest chemistry largely because they provide a well orga-
nized platform for the attachment of pendant groups [1, 2].
Numerous ionophores have been synthesized by using this
approach i.e., attachment of various ligating functionalities
to calixarenes skeleton. These ionophores have unique
complexation properties and selectivity [3]. Lower rim
A. Kumar (&) ꢀ P. Sharma ꢀ B. L. Kalal ꢀ L. K. Chandel
School of Chemical Sciences, Devi Ahilya University,
Takshashila Campus, Indore 452 001, India
e-mail: drashoksharma2001@yahoo.com
123

370
J Incl Phenom Macrocycl Chem (2010) 68:369–379
Synthesis
by dealkylating 1 with phenol and AlCl3 to afford 7 as
starting material (Scheme 2). Complete debutylation was
1
confirmed by the absence of peak at 0.98 ppm in its H
Synthesis of desired calixarenes was accomplished as
depicted in Schemes 1, 2 and 3. The calixarene 1 was syn-
thesized by established literature procedure reported by
Gutsche et al. [24]. Synthesis of lower rim substituted
calixarenes 4,5,6 was initiated by the acylation of 1 with
chloroacetyl chloride and sodium carbonate (Scheme 1).
The conformation of product 2 was confirmed by charac-
teristic pair of doublet at 4.88 and 3.94 ppm for bridged
methylene. Reaction of 2 with 2-aminopyridine and 1,2,4-
triazole (10) in presence of sodium ethoxide yielded 5 and 6,
respectively. Synthesis of 4 was achieved by reaction of 2
with 1,2,4-triazole-3-thiol (3), in presence of NaOH, to
maximize the yield of 4 and to limit the synthesis of other
products. The accomplishment of these reactions was
ascertained by preparative TLC by taking out the reaction
mixture time to time. The conformation of 4,5,6 was
ascertained cone, as the reactant 2 has cone conformation
and the alkyl subsituent i.e., chloroacetyl group at lower rim
is large enough to restrict conformation inversion through
lower rim. The substitution of chloride at lower rim by
heterocycle was ascertained by complete disappearance of
peak at 3.67 ppm for CH2Cl in 1H NMR spectra.
NMR spectrum. The compound 7 was chloromethylated at
para position by HCHO and HCl in presence of glacial
acetic acid and H3PO4 to yield 8. In IR spectrum of 8, a
1
strong band at 684 cm-1 for C–Cl stretching, while in H
NMR spectrum a singlet at 3.67 ppm with area correspond
to 8H has confirmed the tetra substitution. Calixarene 8 was
subjected to tetra alkylation at lower rim by K2CO3 and
propyl iodide to afford 9. From this, calixarenes 11, 12
were synthesized by nucleophilic substitution of chloride
with 2-aminopyridine and 1,2,4-triazole (10) using sodium
ethoxide as base, while 13 was synthesized by 1,2,4-tria-
zole-3-thiol (3) and NaOH (Scheme 2).
Synthesis of upper rim substituted calixarenes 17,18,
and 19 was initiated by lower rim alkylation of 7 with
propyl iodide and sodium hydride to obtain 14 (Scheme 3).
It was subjected to Friedel Craft acylation at para position
by acetylchloride and aluminum chloride in dichloro-
methane. The acetyl group of 15 was oxidized to carbox-
ylic group by bromine and sodium hydroxide in DMF.
Resultant 16 was treated with equivalent amount of thionyl
chloride followed by 2-aminopyridine, 1,2,4-triazole (10)
and 1,2,4-triazole-3-thiol (3) to yield 17, 18, and 19,
respectively. To maximize the yield and to force the
Rest of the calixarene derivatives (11,12,13,17,18,19)
are upper rim derivatized and their syntheses were initiated
CH
3
Scheme 1 An overview of
synthetic strategy for lower rim
substituted calix[4]arenes 4,5,6
CH3
SH
CH3
H C
CH
3
3
H3C
CH3
H3C
CH3
N
N
N
H
ClCH2COCl
3
Na2CO3
CH
2
NaOH
CH
CH
2
2
4
O
S
O
4
4
O
O
OH
2
1
4
Cl
NH
2
N
N
10
N
H
N
N
HN
N
NaOEt
NaOEt
CH
3
H C
CH
3
3
CH
3
H C
3
CH
3
CH
2
4
O
O
CH
2
4
O
O
HN
5
6
N
N
N
N
123

J Incl Phenom Macrocycl Chem (2010) 68:369–379
371
Scheme 2 An overview of
synthetic strategy for upper rim
substituted calix[4]arenes
11,12,13
Cl
HCHO / HCl
CH
CH
2 4
2
4
OH
OH
8
7
C3H7I/K2CO3
Cl
CH
SH
2
4
OC
H
7
3
N
N
3
N
H
N
9
N
H
NH
2
NaOH
N
NaOEt
N
N
HN
S
N
N
NaOEt
N
10
H
CH
CH
2 4
2
N
N
4
N
OC
H
7
OC
H
7
3
3
13
11
CH
2
4
12
OC
H
7
3
reaction in forward direction, the reaction was performed in
the presence of sodium hydroxide. Tetra substitution was
confirmed by molecular ion peak in FAB mass spectra. The
conformation of 17,18, and 19 was assigned cone by
characteristic peak for methylene bridge.
where A0 and A are the absorbance in the absence and
presence of ligand.
Results and discussion
The heterocyclic compounds are very well known for
complexation of metal ions, especially, pyridine/triazole
are quite good ligand for the metal complexation. Hence,
with a view to observe the effects of heterocycles, sulfur,
ester, and carbonyl functionality on metal extraction
behavior, various lower and upper rim substituted calixa-
rene derivatives 4-19 (Schemes 1, 2 and 3) were synthe-
sized. In this perspective, a range of metal ions; alkali,
alkaline, transition and heavy metal ions were taken into
consideration and their extractability towards all the
calixarenes have been evaluated by mean of solvent
extraction of their metal picrates from aqueous to organic
phase. Calix 4, 5, 6 are lower rim heterocyclic substituted
Solvent extraction
A chloroform solution (10 mL) of ligand (1910-3 M) and
an aqueous solution (10 mL) containing 2910-5 M picric
acid and 1910-2 M metal salts (chloride, nitrate, hydrox-
ide, carbonate) were stirred at 298 K for 10 min contact
time. An aliquot of the aqueous solution was withdrawn,
and the UV spectrum was recorded. A similar extraction
was performed in the absence of ligand. The extractability
of the metal cations was calculated by taking into account
the valency of metal ion, using following equation:
Extractabilityð%Þ ¼ 100ðA0 ꢁ AÞ=A0
123

372
J Incl Phenom Macrocycl Chem (2010) 68:369–379
Scheme 3 An overview of
synthetic strategy for upper rim
substituted calix[4]arenes
17,18,19
O
CH3
CH3COCl
AlCl3
C3H7I/NaH
CH
CH
2 4
2
CH
2
4
4
OH
OC
H
7
3
OC
H
7
3
14
15
7
O
OH
Br2/NaOH
CH
2
4
OC
H
7
3
SH
16
N
HN
N
N
H
N
3
N
SOCl2
NH
2
N
N
SOCl2
H
N
HN
O
H
N
O
S
SOCl2
N
10
CH
2
4
N
OC
3
7
CH
2
N
N
O
4
OC
H
7
3
17
19
CH
2
18
4
OC
H
7
3
derivatives, whereas rest are upper rim substituted. All the
synthesized calixarenes have multiple interacting sites viz.,
sulfur, ester, amide, carbonyl, and heterocycles, with dif-
ferent cavity size at their interacting sites. Among syn-
thesized calixarenes, calix 4 has shown extractability
The extractive ability of 5 is similar as 4, but it shows zero
extractability for heavy metal ions due to the absence of
sulfur functionality, which could have responsible for
interaction of calix 5 with heavy metal ions. The extract-
ability of 5 for Na? and Ca2? is slightly higher than 4, due to
the presence of suitably placed NH group, which provide
well preorganized cavity through hydrogen bonding for
interaction of metal ions with carbonyl group of ester
functionality. The extractability of 5 for transition metal
ions is lower than 4 and 6, which suggests that triazole is
better complexing functionality than pyridine. The extract-
ability trend of 6 is similar to 5, but it shows low extract-
ability for Na? and Ca2?, attributable to the absence of
hydrogen bonding to provide well preorganized cavity for
proper fit at lower rim. The calixarene 17 and 18 are quite
selective towards the extraction of Na?, K?, Ca2? and Ag?
metal ions. The low extractability for these metal ions in
comparison to 4, 5, and 6 is a result of expansion of cavity
size at upper rim. On the other hand, 17 and 18 have shown
towards all metal ions (Table 1), except Mg2?, As3?, Pb2?
,
and Hg?. These metal ions are either too small or too large
to fit into the calixarene cavity and hence not extracted by
calix 4. In accordance, calix 4 has shown low extraction for
K? ions owing to big size of latter to fit lower rim of
former. Surprisingly, though the Hg? and Ag? metal ions
have similar size but they differ a lot in extractability
(Hg? = 0, Ag? = 60%). It can be explained by the fact
that at lower rim, as we move from rim to ester, sulfur and
towards the end of substituent, the cavity size become
smaller, successively and at sulfur functionality, where
Hg? ion interact, cavity size is small to fit Hg? ions. On the
other hand, Ag? ions interact with ester functionality
where the cavity size of calixarene is large enough to fit it.
123

J Incl Phenom Macrocycl Chem (2010) 68:369–379
373
the absence of ester/amide functionality on calixarene
skeleton. A different trend of extractability has been
observed for compound 11 and 12. These derivatives are
quite selective toward Pb2? and Ag? ions. Large cavity size
and absence of sulfur, ester and amide functionality in 11
and 12 allows selective extraction of Pb2? and Ag? ions
only. A comparative view of metal extractive ability and
interaction of various substituted calixarenes towards metal
ions is depicted in Figs. 1, 2, 3 and 4.
Table 1 Percentage extraction of alkali, alkaline earth, transition and
heavy metal picrates into CHCl3 at 25 °C
Metal
Calixarenes
4
5
6
17
18
19
1.3
11
2.2
12
1.6
13
2.2
Na?
98.0 99.9 92.1 43.2 16.2
K?
5.1
0.3
0.5
0.3
1.1 86.5 65.3
0.6 1.1 0.4
2.1
1.6
3.3
2.5
1.2
1.6
3.4
2.9
1.2
2.9
3.1
1.5
2.6
1.5
1.9
2.2
1.7
1.9
1.4
1.9
1.1
1.7
1.3
1.4
2.5
1.6
2.1
2.3
1.8
1.4
2.9
2.4
2.1
3.1
2.2
2.8
Mg??
Ca??
As???
Fe??
Co??
Ni??
Cu??
Zn??
Pb??
Hg??
Cd??
Pd??
Hg?
79.9 89.2 79.2 37.8 12.1
1.1
0.6
0.4
0.7
0.1
1.2
0.9
3.1
1.5
0.5
2.1
1.4
0.8
3.5
2.5
1.4
1.2
0.4
1.6
1.8
2.1
2.5
12.1
Conclusion
73.3 61.4 59.8
64.2 51.9 55.2
81.0 72.1 74.8
86.8 81.0 84.2
In summary, we have synthesized new heterocycle substi-
tuted calixarene derivatives and performed solvent extrac-
tion studies with alkali, alkaline earth, transition, and heavy
metal ions. The effect of S, N, ester, and heterocyclic
functionality in calixarene has been carefully envisaged for
extraction purpose. Lower rim substituted calixarenes found
to be effective extractant towards alkali, alkaline and tran-
sition metal ions, but have lack of selectivity. In contrast to
this, upper rim substituted calixarenes exhibited good
selectivity. Among these, 17 and 18 were found to be suit-
able for Na?, K? and Ag?, 19,13 for heavy metal ions i.e.,
Pb2?, Hg?, Hg2? and Ag?, and 11,12 for Pb2? and Ag?
ions, only. This study would be useful for multiple appli-
cations in laboratory, environmental, pharmaceutical, and
industrial processes for the determination and extraction of
various metal ions using two-phase solvent extraction.
0.2
67.2
69.2
75.3
0.1
0.3
0.1
1.5
1.1
0.2
0.8
1.1
1.8
0.6
2.1
1.6
1.2 80.8 52.1 57.5 78.0
3.1 54.1
1.4
1.2
1.8
1.4
1.7 68.9
1.2
1.8
0.6
0.3
1.3
1.6
1.7
1.0
0.9 96.1
1.9 86.8
Ag?
60.1
2.1 51.0 37.2 74.9 36.1 40.3 52.1
no extractability for heavy metal ions due to the absence of
sulfur functionality in their structure. These derivatives have
shown good extractability for K?, Na?, Ag? and Ca2?, in
comparison to transition metal ions. The quite promising
reason for this, K?, Ca2?, Na? and Ag? interact at carbonyl
functionality of amide (Fig. 4), where the cavity size is
appropriate for complexation. On the other hand, transition
metal ions interact primarily with heterocyclic functionality,
at the end of pendant group, where cavity expansion is
maximum (Fig. 4) and hence, calixarene could not provide a
proper fit for metal complexation. Due to the presence of
sulfur and large cavity size at upper rim, calixarenes 19 and
Experimental
Reagents and apparatus
13 have shown extractability for heavy metal ions (Pb2?
,
All the chemicals used were of AR grade purity. IR spectra
were recorded on Perkin Elmer model 377 spectrophotom-
1
eter in KBr pellets. HNMR spectra were recorded on a
Hg2?, Hg?, Ag?). In contrast to this, they have exhibited no
extractability for alkali/alkaline metal ions, attributable to
Fig. 1 A comparative overview
of metal extracting ability of
4,5,6 towards metal ions
115
95
4
5
6
75
55
35
15
-5
123

374
J Incl Phenom Macrocycl Chem (2010) 68:369–379
Fig. 2 A comparative overview
of metal extracting ability of
11,12,13 towards metal ions
95
85
75
65
55
45
35
25
15
5
11
12
13
-5
Fig. 3 A comparative overview
of metal extracting ability of
17,18,19 towards metal ions
115
95
75
55
35
15
-5
17
18
19
Bruker DRX300 MHz instrument. The FAB mass spectra
were recorded on a JEOLSX102/DA-6000 Mass Spec-
trometer using Argon/Xenon (6 kV, 10 mA) as the FAB
gas. Analytical thin layer chromatography was performed
using E. Merck silica gel G, 0.50 mm plates (Merck No.
5700). The melting points were determined on an electric
melting point apparatus in open capillaries.
60 mmol) followed by 4.8 mL (60 mmol) of chloroacetyl
chloride. The reaction was carried out at room temperature
for 1 h. After the completion of reaction, the mixture was
distributed between chloroform and 1 N HCl (100/50 mL).
The chloroform extract was washed with water (about
100 mL) and dried over MgSO4. The chloroform evapo-
ration afforded a crude product, which was recrystallized
by ethanol to yield a pure product 2. Yield 15.0 g (79%),
m.p. 222 °C.
25,26,27,28-Tetrahydroxy-p-tert-butylcalix[4]arene (1)
It was synthesized by literature procedure [24]. m.p. 338 °C.
max
Â
Ã
1
KBr
IR m ðcmꢁ1Þ : 1750 (C=O); HNMR [CDCl3 (d ppm)] :
max
0.94 (s, 36H, –C(CH3)3), 3.67 (s, 8H, CO–CH2–Cl), 3.94
(d, 4H, Ar–CH2–Ar, J = 12.6 Hz), 4.88 (d, 4H, Ar–CH2–
Ar, J = 12.6 Hz), 7.19 (m, 8H, Ar–H); FAB MS, m/z: 954
(M?); Anal calc.(%) for C52H60O8Cl4: C, 65.41; H, 6.33;
Found C, 65.01; H, 6.27
Â
Ã
1
KBr
IR m ðcmꢁ1Þ : 3172 (-OH); HNMR [CDCl3 (d ppm)] :
0.98(s, 36H, –C(CH3)3), 3.86 (d, 4H, Ar–CH2–Ar,
J = 12.4 Hz), 4.49 (d, 4H, Ar–CH2–Ar, J = 12.4 Hz), 7.12
(m, 8H, Ar–H), 10.25 (s, 4H, ArOH); FAB MS, m/z: 648
(M?); Anal calc.(%) for C44H56O4: C, 81.44; H, 8.70;
Found C, 81.12; H, 8.62.
1H-1,2,4-Triazole-3-thiol (3)
25,26,27,28-Tetra[(chloroacetyl)oxy]-p-tert-
butylcalix[4]arene (2)
It was synthesized as per the literature procedure [25].
Yield 2.8 g (70%), m.p. 220 °C.
max
Â
Ã
1
KBr
IR m ðcmꢁ1Þ : 2700–2900 (N–H); HNMR [CDCl3 (d
1 (14.8 g, 20 mmol) was dispersed in 200 mL dry tetra-
hydrofuran and treated with sodium carbonate (6.35 g,
ppm)]: 7.1 (S, H, SH), 8.32 (s, H, –NH–CH=N), 13.5 (s, H,
123

J Incl Phenom Macrocycl Chem (2010) 68:369–379
375
Fig. 4 Interaction of various
calixarene derivatives with best
fit metal ion
Interaction of 4 with Na+
Interaction of 5 with Zn+2
Interaction of 12 with Ag+
Interaction of 18 with Ag+
Interaction of 6 with Zn+2
Interaction of 11 with Pb+2
Interaction of 13 with Hg+
Interaction of 17 with K+
Interaction of 19 with Hg+
N–NH–CH); FAB MS, m/z: 101 (M?); Anal calc.(%) for
C2H2N3S: C, 23.75; H, 5.65; S, 31.71; Found C, 23.66; H,
5.61; S, 31.61.
(25/50 mL) mixture. The chloroform extract was washed
with water (about 50 mL) and dried over MgSO4. The
solvent evaporation afforded a crude mass, which was
purified by column chromatography (Alumina column;
neutral); gradient of chloroform/acetone (20/1 to 3/1).
Yield 0.97 g (68%), m.p. 214 °C.
25,26,27,28-Tetra{[(1H-1,2,4-triazol-3-
ylsulfanyl)acetyl]oxy}-p-tert-butylcalix[4]arene (4)
Â
Ã
KBr
IR m ðcmꢁ1Þ : 2700–2900 (N–H), 1746 (CO–O–Ar);
max
Thiol 3 (2.02 g, 20 mmol) was dispersed in 100 mL of dry
tetrahydrofuran and treated with NaOH (0.8 g, 20 mmol)
followed by 0.95 g (1 mmol) of 2 was added. The reaction
was carried out at reflux temperature for 12 h. Reaction
was monitored by preparative TLC (ethylacetate/xylene,
1:20). After the completion of reaction, the reaction mix-
ture was distributed to the chloroform/diluted aqueous HCl
1HNMR [CDCl3 (d ppm)]: 1.05 (s, 36H, –C(CH3)3), 2.50
(s, 8H, CO–CH2–S), 3.88 (d, 4H, Ar–CH2–Ar, J =
12.4 Hz), 4.36 (d, 4H, Ar–CH2–Ar, J = 12.4 Hz), 7.25 (m,
8H, Ar–H), 8.29 (s, 4H, –NH–CH=N), 13.02 (s, 4H, N–
NH–CH); FAB MS, m/z: 1213 (M?); Anal calc.(%) for
C60H68N12O8S4: C, 59.38; H, 5.65; N, 13.85; S, 10.57;
Found C, 59.15; H, 5.61; N, 13.78; S, 10.51.
123

376
J Incl Phenom Macrocycl Chem (2010) 68:369–379
25,26,27,28-Tetra{[(pyridin-2-ylamino)acetyl]oxy}-p-
tert-butylcalix[4]arene (5)
25,26,27,28-Tetrahydroxy-p-chloromethylcalix[4]arene
(8)
2-amino pyridine (1.86 g, 20 mmol) was dissolved in
100 mL of dry tetrahydrofuran and treated with freshly
prepared sodium ethoxide (1.36 g, 20 mmol) followed by
0.95 g (1 mmol) of 2 was added. The reaction was carried
out at reflux temperature for 16 h. Reaction was monitored
by preparative TLC (ethylacetate/xylene, 1:20). After the
completion of reaction, excess of sodium ethoxide was
quenched with water (about 20 mL) and reaction mixture
distributed to the chloroform/diluted aqueous 1 N HCl (50/
25 mL). The chloroform extract was washed with water
(about 50 mL) and dried over MgSO4. The solvent evap-
oration afforded a crude mass, which was purified by col-
umn chromatography (Alumina column; neutral); gradient
of chloroform/acetone (20/1 to 3/1). Yield 0.64 g (55%),
m.p. 189 °C.
A solution of calix[4]arene 7 (3.54 g, 8.35 mmol), para-
formaldehyde (5.30 g, 175 mmol), glacial acetic acid
(56 mL), conc. H3PO4 (60 mL), and conc. HCl (63 mL) in
dioxane (200 mL) was stirred at 80 °C for 12 h. The
mixture was concentrated to 100 mL, poured into an ice/
water mixture (200 mL) and extracted with CHCl3
(3 9 40 mL). The combined organic layer was washed
with H2O, dried over Na2SO4 and the solvent was evapo-
rated under reduced pressure to give 8. Yield 4.38 g (85%),
m.p. 215 °C.
Â
Ã
IR m ðcmꢁ1Þ : 3172 (–OH), 684 (C–Cl); 1HNMR
KBr
max
[CDCl3 (d ppm)] : 3.67 (s, 8H, Ar–CH2–Cl), 3.86 (d, 4H,
Ar–CH2–Ar, J = 12.4 Hz), 4.49 (d, 4H, Ar–CH2–Ar,
J = 12.4 Hz), 7.1 (m, 8H, Ar–H), 10.25 (s, 4H, ArOH);
FAB MS, m/z: 618 (M?); Anal calc.(%) for C32H28Cl4O4:
C, 62.15; H, 4.56; Found C, 61.89; H, 4.51.
Â
Ã
KBr
IR m ðcmꢁ1Þ : 1742 (CO–O–Ar), 3254 (N–H);
max
1HNMR [CDCl3 (d ppm)]: 0.96 (s, 36H, –C(CH3)3), 2.89
(s, 8H, CO–CH2–NH), 3.91 (d, 4H, Ar–CH2–Ar,
J = 12.4 Hz), 4.14 (s, 4H, Ar–NH–CH2), 4.36 (d, 4H, Ar–
CH2–Ar, J = 12.4 Hz), 6.59 (m, 4H, N=CH–CH), 6.75
(dd, 4H, N–C(NH)=CH), 7.06 (m, 8H, Ar–H), 7.36 (m, 4H,
N–C(NH)=CH–CH), 8.11 (m, 4H, N=CH–CH); FAB MS,
m/z: 1185 (M?); Anal calc.(%) for C72H80N8O8: C, 72.95;
H, 6.80; N, 9.45; Found C, 72.55; H, 6.71; N, 9.39.
25,26,27,28-Tetrapropoxy -p-chloromethylcalix[4]
arene (9)
A total of 6.18 g (10.0 mmol) of 8 was dissolved in
anhydrous acetone followed by 21 g (200 mmol) of K2CO3
and 34 g (200 mmol) of 1-iodopropane were added. The
reaction mixture was heated for 24 h at reflux temperature
followed by cooled at room temperature and filtered. The
filtrate was diluted with water and extracted with chloro-
form. The organic layer was dried over MgSO4 and con-
centrated to dryness. The residual solid was subjected to
column chromatography [silica gel, CHCl3/acetone (15/1
to 2/1)]. Yield 6.7 g (85%), mp 189–190 °C.
25,26,27,28-Tetra[(1H-1,2,4-triazol-1-ylacetyl)oxy]-p-
tert-butylcalix[4]arene (6)
It was synthesized by treating 1,2,4-triazole and 2, as per
the procedure for 5. Yield 0.66 g (61%), m.p. 206 °C.
max
Â
Ã
Â
Ã
1
1
KBr
KBr
max
IR m ðcmꢁ1Þ : 1741 (CO–O–Ar); HNMR [CDCl3 (d
IR m ðcmꢁ1Þ : 675 (C–Cl); HNMR [CDCl3 (d ppm)]
ppm)]: 0.88 (s, 36H, –C(CH3)3), 2.89 (s, 8H, CO–CH2–N),
3.67 (d, 4H, Ar–CH2–Ar, J = 12.4 Hz), 4.36 (d, 4H, Ar–
CH2–Ar, J = 12.4 Hz), 7.25 (m, 8H, Ar–H), 8.15 (s, 8H,
N–CH=N); FAB MS, m/z: 1085 (M?); Anal calc.(%) for
C60H68N12O8: C, 66.40; H, 6.32; N, 15.49; Found C, 66.13;
H, 6.26; N, 15.39.
: 0.81(t, 8H, CH2–CH2–CH3), 1.18 (m, 8H, CH2–CH2–
CH3), 3.52 (t, 8H, O–CH2–CH2), 3.71 (s, 8H, Ar–CH2–Cl),
3.81 (d, 4H, Ar–CH2–Ar, J = 12.4 Hz), 4.44 (d, 4H, Ar–
CH2–Ar, J = 12.4 Hz), 7.09 (m, 8H, Ar–H); FAB MS, m/z:
786 (M?); Anal calc.(%) for C44H52Cl4O4: C, 67.18; H,
6.66; Found C44H52Cl4O4: C, 66.87; H, 6.59.
25,26,27,28-Tetrahydroxycalix[4]arene (7)
1H-1,2,4-Triazole (10)
It was synthesized as per the literature procedure [26].
It was synthesized as per the literature procedure [25].
Yield 68%, m.p. 298 °C.
max
Yield 2.76 g (55%), m.p. 120 °C.
max
Â
Ã
Â
Ã
1
1
KBr
KBr
IR m ðcmꢁ1Þ : 3168 (–OH); HNMR [CDCl3 (d ppm)] :
IR m ðcmꢁ1Þ : 2700-2900 (N–H); HNMR [CDCl3 (d
3.86 (d, 4H, Ar–CH2–Ar, J = 12.7 Hz), 4.58 (d, 4H, Ar–
CH2–Ar, J = 12.7 Hz), 7.22 (m, 8H, Ar–H), 10.39 (s, 4 H,
ArOH); FAB MS, m/z: 424 (M?); Anal calc.(%) for
C28H24O4: C, 79.22; H, 5.70; Found C, 78.88; H, 5.65.
ppm)] : 8.32 (s, 2H, –NH–CH=N), 13.42 (s, H, N–NH–
CH); FAB MS, m/z: 69 (M?); Anal calc.(%) for C2H3N3:
C, 34.78; H, 4.38; N, 60.84; Found C, 29.63; H, 4.34; N,
60.62.
123

J Incl Phenom Macrocycl Chem (2010) 68:369–379
377
25,26,27,28-Tetrapropoxy-p-(pyridn-2-
ylamino)methylcalix[4]arene (11)
removal of solvent under reduced pressure, 300 mL of
water was added followed by stirred additional 5 min. The
solid organic product was separated, washed with methanol
(3 9 100 mL) and recrystallized from acetone. Yield
4.68 g (79%), m.p. 165 °C.
It was synthesized by reacting 9 with 2-amino pyridine, as
per the procedure for 5. Yield (60%), m.p. 222 °C.
max
Â
Ã
1
1HNMR [CDCl3 (d ppm)]: 0.86 (t, 12H, CH2–CH2–
CH3), 1.18 (m, 8H, CH2–CH2–CH3), 3.52 (t, 8H, O–CH2–
CH2), 3.79 (d, 4H, Ar–CH2–Ar, J = 12.7 Hz), 4.52 (d, 4H,
Ar–CH2–Ar, J = 12.7 Hz), 6.92 (m, 12H, Ar–H); FAB
MS, m/z: 592 (M?); Anal calc.(%) for C40H48O4: C, 81.04;
H, 8.16; Found C, 80.64; H, 8.11.
KBr
IR m ðcmꢁ1Þ : 3280 (N–H); HNMR [CDCl3 (d ppm)]
: 0.85 (t, 12H, CH2–CH2–CH3), 1.25 (m, 8H, CH2–CH2–
CH3), 3.15 (s, 8H, Ar–CH2–NH), 3.67 (t, 8H, O–CH2–
CH2), 3.91 (d, 4H, Ar–CH2–Ar, J = 12.4 Hz), 4.14 (s, 4H,
Ar–NH–CH2), 4.35 (d, 4H, Ar–CH2–Ar, J = 12.4 Hz),
6.59 (m, 4H, N = CH–CH), 6.75 (dd, 4H, N–C(NH)=CH),
7.06 (m, 8H, Ar–H), 7.36 (m, 4H, N–C(NH)=CH–CH),
8.02 (m, 4H, N=CH–CH); FAB MS, m/z: 1017 (M?); Anal
calc.(%) for C64H72N8O4: C, 75.56; H, 7.13; N, 11.01;
Found C, 75.24; H, 7.01; N, 10.92.
25,26,27,28-Tetrapropoxy-p-acetylcalix[4]arene (15)
In a 250 mL round bottomed flask, aluminum chloride
(5.13 g, 38.4 mmol) was added to 100 mL of CH2C12, fol-
lowed by acetyl chloride (24.95 g, 108 mmol). To this, 4.15 g
(7 mmol) of 14, dissolved in 70 mL CH2C12, was added
dropwise with stirring and then the reaction mixture stirred for
5 h at room temperature. After that, 30 mL of water followed
by 34.65 mL of 1 N HC1 was added and product was
extracted with 150 mL of CH2C12. The CH2C12 layer was
separated, evaporated and obtained solid was purified with
column chromatography (300 g silica gel, gradient of CHCl3/
acetone (20/1 to 3/1). Yield 2.4 g (45%), m.p.195 °C.
25,26,27,28-Tetrapropoxy-p-(1H-1,2,4-triazol-1-
yl)methylcalix[4]arene (12)
It was synthesized by reacting 9 with 1,2,4-triazole, as per
the procedure for 5. Yield (58%), m.p. 219 °C.
1HNMR [CDCl3 (d ppm)] : 0.88 (t, 12H, CH2–CH2–
CH3), 1.21 (m, 8H, CH2–CH2–CH3), 2.89 (s, 8H, Ar–CH2–
N), 3.57 (t, 8H, O–CH2–CH2), 3.83 (d, 4H, Ar–CH2–Ar,
J = 12.4 Hz), 4.36 (d, 4H, Ar–CH2–Ar, J = 12.4 Hz), 7.17
(m, 8H, Ar–H), 8.14 (s, 8H, N–CH=N); FAB MS, m/z: 917
(M?); Anal calc.(%) for C52H60N12O4: C, 68.10; H, 6.59;
N, 18.33; Found C, 67.81; H, 6.51; N, 18.22.
Â
Ã
IR m ðcmꢁ1Þ : 1710 (C=O); 1HNMR [CDCl3 (d
KBr
max
ppm)]: 0.79 (t, 12H, CH2–CH2–CH3), 1.16 (m, 8H, CH2–
CH2–CH3), 2.22 (m, 12H, CO–CH3), 3.57 (t, 8H, O–CH2–
CH2), 3.86 (d, 4H, Ar–CH2–Ar, J = 13.5 Hz), 4.49 (d, 4H,
Ar–CH2–Ar, J = 13.5 Hz), 7.14 (m, 8H, Ar–H); FAB MS,
m/z: 760 (M?); Anal calc.(%) for C48H56O8: C, 75.76; H,
7.42; Found C, 75.51; H, 7.35.
25,26,27,28-Tetrapropoxy-p-(1H-1,2,4-triazol-1-
ylsulfanyl)methylcalix[4] arene (13)
It was synthesized by reacting 9 with 1,2,4-triazole-3-thiol,
as per the procedure for 4. Yield 54% m.p. 235 °C.
1HNMR [CDCl3 (d ppm)] : 0.84 (t, 12H, CH2–CH2–
CH3), 1.15 (m, 8H, CH2–CH2–CH3), 2.38 (s, 8H, Ar–CH2–
S), 3.60 (t, 8H, O–CH2–CH2), 3.91 (d, 4H, Ar–CH2–Ar,
J = 12.4 Hz), 4.33 (d, 4H, Ar–CH2–Ar, J = 12.4 Hz), 7.11
(m, 8H, Ar–H), 8.38 (s, 4H, –NH–CH=N), 13.02 (s, 4H, N–
NH–CH); FAB MS, m/z: 1045 (M?); Anal calc.(%) for
C52H60N12O4S4: C, 59.74; H, 5.79; N, 16.08; S, 12.27;
Found C, 59.49; H, 5.72; N, 15.89; S, 12.16.
25,26,27,28-Tetrapropoxy-p-carboxycalix[4]arene (16)
A fresh sodium hypobromite solution, prepared by adding
30.46 mg (191 mmol) of Br2 to 77 mL of aqueous NaOH
solution (23%), was cooled to 0 °C. To this, 2.28 g (3 mmol)
of 15 (dissolved in 350 mL of DMF) was added slowly
within 30 min. By adding subsequent 200 mL of DMF, it
was heated for 18 h at 80 °C. It was then cooled to room
temperature and quenched with 517 mL of 1 M HC1. A
solvent extraction was performed with 3 9 500 mL of
CHCl3. The chloroform layer was collected and evaporated
under reduced pressure by heating. The obtained residue was
washed by 3 9 200 mL of water and purified by column
chromatography; (300 g silica gel, CHC13/MeOH/H2O (65/
25/4). Colorless solid of 16 was obtained. Yield 1.3 g (33%),
m.p. 205 °C.
25,26,27,28-Tetrapropoxycalix[4]arene (14)
To a suspension of 4 g of NaH (100 mmol; washed with
3 9 90 mL of hexane) in 250 mL of anhydrous THF,
4.24 g of 7 (10 mmol) was added. The reaction mixture
was stirred for 10 min at reflux temperature, followed by 1-
iodopropane (17 g, 100 mmol) was added. The reaction
mixture was stirred for an additional 1 h at reflux tem-
perature, cooled to room temperature, and then quenched
by the dropwise addition of 7 mL of methanol. After the
Â
Ã
IR m ðcmꢁ1Þ : 2700 (COOH); 1HNMR [CDCl3 (d
KBr
max
ppm)]: 0.80 (t, 12H, CH2–CH2–CH3), 1.18 (m, 8H, CH2–
CH2–CH3), 3.53 (t, 8H, O–CH2–CH2), 3.86 (d, 4H, Ar–
CH2–Ar, J = 12.9 Hz), 4.57 (d, 4H, Ar–CH2–Ar,
123

378
J Incl Phenom Macrocycl Chem (2010) 68:369–379
Â
Ã
IR m ðcmꢁ1Þ : 1738 (COS); 1HNMR [CDCl3 (d
KBr
max
J = 12.9 Hz), 7.48 (m, 8H, Ar–H), 12.05 (m, 4H, COOH);
FAB MS, m/z: 842 (M?); Anal calc.(%) for C44H44Cl4O8:
C, 62.72; H, 5.26; Found C, 62.32; H, 5.22.
ppm)]: 0.88 (t, 12H, CH2–CH2–CH3), 1.25 (m, 8H, CH2–
CH2–CH3), 3.34 (t, 8H, O–CH2–CH2), 3.91 (d, 4H, Ar–
CH2–Ar, J = 12.4 Hz), 4.34 (d, 4H, Ar–CH2–Ar,
J = 12.4 Hz), 7.06 (m, 8H, Ar–H), 8.38 (s, 4H, –NH–
CH=N), 13.02 (s, 4H, N–NH–CH); FAB MS, m/z: 1101
(M?); Anal calc.(%) for C52H52N12O8S4: C, 56.71; H,
4.76; N, 15.26; S, 11.65; Found C, 56.42; H, 4.72; N,
15.16; S, 11.57.
25,26,27,28-Tetrapropoxy-p-(pyridn-2-
yl)carbonylcalix[4]arene (17)
In a 250 cc round bottomed flask, 0.84 g (1 mmol) of 16 was
taken followed by 0.6 mL (5 mmol) of SOCl2 was added.
The reaction mixture was stirred for 15 min at room tem-
perature. Now, the reaction mixture was suspended into
100 mL THF followed by 0.8 g (20 mmol) of NaOH and
1.88 g (20 mmol) of 2-aminopyridine was added. The
reaction mixture was refluxed for 20 h and reaction was
monitored by TLC (ethylacetate/xylene, 1:10). After the
completion of reaction, the remaining THF was removed
under reduced pressure by heating. The residue was dis-
tributed between chloroform/diluted aqueous 1 N HCl (100/
50 mL). The chloroform layer was separated and evaporated
to dryness. Obtained residue was purified by column chro-
matography (Alumina column; neutral); gradient of CHCl3/
acetone (20/1 to 3/1). Yield 0.73 g (58%), m.p. 192 °C.
Acknowledgements We thank Council of Scientific and Industrial
Research (CSIR), India for the financial support of this work through
project No. 01(1991)/05/EMR-II. We are also thankful to Central
Drug Research Institute, Lucknow for providing spectroanalytical
facilities.
References
¨
1. Bohmer, V.: Calixarenes: macrocycles with (almost) unlimited
possibilities. Angew. Chem. Int. Ed. 34, 713–745 (1995)
2. Gutsche C.D.: Calixarenes revisited. In: Stoddart J.F. (ed) RSC
monographs in supramolecular chemistry. Royal Society of
Chemistry, Cambridge, UK (1998)
3. McKervey M.A., Schwing-Weill M.J., Arnaud-Neu F. In: Gokel
GW (ed.) Comprehensive Supramolecular Chemistry, vol. 1, pp
537–603. Pergamon, Oxford, UK (1996)
4. Schwing-Weill, M.J., Arnaud-Neu, F., McKervey, M.A.: Modu-
lation of the cation complexing properties in the lower rim of
chemically modified calixarene series. J. Phys. Org. Chem. 5,
496–501 (1992)
5. Casnati, A., Pochini, A., Ungaro, R., Bocchi, C., Ugozzoli, F.,
Egberink, R.J.M., Struijk, H., Lugtenberg, R., De Jong, F.,
Reinhoudt, D.N.: 1,3-Alternate calix[4]arenecrown-5 conformers:
new synthetic ionophores with better K?/Na? selectivity than
valinomycin. Chem. Eur. J. 2, 436–445 (1996)
Â
Ã
1
KBr
max
IR m ðcmꢁ1Þ : 3280 (N–H), 1738 (CONH); HNMR
[CDCl3 (d ppm)]: 0.87 (t, 12H, CH2–CH2–CH3), 1.19 (m,
8H, CH2–CH2–CH3), 3.67 (t, 8H, O–CH2–CH2), 3.94 (d,
4H, Ar–CH2–Ar, J = 12.4 Hz), 4.16 (s, 4H, Ar–NH–CO),
4.36 (d, 4H, Ar–CH2–Ar, J = 12.4 Hz), 6.59 (m, 4H,
N=CH–CH), 6.75 (dd, 4H, N–C(NH)=CH), 7.14 (m, 8H,
Ar–H), 7.44 (m, 4H, N–C(NH)=CH–CH), 8.08 (m, 4H,
N=CH–CH); FAB MS, m/z: 1331 (M?); Anal calc.(%) for
C78H78N10O11: C, 70.36; H, 5.90; N, 10.52; Found C,
70.11; H, 5.86; N, 10.47.
6. Ungaro, R., Casnati, A., Ugozzoli, F., Pochini, A., Dozol, J.F.,
Hill, C., Rouquette, H.: Dialkoxycalix[4]arenecrowns-6 in 1,3-
alternate conformation: cesium selective ligand that exploit cat-
ion–arene interactions. Angew. Chem. Int. Ed. 33, 1506–1509
(1994)
25,26,27,28-Tetrapropoxy-p-(1H-1,2,4-triazol-1-
yl)carbonylcalix[4]arene (18)
7. Dozol, J.F., Simon, N., Lamare, V., Rouquette, H., Eymard, S.,
Tournois, B., De Marc, D., Macias, R.M.: A solution for cesium
removal from high-salinity acidic or alkaline liquid waste: the
crown calix[4]arenes. Sep. Sci. Technol. 34, 877–909 (1999)
8. Halouani, H., Dumazet-Bonnamour, I., Lamartine, R.: Synthesis
of novel chromogenic bi- and tri-functionalized calix[4]arenes.
Tetrahedron Lett. 43, 3785–3788 (2002)
9. Halouani H., Dumazet-Bonnamour I., Duchamp C., Bavoux C.,
Ehlinger N., Perrin M., Lamartine R.: Synthesis, conformations
and extraction properties of new chromogenic calix[4]arene
amide derivatives. Eur. J. Org. Chem. 24, 4202–4210 (2002)
10. Oueslati, F., Dumazet-Bonnamour, I., Lamartine, R.: New chro-
mogenic azocalix[4]arene podands incorporating 2,2-bipyridyl
subunits. New J. Chem. 27, 644–647 (2003)
It was synthesized by reacting 16 with thionyl chloride
followed by 1,2,4-triazole, as per the procedure for 17.
Yield (65%), m.p. 232 °C.
Â
Ã
IR m ðcmꢁ1Þ : 1738 (CONH); 1HNMR [CDCl3 (d
KBr
max
ppm)]: 0.84 (t, 12H, CH2–CH2–CH3), 1.21 (m, 8H, CH2–
CH2–CH3), 3.35 (t, 8H, O–CH2–CH2), 3.67 (d, 4H, Ar–CH2–
Ar, J = 12.4 Hz), 4.33 (d, 4H, Ar–CH2–Ar, J = 12.4 Hz),
7.22 (m, 8H, Ar–H), 8.20 (s, 8H, N–CH=N); FAB MS, m/z:
973 (M?); Anal calc.(%) for C52H52N12O8: C, 64.19; H,
5.39; N, 17.27; Found C, 63.85; H, 5.52; N, 17.18.
25,26,27,28-Tetrapropoxy-p-(1H-1,2,4-triazol-3-
ylsulfanyl)carbonylcalix [4]arene (19)
11. Oueslati, F., Dumazet-Bonnamour, I., Lamartine, R.: Synthesis of
new chromogenic 2,20-bithiazoylcalix[4]arenes. Tetrahedron
Lett. 42, 8177–8180 (2001)
12. Goodgame, D.M.L., Grachvogel, D.A., White, A.J.P., Williams,
D.J.: Diverse polymeric metal complexes formed by the ambid-
entate ligand 1-(40-pyridyl)pyridin-4-one. Inorg. Chim. Acta 348,
187–193 (2003)
It was synthesized by reacting 16 with thionyl chloride
followed by 1,2,4-triazole-3-thiol, as per the procedure for
17. Yield (60%), m.p. 212 °C.
123

J Incl Phenom Macrocycl Chem (2010) 68:369–379
379
13. Osz, K., Varnagy, K., Sovago, I., Lennert, L., Vargha, H.S.,
Sanna, D., Micera, G.: Equilibrium and structural studies on
transition metal complexes of amino acid derivatives containing
the bis(pyridin-2-yl)methyl residue. New J. Chem. 25, 700–706
(2001)
20. Sharma, P., Kumar, A., Rane, N., Gurram, V.: Hetero Diels–
Alder reaction: a novel strategy to regioselective synthesis of
pyrimido[4,5-d]pyrimidine analogues from Biginelli derivative.
Tetrahedron 61, 4237–4248 (2005)
21. Kumar, A., Sharma, P., Mandloi, A.: Synthesis of 25,26,27-
tris(ethoxycarbonylmethoxy)-28-
14. Schweinfurth D., Pattacini R., Strobel S., Sarkar B.: New 1,2,3-
triazole ligands through click reactions and their palladium and
platinum complexes. Dalton Trans. 9291–9297 (2009)
15. Mukai, H., Sohrin, Y.: 4,5-Bis(diphenylphosphinoyl)-1,2,3-tria-
zole ligand: studies on metal complex formations in liquid–liquid
distribution systems. Inorg. Chim. Acta 362, 4526–4533 (2009)
16. Meng Z. S., Yun L., Zhang W. X., Hong C. G., Herchel R., Ou Y.
C., Leng J. D., Peng M. X., Lina Z. J., Tong M. L. (2009)
Reactivity of 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole, struc-
tures and magnetic properties of polynuclear and polymeric
Mn(II), Cu(II) and Cd(II) complexes. Dalton Trans. 10284–10295
17. Drabent, K., Ciunik, Z.: Copper(I) complexes with N4-func-
tionalized-1,2,4-triazole and bidentate spacer ligands: from one-
to three-dimensional architecture. Cryst. Growth Des. 9, 3367–
3375 (2009)
18. Chen, D., Wang, D.Z., Zhang, J.B., Cao, L.H.: Synthesis, struc-
tures of novel zinc and copper compounds based on pyridazi-
no[3,2-c]1,2,4-triazole derivatives. J. Mol. Struct. 920, 342–349
(2009)
19. Sharma, P., Kumar, A., Rane, N.: An expedient synthesis of
novel, fused pyrimido[4,5-d]pyrimidine and pyrimido[5,4-
e][1,2,4]triazolo[4,3-c]pyrimidine analogues from 4-amino-2,6-
dichloropyrimidine. Heteroat. Chem. 17, 245–253 (2006)
(substitutedoxycarbonylmethoxy)calixarene: first example of
calix-imidazole/benzimidazole analogue. Synth. Commun. 33,
373–380 (2003)
22. Kumar, A., Sharma, P., Chandel, L.K., Kalal, B.L.: Synergistic
extraction and spectrophotometric determination of palladium(II),
iron(III), and tellurium(IV) at trace level by newly synthesized p-
[4-(3,5-dimethylisoxazolyl)azophenylazo]calix(4)arene. J. Inclu-
sion Phenom. Macrocycl. Chem. 61, 335–342 (2008)
23. Kumar, A., Sharma, P., Chandel, L.K., Kalal, B.L., Mate, S.K.:
Synergistic solvent extraction of copper, cobalt, rhodium and
iridium into 1,2-dichloroethane at trace level by newly synthe-
sized 25,26,27,28-tetrahydroxy-5,11,17,23-tetra-[4-(N-hydroxyl-
3-phenylprop-2-enimidamido)phenylazo]calix[4]arene. J. Inclu-
sion Phenom. Macrocycl. Chem. 62, 285–292 (2008)
24. Gutsche, C.D., Iqbal, M., Stewart, D.: Synthesis procedures for p-
tert-butylcalix[4]arene. J. Org. Chem. 51, 742–745 (1986)
25. Ainsworthl C.: Org Synth 40, 99–102 (1960)
26. Gutsche, C.D., Levine, J.A., Sujeeth, P.K.: Functionalized
calixarenes: the Claisen rearrangement route. J. Org. Chem. 50,
5802–5806 (1985)
123