Synthesis and catalytic applications of sulfonic acid group-functionalized nano- and microsilica structures

Article abstract of DOI:10.1080/00397911.2010.497597

Sulfonic acid group-functionalized nano- and microsilica with different sizes and shapes were synthesized. Silica nanospheres with an average size of 225 nm, silica microtubes, and fine silica gel were prepared and functionalized by sulfonic acid. Their c

Full text of DOI:10.1080/00397911.2010.497597

This article was downloaded by: [Pennsylvania State University]
On: 14 May 2012, At: 03:14
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered
office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Synthetic Communications: An
International Journal for Rapid
Communication of Synthetic Organic
Chemistry
Publication details, including instructions for authors and
subscription information:
http://www.tandfonline.com/loi/lsyc20
Synthesis and Catalytic Applications
of Sulfonic Acid Group–Functionalized
Nano- and Microsilica Structures
a
b
a
Laleh Torkian , Peyman Salehi , Minoo Dabiri & Sharmin Kharrazi
c
a
Faculty of Science, Department of Chemistry, Shahid Beheshti
University, Tehran, Iran
b
Department of Phytochemistry, Medicinal Plant, and Drugs
Research Institute, Shahid Beheshti University, Tehran, Iran
c
Faculty of Science, Department of Physics, Shahid Beheshti
University, Tehran, Iran
Available online: 20 May 2011
To cite this article: Laleh Torkian, Peyman Salehi, Minoo Dabiri & Sharmin Kharrazi (2011): Synthesis
and Catalytic Applications of Sulfonic Acid Group–Functionalized Nano- and Microsilica Structures,
Synthetic Communications: An International Journal for Rapid Communication of Synthetic Organic
Chemistry, 41:14, 2115-2122
To link to this article: http://dx.doi.org/10.1080/00397911.2010.497597
PLEASE SCROLL DOWN FOR ARTICLE
Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditions
This article may be used for research, teaching, and private study purposes. Any
substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,
systematic supply, or distribution in any form to anyone is expressly forbidden.
The publisher does not give any warranty express or implied or make any representation
that the contents will be complete or accurate or up to date. The accuracy of any
instructions, formulae, and drug doses should be independently verified with primary
sources. The publisher shall not be liable for any loss, actions, claims, proceedings,

demand, or costs or damages whatsoever or howsoever caused arising directly or
indirectly in connection with or arising out of the use of this material.

1
Synthetic Communications , 41: 2115–2122, 2011
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2010.497597
SYNTHESIS AND CATALYTIC APPLICATIONS OF
SULFONIC ACID GROUP–FUNCTIONALIZED
NANO- AND MICROSILICA STRUCTURES
1
Laleh Torkian, Peyman Salehi, Minoo Dabiri, and
2
1
3
Sharmin Kharrazi
1
Faculty of Science, Department of Chemistry, Shahid Beheshti University,
Tehran, Iran
2
Department of Phytochemistry, Medicinal Plant, and Drugs Research
Institute, Shahid Beheshti University, Tehran, Iran
3
Faculty of Science, Department of Physics, Shahid Beheshti University,
Tehran, Iran
GRAPHICAL ABSTRACT
Abstract Sulfonic acid group–functionalized nano- and microsilica with different sizes and
shapes were synthesized. Silica nanospheres with an average size of 225 nm, silica micro-
tubes, and fine silica gel were prepared and functionalized by sulfonic acid. Their catalytic
activity was investigated in the three-component Biginelli reaction for the synthesis of
dihydropyrimidinones.
Keywords Biginelli reaction; silica microtubes; silica nanospheres; silica sulfuric acid;
supported catalyst
INTRODUCTION
Acidic catalysts are widely used, in various industries, for producing a
[
1]
huge amount of valuable products every year. Immobilization of an acid or
base on silica via covalent bonding has many advantages over homogeneous
Received May 5, 2010.
Address correspondence to Minoo Dabiri, Faculty of Science, Department of Chemistry, Shahid
Beheshti University, G. C., Evin, Tehran 1983916113, Iran, or Peyman Salehi, Department of
Phytochemistry, Medicinal Plants, and Drugs Research Institute, Shahid Beheshti University, G. C.,
Evin, Tehran 1983916113, Iran. E-mail: m-dabiri@sbu.ac.ir; p-salehi@sbu.ac.ir
2
115

2116
L. TORKIAN ET AL.
catalysts. Heterogeneous catalysts can be recovered and reused, whereas homo-
[
2]
geneous catalysts are less stable and contaminate reaction mixtures. Hetero-
geneous systems are of great interest and importance because of their
[
3]
applications in industry and developing technologies. The use of solid acids
has many advantages over liquid acids such as ease of handling, decreasing
[
1,4]
reactor and plant corrosion problems, and environmentally safe disposal.
Also, wastes and by-products can be minimized or avoided by developing
[
5]
cleaner synthetic routes.
The immobilization of the reagents on the surface of porous solid sup-
ports has advantages over the conventional solution-phase reactions because
of the good dispersion of active reagent sites, associated selectivity, and easier
[
6]
workup. High surface area of porous solids makes them good candidates for
reagent support in heterogeneous reactions since the catalytic reactions take
place on or near the catalyst’s surface. Mesoporous structures of silica have,
[
7]
so far, been very popular as catalyst supports. The functionalization of silica
surface, by using required reagents and=or linkers, results in the production of
[
solid catalysts. The silica surface consists of two types of functional groups,
8]
[
9–11]
namely siloxane (SiꢀOꢀSi) and silanol (SiꢀOH),
which provide functiona-
lization with different functional groups. Thus, silica modification can occur via
[
12]
the reaction of particular molecules with either the siloxane or the silanol.
13,14]
[
Zolfigol et al. have synthesized and applied silica sulfuric acid (SSA),
[
silica
as reagents or as
15]
[16]
chloride (SC),
and silica phosphoric acid (SPA)
catalysts under heterogeneous conditions for different organic functional group
transformations.
3
three-component Biginelli reaction
,4-Dihydropyrimidin-2-(1H)-one (DHPM) was first synthesized by the
in 1893, and its derivatives show a diverse
[
17]
[
range of therapeutical properties and pharmacological activities such as antimito-
18]
[
19]
[20]
[21]
antiviral,
[22]
tic,
analgesic,
and antihypertensive agents.
The simple and
direct method for the synthesis of DHPMs involves the one-pot condensation of
an aldehyde, an b-ketoester, and urea under acidic conditions.
Here, we report the synthesis of sulfonic acid group–functionalized particles of
silica, with different sizes and shapes, and catalytic performance of these reagents as
reusable catalysts for the one-pot synthesis of 3,4-dihydropyrimidin-2-(1H)-ones in
[
23]
good yields.
EXPERIMENTAL
Techniques and Materials
ꢀ
1
The infrared (IR) spectrum was obtained in the 400–4000 cm range by a
Fourier transform (FT)–IR 10MB BOMEM spectrometer. KBr pellets were used
for solid samples. Scanning electron microscopy (SEM) of the particles was carried
out using a Philips XLO SEM instrument. Samples were prepared by dispensing
drops of an aqueous suspension of particles onto a glass plate. This was allowed
to dry at room temperature and was then coated with a thin Au film. All commer-
cially available chemicals were obtained from Merck and Fluka companies and used
without further purifications.

NANO- AND MICROSILICA STRUCTURES
2117
Preparation of Silica Nanospheres
Monodispersed silica spheres were prepared by the modified St o¨ ber process.
[
24]
A mixture of 2.79 ml tetraethyl orthosilicate (TEOS) and 22.2 ml ethanol was added
to the mixture of 0.638 ml 28 wt% ammonia, 6.8 ml deionized water, and 17.6 ml
ethanol, under stirring, at room temperature. The reaction was allowed to continue
for 3.5 h with stirring. The particles were then separated by centrifugation and
washed with doubly distilled water. The size, as well as the size distribution for these
particles, was calculated from SEM images.
Preparation of Silica Microtubes
Silica microtubes were synthesized by hydrolyzing TEOS in a mixture of etha-
nol, ammonia, water, and dl-tartaric acid, following the procedure reported by
[25]
Nakamura et al. Thus, 7.8 ml of TEOS was dissolved in 50 ml of ethanol contain-
ing 0.2 g of dl-tartaric acid and 0.6 ml of water. The solution was permitted to stand
for 30 min to form SiO solution, and finally 20 ml of ammonium hydroxide solution
2
(28% NH solution) was added. After 15–20 min, the reaction was observed to be
3
completed. The precipitate was separated and washed several times after filtering,
redispersing in water, and centrifugating.
Preparation of Silica Sulfuric Acid
Silica powder (2.0 g, fine silica gel, silica nanosphere, or silica microtube) was
dispersed in 10 ml of dry dichloromethane and stirred in a round-bottomed flask.
–
3
ꢀ3
Chlorosulfonic acid (6.3 ꢁ 10 mmol for fine silica gel, 6 ꢁ 10 mmol for silica
ꢀ3
microtube, and 4.5 ꢁ 10 mmol for silica nanosphere) was added dropwise at room
temperature. HCl gas evolved from the reaction vessel immediately. After the
addition was complete, the mixture was stirred for 30 min. Evaporation of the sol-
vent on a rotary evaporator resulted in formation of silica sulfuric acid (SSA) as a
white solid.
General Procedure for the Synthesis of DHPMs
A mixture of the aldehyde (2 mmol), the b-dicarbonyl compound (2 mmol),
urea or thiourea (3 mmol), and the catalyst (equal to 0.6 mmol H ) in ethanol
þ
(10 ml) was refluxed for 6 h. Then, the solvent was evaporated under reduced press-
ure. The solid mixture was washed with cold water (20 ml) to remove the excess of
urea or thiourea and filtered. The remaining solid material was washed with hot ethyl
acetate (30 ml). The filtrate was concentrated, and the solid product was recrystal-
lized from ethyl acetate=n-hexane or ethanol.
RESULTS AND DISCUSSION
Two types of nanosilica structures were synthesized. The size and shape of the
synthesized silica particles were confirmed by using scanning electron microscopy

2118
L. TORKIAN ET AL.
Figure 1. SEM micrographs of the silica nanospheres (a) and their size distribution (b) and silica micro-
tubes (c) and (d).
(SEM). Figure 1 shows the SEM micrographs of the silica nanospheres (a), their size
distribution (b), and silica microtubes (c) and (d).
The silica nanospheres, as seen in the SEM images, have an average size of
25 nm with a narrow size distribution of 1%. SEM micrographs of silica tubes con-
2
firm the formation of hollow tubes with a submicrometer diameter. However, large
agglomerates of silica spherical particles can also be observed. Figure 1(d) shows the
magnified view of a bunch of tubes, where the color contrast confirms the hollow
nature of the structures.
The IR spectroscopy presents a useful tool to initially detect the success of the
immobilization process. This proposal can be clarified by comparing the precursor
and modified surfaces. IR spectroscopy was applied to find the surface groups on
all samples. The presence of a silanol (SiꢀOH) group on the SiO surface results
2
–
1
in the appearance of an absorption band around 950 cm . This can be used as a ref-
erence to qualitatively investigate the replacement of OH group with sulfonic acid,
on the surface of the particles. Figure 2 shows the Fourier transform (FT)–IR spec-
tra of all samples, before and after sulfonic acid functionalization. As it could be
ꢀ1
observed, the intensity of the peak around 950 cm was reduced, as compared to
ꢀ
1
other peaks [viz., 1100 cm (SiꢀOꢀSi),] in all samples. The other evidence is the
ꢀ
1
appearance of signature bands of the SO group (1070 cm ) on the surface, after
3
functionalization.

NANO- AND MICROSILICA STRUCTURES
2119
Figure 2. FT-IR spectra of the silica gelfine (a), silica nanospheres (b), and silica microtubes (c) before
(black) and after (light gray) functionalization with chlorosulfonic acid.
Next, we studied the three-component Biginelli condensation catalyzed by sul-
fonic acid group–functionalized particles of silica, with different sizes and shapes, to
afford the DHPM (Scheme 1).
A summary of the results obtained is provided in Table 1. The reactions pro-
ceeded smoothly in refluxing ethanol and were completed within 6 h. Table 1 shows
the generality of the present protocol, which is equally effective for urea and thiourea
in the presence of a variety of aldehydes and b-dicarbonyl compound.
Scheme 1. Three-component Biginelli reaction.

2120
L. TORKIAN ET AL.
Table 1. Synthesis of dihydropyrimidin-ones and -thiones (DHPMs) by the condensation of aldehydes,
dicarbonyls, and urea or thiourea catalyzed by silica sulfuric acid in ethanol
1
R
2
R
3
R
a
b
c
Entry
X
Yield (%)
Yield (%)
Yield (%)
1
2
3
4
5
6
7
8
9
4-Cl-C
2,4-(Cl) -C
2-O N-C
4-F-C
6
H
4
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
OEt
OEt
OEt
OEt
OEt
OMe
OEt
OEt
OEt
OMe
O
O
O
O
O
O
S
89
90
87
88
93
95
85
94
90
90
88
88
85
87
93
94
84
92
86
88
85
86
82
84
90
92
80
89
85
87
2
6 3
H
2
6
H
4
6
H
4
4-CH
4-CH
4-CH
3
3
3
O-C
O-C
O-C
6
H
H
H
4
4
4
6
6
4-O
4-F-C
4-O N-C
2
N-C
6
H
4
S
6
H
4
S
1
0
2
6
H
4
S
a
b
c
Silica microtubes.
Silica nanospheres.
Fine silica gel.
According to the type of the used silica structures, the maximum amount of
chlorosulfonic acid was loaded on the surface of the silica powder in the functionali-
zation reactions (0.209, 0.199, and 0.15 ml per gram of fine silica gel, silica microtube
and silica nanosphere, respectively). Great amounts of chlorosulfonic acid changed
the color of the catalyst to pale yellow or light brown. To compare the activity of
þ
the catalysts, the reactions were carried out with equal amounts of H for different
catalysts (i.e., 0.3 g SSA based on fine silica gel, 0.33 g SSA based on silica microtubes,
and 0.44 g SSA based on silica nanospheres).
The results in Table 1 show that all of the catalysts were effective for progress
of the reaction in a similar way, although the amounts of silica used were in the order
of nanosphere > microtube > fine. This can be attributed to the amount of the silanol
(
SiꢀOH) groups, which are functionalized by chlorosulfonic acid.
The reusability of the catalyst is an important factor from economical and
environmental points of view. Therefore, the reusability of SSA was examined in
the reaction of 4-chlorobenzaldehyde, urea, and ethyl acetoacetate under optimized
reaction conditions. The product was isolated by filtration, and after washing the
solid residues with ethyl acetate, the remaining catalyst was reloaded with fresh
reagents for further runs. The results showed that the catalyst can be used four times
without loss of its activity (Table 2).
Table 2. Reusability of SSA in the reaction of ethyl acetoacetate, 4-chlorobenzaldehyde, and urea
a
b
c
Run
Yield (%)
Yield (%)
Yield (%)
1
2
3
4
89
90
89
88
88
89
88
87
85
86
84
84
a
Silica microtubes.
Silica nanospheres.
Fine silica gel.
b
c

NANO- AND MICROSILICA STRUCTURES
2121
CONCLUSIONS
Different types of silica structures were synthesized and functionalized by sul-
fonic acid. The loading of ꢀSO H functional group per gram of the silica was depen-
3
dent on the amount of available silanol groups, which were in the order of
fine > microtube > nanosphere. All of the catalysts were effective for the synthesis
of DHPMs in the three-component Biginelli reaction.
ACKNOWLEDGMENT
Financial support from the Research Council of Shahid Beheshti University
and the Catalyst Center of Excellence (CCE) is gratefully acknowledged.
REFERENCES
1
2
. Corma, A. Solid acid catalysts. Curr. Opin. Solid State Mat. Sci. 1997, 2, 63–75.
. Minakata, S.; Komatsu, M. Organic reactions on silica in water. Chem. Rev. 2009, 109,
711–724.
3
4
5
6
7
8
9
. Sheldon, R. A.; Downing, R. S. Heterogeneous catalytic transformations for environmen-
tally friendly production. Appl. Catal. A: Gen. 1999, 189, 163–183.
. Corma, A.; Garcia, H. Organic reactions catalyzed over solid acids. Catal. Today 1997,
3
8, 257–308.
. Sikdar, S. K.; Howell, S. G. On developing cleaner organic unit processes. J. Clean. Prod.
998, 6, 253–259.
1
. Varma, R. S. Solvent-free organic syntheses: Using supported reagents and microwave
irradiation. Green Chem. 1999, 1, 43–55.
. Ariga, K.; Vinu, A.; Hill, J. P.; Mori, T. Coordination chemistry and supramolecular
chemistry in mesoporous nanospace. Coordin. Chem. Rev. 2007, 251, 2562–2591.
. Kuschel, A.; Sievers, H.; Polarz, S. Amino acid silica hybrid materials with mesoporous
structure and enantiopure surfaces. Angew. Chem. Int. Ed. 2008, 47, 9513–9517.
. Akl, M. A. A.; Kenawy, I. M. M.; Lasheen, R. R. Organically modified silica gel and
flame atomic absorption spectrometry: Employment for separation and preconcentration
of nine trace heavy metals for their determination in natural aqueous systems. Microchem.
J. 2004, 78, 143–156.
1
0. Filha, V. L. S. A.; Wanderley, A. F.; Sousa, K. S. D.; Espinola, J. G. P.; Fonseca, M. G.
D.; Arakaki, T.; Arakaki, L. N. H. Thermodynamic properties of divalent cations
complexed by ethylenesulfide immobilized on silica gel. Colloids Surf. A 2006, 279, 64–68.
1. Antonio, P.; Ihac, K.; Suarez-Iha, M. E. V. Adsorption of di-2-pyridyl ketone salicyloyl-
hydrazone on silica gel: Characteristics and isotherms. Talanta 2004, 64, 485–490.
2. Cestari, A. R.; Viera, E. F. S.; Nascimento, A. J. P.; Oliveira, F. J. R.; Bruns, R. E.;
Airoldi, C. New factorial designs to evaluate chemisorption of divalent metals on ami-
nated silicas. J. Colloid Interface Sci. 2001, 241, 45–51.
1
1
1
3. Zolfigol, M. A. Silica sulfuric acid=NaNO
production of thionitrites and disulfides under mild conditions. Tetrahedron 2001, 57,
509–9511.
2
as a novel heterogeneous system for
9
14. Salehi, P.; Zolfigol, M. A.; Shirini, F.; Baghbanzadeh, M. Silica sulfuric acid and silica
chloride as efficient reagents for organic reactions. Curr. Org. Chem. 2006, 10, 2171–2189.
1
5. Zolfigol, M. A.; Torabi, M.; Mallakpour, S. E. Silica chloride=NaNO
geneous system for the oxidation of urazoles under mild conditions. Tetrahedron 2001, 57,
381–8384.
2
as a novel hetero-
8

2122
L. TORKIAN ET AL.
1
6. Zolfigol, M. A.; Shirini, F.; Zamani, K.; Ghofrani, E.; Ebrahimi, S. Silica phosphoric
acid=NaNO as a novel heterogeneous system for the coupling of thiols to their corre-
2
sponding disulfides. Phosphorus Sulfur Silicon Relat. Elem. 2004, 179, 2177–2182.
7. Biginelli, P. Derivati aldeiduredici degli eteri acetil- e dossal-acetico. Gazz Chim. Ital.
1
1
1
1893, 23, 360–416.
8. Kappe, C. O. Recent advances in the Biginelli dihydropyrimidine synthesis: New tricks
from an old dog. Acc. Chem. Res. 2000, 33, 879–888.
9. Mayer, T. U.; Kapoor, T. M.; Haggarty, S. J.; King, R. W.; Schreiber, S. I.; Mitchison,
T. J. Smart molecule inhibitor of mitotic spindle bipolarity identified in a phenotype-based
screen. Science 1999, 286, 971–974.
2
0. Sadanandam, Y. S.; Shetty, M. M.; Diwan, P. V. Synthesis and biological evaluation
of new 3,4-dihydro-6-methyl-5-N-methyl-carbamoyl-4-(substituted phenyl)-2(1H)-
pyrimidinones and pyrimidinethiones. Eur. J. Med. Chem. 1992, 27, 87–92.
1. Hurst, E. W.; Hull, R. Two new synthetic substances active against viruses of the
psittacosis-lymphogranuloma-trachoma group. J. Med. Pharm. Chem. 1961, 3, 215–229.
2. Atwal, K. S.; Rovnyak, G. C.; Schwartz, J.; Moreland, S.; Hedberg, A.; Gougoutas, J. Z.;
Malley, M. F.; Floyd, D. M. Dihydropyrimidine calcium channel blockers: 2-Heterosub-
stituted 4-aryl-1,4-dihydro-6-methyl-5-pyrimidinecarboxylic acid esters as potent mimics
of dihydropyridines. J. Med. Chem. 1990, 33, 1510–1515.
2
2
23. Salehi, P.; Dabiri, M.; Zolfigol, M. A.; Bodaghi Fard, M. A. Silica sulfuric acid: An
efficient and reusable catalyst for the one-pot synthesis of 3,4-dihydropyrimidin-2
(
1H)-ones. Tetrahedron Lett. 2003, 44, 2889–2891.
2
2
4. St o¨ ber, W.; Fink, A.; Bohn, E. Controlled growth of monodisperse silica spheres in the
micron size range. J. Colloid Interface Sci. 1968, 26, 62–69.
5. Nakamura, H.; Matsui, Y. Silica gel nanotubes obtained by the sol-gel method. J. Am.
Chem. Soc. 1995, 117, 2651–2652.