Calix[4]arene-based Mannich and Schiff bases as versatile receptors for dichromate anion extraction: Synthesis and comparative studies

Article abstract of DOI:10.1016/j.tet.2012.08.015

A series of novel calix[4]arene-based Mannich (5 and 6) and Schiff base (9-11) receptors have been synthesized and characterized by various analytical techniques. Competitive two-phase extraction experiments of these novel calix[4]arene amine- and imine-c

Full text of DOI:10.1016/j.tet.2012.08.015

Tetrahedron 68 (2012) 8739e8745
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Calix[4]arene-based Mannich and Schiff bases as versatile receptors
for dichromate anion extraction: synthesis and comparative studies
*
Asli Sap, Begum Tabakci, Aydan Yilmaz
Selc¸ uk University, Department of Chemistry, 42075 Konya, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of novel calix[4]arene-based Mannich (5 and 6) and Schiff base (9e11) receptors have been
synthesized and characterized by various analytical techniques. Competitive two-phase extraction
experiments of these novel calix[4]arene amine- and imine-containing derivatives revealed a strong
affinity for dichromate anions ðCr2O27ꢀ=HCr2Oꢀ7 Þ. The protonated alkylinium form of 5, 6 and 9e11
proved to be effective extractants for transferring the dichromate anions from an aqueous into an
organic phase. Moreover, the extraction of dichromate anions by 5 and 9 in the presence of competitive
anions such as Fꢀ, Clꢀ, Brꢀ, NOꢀ3 , NO2ꢀ, PO43ꢀ and SO24ꢀ showed that 5 and 9 could be selective anion
receptors for dichromate anions in the presence of those anions.
Received 25 March 2012
Received in revised form 19 July 2012
Accepted 7 August 2012
Available online 14 August 2012
Keywords:
Calix[4]arene
Anion extraction
Mannich base
Schiff base
Ó 2012 Published by Elsevier Ltd.
Selectivity
1. Introduction
Cr(VI) mainly exists as dianions CrO24ꢀ and Cr2O72ꢀ. Due to their
oxide functionality these are known as oxyanions, and because of
Industrialization and population increases have enhanced
environmental degeneration. Industrial processing sites are
frequently polluted by mixtures of metals and organic com-
pounds. Among them, chromium compounds are widely used in
industrial applications, e.g., corrosion control, oxidation pro-
cesses, leather manufacture, electroplating, etc. These industries
discharge a significant concentration of chromium in aqueous
waste, which is responsible for a serious threat to microor-
ganisms in aquatic systems as well as human life in nearby
areas.1
that, they prefer hydrogen bonding sites. However, due to their
toxic effects, different conventional techniques for removing ex-
cessive amounts of toxic metal ions from wastewater including
chemical precipitation, membrane separation, reverse osmosis,
evaporation and electrochemical treatment, and solvent extraction
were employed.1 Among them, the solvent extraction technique is
commonly used. There have been reports of numerous complexing
agents to selective complex Cr(VI) in aqueous environment6e8 but
calixarenes9 have unique properties, which may make them more
suitable extractants.
In aqueous systems, the major oxidation states of chromium are
Cr(III) and Cr(VI) and the metal occurs frequently in chromate and
dichromate salts of alkali and heavy metals.2,3 The toxicity and
reactivity depend on the chemical form or oxidation state of
chromium. In trace amounts, Cr(III) is an essential nutrient for
humans and the mammals for their maintenance of normal glucose
tolerance and other metabolic processes.4 The exposure of Cr(VI) in
both occupational and environmental samples is highly known as
carcinogenic due to its solubility, high oxidation potential and
comparatively small size, which enables it to penetrate cell mem-
branes and cause damage to DNA.5
A calixarene is a macrocycle and/or cyclic oligomer product of
a phenol and a formaldehyde condensation reaction. In the field of
macrocyclic compounds, the calix[4]arene platform shows attrac-
tive organizational properties for the synthesis of calixarene de-
rivatives having suitable ligating sites to recognize various species
including cations, anions and neutral molecules. A variety of calix
[4]arene-based receptors that possess unusually-shaped cavities
have been prepared via ‘upper’ and ‘lower’ rim functionalization.
Calixarenes are applied in different fields of analytical as well as
material chemistry such as enzyme mimetics,10 ion sensitive elec-
trodes or sensors,11,12 catalysis,13,14 non-linear optics15 and HPLC
stationary phases.16 In addition, in nanotechnology, calixarenes are
used as a negative resist for high-resolution electron beam lithog-
raphy.17 The molecular recognition of anionic guest species by
positively charged or electron deficient neutral abiotic receptor
molecules is an area of intense current interest. The importance of
* Corresponding author. Tel.: þ90 332 2233866; fax: þ90 332 2412499; e-mail
address: aydan@selcuk.edu.tr (A. Yilmaz).
0040-4020/$ e see front matter Ó 2012 Published by Elsevier Ltd.
http://dx.doi.org/10.1016/j.tet.2012.08.015

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A. Sap et al. / Tetrahedron 68 (2012) 8739e8745
favourable amine, amide, or imide (eNH2/OCeNH/OC]N) hydro-
gen bonding interactions for anion binding has recently been
exploited in the design of calix[4]arene anion receptors,18e20 al-
though such host molecules are still relatively rare. Several studies
on anion coordination have been reported using calixarene-based
chelating units.18e20 For example, a few excellent approaches em-
phasized by Beer et al.18i,j regarding calixarene-based anion re-
ceptors, and the work highlighted by Gale19k,l for anion and ion-pair
receptor chemistry are complimentary studies in the field of anion
coordination.
We have also reported various dichromate anion receptors in
the literature. From previous studies, it can be concluded that the
calixarene derivatives having nitrogen donor atoms such as
amino- and imino-functionalized calixarenes are effective ligands
for dichromate anions due to their protonation and/or hydrogen
binding abilities in more acidic conditions. A cyclic imino de-
rivative of 4-tert-butylcalix[4]arene showed a high extraction
ability towards dichromate anions, and in a recent comparative
study between calix[4]arene amine and amides for the extraction
of oxyanions including dichromate anions, aminocalixarenes
yielded more anion extraction than the amide derivatives. As
a result, based on the previous studies,18e20 herein we report
further work regarding the design of calix[4]arene moieties for
the extraction of Cr(VI) form the aqueous phase. Thus, the present
work reports the synthesis of new calix[4]arene derivatives
(Schemes 1 and 2) with amino and imino ionophoric groups
(Mannich and Schiff base derivatives) and their comparative ex-
traction efficiencies towards dichromate anions from aqueous
media.
2. Results and discussion
2.1. Synthesis
The selectively functionalized calix[4]arene-based Mannich and
Schiff bases were prepared in order to evaluate comparative ex-
traction efficiencies towards the dichromate anions from aqueous
media. The targeted compounds were synthesized as shown in
Schemes 1 and 2. Compounds 1e4 and 7 were synthesized by
previously published procedures,21e25 while the rest of the com-
pounds 5, 6 and 8e11 reported in the present study are novel
according to the best of our knowledge.
The desired ligands were prepared by substituting the di-4-tert-
butylcalix[4]arene 4 at its upper rim (Mannich reaction) in THF,
DMF and AcOH with a secondary amine (N-benzylpiperazine or 1,4-
dioxa-8-azaspiro[4.5]decane) and formaldehyde to achieve the
cone conformer 5 and 6 in 44 and 51% yields, respectively. Com-
pound 6 was confirmed to be present in the cone conformation by
detailed study of its 1H NMR spectra (doublets at 3.32 ppm and
4.27 ppm, J¼12.3 Hz) whereas the conformation of 5 could not be
determined due to the peaks, which belong to its ArCH2Ar protons
overlapping with those of other eCH2e protons.
Compounds 1 and 7 were reported previously,21,23 while the
selective p-diformylation onto the upper rim of calix[4]arene de-
rivative was achieved to obtain compound 8 by a well-known
procedure.22 Compound 8 was treated with benzylamine, furfur-
ylamine and cyclohexylamine in a THF/MeOH mixture (1:1) to give
9e11, respectively. These new compounds (9e11) were confirmed
by the appearance of a new band in the IR spectra at 1640, 1637 and
(6)
(5)
Scheme 1. A schematic representation showing the synthesis pathway for calix[4]arene Mannich bases 5 and 6. (i) Benzoyl chloride, K2CO3, MeCN, 91%; (ii) AlCl3, toluene, 75%; (iii)
EtOH/H2O, NaOH, 90%; (iv) N-benzylpiperazine, THF/DMF, AcOH, HCHO, 44%; (v) 1,4-dioxa-8-azaspiro[4.5]decane, THF/DMF, AcOH, HCHO, 51%.

A. Sap et al. / Tetrahedron 68 (2012) 8739e8745
8741
Scheme 2. A schematic representation showing the synthesis pathway for calix[4]arene Schiff bases 9e11. (i) MeI, K2CO3, MeCN, 59%; (ii) HMTA, TFA, 71%; (iii) benzylamine, THF/
MeOH, 68%; (iv) furfurylamine, THF/MeOH, 41%; (v) cyclohexylamine, THF/MeOH, 46%.
1636 cmꢀ1 (C]N), respectively. The 1H NMR data confirm that
these compounds exist in the cone conformation due to the ap-
pearance of ArCH2Ar signals as doublets at 3.44 and 4.26
(J¼13.3 Hz), 3.44 and 4.25 (J¼13.3 Hz) and 3.37 and 4.18 ppm
(J¼13.3 Hz), respectively.
features and protonation of tert-amine and/or imine groups of 5, 6
and 9e11, as compared to 4 and 7, respectively.
Moreover, in acidic conditions, Na2Cr2O7 is converted into
H2Cr2O7, and after ionization in aqueous solution, it exists in the
Cr2O72ꢀ=HCr2O7ꢀ form. In strong acidic conditions, Cr2O27ꢀ and
Table 1
2.2. Two-phase solvent extraction
The extraction percentages (ꢁ0.1) of dichromate anions by the compounds 4e7 and
9e11a
The present study strategically demonstrates the comparative
efficiency of two-phase extraction for dichromate anions. A pre-
liminary evaluation of binding efficiencies of 4e7 and 9e11 for
chromium (VI) anions was carried out by solvent extraction from
water into dichloromethane in the pH range of 1.5e4.5. From the
two-phase solvent extraction results (Table 1), it is clear that the
starting materials 4 and 7 do not have significant extraction effi-
ciency towards the Cr2O72ꢀ=HCr2Oꢀ7 ions. However, on the conver-
sion of 4 into Mannich bases (Scheme 1, 5 and 6) and 7 into Schiff
bases (Scheme 2, 9e11) the extraction efficiency is significantly
enhanced. Such high extraction efficiency of calix[4]arene-based
Mannich and Schiff bases may be due to the more rigid structural
Ligand
pH
1.5
2.5
5.8
69.4
61.5
6.3
25.7
12.5
75.1
3.5
4.5
4.6
9.7
6.3
4b
5
6
7
9
11.2
80.7
81.0
15.8
85.3
66.4
91.5
d
36.4
30.4
3.5
4.2
<1.0
8.2
2.7
<1.0
<1.0
<1.0
10
11
a
Aqueous phase, [Na2Cr2O7]¼1.0ꢂ10ꢀ4 M; organic phase, dichloromethane,
[ligand]¼1.0ꢂ10ꢀ3 M, at 25 ꢃC, for 1 h.
b
Previously reported [Ref. 20d].

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A. Sap et al. / Tetrahedron 68 (2012) 8739e8745
HCr2Oꢀ7 dimers become predominant as the Cr(VI) form; the pKa
values of these are reported as 0.74 and 6.49, respectively. However,
at pH<6, the oxyanions’ structure changes from the monomeric
CrO24ꢀ to the dimeric HCr2Oꢀ7 . These oxyanions have significant
potential for the hydrogen bonding to the host molecule.26 It is also
reported20 that calix[4]arenes with nitrogen functionality such as
pyridine, crown amide and imines are effective extractants for
oxyanions. For this purpose, in the present study, we have designed
calix[4]arene-based derivatives possessing amino and imine
groups (5, 6 and 9e11) at the upper rim for the comparative study.
Furthermore, from the extraction results it is concluded that for the
Mannich bases 5 and 6 and Schiff bases 9e11, more or less the same
extraction results were observed at lower pH. As the pH of the
solution increases, the percentage extraction decreases, which may
be due to decreasing the concentration of proton in the solution.
Furthermore, from the extraction results, it can be concluded that
the aromaticity of binding sites (benzyl groups) in 9 causes a neg-
ative effect on dichromate anion extraction when compared with
11 having non-aromatic binding sites (cyclohexyl group).
1,75
1,25
0,75
0,25
-0,25
-0,75
5
6
9
10
11
-3,70
-3,50
-3,30
-3,10
-2,90
log[L]
Fig. 1. log D versus log [L] for the extraction of dichromate anions by the ligands 5, 6
and 9e11 from an aqueous phase into dichloromethane at 25 ꢃC and pH 1.5.
To gain a deeper insight into the complexation process, the
extraction data for 5, 6 and 9e11 were also evaluated by using the
classical slope analysis method. Assuming the extraction of an an-
ion (A) by the anion receptor (L) according to the following
equilibrium:
them. Furthermore, it is understood that the equilibrium is pH
dependent. At higher pH, the OHꢀ ions compete with dichromate
anion for the exchange sites on the ligands. The dichromate anions
can be released under basic conditions. Thus, these calixarene de-
rivatives may be employed as reusable extractants. Moreover, the
interaction mechanism between ligands and dichromate anions
can be inferred from log D versus log [L] plot results. So, the pro-
posed interactions of the Mannich and Schiff bases derivatives of
calix[4]arene (5, 6 and 9e11) with dichromate anions are shown in
Schemes 3 and 4.
Moreover, in order to understand the selectivity of dichromate
anion extraction by 5 and 9 (they were selected as typical examples
of Mannich and Schiff base derivatives) in the presence of com-
petitive anions the extraction studies were also carried out using an
equimolar amount of the sodium salts of different anions such as
Fꢀ, Clꢀ, Brꢀ, NO3ꢀ, NOꢀ2 , PO43ꢀ and SO24ꢀ. The results illustrated in
Fig. 2 indicate that the extraction of dichromate anions by 5 and 9 is
a little affected by the presence of these anions. However, nitrate
anions have little effect. Nevertheless, it can be considered that the
removal of dichromate anions in a two-phase extraction system by
5 and 9 can still occur in a somewhat selective manner in the
presence of these competitive anions.
À
Á
nðLÞorg þ nðAÞaq# ðLÞn; ðAÞn
(1)
org
The extraction constant Kex is then defined by:
ÂÀ
Á Ã
ðLÞn; ðAÞ
½Aꢄaq½Lꢄorg
n
n
org
Kex
¼
(2)
(3)
n
Eq. 2 can be re-written as:
log DA ¼ log Kex þ n log½Lꢄorg
where DA is defined as ratio of the analytical concentration of the
anion (A) in both phases:
DA ¼ ½Aꢄorg=½Aꢄaq
(4)
Consequently, a plot of log D versus log [L] yields a straight line
with a slope for the determination of the stoichiometry of the
extracted dichromate anions at different concentrations, where [L]
is defined as the analytical concentration of the ligand in the or-
ganic phase.
3. Conclusions
In conclusion, the present study describes a series of new de-
rivatives of calix[4]arene as Mannich and Schiff bases. The di-
chromate anion-selective extraction behaviour of 5, 6, 9e11 and
their starting materials (4 and 7) suggest that the Mannich (5 and 6)
and Schiff base (9e11) derivatives of calix[4]arene are efficient
ionophores for the extraction of dichromate anions from an aque-
ous to an organic phase at lower pH. Additionally, the selectivity
experiments demonstrated that the extraction of dichromate an-
ions by 5 and 9 was not affected by the presence of some selected
anions such as Fꢀ, Clꢀ, Brꢀ, NO3ꢀ, NOꢀ2 , PO43ꢀ and SO24ꢀ and their
mixture. Consequently, we have reported efficient and selective
calix[4]arene-based anion receptors bearing amine and imine units
for dichromate anions. The study may find applicability in various
fields of material science.
Fig. 1 describes the dichromate anion extraction into dichloro-
methane at different concentrations of ligands 5, 6 and 9e11, which
display a linear relationship between log D versus log [L] with
a slope roughly equal to 1.19, 1.15, 1.05, 0.92 and 0.86, respectively.
The log D versus log [L] plot results suggest that ligands 5, 6 and
9e11 bind to dichromate anions in a 1:1 mode under the experi-
mental conditions according to Eq. 1. Moreover, the logarithmic
extraction constants for dichromate anions with these ligands (5, 6
and 9e11) were determined. According to these assumptions, the
extraction constant (Kex) has been calculated by using Eq. 3. The
calculation of this constant values lead to log Kex (ꢁ0.2)¼4.3, 4.1,
3.4, 4.0 and 3.7, respectively.
To understand the extraction phenomenon, different experi-
ments were evaluated and it was observed that Mannich and Schiff
bases derivatives of calix[4]arene (5, 6 and 9e11) have an electron-
accepting nature in an acidic medium and the electron-donating
nature of dichromate anions, the hydrogen bonding could be
preferentially considered. For example, a dichromate anion may
attach itself to positively charged tert amine and/or imine groups
(alkylinium moieties), which can accept a pair of electrons from the
dichromate anion and have forming a hydrogen bond between
4. Experimental section
4.1. General
€
Melting points were determined using a Buchi B-540 melting-
point apparatus in a sealed capillary tube and or uncorrected. 1H

A. Sap et al. / Tetrahedron 68 (2012) 8739e8745
8743
R
R
O
O
(6) R:
N
(5) R:
N
N
HO
OH
HO OH
A
A
O
O
O
O
H
H
N
+
N
+
A
A
N
N
N
N
H
H
H
H
HO
OH
HO OH
HO
OH
HO OH
Scheme 3. Proposed interactions of 5 and 6 with dichromate anions at 25 ꢃC and pH 1.5.
NMR spectra were recorded on a Bruker 400 MHz spectrometer in
CDCl3/DMSO-d6 with TMS as the internal standard. IR spectra were
obtained on a Perkin Elmer 1605 FTIR spectrophotometer as KBr
pellets. UVevisible spectra were obtained on a Shimadzu 160A
UVevisible recording spectrophotometer. Elemental analyses were
performed using a Leco CHNS-932 analyzer. FABMS spectra were
taken on a Varian MAT 312 spectrometer. An Orion 420A pH meter
was used for the pH measurements. Analytical TLC was performed
using Merck prepared plates (silica gel 60 F254 on aluminium). The
chromatographic separations were performed on a Merck Silica Gel
60 (230e400 mesh). All reactions were conducted under a nitrogen
atmosphere. All starting materials and reagents used were of
standard analytical grade from Fluka, Merck and SigmaeAldrich,
and used without further purification. The commercial grade sol-
vents were distilled and stored over molecular sieves. The drying
agent employed was anhydrous sodium sulfate. Anions were used
as their sodium salts in the extraction studies. All aqueous solutions
were prepared with deionized water that had been passed through
a Millipore milli-Q Plus water purification system.
products were dried in vacuo and recrystallized from chloroform/
methanol to give pure 5 and 6.
4.2.1.1. 5,17-Di-tert-butyl-11,23-bis[(N-benzylpiperazino)methyl-
25,26,27,28-tetrahydroxycalix[4]arene (5). This compound was
prepared with N-benzylpiperazine as described in general pro-
cedure above. Yield: 1.87 g (44%). Mp: 116 ꢃC. IR (KBr, cmꢀ1): 3165,
2951, 1481, 1455, 1283, 1199, 1135, 1011, 737. 1H NMR (CDCl3):
d 1.20
(s, 18H, tBu), 2.38 (br s, 16H, NCH2CH2), 3.22 (s, 4H, ArCH2N),
3.42e3.60 (overlapped, 8H, ArCH2Ar and ArCH2N), 4.09 (d,
J¼13.3 Hz, 4H, ArCH2Ar), 6.98 (s, 4H, ArH), 7.11 (m, 14H, ArH). 13
C
NMR (CDCl3):
d 147.9, 146.7, 144.6, 137.8, 131.2, 129.7, 129.3, 128.9,
128.2, 127.7, 127.1, 125.9, 63.1, 62.5, 53.1, 52.9, 34.1, 32.2, 31.5. FABMS
m/z: 936.07 (MþNa)þ. Anal. Calcd for C60H72N4O4 (913.24): C,
78.91; H, 7.95; N, 6.13. Found: C, 78.83; H, 7.90; N, 6.12.
4.2.1.2. 5,17-Di-tert-butyl-11,23-bis[(1,4-dioxa-8-azaspiro[4.5]
decanyl)methyl]-25,26,27,28-tetrahydroxycalix[4]arene
(6). This
compound was prepared with 1,4-dioxa-8-azaspiro[4.5]decane as
described in general procedure above. Yield: 2.0 g (51%). Mp:
209 ꢃC. IR (KBr, cmꢀ1): 3230, 2949, 1479, 1452, 1299, 1147, 1094,
4.2. Synthesis of anion receptors
872, 792, 667. 1H NMR (CDCl3):
8H, CH2NCH2), 2.42 (br s, 8H, NCH2), 3.32 (s, 4H, ArCH2N), 3.40 (d,
J¼12.3 Hz, 4H, ArCH2Ar), 3.95 (s, 8H, OCH2), 4.21 (d, J¼12.3 Hz, 4H,
ArCH2Ar), 6.98 (s, 4H, ArH), 7.22 (s, 4H, ArH). 13C NMR (CDCl3):
d
1.20 (s, 18H, tBu), 1.63 (t, J¼5.5 Hz,
Compounds 1e4 and 7 (Schemes 1 and 2) were synthesized by
previously published procedures,21e25 while the rest of the com-
pounds 5, 6 (Scheme 1) and 8e11 (Scheme 2) are reported in the
present study.
d
148.3, 146.9, 144.9, 130.1, 128.5, 128.1, 127.8, 126.2, 64.5, 62.3,
51.6, 34.8, 34.4, 32.5, 31.7. FABMS m/z: 869.91 (MþNa)þ. Anal.
Calcd for C52H66N2O8 (847.09): C, 73.73; H, 7.85, N, 3.31. Found: C,
73.65; H, 7.80; N, 3.30.
4.2.1. General procedure for Mannich reaction. To a solution of 4
(1.50 g; 4.6 mmol) in a mixture of 70 mL of THF/DMF (5:2) were
added acetic acid (2.66 mL), respective amine (11.5 mmol; N-ben-
zylpiperazine or 1,4-dioxa-8-azaspiro[4.5]decane) and aqueous
formaldehyde (0.31 mL, 37%), and the reaction mixture was stirred
for 24 h at room temperature. The solvent was removed in vacuo
and the residue was dissolved in deionized water (75 mL). The
aqueous solution was extracted twice with diethyl ether (50 mL)
and then neutralized with aqueous K2CO3 solution (10%). The
precipitate that formed was removed by suction filtration. The
4.2.2. 5,17-Di-tert-butyl-11,23-diformyl-26,28-dimethoxycalix[4]
arene-25,27-diol (8). Compound 7 (1.0 g, 1.48 mmol) and hexa-
methylenetetramine (HMTA, 8.5 g, 60.7 mmol) were taken in tri-
fluoroacetic acid (TFA, 60 mL). The reaction mixture was refluxed
until the starting material (8) had disappeared (TLC). On comple-
tion, the mixture was quenched with cold water and extracted with
chloroform. The organic layer was washed with water and dried

8744
A. Sap et al. / Tetrahedron 68 (2012) 8739e8745
R
R
(11) R:
(9) R
:
N
N
HO
OH
MeO OMe
O
(10) R':
N
A
A
A
A
A
N
N
H
N
N
H
H
H
HO
OH
MeO OMe
OH
HO
MeO OMe
O
O
A
H
N
N
H
OH
HO
MeO OMe
Scheme 4. Proposed interactions of 9e11 with dichromate anions at 25 ꢃC and pH 1.5.
4H, AreCH2eAr), 3.90 (s, 6H, OCH3), 4.18 (d, J¼13.3 Hz, 4H,
AreCH2eAr), 6.75 (s, 4H, ArH), 7.57 (s, 4H, ArH), 7.54 (s, 2H, OH),
5 (amine derivative)
9 (imine derivative)
100
9.72 (s, 2H, CHO). 13C NMR (CDCl3):
d 191.1, 159.3, 151.1, 148.1, 131.1,
80
60
40
20
0
130.8, 128.9, 128.5, 126.0, 63.7, 34.1, 31.1, 30.3. FABMS m/z: 617.56
(MþNa)þ. Anal. Calcd for C38H42O6 (594.73): C, 76.74; H, 7.12.
Found: C, 76.55; H, 6.98.
4.2.3. General procedure for Schiff base reaction. To a solution of 8
(1 mmol) in 50 mL of THF/methanol (1:1) required respective
amine (benzylamine or furfurylamine or cyclohexylamine) was
added and the mixture was refluxed for 3 d. The solvent was then
evaporated under reduced pressure and the remaining solid was
washed with water and then with methanol. The crude product
was filtered and recrystallized from chloroform/methanol to yield
pure products 9e11.
Fig. 2. The dichromate anion extraction results (ꢁ0.1) by 5 and 9 in the presence of
competitive anions (Fꢀ, Clꢀ, Brꢀ, NOꢀ3 , NOꢀ2 , PO43ꢀ and SO24ꢀ
) and their mixture.
[Na2Cr2O7]¼1.0ꢂ10ꢀ4 M; [sodium salt of competitive anions]¼1.0ꢂ10ꢀ4 M; [ligand]¼
4.2.3.1. 5,17-Di-tert-butyl-11,23-dibenzylimino-26,28-dimethoxy-
calix[4]arene-25,27-diol (9). This compound was prepared with
benzylamine as described in general procedure above. Yield: 0.42 g
(68%). Mp: 263e265 ꢃC. IR (KBr, cmꢀ1): 1640 (C]N). 1H NMR
1.0ꢂ10ꢀ3 M, at 25 ꢃC and pH 1.5.
over Na2SO4. Evaporation of the solution gave a white solid residue,
which was crystallized from a mixture of acetone/hexane (2:3) to
give 8. Yield: 0.65 g (71%). Mp: 310e314 ꢃC. IR (KBr, cmꢀ1): 1678
(CDCl3):
d
0.97 (s, 18H, tBu), 3.44 (d, J¼13.3 Hz, 4H, ArCH2Ar),
(C]O). 1H NMR (DMSO-d6):
d
0.88 (s, 18H, tBu), 3.42 (d, J¼13.3 Hz,
3.95 (s, 6H, OCH3), 4.26 (d, J¼13.3 Hz, 4H, ArCH2Ar), 4.82 (s, 4H,

A. Sap et al. / Tetrahedron 68 (2012) 8739e8745
8745
NCH2), 6.84 (s, 4H, ArHcalix), 7.25e7.33 (m, 10H, ArHbenzyl), 7.55 (s,
4H, ArHcalix), 7.88 (s, 2H, OH), 8.27 (s, 2H, HCN). 13C NMR (CDCl3):
162.3, 155.8, 151.3, 147.6, 139.8, 131.7, 128.8, 128.7, 128.4, 127.8,
127.4, 126.8, 125.9, 64.8, 63.5, 34.1, 31.3, 31.2. FABMS m/z: 821.87
(MþNa)þ. Anal. Calcd for C54H58N2O4 (799.05): C, 81.17; H, 7.32; N,
3.51. Found: C, 81.01; H, 7.14; N, 3.46.
References and notes
1. Tabakci, M. J. Inclusion Phenom. Macrocycl. Chem. 2008, 61, 53e60.
2. Richard, F. C.; Bourg, A. C. M. Water Res. 1991, 25, 807e816.
3. Saha, B.; Orvig, C. Coord. Chem. Rev. 2010, 254, 2959e2972.
€
d
4. Deligoz, H.; Ak, M. S.; Memon, S.; Yilmaz, M. Pak. J. Anal. Environ. Chem. 2008, 9,
1e5.
5. Sobol, Z.; Schiestl, R. H. Environ. Mol. Mutagen. 2012, 53, 94e100.
6. Kalidhasan, S.; Rajesh, N. J. Hazard. Mater. 2009, 170, 1079e1085.
7. Venkateswaran, P.; Palanivelu, K. Sep. Purif. Technol. 2004, 40, 279e284.
8. Wang, Q.; Guan, Y.; Ren, X.; Yang, M.; Liu, X. Chem. Eng. J. 2012, 183,
339e348.
9. For books on calixarenes, see: (a) Gutsche, C. D. Calixarenes an Introduction, 2nd
ed.; The Royal Society of Chemistry, Thomas Graham House: Cambridge, 2008;
(b) Calixarenes in the Nanoworld; Vicens, J., Harrowfield, J., Backlouti, L., Eds.;
4.2.3.2. 5,17-Di-tert-butyl-11,23-difurfurylimino-26,28-dimethoxy-
calix[4]arene-25,27-diol (10). This compound was prepared with
furfurylamine as described in general procedure above. Yield:
0.41 g (41%). Mp: 189 ꢃC. IR (KBr, cmꢀ1): 1637 (C]N). 1H NMR
t
(CDCl3):
d
0.97 (s, 18H, Bu), 3.44 (d, J¼13.3 Hz, 4H, ArCH2Ar), 3.94
€
Springer: Dordrecht, 2007; (c) Calixarenes 2001; Asfari, Z., Bohmer, V.,
(s, 6H, OCH3), 4.25 (d, J¼13.3 Hz, 4H, ArCH2Ar), 6.25e6.26 (m, 2H,
ArHfurfuryl), 6.34e6.35 (m, 2H, ArHfurfuryl), 6.80 (s, 4H, ArHcalix),
7.37e7.40 (m, 2H, ArHfurfuryl), 7.52 (s, 4H, ArHcalix), 7.75 (s, 2H, OH),
Harrowfield, J., Vicens, J., Eds.; Kluwer Academic: Dordrecht, 2001; (d)
Mandolini, L.; Ungaro, R. Calixarenes in Action; Imperial College: London, 2000;
(e) Calixarenes 50th Anniversary: Commemorative Issue; Vicens, J., Asfari, Z.,
Harrowfield, J. M., Eds.; Kluwer Academic: Dordrecht, 1994; (f) Calixarenes: A
Versatile Class of Macrocyclic Compounds; Vicens, J., Bohmer, V., Eds.; Kluwer
Academic: Dordrecht, 1991.
8.24 (s, 2H, HCN). 13C NMR (CDCl3):
d 163.3, 156.0, 152.8,151.3,147.6,
€
142.1, 131.6, 128.9, 128.6, 127.0, 125.9, 110.3, 107.2, 63.5, 57.4, 34.1,
31.2, 31.1. FABMS m/z: 801.80 (MþNa)þ. Anal. Calcd for C50H54N2O6
(778.97): C, 77.09; H, 6.99; N, 3.60. Found: C, 76.81; H, 6.74; N, 3.49.
10. Tabakci, B.; Yilmaz, M.; Beduk, A. D. J. Appl. Polym. Sci. 2012, 125,
1012e1019.
11. El Nashar, R. M.; Wagdy, H. A. A.; Aboul-Enein, H. Y. Curr. Anal. Chem. 2009, 5,
249e270.
4.2.3.3. 5,17-Di-tert-butyl-11,23-dicyclohexylimino-26,28-dimethoxy-
calix[4]arene-25,27-diol (11). This compound was prepared with
cyclohexylamine as described in general procedure above. Yield:
12. Kimura, K.; Tatsumi, K.; Yokoyama, M.; Ouchi, M.; Mocerino, M. Anal. Commun.
1999, 36, 229e230.
13. Li, Z. Y.; Chen, J. W.; Liu, Y.; Xia, W.; Wang, L. Y. Curr. Org. Chem. 2011, 15,
39e61.
14. Homden, D. M.; Redshaw, C. Chem. Rev. 2008, 108, 5086e5130.
15. Hennrich, G.; Murillo, M. T.; Prados, P.; Song, K.; Asselberghs, I.; Clays, K.;
Persoons, A.; Benet-Buchholz, J.; de Mendoza, J. Chem. Commun. 2005,
2747e2749.
0.37 g (46%). Mp: 290e293oC. IR (KBr): 1636 (C]N). 1H NMR
t
(DMSO-d6):
d
0.97 (s, 18H, Bu), 1.10e1.78 (m, 21H, CH2(cyclohexyl)),
3.37 (d, J¼13.3 Hz, 4H, ArCH2Ar), 3.89 (s, 6H, OCH3), 4.18 (d,
J¼13.3 Hz, 4H, ArCH2Ar), 6.86 (s, 4H, ArH), 7.36 (s, 4H, ArH), 7.68 (s,
16. Gezici, O.; Tabakci, M.; Kara, H.; Yilmaz, M. J. Macromol. Sci., Pure Appl. Chem.
2H, OH), 8.06 (s, 2H, HCN). 13C NMR (CDCl3):
d 158.9, 155.4, 151.3,
2006, 43, 221e231.
17. Fujita, J.; Ohnissi, Y.; Ochiai, Y.; Matsui, S. Appl. Phys. Lett. 1996, 68, 1297e1299.
18. For recent reviews/books on anion-recognition, see: (a) Amendola, V.;
Fabbrizzi, L. Chem. Commun. 2009, 513e531; (b) Cametti, M.; Rissanen, K.
Chem. Commun. 2009, 2809e2829; (c) Gale, P. A.; Garcia Garrido, S. E.;
Garric, J. Chem. Soc. Rev. 2008, 37, 151e190; (d) Recognition of Anions; Vilar,
R., Ed.; Springer: Berlin, 2008; (e) Sessler, J. L.; Gale, P. A.; Cho, W. S. Anion
Receptor Chemistry; The Royal Society of Chemistry: Cambridge, 2006; (f)
Anion Sensing In. Topics in Current Chemistry; Stibor, I., Ed.; Springer: Berlin,
2005; Vol. 255; (g) Gale, P. A.; Beer, P. D. Angew. Chem., Int. Ed. 2001,
40, 486e516; (h) Supramolecular Chemistry of Anions; Bianchi, A.,
Bowman-James, K., Garcia-Espana, E., Eds.; Wiley-VCH: New York, NY, 1997;
(i) Calixarenes 2001; Matthews, S. E., Beer, P. D., Eds.; 2001; pp 421e439 see
Ref. 9c; (j) Calixarenes in Action; Beer, P. D., Cooper, J. B., Eds.; 2000;
pp 111e143 see Ref. 9d.
147.5, 131.8, 128.6, 128.5, 127.8, 125.9, 70.3, 63.4, 34.5, 34.1, 31.2, 31.1,
25.7, 25.1. FABMS m/z: 805.91 (MþNa)þ. Anal. Calcd for
C52H66N2O4 (783.09): C, 79.76; H, 8.49; N, 3.58. Found: C, 79.62; H,
8.28; N, 3.48.
4.3. Two-phase extraction studies
The anion extraction experiments by the calix[4]arene-based
Mannich and Schiff base derivatives 5, 6 and 9e11 were performed
following Pedersen’s procedure.27 An aqueous solution of sodium
salt of anion (10 mL of a 1.0ꢂ10ꢀ4 M; 0.01 M KOH/HCl solution was
used in order to obtain the desired pH at equilibrium) and calix-
arene ligand (10 mL of 1.0ꢂ10ꢀ3 M) in dichloromethane was
shaken vigorously in a stoppered glass tube with a mechanical
shaker for 2 min and then magnetically stirred in a thermostated
water bath at 25 ꢃC for 1 h, and finally left standing for an additional
30 min. The concentration of anion remaining in the aqueous phase
was then determined as described previously for dichromate an-
ions.20 Blank experiments showed that no dichromate anions ex-
traction occurred in the absence of calix[4]arene derivatives. The
percent extraction (E%) was calculated from the absorbance A of the
aqueous phase measured at 350 nm (for pH 1.5e4.5) using the
following expression:
19. For some recent examples of calixarene-based anion receptors see: (a) Minhas,
F. T.; Memon, S.; Bhanger, M. I. J. Inclusion Phenom. Macrocycl. Chem. 2010, 67,
295e302; (b) Qureshi, I.; Memon, S.; Yilmaz, M. J. Hazard. Mater. 2009, 164,
675e682; (c) Akkus, G. U.; Memon, S.; Sezgin, M.; Yilmaz, M. Clean-Soil Air
Water 2009, 37, 109e114; (d) Kalchenko, V. I. Pure Appl. Chem. 2008, 80,
1449e1458; (e) Tabakci, M.; Memon, S.; Yilmaz, M. Tetrahedron 2007, 63,
6861e6865; (f) Matthews, S. E.; Beer, P. D. Supramol. Chem. 2005, 17, 411e435;
ꢀ
(g) Lhotak, P. Top. Curr. Chem. 2005, 255, 65e96 see Ref. 18f; (h) Tabakci, M.;
Memon, S.; Sap, B.; Roundhill, D. M.; Yilmaz, M. J. Macromol. Sci., Pure Appl.
Chem. 2004, 41, 811e825; (i) Ediz, O.; Tabakci, M.; Memon, S.; Yilmaz, M.;
Roundhill, D. M. Supramol. Chem. 2004, 16, 199e204; (j) Tabakci, M.; Memon, S.;
Yilmaz, M. J. Inclusion Phenom. Macrocycl. Chem. 2003, 45, 265e270; (k) Gale, P.
A. Coord. Chem. Rev. 2003, 240, 17e55; (l) Gale, P. A. Coord. Chem. Rev. 2001, 213,
79e128.
20. For some recent examples of calixarene-based receptors for dichromate anions
from our group see: (a) Yilmaz, A.; Tabakci, B.; Tabakci, M. Supramol. Chem.
2009, 21, 435e441; (b) Yilmaz, A.; Tabakci, B.; Akceylan, E.; Yilmaz, M. Tetra-
hedron 2007, 63, 5000e5005; (c) Memon, S.; Yilmaz, A.; Roundhill, D. M.;
Yilmaz, M. J. Macromol. Sci., Pure Appl. Chem. 2004, 41, 433e447; (d) Yilmaz, A.;
Memon, S.; Yilmaz, M. Tetrahedron 2002, 58, 7735e7740.
21. Gutsche, C. D.; Iqbal, M.; Stewart, D. J. Org. Chem. 1986, 51, 742e745.
22. Dalbavie, J.-O.; Regnouf-de-Vains, J.-B.; Lamartine, R.; Lecocq, S.; Perrin, M. Eur.
J. Inorg. Chem. 2000, 683e691.
E% ¼ ½ðA0 ꢀ A=A0Þꢄ ꢂ 100
(5)
where A0 and A are the initial and final concentrations of di-
chromate anions before and after the extraction, respectively.
23. Casnati, A.; Arduini, A.; Ghidini, E.; Pochini, A.; Ungaro, R. Tetrahedron 1991, 47,
2221e2228.
Acknowledgements
24. See, K. A.; Froncsek, F. R.; Watson, W. H.; Kashyap, R. P.; Gutsche, C. D. J. Org.
Chem. 1991, 56, 7256e7268.
25. Huang, Z. T.; Wang, G.-Q. Synth. Commun. 1994, 24, 11e22.
26. Memon, S.; Roundhill, D. M.; Yilmaz, M. Collect. Czech. Chem. Commun. 2004, 69,
1231e1250.
We thank The Scientific Research Projects Foundation of Selc¸ uk
University (SUBAP-09201021) and The Scientific and Technological
Research Council of Turkey (TUBITAK-108T276) for their financial
support of this work.
27. Pedersen, C. J. J. Fed. Proc. Fed. Am. Soc. Exp. Biol. 1968, 27, 1305e1309.