Synthesis and lead(II) sorption of silica gel-immobilized, di-ionizable calix[4]arenes

Article abstract of DOI:10.1016/j.tet.2007.03.104

Di-ionizable calix[4]arenes with two lower-rim N-(X)sulfonyl carboxamide groups were covalently linked to silica gel via a single attachment on the upper rim. Both the acidity of the ionizable groups (X group variation) and the length of the spacer that joins the ligands to the silica gel matrix were varied. Preliminary evaluation of these new ion-exchange resins for sorption of lead(II) from aqueous solutions was conducted.

Full text of DOI:10.1016/j.tet.2007.03.104

Tetrahedron 63 (2007) 5076–5082
Synthesis and lead(II) sorption of silica gel-immobilized,
di-ionizable calix[4]arenes
*
Dongmei Zhang, Jing Wang, Thomas R. Lawson and Richard A. Bartsch
Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX 79409, USA
Received 11 January 2007; revised 13 March 2007; accepted 16 March 2007
Available online 21 March 2007
Abstract—Di-ionizable calix[4]arenes with two lower-rim N-(X)sulfonyl carboxamide groups were covalently linked to silica gel via a single
attachment on the upper rim. Both the acidity of the ionizable groups (X group variation) and the length of the spacer that joins the ligands to
the silica gel matrix were varied. Preliminary evaluation of these new ion-exchange resins for sorption of lead(II) from aqueous solutions was
conducted.
Ó 2007 Elsevier Ltd. All rights reserved.
1. Introduction
Calixarenes are one of the most important platforms for the
preparation of new macrocyclic hosts for complexation of
neutral and ionic guest species.1–5 We have synthesized and
OCH3
OCH3
OCH2C(O)NHSO2X
evaluated novel di-ionizable calix[4]arenes with two acidic
groups attached via the phenolic oxygens on the lower
rim.6–11 Such ligands are efficient agents for extraction of
divalent metal ions from aqueous solutions into organic sol-
vents by an ion-exchange mechanism in which the di-ionized
ligand and the complexed metal ion form electroneutral com-
plexes. This avoids the need to extract an anion from the
aqueous phase into the organic medium and is especially
important for potential practical applications in which the
aqueous phase anions are highly hydrophilic chloride,
nitrate, and sulfate.
OCH2C(O)NHSO2X
(X = CH3, C6H5, C6H4-4-NO2, CF3)
Figure 1. Di-ionizable calix[4]arene ligands with high extraction propen-
sity for Pb2+ and Hg2+
.
Recently, the topic of polymer-appended calixarenes as ion
carriers was reviewed.12 Only a few studies of calixarene
immobilization on silica gel have appeared in the literature.
Glennon and co-workers were the first to bind calix[4]arene
ligands to silica gel.13–15 In their work, an upper-rim attach-
ment site was present on each of the four aromatic units of
the calix[4]arene. Other workers have bound a calix[4]ar-
ene-crown ether to silica gel via two upper-rim attachment
sites.16 In both cases, the multiple attachments will restrict
the conformational mobility of the calix[4]arene units. Since
we have demonstrated that conformationally mobile di-
ionizable calix[4]arenes provide more selective metal ion
complexation than conformationally locked analogues,10
our objective was to utilize a single linkage to bind the upper
rim of our ligands to silica gel.
To provide ligands with ‘tunable’ acidity, we have attached
N-(X)sulfonyl carboxamide functions to the lower rim of
calix[4]arenes.6–11 Variation of the electron-withdrawing
properties of X changes the acidity of the ligand.
We have reported efficient extraction of Pb2+ and Hg2+ from
acidic aqueous solutions into chloroform by di-ionizable
calix[4]arenes 1 with high selectivity over alkali and alkaline
earth metal ions, as well as other transition and heavy metal
cations (Fig. 1).6,7 To explore the behavior of such ligands in
ion-exchange chromatography, their immobilization on
a polymeric support is required.
We now report the synthesis of novel ion-exchange resins 2–
10 (Fig. 2) in which the di-ionizable calix[4]arene units are
connected to silica gel by a single, upper-rim linkage. Re-
sults from preliminary studies of Pb2+ sorption from aqueous
solutions are also presented. To our knowledge, this is the
Keywords: Functionalized calix[4]arenes; Ion-exchange resins; Heavy
metal sorption.
* Corresponding author. Tel.: +1 806 742 3069; fax: +1 806 742 1289;
e-mail: richard.bartsch@ttu.edu
0040–4020/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2007.03.104

D. Zhang et al. / Tetrahedron 63 (2007) 5076–5082
5077
out with excess benzoyl chloride and pyridine using a modi-
fied method based on the literature.17 Several trial reactions
were performed to determine the optimal conditions for ob-
taining monobenzoyl-protected calix[4]arene 11 (Table 1).
The best result was achieved when the calixarene was treated
with 8 equiv of benzoyl chloride at 50 ꢀC overnight. When
the reaction was repeated under these conditions on larger
scale, a 73% yield of 11 was obtained.
Silica
O
EtO
EtO
Si
CH2
n
S
CH2
3
Reaction of 25,27-dimethoxy-26-benzoyloxy-28-hydroxyl-
oxycalix[4]arene (11) with NaH and allyl bromide in THF
afforded 25,27-dimethoxy-26-benzoyloxy-28-(20-propenyl)-
oxycalix[4]arene (12) in 88% yield. Claisen rearrangement
of 12 in refluxing N,N-dimethylaniline18 gave 5-(20-prop-
enyl)-25,27-dimethoxy-26-benzoyloxy-28-(20-propenyl)oxy-
calix[4]arene (13) in 97% yield. Hydrolysis of ester 13 with
aqueous NaOH in EtOH–THF gave 14 in 82% yield.17 The
1H NMR spectra of compounds 11–14 revealed that all were
conformationally mobile in CDCl3.
OCH3
OCH3
OCH2C(O)NHSO2X
OCH2C(O)NHSO2X
X
n
CH3
C6H5
3
2
3
3
C6H4-4-NO2
CH3
3
4
6
5
C6H5
6
6
C6H4-4-NO2
CH3
6
7
10
10
10
8
Preparation of the di-ionizable calix[4]arene precursors is
illustrated in Scheme 2. 5-(20-Propenyl)-25,27-dimethoxy-
26,28-dihydroxycalix[4]arene (14) was treated with NaH
and ethyl bromoacetate to give 5-(20-propenyl)-25,27-di-
methoxy-26,28-di[(ethoxycarbonyl)methoxy]calix[4]arene
(15) in 78% yield. Diester 15 was hydrolyzed with Me4NOH
in aqueous THF to give diacid 16 in 92% yield. Diacid 16
was then converted into the corresponding di(acid chloride)
by reaction with oxalyl chloride in benzene. Reaction of the
di(acid chloride) with four different sulfonamide anions
gave the target di-ionizable calix[4]arenes 17–20 in high
yields.
C6H5
9
C6H4-4-NO2
10
Figure 2. Di-ionizable calix[4]arenes ligands bound to silica gel.
first reported immobilization of a proton-ionizable calix-
arene on silica gel.
2. Results and discussion
2.1. Synthesis of functionalized calixarenes
2.2. Linker synthesis
Synthesis of the dimethylated calix[4]arene with a single al-
lyl substituent on the upper rim involved a total of four reac-
tions (Scheme 1). Monoprotection of one hydroxyl group on
25,27-dimethoxy-26,28-dihydroxycalix[4]arene was carried
The length of the spacer that separates the di-ionizable
calix[4]arene unit from the silica gel matrix was system-
atically varied. In addition to commercially available
NaH, BrCH2CH=CH2
THF, reflux
BzCl
Pyridine, 50 °C
2
OCH3
OH
OCH3
OBz
OCH3
OH
11
N,N-dimethylaniline
THF, reflux
OCH3
OBz
OCH3
O
OCH3
OBz
OCH3
OH
12
13
10 wt % aq NaOH
THF/EtOH, reflux
OCH3
OH
OCH3
OH
14
Scheme 1. Synthesis of 5-(20-propenyl)-25,27-dimethoxy-26,28-dihydroxycalix[4]arene (14).

5078
D. Zhang et al. / Tetrahedron 63 (2007) 5076–5082
Table 1. Optimization of reaction conditions for monoprotection of calix[4]arene 11
Entry
1
2
3
4
5
Reaction temperature
BzCl (equiv)
rt
1.1
rt
4
50 ꢀC
4
rt
8
50 ꢀC
8
BzCl (equiv) for second addition
Reaction after 48 h
Starting material recovered
Monobenzoylated product
Dibenzoylated product
17
Complete
0
38%
26%
4
8
4
0
Incomplete
42%
15%
Complete
0
44%
Incomplete
56%
20%
Complete
0
73%
Trace
40%
Trace
12%
Me4NOH, H2O
THF, reflux
NaH, BrCH2CO2Et
THF
OCH3
OCH3
OCH2CO2Et
OCH2CO2Et
OCH3
OH
OCH3
OH
14
15
1) Oxalyl chloride
2) NaH, NH2SO2X
OCH3
OCH3
OCH2C(O)NHSO2X
OCH3
OCH3
OCH2CO2H
OCH2CO2H
OCH2C(O)NHSO2X
16
X
17
18
19
20
CH3
C6H5
C6H4-4-NO2
CF3
Scheme 2. Preparation of di-ionizable calix[4]arene ligands.
3-mercaptopropyltriethoxysilane, 6-mercaptohexyltrieth-
oxysilane (21) and 10-mercaptodecyltriethoxysilane (22)
were needed. Compounds 21 and 22 were synthesized fol-
lowing a literature method19 (Scheme 3). Commercially
available 9-decen-1-ol and 5-hexen-1-ol were reacted with
CBr4 and PPh3 to give 10-bromodecene (23) and 6-bromo-
hexene (24), respectively. The starting material and solvent
had to be scrupulously dry for clean conversions. u-Bromo-
alk-1-enes 23 and 24 were reacted with trichlorosilane and
hexachloroplatinic acid in THF at reflux and then treated
with cold ethanol in hexane to give u-triethoxysilylalkyl
bromides 25 and 26 in yields over 70% after distillation
under reduced pressure. u-Triethoxysilylalkyl bromides 25
and 26 were treated with thiourea in DMF with an anhydrous
ammonia gas flow at 125 ꢀC for 5 h to give u-triethoxysilyl-
alkyl mercaptans 21 and 22 in 30–40% yields after distilla-
tion under reduced pressure.
2.3. Immobilization of di-ionizable calix[4]arenes on
silica gel
Immobilization of calix[4]arenes 17–20 with a single allyl
group on the upper rim on silica gel was achieved through
reaction of the allyl group with u-triethoxysilylalkyl mer-
captan and cumene hydroperoxide (CHP) catalyst in 1,2-di-
chloroethane by radical addition and then refluxing the
product with activated silica gel.13,15 Combustion analysis
of the immobilized silica gel for nitrogen was performed
to determine the ligand loading. Following reactions of di-
ionizable calix[4]arene 20 with the three linkers and then
with silica gel, no nitrogen was detected in the product
resins. This reveals cleavage of the ionizable groups under
the conditions of immobilization.
CBr4, PPh3
CH2Cl2
1) H2PtCl6 6H2O, trichlorosilane, THF, reflux
2) hexane, EtOH, 0 °C
Br
OH
n
n
n
4
8
23
24
Et
Et
O
O
Si
O
Et
Et
anhydrous ammonia gas flow, thiourea
DMF, 125 °C
SH
O
Si
Br
O
n
n
O
Et
Et
n
4
8
2.4. Metal ion sorption by new ion-exchange resins
n
4
8
21
22
25
26
Initial probing of the complexation ability by the new ion-
exchange resins 2–10 was conducted with Pb2+ sorption
Scheme 3. Synthesis of u-triethoxysilylalkyl mercaptans 21 and 22.

D. Zhang et al. / Tetrahedron 63 (2007) 5076–5082
5079
from CH2Cl2 solution on a NaCl plate. The 1H and 13C NMR
spectra were recorded with a Varian Unity INOVA 500 MHz
FTNMR (1H 500 MHz and 13C 126 MHz) spectrometer in
CDCl3 with Me4Si as an internal standard, unless mentioned
otherwise. Chemical shifts (d) are given in parts per million
downfield from TMS and coupling constants (J) values are in
hertz. A Shimadzu Model 6300 atomic absorption spectro-
photometer was used for the Pb2+ analysis. The pH was
measured with a Fisher Accumet AR25 pH meter with a
microcombination electrode. Elemental analysis was per-
formed by Desert Analytics Laboratory of Tucson, Arizona.
25
20
15
10
5
0
SG
2
3
4
5
6
7
8
9
10
3.2. Synthesis
Resin
Reagents were obtained from commercial suppliers and used
directly, unless otherwise noted. Tetrahydrofuran (THF)
was dried over sodium with benzophenone as indicator and
distilled just before use. 25,27-Dimethoxycalix[4]arene
was prepared by a reported method.20 6-Bromohex-1-ene
(23),21 10-bromodec-1-ene (24),19 6-triethoxysilylhexyl
bromide (25),22 10-triethoxysilyldecyl bromide (26),19 and
10-triethoxysilyldecyl mercaptan (22)19 were synthesized by
literature methods. Silica gel (Mallinckrodt SiliCARÒ, 60–
200 mesh) was activated by heating at 150 ꢀC under oil
pump vacuum overnight.
Figure 3. Percent Pb2+ sorption by unfunctionalized silica gel (SG) and by
di-ionizable calix[4]arenes 2–10 immobilized on silica gel.
from aqueous solutions at pH 5.3. A 1.00-g sample of the
resin was packed in a 42 mm ID Tefzel column. Through
the resin bed was passed a dilute aqueous solution of
Pb(NO3)2 of such concentration that there was a 1:1 ratio
of calixarene units in the resin bed and Pb2+ in solution.
After loading with the sample solution, the column was
rinsed with DI water to remove any unbound metal ions.
The sorbed Pb2+ ions were then eluted from the column
with dilute HNO3 and their concentration in the eluant was
determined by atomic absorption spectrophotometry. The
percentage of Pb2+ ions in the sample solution that were
sorbed by the ion-exchange resin was then calculated.
3.2.1. 25,27-Dimethoxy-26-benzoyloxy-28-hydroxyca-
lix[4]arene (11). Into pyridine (30 mL), 25,27-dimethoxy-
calix[4]arene (1.36 g, 3.0 mmol) was added followed by
BzCl (2.8 mL, 24 mmol). The solution was stirred at 50 ꢀC
overnight. DiluteHCl(300 mL)wasaddedtoproduceawhite
solid, which was filtered and recrystallized from CHCl3 with
slow addition of MeOH to yield a white solid (9.07 g, 73%)
with mp 287–288 ꢀC. IR (deposit from CH2Cl2 solution on
Results for Pb2+ sorption by silica gel itself and by new ion-
exchange resins 2–10 containing immobilized di-ionizable
calix[4]arene ligands are presented in Figure 3. There was lit-
tle sorption of Pb2+ by a column of silica gel itself. For resins
2–10, the percent Pb2+ sorption values are in the range of 10–
25% depending upon the length of the spacer and the identity
of X in the di-ionizable calix[4]arene unit. In general, resins
2–4 with the shortest spacer (n¼3) gave higher levels of Pb2+
sorption than did resins 5–7 with intermediate spacer length
(n¼6) or resins 8–10 with the longest spacer length (n¼10).
For variation of the X in resins 2–4 with the shortest spacer
length, Pb2+ sorption was significantly higher for the more
strongly electron-withdrawing 4-nitrophenyl group than for
the phenyl and methyl groups. Thus, the more acidic di-ioniz-
able calix[4]arene ligand unit gave the highest Pb2+ sorption.
However, with the intermediate and longest spacers, the
highest Pb2+ sorption levels were observed with X¼phenyl
than with X¼methyl or 4-nitrophenyl.
1
a NaCl plate): 3301 (O–H), 1721 (C]O) cmꢁ1. H NMR
(CDCl3): d 3.75 (s, 6H, OCH3), 2.82–4.20 (m, 8H, ArCH2),
6.20–7.43 (m, 18H, ArH, OH); 13C NMR (CDCl3): d 30.7,
37.4, 61.1, 118.8, 123.8, 125.3, 127.5, 128.1, 128.3, 128.4,
129.6, 130.8, 132.3, 132.8, 133.1, 147.8, 153.1, 155.5,
163.9. Anal. Calcd for C37H32O5: C, 79.83; H, 5.79. Found:
C, 79.79; H, 5.81%.
3.2.2. 25,27-Dimethoxy-26-benzoyloxy-28-(20-propenyl)-
oxycalix[4]arene (12). To a suspension of NaH (0.14 g,
5.83 mmol) in THF (20 mL) was added a solution of 11
(1.00 g, 1.80 mmol) in THF (20 mL). After stirring for
30 min, allyl bromide (0.44 g, 3.6 mmol) was added and
the mixture was refluxed overnight. The excess NaH was
destroyed by careful addition of water and the organic sol-
vent was evaporated in vacuo. To the residue, CH2Cl2
(50 mL) was added and the organic layer was washed
with 1 N HCl (30 mL) and then with brine (30 mL), dried
over MgSO4, and evaporated in vacuo to afford a white
solid (0.71 g, 60%) with mp 202–205 ꢀC. IR (deposit
from CH2Cl2 solution on a NaCl plate): 1727 (C]O),
Further studies on the influence of structural variations in the
organic portions of the new ion-exchange resins on their
metal ion sorption behaviors are in progress and the results
will be reported in due course.
1587 (C]C) cmꢁ1 1H NMR (CDCl3): d 3.63 (s, 6H,
.
3. Experimental
3.1. General
OCH3), 2.66–4.25 (m, 12H, ArCH2), 4.87–4.98 (m, 2H,
CH]CH2), 5.49–5.60 (m, 1H, CH]CH2), 6.27–7.58 (m,
17H, ArH); 13C NMR (CDCl3): d 30.8, 37.0, 59.9, 74.1,
112.6, 122.2, 123.1, 127.7, 129.0, 130.3, 131.6, 132.3,
133.2, 133.4, 133.8, 136.9, 138.2, 156.0, 156.8, 164.4.
Anal. Calcd for C40H36O5: C, 80.51; H, 6.08. Found: C,
80.77; H, 6.24%.
Melting points were determined with a Mel-Temp melting
point apparatus. Infrared (IR) spectra were recorded with
a Perkin–Elmer Model 1600 FTIR spectrometer as deposits

5080
D. Zhang et al. / Tetrahedron 63 (2007) 5076–5082
3.2.3. 5-(20-Propenyl)-25,27-dimethoxy-26-benzoyloxy-
28-hydroxycalix[4]arene (13). A solution of 12 (1.00 g,
1.68 mmol) in N,N-dimethylaniline (10 mL) was refluxed
for 3 h. The mixture was allowed to cool and then poured
into a 1:1 mixture of concentrated HCl–ice (150 mL). The
precipitate was taken up in CH2Cl2 (100 mL) and the organic
layer was washed with 6 N HCl (3ꢂ50 mL), water (50 mL),
and brine (50 mL), dried over MgSO4, and evaporated
in vacuo. Recrystallization of the residue from CH2Cl2–
MeOH gave a white solid (0.97 g, 97%) with mp 244–
246 ꢀC. IR (deposit from CH2Cl2 solution on a NaCl plate):
153.4, 155.8, 158.1, 159.0, 169.4. Anal. Calcd for
C41H44O8: C, 74.08; H, 6.67. Found: C, 73.79; H, 6.86%.
3.2.6. 5-(20-Propenyl)-25,27-dimethoxy-26,28-bis(car-
boxymethoxy)calix[4]arene (16). A solution of 15 (5.00 g,
7.53 mmol) in THF (100 mL) and 10% aq Me4NOH
(100 mL) was refluxed overnight, and the THF was evapo-
rated in vacuo. To the residue, CH2Cl2 was added and the or-
ganic layer was separated and washed with 5% HCl until pH
1 and then with brine, dried over MgSO4, and evaporated in
vacuo to give a white solid (4.23 g, 92%) with mp 93–97 ꢀC.
IR (deposit from CH2Cl2 solution on a NaCl plate): 3169
(OH), 1761 (C]O), 1640 (C]C), 1203 and 1053 (C–
O) cmꢁ1. 1H NMR (CDCl3): d 3.42–3.27 (m, 2H, CH2CH]
CH2), 3.33 (d, J¼13.0 Hz, 2H, ArCH2), 3.84 (s, 6H, OCH3),
4.25 (d, J¼13.0 Hz, 2H, ArCH2), 3.37 (d, J¼13.5 Hz, 2H,
ArCH2), 4.28 (d, J¼13.5 Hz, 2H, ArCH2), 4.70 (d, J¼
10.0 Hz, 4H, CH2CO2H), 5.00–5.15 (m, 2H, CH]CH2),
5.91–6.05 (m, 1H, CH]CH2), 6.48–6.62 (m, 6H, ArH), 6.97
(s, 2H, ArH), 7.02 (t, J¼7.5 Hz, 1H, ArH), 7.19 (d, J¼7.5 Hz,
2H, ArH); 13C NMR (CDCl3): d 30.7, 39.4, 53.4, 63.8, 72.1,
116.0, 124.9, 128.7, 129.5, 132.6, 135.0, 137.3, 153.0, 154.1,
155.8, 169.7. Anal. Calcd for C37H36O8$0.1CH2Cl2: C,
72.20; H, 5.91. Found: C, 72.08; H, 6.23%.
1
3337 (OH), 1733 (C]O), 1638 (C]C) cmꢁ1. H NMR
(CDCl3): d 3.74 (s, 6H, OCH3), 4.32–2.18 (m, 10H,
ArCH2Ar, ArCH2O), 5.17–5.08 (m, 2H, CH]CH2), 5.98–
6.12 (m, 1H, CH]CH2), 7.67–6.16 (m, 17H, ArH); 13C
NMR (CDCl3): d 30.75, 37.41, 39.53, 61.06, 115.12, 123.79,
125.27, 127.45, 127.99, 128.38, 128.45, 128.50, 128.98,
129.39, 129.54, 129.62, 129.94, 130.84, 132.32, 132.80,
133.08, 133.16, 138.45, 147.77, 151.36, 155.48, 163.86.
Anal. Calcd for C40H36O5: C, 80.51; H, 6.08. Found: C,
80.92; H, 6.13%.
3.2.4. 5-(20-Propenyl)-25,27-dimethoxy-26,28-dihydroxy-
calix[4]arene (14). To 13 (1.00 g, 1.68 mmol) was added
50 mL each of 10% NaOH, EtOH, and THF and the mixture
was refluxed overnight. After adding 5% HCl, the precipi-
tate was filtered and dissolved in CH2Cl2 (100 mL). The
solution was washed with brine, dried over MgSO4, and
evaporated in vacuo. Recrystallization of the residue from
CH2Cl2–MeOH gave a white solid (0.68 g, 82%) with mp
242–243 ꢀC. IR (deposit from CH2Cl2 solution on a NaCl
3.2.7. General procedure for synthesis of 5-(20-propenyl)-
25,27-dimethoxy-26,28-di[N-(X)sulfonyl carbamoyl-
methoxy]calix[4]arenes 17–20. Oxalyl chloride (1.39 mL,
16.3 mmol) was added to 16 (1.00 g, 1.63 mmol) in benzene
(50 mL). The mixture was refluxed for 6 h and the solvent
was evaporated in vacuo to give the di(acid chloride). The
appropriate sulfonamide (4.0 mmol) in THF (5 mL) was
added to NaH (0.38 g, 16.3 mmol) in THF (20 mL) and
the mixture was stirred at room temperature for 2 h. The
di(acid chloride) was added and the mixture was stirred
overnight. The excess NaH was destroyed with careful addi-
tion of water. The THF was evaporated and the residue was
washed with dilute HCl until pH 1 and the mixture was
extracted with CH2Cl2. The organic layer was dried over
MgSO4 and evaporated in vacuo.
1
plate): 3284 (OH), 1642 (C]C) cmꢁ1. H NMR (CDCl3):
d 3.27 (d, J¼7.0 Hz, 2H, CH2CH]CH2), 3.95 (s, 6H,
OCH3), 3.37 (d, J¼13.0 Hz, 2H, ArCH2), 4.28 (d, J¼
13.0 Hz, 2H, ArCH2), 3.39 (d, J¼13.0 Hz, 2H, ArCH2),
4.30 (d, J¼13.0 Hz, 2H, ArCH2), 4.98–5.12 (m, 2H, CH]
CH2), 5.88–6.02 (m, 1H, CH]CH2), 6.67 (t, J¼7.5 Hz,
1H, ArH), 6.73 (t, J¼7.5 Hz, 2H, ArH), 6.87 (d, J¼
7.5 Hz, 6H, ArH), 7.05 (d, J¼8.0 Hz, 2H, ArH), 7.63 (s,
1H, OH), 7.75 (s, 1H, OH); 13C NMR (CDCl3): d 31.1,
31.2, 39.4, 63.6, 115.2, 119.1, 125.3, 128.0, 128.1, 128.5,
129.0, 130.3, 132.9, 133.0, 138.2, 151.3, 153.0, 153.2,
166.6. Anal. Calcd for C33H32O4: C, 80.46; H, 6.55. Found:
C, 80.28; H, 6.76%.
3.2.7.1. 5-(20-Propenyl)-25,27-dimethoxy-26,28-di(N-
methanesulfonyl carbamoylmethoxy)calix[4]arene (17).
Compound 17 was obtained as white solid (1.18 g, 95%)
with mp 105–110 ꢀC. IR (deposit from CH2Cl2 solution on
a NaCl plate): 3341 (NH), 1730 (C]O), 1642 (C]C),
3.2.5. 5-(20-Propenyl)-25,27-dimethoxy-26,28-di[(ethoxy-
carbonyl)methoxy]calix[4]arene (15). A solution of 14
(1.00 g, 2.0 mmol) in THF (30 mL) was added dropwise to
a suspension of NaH (0.20 g, 8.3 mmol) in THF (5 mL). Af-
ter stirring for 2 h, ethyl bromoacetate (2.03 g, 12.2 mmol)
was added and the mixture was stirred at room temperature
overnight. The solvent was evaporated in vacuo and the res-
idue was dissolved in CH2Cl2. The solution was washed with
brine, dried over MgSO4, and evaporated in vacuo. Chroma-
tography on silica gel with hexanes–EtOAc (17:3) as eluant
gave a colorless oil (1.04 g, 78%). IR (deposit from CH2Cl2
1350 (S]O), 1146 (S]O) cmꢁ1 1H NMR (CDCl3):
.
d 3.08–5.18 (m, 28H, CH]CH2, ArCH2, OCH3, CH2CH]
CH2, CH3), 5.79–7.22 (m, 12H, ArH, CH]CH2), 8.80–
8.97 (s, 2H, NH); 13C NMR (CDCl3): d 31.1, 36.8, 39.0,
41.5, 58.1, 64.0, 71.1, 115.8, 123.9, 126.0, 128.8, 129.7,
131.1, 132.5, 135.0, 151.4, 152.9, 158.0, 168.2, 169.8.
Anal. Calcd for C39H42N2S2O10$0.5C6H6: C, 62.90; H,
5.66; N, 3.49. Found: C, 62.96; H, 5.38; N, 3.22%.
3.2.7.2. 5-(20-Propenyl)-25,27-dimethoxy-26,28-di(N-
benzenesulfonyl carbamoylmethoxy)calix[4]arene (18).
Compound 18 was obtained as white solid (1.31 g, 90%)
with mp 75–77 ꢀC. IR (deposit from CH2Cl2 solution on a
NaCl plate): 3324 (NH), 1733 (C]O), 1636 (C]C), 1349
solution on a NaCl plate): 1762 (C]O), 1644 (C]C) cmꢁ1
.
1H NMR (CDCl3): d 1.32 (t, J¼7.0 Hz, 6H, CH3), 2.68–4.48
(m, 24H, ArCH2, CH2CH]CH2, OCH2CO, CH2CH3,
OCH3), 4.48–5.55 (m, 2H, CH]CH2), 5.39–5.81 (m, 1H,
CH]CH2), 6.00–7.43 (m, 11H, ArH); 13C NMR (CDCl3):
d 14.22, 30.7, 60.9, 114.7, 122.5, 127.5, 128.3, 128.7,
128.9, 132.9, 133.1, 133.4, 133.8, 136.7, 136.8, 138.0,
1
(S]O), 1154 (S]O) cmꢁ1. H NMR (CDCl3): d 2.83–
5.18 (m, 22H, CH]CH2, ArCH2, OCH3, CH2CH]CH2,
OCH2), 5.62–5.84 (br s, 1H, CH]CH2), 6.07–8.38 (m,

D. Zhang et al. / Tetrahedron 63 (2007) 5076–5082
5081
21H, ArH), 9.18–9.32 (s, 2H, NH); 13C NMR (CDCl3):
d 25.6, 30.7, 39.0, 39.2, 53.4, 68.0, 71.7, 115.4, 123.6,
126.4, 128.6, 129.1, 129.2, 132.8, 134.3, 134.5, 135.2,
137.6, 138.5, 141.9, 151.0, 152.6, 166.3. Anal. Calcd for
C49H46N2S2O10: C, 66.35; H, 5.23; N, 3.16. Found: C,
66.01; H, 5.11; N, 3.34%.
room temperature and filtered. The functionalized silica
gel was washed with 50 mL each of toluene, acetone, and
MeOH, and then dried in oven for 1 h.
3.2.9.1. 25,27-Dimethoxy-26,28-di(N-methanesulfonyl
carbamoylmethoxy)calix[4]arene immobilized by a di-
propyl sulfide linkage on silica gel. Resin 2 was obtained
as a cream-colored solid. Elemental analysis: C, 6.64;
H, 1.07; N, 0.22%. Ion-exchange capacity¼78 mmol of
ligand/g of resin.
3.2.7.3. 5-(20-Propenyl)-25,27-dimethoxy-26,28-di[N-
(4-nitrobenzene)sulfonyl carbamoylmethoxy]calix[4]-
arene (19). Compound 19 was obtained as a yellow solid
(1.55 g, 96%) with mp 100–105 ꢀC. IR (deposit from
CH2Cl2 solution on a NaCl plate): 3326 (NH), 1735
3.2.9.2. 25,27-Dimethoxy-26,28-di(N-benzenesulfonyl
carbamoylmethoxy)calix[4]arene immobilized by a di-
propyl sulfide linkage on silica gel. Resin 3 was obtained
as a cream-colored solid. Elemental analysis: C, 8.97;
H, 1.22; N, 0.33%. Ion-exchange capacity¼118 mmol of
ligand/g of resin.
(C]O), 1642 (C]C), 1350 (S]O), 1165 (S]O) cmꢁ1
.
1H NMR (CDCl3): d 3.02–5.17 (m, 22H, CH]CH2,
ArCH2, OCH3, CH2CH]CH2, OCH2), 5.68–6.04 (m, 1H,
CH]CH2), 6.32–7.38 (m, 11H, ArH), 8.12–8.58 (m, 8H,
ArH), 9.41–9.57 (br s, 2H, NH); 13C NMR (CDCl3)
d 25.6, 30.8, 38.8, 53.4, 68.0, 70.9, 123.5, 123.9, 124.4,
127.9, 128.7, 129.4, 129.7, 130.2, 130.6, 132.7, 134.8,
135.3, 137.5, 144.1, 147.5, 151.0. Anal. Calcd for
C49H44N4S2O14$0.2C6H6: C, 60.74; H, 4.59; N, 5.64.
Found: C, 60.98; H, 4.57; N, 5.54%.
3.2.9.3. 25,27-Dimethoxy-26,28-di[N-(4-nitrobenzene)-
sulfonyl carbamoylmethoxy]calix[4]arene immobilized
by a dipropyl sulfide linkage on silica gel. Resin 4 was
obtained as a cream-colored solid. Elemental analysis: C,
3.19; H, 0.72; N, 0.15%. Ion-exchange capacity¼54 mmol
of ligand/g of resin.
3.2.7.4. 5-(20-Propenyl)-25,27-dimethoxy-26,28-di(N-
trifluoromethanesulfonyl carbamoylmethoxy)calix[4]-
arene (20). Compound 20 was obtained as a white solid
(1.30 g, 93%) with mp 115–117 ꢀC. IR (deposit from
CH2Cl2 solution on a NaCl plate): 3200 (NH), 1739
3.2.9.4. 25,27-Dimethoxy-26,28-di(N-methanesulfonyl
carbamoylmethoxy)calix[4]arene immobilized by a pro-
pylhexylsulfide linkage on silica gel. Resin 5 was obtained
as a cream-colored solid. Elemental analysis: C, 4.19;
H, 0.83; N, 0.17%. Ion-exchange capacity¼61 mmol of
ligand/g of resin.
(C]O), 1640 (C]C), 1388 (S]O), 1198 (S]O) cmꢁ1
.
1H NMR (CDCl3): d 2.84–5.14 (m, 22H, CH]CH2,
ArCH2, OCH3, CH2CH]CH2, OCH2), 6.27–7.24 (m,
11H, ArH), 5.70–6.04 (br s, 1H, CH]CH2), 8.63–9.89 (s,
2H, NH); 13C NMR (CDCl3): d 30.3, 30.8, 38.9, 39.1,
53.4, 58.6, 68.0, 71.1, 115.6, 117.8, 120.4, 124.1, 128.7,
129.7, 130.2, 131.1, 132.6, 135.2, 137.5, 150.8, 152.5,
158.0, 165.8. Anal. Calcd for C39H36N2F6S2O10: C, 53.79;
H, 4.17; N, 3.22. Found: C, 53.66; H, 3.98; N, 2.99%.
3.2.9.5. 25,27-Dimethoxy-26,28-di(N-benzenesulfonyl
carbamoylmethoxy)calix[4]arene immobilized by a pro-
pylhexylsulfide linkage on silica gel. Resin 6 was obtained
as a cream-colored solid. Elemental analysis: C, 9.53;
H, 1.08; N, 0.37%. Ion-exchange capacity¼132 mmol of
ligand/g of resin.
3.2.8. 6-Triethoxysilylhexyl mercaptan (21). A stream of
anhydrousammoniagaswasslowlyintroducedintoamixture
of 6-triethoxysilylhexyl bromide (25) (26.20 mmol), thio-
urea (2.39 g, 31.57 mmol), and DMF (1.68 mL). While the
ammonia flow was maintained, the mixture was heated at
125 ꢀC for 5 h with stirring. Filtration followed by concentra-
tion of the filtrate in vacuo gave an oil, which was distilled
under reduced pressure (3.10 g, 59%) with bp 88 ꢀC/
0.5 mmHg. IR (deposit from CH2Cl2 solution on a NaCl
3.2.9.6. 25,27-Dimethoxy-26,28-di[N-(4-nitrobenzene)-
sulfonyl carbamoylmethoxy]calix[4]arene by a pro-
pylhexylsulfide linkage on silica gel (7). Resin 7 was
obtained as a cream-colored solid. Elemental analysis: C,
6.25; H, 0.91; N, 0.27%. Ion-exchange capacity¼96 mmol
of ligand/g of resin.
3.2.9.7. 25,27-Dimethoxy-26,28-di(N-methanesulfonyl
carbamoylmethoxy)calix[4]arene immobilized by a pro-
pyldecylsulfide linkage on silica gel (8). Resin 8 was ob-
tained as a cream-colored solid. Elemental analysis: C,
9.37; H, 1.45; N, 0.53%. Ion-exchange capacity¼189 mmol
of ligand/g of resin.
plate): 2590 (SH), 1082 (Si–O), 1106 (C–O) cmꢁ1 1H
.
NMR (CDCl3): d 0.63 (t, J¼8.0 Hz, 2H, CH2Si), 1.23 (t,
J¼7.0 Hz, 9H, CH3), 1.31–1.42 (m, 7H, SH, CH2), 1.57–
1.64 (m, 2H, CH2CH2SH), 2.49–2.58 (m, 2H, CH2SH),
3.79–3.84 (m, 6H, OCH2); 13C NMR (CDCl3): d 10.34,
18.29, 22.66, 24.63, 27.98, 32.52, 33.92, 58.29, 70.25.
Anal. Calcd for C12H28SSiO3$0.5H2O: C, 49.82; H, 9.69.
Found: C, 49.85; H, 9.66%.
3.2.9.8. 25,27-Dimethoxy-26,28-di(N-benzenesulfonyl
carbamoylmethoxy)calix[4]arene immobilized by a pro-
pyldecylsulphide linkage on silica gel. Resin 9 was
obtained as a cream-colored solid. Elemental analysis: C,
9.24; H, 1.48; N, 0.36%. Ion-exchange capacity¼128 mmol
of ligand/g of resin.
3.2.9. General procedure for immobilization of proton-
ionizable calix[4]arenes on silica gel. The di-ionizable cal-
ix[4]arenes 19–22 (2.20 mmol) were reacted with u-tri-
ethoxysilylalkyl mercaptan (2.20 mmol) in the presence of
CHP in ClCH2CH2Cl (5 mL) at 70 ꢀC overnight. Activated
silica gel (10.00 g) in toluene (40 mL) was added and mix-
ture was refluxed for 72 h. The mixture was cooled to
3.2.9.9. 25,27-Dimethoxy-26,28-di[N-(4-nitrobenzene)-
sulfonyl carbamoylmethoxy]calix[4]arene immobilized
by a propyldecylsulfide linkage on silica gel. Resin 10

5082
D. Zhang et al. / Tetrahedron 63 (2007) 5076–5082
4. Calixarenes for Separations; Lumetta, G. J., Rogers, R. D.,
Gopalan, A. S., Eds.; ACS Symposium Series 757; American
Chemical Society: Washington, DC, 2000.
was obtained as a cream-colored solid. Elemental analy-
sis: C, 9.38; H, 1.25; N, 0.62%. Ion-exchange capacity¼
221 mmol of ligand/g of resin.
€
5. Calixarenes 2001; Asfari, Z., Bohmer, V., Harrowfield, J.,
3.3. Pb2D sorption by ion-exchange resins 2–10
Vicens, J., Eds.; Kluwer Academic: Dordrecht, The
Netherlands, 2001.
6. Talanova, G. G.; Hwang, H.-S.; Talanov, V. S.; Bartsch, R. A.
Chem. Commun. 1998, 419–420.
7. Talanova, G. G.; Hwang, H.-S.; Talanov, V. S.; Bartsch, R. A.
Chem. Commun. 1998, 1329–1330.
8. Talanova, G. G.; Elkarim, N. S. A.; Talanov, V. S.; Bartsch,
R. A. Anal. Chem. 1999, 71, 3106–3109.
9. Talanova, G. G.; Talanov, V. S.; Gorbunova, M. G.; Hwang,
H.-S.; Bartsch, R. A. J. Chem. Soc., Perkin Trans. 2 2002,
2072–2077.
10. Talanova, G. G.; Talanov, V. S.; Hwang, H.-S.; Park, C.;
Surowiec, K.; Bartsch, R. A. Org. Biomol. Chem. 2004, 2,
2585–2592.
11. Zhou, H.; Surowiec, K.; Purkiss, D. W.; Bartsch, R. A. Org.
Biomol. Chem. 2005, 3, 1676–1684.
12. Yilmaz, M.; Memon, S.; Tabakci, M.; Bartsch, R. A. New
Frontiers in Polymer Research; Bregg, R. K., Ed.; Nova
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Harris, S. J.; McKervey, M. A. Anal. Lett. 1993, 26, 153–
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An aqueous (PbNO3)2 solution was prepared such that the
molar ratio of the metal ion to calixarene units in the resin
packing was 1:1. The Pb(NO3)2 was dissolved in 0.50 L of
DI water. A column containing 1.00 g of resin was washed
with 25 mL of 0.010 M HNO3 and then with 100 mL of
DI water at a flow rate of 3.0 mL/min. Of the 0.50-L sample
solution, a 2.0-mL portion was removed for Pb2+ analysis
and a 5.0-mL portion for pH determination. The remainder
of the sample solution was passed through the column. A
2.0-mL portion of the effluent was collected for Pb2+ analy-
sis. The column was then washed with 100 mL of DI water
to remove any unbound metal ions from the packing. The
sorbed metal ions were then stripped with 0.010 M HNO3
at a flow rate of 0.3 mL/min. The Pb2+ concentration of
the eluant solution, sample solution, and loading effluent
was determined by atomic absorption spectrophotometry
after appropriate dilution with DI water.
Acknowledgements
€
14. Brindle, R.; Albert, K.; Hassis, S. J.; Troltasch, C.; Horne, E.;
Glennon, J. D. J. Chromatogr., A 1996, 731, 41–46.
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Harris, S. J.; McKervey, M. A. J. Chromatogr., A 1996, 731,
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16. Arena, G.; Casnati, A.; Mirone, L.; Sciotto, D.; Ungaro, R.
Chem. Commun. 1996, 2277–2278.
17. Shu, C. M.; Chung, W. S.; Wu, S. H.; Ho, Z. C.; Lin, L. G.
J. Org. Chem. 1999, 64, 2673–2679.
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This research was supported by Project 003644-0263-2003
from the Technology Development and Transfer Program
of the Texas Higher Education Coordinating Board and
Grant DE-FG02-90ER14416 from the Division of Chemical
Sciences, Geosciences, and Biosciences of the Office of
Basic Energy Sciences of the U.S. Department of Energy.
We thank the National Science Foundation of Grant CHE-
9808436 that was used to purchase the Varian INOVA
NMR spectrometer.
References and notes
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