Modified SBA-15 as an efficient environmentally friendly nanocatalyst for one-pot synthesis of tetrahydrobenzo[b]pyrane derivatives

Article abstract of DOI:10.1080/15533174.2011.591646

SBA-15 mesoporous silicas modified with proline and aminopropyl functional groups were employed for synthesis of tetrahydrobenzo[b]pyrane derivatives by simply mixing the precursors with surface-modified catalyst in a mortar. The mesoporous catalysts were characterized by Fourier-transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), small-angle x-ray diffractometry (SAXS), thermogravimetric/differential thermal analyzer (TG/DTA), Barrett-Joiner-Halenda (BJH) pore size and volume analysis, and Brunauer-Emmett-Teller (BET) surface area measurement methods. The results indicate that SBA-15 mesoporous silica modifiedwith proline and aminopropyl functional groups can be effectively utilized for synthesis of tetrahydrobenzo[b]pyrane derivatives. Copyright Taylor & Francis Group, LLC.

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Modified SBA-15 as an Efficient Environmentally
Friendly Nanocatalyst for One-Pot Synthesis of
Tetrahydrobenzo[b]pyrane Derivatives
Mahmood Kazemzad a , Amir Ali Yuzbashi a , Saeed Balalaie b & Morteza Bararjanian b
a Materials and Energy Research Center, Tehran, I. R. Iran
b Department of Chemistry, K. N. Toosi University of Technology, Tehran, I. R. Iran
Version of record first published: 07 Nov 2011.
To cite this article: Mahmood Kazemzad , Amir Ali Yuzbashi , Saeed Balalaie & Morteza Bararjanian (2011): Modified
SBA-15 as an Efficient Environmentally Friendly Nanocatalyst for One-Pot Synthesis of Tetrahydrobenzo[b]pyrane
Derivatives, Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 41:9, 1182-1187
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Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 41:1182–1187, 2011
Copyright ꢀ Taylor & Francis Group, LLC
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ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533174.2011.591646
Modified SBA-15 as an Efficient Environmentally Friendly
Nanocatalyst for One-Pot Synthesis of
Tetrahydrobenzo[b]pyrane Derivatives
Mahmood Kazemzad,1 Amir Ali Yuzbashi,1 Saeed Balalaie,2
and Morteza Bararjanian2
1Materials and Energy Research Center, Tehran, I. R. Iran
2Department of Chemistry, K. N. Toosi University of Technology, Tehran, I. R. Iran
Several nanostructured materials such as zeolites are widely
applied as catalysts or catalyst support, in both batch and con-
tinuous processes. However, the pore size limitation is the
main disadvantage of these materials that prevents their cat-
alytic sites being accessible for large molecules. Ordered meso-
porous compounds, discovered in1992 by Mobil Company, have
been introduced as a substitute for the zeolites in reactions
containing large molecules. They have two-dimensional (2D)
or three-dimensional (3D) structures, and their functionaliza-
tion with organic groups has become a major area of research
for a variety of applications. They have potential applications
in separation, adsorption, sensors, catalyst support, and cataly-
sis.[1–5]
SBA-15 mesoporous silicas modified with proline and
aminopropyl functional groups were employed for syn-
thesis of tetrahydrobenzo[b]pyrane derivatives by simply
mixing the precursors with surface-modified catalyst in a
mortar. The mesoporous catalysts were characterized by
Fourier-transform infrared spectroscopy (FTIR), transmission
electron microscopy (TEM), small-angle x-ray diffractome-
try (SAXS), thermogravimetric/differential thermal analyzer
(TG/DTA), Barrett–Joiner–Halenda (BJH) pore size and volume
analysis, and Brunauer–Emmett–Teller (BET) surface area mea-
surement methods. The results indicate that SBA-15 mesoporous
silica modified with proline and aminopropyl functional groups can
be effectively utilized for synthesis of tetrahydrobenzo[b]pyrane
derivatives.
Mbaraka et al. at Iowa State University described the syn-
thesis and characterization of multifunctionalized mesoporous
silica materials as catalysts in the esterification reaction of oils
with high free fatty acid content as a pretreatment step in
the production of biodiesel.[6] Catalytic cracking of palm oil
has been also carried out over HZSM-5 zeolite, mesoporous
MCM-41, and composite micromesoporous zeolite.[7] The
same goal was also followed for MgO-modified mesoporous
catalyst.[8]
Heteropoly acids immobilized on mesoporous silica were uti-
lized as an efficient catalyst for acylation of anisole by another
research team.[9] K. P. Prasanth reported hydrogen adsorption
in the Ni-, Rh-, and Pd-incorporated mesoporous MCM-41,
MCM-48, HMS, and SBA-15 samples.[10] Mesoporous silicas
containing carboxylic acid have been recently applied to hy-
drolysis of sucrose.[11] Fajula’s group is focused on the synthesis
and modification of mesoporous silica for its application in vari-
ous chromatography techniques.[12] Flavanone was synthesized
over aminopropyl-functionalized SBA-15 materials through a
solvent-free reaction procedure.[13] Transesterification activities
of the same catalysts were found to be very much dependent on
morphologies, dispersion of amino groups, and molecular shape
of aliphatic alcohols.[14]
Keywords functional groups, SBA-15 mesoporous silica, tetrahy-
drobenzo[b]pyranederivatives
INTRODUCTION
Homogeneous catalysis possesses a large number of active
sites at the molecular level, but their limited stability, recovery,
and recycling represents a weak point. Heterogeneous catalysts,
on the other hand, can be easily isolated by centrifuging or filter-
ing from reaction media. Thus, there have been several attempts
to get the advantages of both homogeneous and heterogeneous
catalysts. Grafting through covalent bonding should be an effi-
cient method among these, although the adsorbed, ion-paired,
and entrapped homogeneous catalyst species are also applied in
hetrogenizing the conventional or new types of homogeneous
catalysis.
Received 20 March 2011; accepted 29 March 2011.
The authors gratefully acknowledge financial aid from Materials
and Energy Research Center.
Address correspondence to Mahmood Kazemzad, Materials and
Energy Research Center, PO Box 14155–4777, Tehran, I. R. Iran.
E-mail: kazemzad@gmail.com
The use of simple (S)-proline as a catalyst for the inter-
molecular direct aldol reaction at the beginning of this century
1182

MODIFIED SBA-15 AS A NANOCATALYST
1183
became a true milestone in the growth of organocatalysis as trical furnace in order to burn off the organic template. It was
a useful synthetic strategy.[15] Since then, a plethora of new characterized by FTIR, BJH surface characterization, and TEM
organocatalytic[16] systems have been developed, allowing re- methods.
actions to reach extraordinary levels of efficiencies and widening
Amine-functionalized SBA-15 has been prepared using a
the scope of substrates used. The main publications in this field known procedure by refluxing a desired amount of aminopropyl
are related to B. List, in addition to his other reports related to triethoxysilane dissolved in toluene with mesopoporous silica
catalytic reactions.[17–22] Although proline is an abundant amino dispersed in it for 24 h. The obtained product was filtered and
acid that can be easily obtained, immobilization of molecular washed with toluene for removal of excess aminosilane and
catalysts on mesoporous silica can be exemplified as an efficient dried at 70◦C in an oven for 12 h.
hetrogenizing method for easy separation of molecular catalysts
by filtration.
Proline-modified mesoporous silica started with dissolution
of EDIA in acetonitrile. Then silica catalyst was dispersed in
Use of immobilized organic catalysts is not a new strat- this solution for 5–6 hours, followed by addition of L-proline.
egy in catalytic synthesis.[23] Chiral proline derivative was an- The whole mixture was stirred overnight, and finally water was
chored on mesoporous SBA-15 materials by nucleophilic sub- added into the mixture in order to decompose the unreacted
stitution of chloropropyl-functionalized SBA-15 with (S)-(–)-α, EDIA. The suspension was centrifuged and washed with water
α-diphenyl-2-pyrrolidinemethanol.[24]
and ethanol and dried at 70◦C for 12 h.
Herein we report an easy method for anchoring proline
via its carboxylic acid functional group using dicyclohexyl-
carbodiimide (DCC) in the presence of ethyldiisopropyl amine
(EDIA) on mesoporous silica as catalyst and catalyst support.
Proline-functionalized silica, as well as amine-functionalized
SBA-15, was applied as a catalyst for the synthesis of tetrahy-
drobenzo[b]pyrane derivatives as a typical base-catalyzed or-
ganic reaction.
Catalytic Tests
Two types of catalytic tests were followed for checking of the
modified mesoporous catalyst, the first procedure in a solution
and the second in the neat condition.
In a typical solution-based reaction, 1.2 mmol malononitrile
was added to a mixture of 1 mmol of an aromatic aldehyde and
dimedone (1.1 mmol; 154 mg) containing 50 mg solid catalyst;
3 ml of CH2Cl2 or ethanol as solvent was added into the reaction
vessel containing this mixture and it was stirred at room tem-
perature for 0.5–2 h (Scheme 1). Progress of the reaction was
simply followed by turning the magnetic mixer off and sam-
EXPERIMENTAL
Materials and Instruments
All of the chemicals used here were purchased from
Merck, except Genapol PF10 triblock copolymer, which is
a commercial cosurfactant from Clariant. Melting points
were determined with the Electrothermal 9100 apparatus
and reported without correction. Fourier-transform infrared
(FTIR) spectra were obtained on Bruker v33 with KBr
discs. Transmission electron microscopy (TEM) investigations
were carried out using the Philips CM-200 FEG instrument.
Brunauer–Emmett–Teller/Barrett–Joiner–Halenda (BET-BJH)
surface properties were determined using the Micromeritics Gi-
mini III 2375 instrument. The thermogravimetric/differential
thermal analyzer (TG/DTA) curves were recorded in air with
a heating rate of 10◦C/min using a simultaneous thermal an-
alyzer, STA/1640, and small-angle x-ray diffraction (SAXS)
patterns were recorded by a Philips X’Pert MPD instrument
using Co Kα radiation at 40 kV and 30 mA in 2θ range of
0.7–7◦.
TABLE 1
Finishing points of reactions based on aldehyde consumption
(minutes) for various aldehydes in catalytic reactions using
methods A (reaction in solution) and B (neat condition)
Melting
point
Ar
Catalyst SBA-PrNH2 SBA-Pro
(◦C)
C6H5
A
B
A
B
A
B
A
B
A
B
A
B
A
B
75
75
15
15
—
—
5
75∗
75
10
5
40
40
—
—
30
—
20
20
10
10
228–230
4-Br-C6H4
4-Cl-C6H4
4-CN-C6H4
3-OH-C6H4
4-OH-C6H4
3-NO2-C6H4
207–209
215–217
180–182
231–233
204–205
211–215
5
Synthesis of Mesoporus Silica and Its Surface
Modification
30
—
—
—
15
15
Mesoporous silica was prepared through a known proce-
dure as described in our previous report[4] by dissolution of
copolymer, as the structure-directing compound, in aqueous
acid solution and addition of tetraethyl orthosilicate (TEOS)
as the silica source, followed by hydrothermal condensation of
silica. The hybrid material obtained was heat-treated in an elec-
∗The reaction was not complete at the end of reaction time.

1184
M. KAZEMZAD ET AL.
FIG. 1. TEM image of the catalyst support (SBA-15 sample).
pling small aliquots of the solution with a glass capillary tube,
following by thin-layer chromatography (TLC) testing.
The reaction products in both methods were collected as
filtrate after separation of the catalyst. The filtrate was dried in
In the second procedure, the reaction mixture was treated by a rotary evaporator and the solid product crystallized in 96%
a mortar for 5–30 min until the completion of the reaction could EtOH; addition of a few drops of water was needed for getting
be confirmed by TLC for test samples extracted by solvent.
the best result. Table 1 lists the results of catalytic tests.

MODIFIED SBA-15 AS A NANOCATALYST
1185
SCH. 1. Chemical equation of catalytic reaction.
FIG. 4. SAXS pattern of SBA-15 sample.
FIG. 2. Nitrogen adsorption isotherms of the SBA-15 sample.
RESULTS AND DISCUSSION
Figure 1 shows the TEM image of the prepared SBA sample.
The ordered structure of mesopoprous silica can be observed in
this image. These images clearly indicate the high porosity of
the prepared SBA-15 mesoporous silica.
Figure 2 shows N2 adsorption-desorption isotherms for the
prepared SBA-15 sample. The mesoporous structure of the cat-
alyst is also obviously confirmed by BJH data. As can be ob-
served in this figure, the type 4 isotherm relating to mesoporous
FIG. 3. FTIR data for modified and unmodified SBA-15 sample (color figure
available online).
FIG. 5. TG/DTA profiles of (a) proline-modified SBA-15 and (b) propylamine-
modified SBA-15 (color figure available online).

1186
M. KAZEMZAD ET AL.
structures supports the TEM data. The average surface area is of proline. Thus, the proline-functionalized silica catalyst
calculated to be 620–650 m2/g (636 m2/g for a typical sample) is a dual catalyst containing both amine and OH catalytic
for different samples with the BET pore diameter of 5.93 nm. sites.
Pore size calculated by BJH adsorption branch is 6.18 nm and
that of the Cranston and Inkley (CI) plot[25] of desorption branch of solvated molecules of reactants on the solid catalyst surface
is 6.24 nm. and desorption of products with solvent molecules. It is clear that
The solution-phase catalytic reaction starts with adsorption
Figure 3 shows the FTIR spectrum of the catalyst both be- many controlling parameters, such as concentration of reactants,
fore and after modification of its surface. Functionalizing of the type of the solvents, and mixing rate, may affect the kinetics of
mesoporous silica by proline was confirmed by appearance of reactions.
new peaks added to the original support.
It is obvious that the neat condition is preferred because
There are two mechanisms illustrated in the literature for more catalytic sites are available that are not capped by solvent
proline catalyzed reactions. It seems that Si-OH functional molecules. There is just diffusion-controlled reaction, wherein
groups existing on the surface of the mesoporous silica take the reactants need to diffuse into the mesopores containing cat-
part as acid sites instead of the eliminated carboxylic acids alytic sites.
FIG. 6. Reaction mechanism.

MODIFIED SBA-15 AS A NANOCATALYST
1187
Figure 4 shows the SAXS pattern of SBA-15, which is in
agreement with the typical patterns reported in the literature.
The sharp peak around 2θ = 0.8 originates from the ordered
porous structure of SBA-15. This pattern and the BJH data
represented in Figure 2 confirm mesoporous characteristics of
synthesized silica.
TG/DTA data are shown in Figure 5. As can be observed in
these patterns, there are two weight losses, at 100◦C and 300◦C,
which are mainly attributed to water evaporation and redox reac-
tion of organic compound, respectively. There is a broad exother-
mic peak in the DTA curve of the proline-modified SBA-15 sam-
ple, while there is a sharp exothermic peak for the propylamine-
modified SBA-15 sample. It seems that higher hygroscopicity
of functionalized compound in the proline-modified SBA-15
sample caused the broadening of the DTA curve.
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SBA-15 mesoporous silicas modified with proline and
aminopropyl functional groups were employed for synthesis
of tetrahydrobenzo[b]pyrane derivatives by simply mixing the
precursors with surface-modified catalyst in a mortar. The
mesoporosity of the catalysts were confirmed by TEM, BJH,
SAXS, TG/DTA, and BET surface area measurement methods.
TLC, FTIR, and melting-point measurements also confirmed
the progress of the reaction, comparing with previous data.
Compared with functionalizing methods reported in the liter-
ature, direct immobilizing of proline through its carboxylic acid
functional group (developed in this research) is both a simple
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