Synthesis of Pyranopyrazoles Using Magnetically Recyclable Heterogeneous Iron Oxide-silica Core-shell Nanocatalyst

Article abstract of DOI:10.1002/jccs.201400387

The Fe₃O₄@SiO₂ core-shell nanocatalyst were prepared and efficiently used for four-component coupling reaction of aromatic aldehydes, malononitrile, ethyl acetoacetate and hydrazine hydrate in water/ethanol mixture. Various aromatic aldehydes possessing electron-withdrawing and electron-donating groups in different positions on the ring were successfully transformed to substituted pyranopyrazoles in high yields in short time. The nanocatalyst was easily recovered, and reused five times without significant loss in cata- lytic activity and performance. The structure, size and morphology of the nanosized catalyst were studied by various techniques such as Fourier transform infrared spectroscopy, powder X-ray diffraction, dynamic light scattering and transmission electron microscopy.

Full text of DOI:10.1002/jccs.201400387

JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
Article
Synthesis of Pyranopyrazoles Using Magnetically Recyclable Heterogeneous Iron
Oxide-silica Core-shell Nanocatalyst
Ebrahim Soleimani,a* Mohammad Jafarzadeh,a* Parastoo Norouzi,a Jedol Dayou,b
Coswald Stephen Sipaut,c Rachel Fran Mansac and Parisa Saeia
aFaculty of Chemistry, Razi University, Kermanshah 67149-67346, Iran
bFaculty of Science and Natural Resources, Universiti Malaysia Sabah, 88400 Kota Kinabalu, Sabah, Malaysia
cFaculty of Engineering, Universiti Malaysia Sabah, UMS Road, 88400, Kota Kinabalu, Sabah, Malaysia
(Received: Sept. 14, 2014; Accepted: Oct. 28, 2015; Published Online: Dec. 14, 2015; DOI: 10.1002/jccs.201400387)
The Fe3O4@SiO2 core-shell nanocatalyst were prepared and efficiently used for four-component coupling
reaction of aromatic aldehydes, malononitrile, ethyl acetoacetate and hydrazine hydrate in water/ethanol
mixture. Various aromatic aldehydes possessing electron-withdrawing and electron-donating groups in
different positions on the ring were successfully transformed to substituted pyranopyrazoles in high yields
in short time. The nanocatalyst was easily recovered, and reused five times without significant loss in cata-
lytic activity and performance. The structure, size and morphology of the nanosized catalyst were studied
by various techniques such as Fourier transform infrared spectroscopy, powder X-ray diffraction, dy-
namic light scattering and transmission electron microscopy.
Keywords: Pyranopyrazole; Multi-component reactions; Nanocatalyst; Core-shell; Silica.
INTRODUCTION
Pyranopyrazoles have found remarkable attention for
of the nanocatalysts is important factor as the number of
contact between the reactant molecules and catalyst signifi-
cantly increased. It is expected that the catalytic activity of
heterogeneous nanocatalysts efficiently enhanced compa-
rable with its homogeneous counterpart. The size of the
nanocatalysts is important due to providing a highly active
catalyst surface, which maximizes the reaction rates and
minimizes consumption of the catalyst.13 In addition, be-
cause of effectiveness of the active site of nanocatalyst, the
smaller amount of catalyst can be used that could lead to
limited usage of the catalyst.
the synthesis of promising biologically significant com-
pounds.1 They exhibit appreciable biological activities
such as analgesic, anti-tumor, anti-cancer, and anti-inflam-
matory properties, and also serve as potential inhibitors of
human Chk1 kinase.1 There have been reported some cata-
lytic system, homogeneous and heterogeneous, for the
preparation of pyrano[2,3-c]pyrazol-6-ones via multicom-
ponent reactions, such as g-alumina,1 Mg/Al hydrotalcite,2
MgO nanoparticle,3 H4SiW12O40,4 Ba(OH)2,5 silica gel 60,6
trichloroacetic acid,7 ceric sulfate,7 ZnO nanoparticle,8
L-proline,9 per-6-amino-b-cyclodextrin.10 Some of the re-
ported methods suffer high reaction temperature, poor
catalyst recoverability, and in some cases tedious proce-
dure for catalyst recyclability and low reusability. Mag-
netic-assisted in recyclability of the catalyst can efficiently
overcome the difficulty of catalyst recoverability.
Silica is one of the best inorganic heterogeneous mate-
rials for organic transformations. It has exceptional thermal
and chemical stability in the presence of majority of chemi-
cals, except bases, and it is also an abundant and inexpensive
material.14 The sol-gel process as a wet chemical method is
commonly applied for the fabrication of silica through hy-
drolysis and condensation of corresponding alkoxides and
inorganic salts.15 A main feature of silica is the existence of
porosity within the silica structure. Porosity introduces a
large surface area inside the silica particles.16,17 They are
usually used for preparation of magnetite-silica core-shell
nanoparticles by coating of magnetite (Fe3O4) surface with
silica because of the strong affinity of iron oxide surfaces to-
ward silica.18 Many efforts have been devoted in the con-
Nanoparticulate heterogeneous solid catalysts have
received considerable attention in organic transformations
compared to their corresponding bulk materials in term of
their ability to accelerate the rates of reactions, high cata-
lytic activity, reusability and higher yield of products
which is due to their high surface area-to-volume ratio and
large specific surface area.11,12 The available surface area
* Corresponding author. Email: mjafarzadeh1027@yahoo.com; e_soleimanirazi@yahoo.com
Supporting information for this article is available on the www under http://dx.doi.org/10.1002/jccs.201400387
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Soleimani et al.
trolled synthesis of iron oxide/SiO2 in literature.19-21 The use
of magnetic nanoparticles as a catalyst support can also en-
able easy and efficient separation of the catalysts from the
reaction mixture with an external magnet.22
acetoacetate and hydrazine hydrate, and using of water/
ethanol (50:50 v:v%) mixture as a medium were applied.
4-chlorobenzaldehyde and malononitrile were then added
into the mixture in the presence of Fe3O4@SiO2 NPs (0.075
g) for 25 min which afforded in 70% yield (Table 1, Entry
1). The elevated temperature was required to accelerate the
reaction rate. Moreover, decrease in polarity of the solvent
by addition of ethanol to water facilitated the dissolution of
the reactants in the solvent and homogenized the reaction
medium. Therefore, temperature and solvent composition
were two effective parameters to achieve higher yield
within shorter time. The same reaction condition with 0.1 g
of the catalyst gave an increased yield of 90% (Table 1, En-
try 2). By varying the amount of the catalyst, the optimized
value was obtained at 0.2 g which resulted in 94% yield
(Table 1, Entry 3). Further increase in the amount of the
catalyst was not efficient. It might be due to high agglomer-
ation and low dispersity of the catalyst in the reaction me-
dium that leads to decrease in the number of active sites
(Table 1, Entry 4). Using non-toxic catalyst and avoid to
use organic and volatile solvent provide a mild reaction
condition for this approach.
The aim of this research is applying magnetically
separable nanocatalyst, Fe3O4@SiO2 core-shell nanopar-
ticles (NPs), for the synthesis of pyrazoles. The catalytic
capability and reusability of the catalyst were also investi-
gated.
RESULTS AND DISCUSSION
Catalytic reaction
Scheme 1 exhibits the application of magnetic hetero-
geneous nanocatalysts for the synthesis of pyranopyrazoles.
Fe3O4-supported SiO2 NPs can be enabled to easily separate
from the reaction mixture by an external magnet and reused
several times. Silica, as a non-toxic catalyst, can be easily re-
generated through rinsing with ethanol and dried in oven
overnight. Due to the nano-size of silica, large surface area,
high porosity and high number of active functional groups
(silanol: Si-OH)23 can be available on the surface of the cata-
lyst. High quantity of active sites in silica shell is expected to
show good catalytic activity in organic reactions. High
dispersity and homogeneity of nanocatalyst in reaction me-
dium can also affect on the catalyst reactivity.
The catalytic system was further extended to the syn-
thesis of various pyranopyrazoles, as hydrazine hydrate,
ethyl acetoacetate (EAA), malononitrile and variety of
benzaldehyde were used under the optimized reaction con-
ditions. The resulting products with yield of synthesis and
time of reaction completion are presented in Table 2. Al-
most all the employed aldehydes were smoothly preceded
the reactions towards the desired products in good yields ir-
Synthesis of pyranopyrazoles
Scheme 1
Table 1. Optimization of the reaction condition with 4-
chlorobenzaldehyde using different amount of
Fe3O4@SiO2 NPs
Cl
Me
Me
CHO
CN
CN
NH2
NH2
O
+
+
+
N
CN
Cl
N
H
O
NH2
O
OEt
The catalytic activity of the Fe3O4@SiO2 NPs was in-
vestigated in the synthesis of pyranopyrazoles. The reac-
tion between hydrazine hydrate, ethyl acetoacetate (EAA),
malononitrile and benzaldehyde was chosen as a model
condensation reaction. For optimizing the reaction condi-
tion, the reaction was initially carried out in the presence of
0.1 g Fe3O4@SiO2 NPs at room temperature in water. The
results showed that the reaction was not completed even
after 4-5 h. Therefore, heating up the mixture of ethyl
Entry
Reaction condition
Yield (%)a
1
2
3
4
Fe3O4@SiO2 (0.075 g), 25 min, 70 °C
Fe3O4@SiO2 (0.1 g), 25 min, 70 °C
Fe3O4@SiO2 (0.2 g), 25 min, 70 °C
Fe3O4@SiO2 (0.3 g), 25 min, 70 °C
70
90
94
70
a Reaction conditions: Ethyl acetoacetate (1 mmol), hydrazine
hydrate (1 mmol), 4-chlorobenzaldehyde (1 mmol), malononitril
(1 mmol) in water/ethanol mixture (1 mL).
b Isolated yields.
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Fe3O4@SiO2 Nanocatalyst for Synthesis of Pyranopyrazoles
Table 2. Synthesis of pyranopyrazoles from various aromatic aldehydes, malononitrile, ethyl
acetoacetate and hydrazine hydrate in the presence of Fe3O4@SiO2 core-shell NPsa
R
Me
Me
CN
O
CN
NH2
NH2
Fe3O4@SiO2 NPs
H2O/EtOH, 70 o
O
+
+
+
N
R
H
C
CN
N
H
O
NH2
O
OEt
mp (°C)
Reported
Time Yield
(min) (%)
Entry
Aldehydes
Product
Found
O
Me
1
2
3
4
35
25
30
20
85 242-246 (243-245) 8
94 233-234 (233-235) 8
90 144-147 (145-147) 1
92 177-180 (180-183) 22
H
CN
N
N
O
NH2
H
Cl
O
H
Me
CN
Cl
N
N
H
O
NH2
O
Cl
Me
H
CN
Cl
N
N
H
O
NH2
Br
O
O
O
H
Me
Me
Me
CN
Br
N
N
N
N
H
O
NH2
OH
80 222-226 (224-226) 1
H
5
30
CN
HO
N
H
O
NH2
NO2
94 249-253 (251-253) 1
H
6
30
CN
O2N
N
H
O
NH2
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Soleimani et al.
O2N
O
H
7
8
Me
35
40
90 193-195 (190-192) 22
CN
N
NO2
N
H
O
NH2
O
O2N
88 218-221 (220-222) 1
H
NO2
Me
CN
N
N
H
O
NH2
OMe
O
83 209-211 (210-212) 1
H
9
30
Me
CN
MeO
N
N
H
O
NH2
Me
O
84 205-208 (206-207) 8
H
10
20
Me
CN
Me
N
N
H
O
NH2
a Reaction conditions: Ethyl acetoacetate (1 mmol), hydrazine hydrate (1 mmol), various
aromatic aldehydes (1 mmol), malononitril (1 mmol) and Fe3O4@SiO2 (0.2 g).
b Isolated yield.
c Data from literature [1,8,22].
respective of the presence of electron withdrawing or do-
nating substituents in the ortho, meta or para positions on
the ring of various aromatic aldehydes. The results are also
revealed that high yields of the products were obtained for
the electron-withdrawing benzaldehydes, such as 2-nitro-
benzaldehyde, 3-nitrobenzaldehyde and 4-nitrobenzalde-
hyde aldehydes (Table 2, Entries 6-8). In addition, this re-
action was affected by steric effect. For example, 2-nitro-
benzaldehyd (Table 2, Entry 8) required longer reaction
time compared to 4-nitrobenzaldeyde (Table 2, Entry 6)
due to sterically hindered effect of ortho position.
sults showed that this catalyst could be reusable several
times without loss of activity in the reaction. These results
are summarized in Figure 1. The loss of activity might be re-
lated to the agglomeration among core-shell nanoparticles,
as the layer of silica with silanol groups is susceptible for ag-
gregation and agglomeration with silanols in neighboring
particles. Decrease in specific surface area arising from the
agglomeration is generally main reason in decreasing the
number of active sites on the surface of Fe3O4@SiO2 NPs.
To extent the synthetic methodology for pyranopy-
razoles, the monodisperse SiO2 nanoparticles with average
size of 10 nm (prepared according to our previous work23)
were utilized as a catalyst to promote the rate and yield of
the reaction. The results were exhibited similar trend to the
results of using the Fe3O4@SiO2 NPs, however Fe3O4@
SiO2 NPs were more efficient in catalytic activity com-
pared to the SiO2 NPs. Moreover, SiO2 NPs showed good
catalytic activity even after five times recycle and reuse.
The reusability of the Fe3O4@SiO2 nanocatalyst was
evaluated by using the reaction of 4-chlorobenzaldehyd as
a model reaction. The catalyst was recovered by simple ap-
plying an external magnetic field and washed with boiling
ethanol. The resulting catalyst was further used for the re-
action in several runs. Fe3O4@SiO2 NPs were remained ac-
tive even after 5 repeated cycles of each reaction. The re-
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3250 cm–1, which is the characteristic peak of OH stretch-
ing vibration and is also indicated to the presence of some
amount of ferric hydroxide in Fe3O4. The three distinct ab-
sorption peaks at 893 cm–1, 634 cm–1, and 564 cm–1 are
characteristic vibrations of spinel and attributed to the vi-
brations of Fe2+–O and Fe3+–O, respectively.20 The sharp
and high intense peak appears at ~880 cm–1 demonstrates
high degree of crystallinity in the Fe3O4 NPs.26 This char-
acteristic absorption band therefore confirm the existence
of crystal phase in Fe3O4. On the other hand, the absorption
bands at 3450 cm–1, 1100 cm–1, and 952 cm–1 corresponded
to the stretching, asymmetric stretching and bending of
silanols groups (Si–OH) on the silica surface, respectively.
Intensive bands at 1100–1200 cm–1 and 473 cm–1 repre-
Fig. 1. The catalytic activity of recycled Fe3O4@SiO2
NPs in a model reaction with 4-chlorobenzal-
dehyde.
Preparation and characterization of the nanocatalyst
Magnetic NPs have found great applications due to
rapidly and easily separation from reaction media using a
magnetic field.22 Magnetite (Fe3O4) NPs were prepared via
a chemical co-precipitation of Fe2+ and Fe3+ ions in basic
solution,20 and then silica was coated onto the surface of the
Fe3O4 NPs by sol-gel process through hydroxyl groups in
the aqueous medium. The formation of silica was involved
the hydrolysis and condensation of alkoxysilanes in etha-
nol, in the presence of water and ammonia.24 This proce-
dure was expected to give the NPs with better dispersion
and less agglomeration and aggregation because the growth
of silica layer took place on the surface of magnetite NPs.
The crystalline of Fe3O4 NPs before and after silica
coating, were identified with XRD technique (Fig. 2). For
Fe3O4 NPs, diffraction peaks with 2q at 30°, 35.5°, 43°,
53.8°, 56.9° and 62.5° were referred to [220], [311], [400],
[422], [511], and [440] planes of cubic spinel of Fe3O4, re-
spectively. The results are in good agreement with the XRD
patterns of Fe3O4 NPs reported previously.25 The (311)
XRD peak was used to estimate the size of crystallite of
magnetite using Scherrer’s formula; D = 0.9l/(bCosq),
where D is the average crystalline size, l is wavelength of
X-ray source (Cu Ka, 1.54 A°), b is the angular line width
of half-maximum intensity (full width at the half-maxi-
mum; FWHM) and q is Bragg’s diffraction angle in degree.
The mean crystallite size calculated to be about 27 nm. Af-
ter silica coating, no change observed in the crystalline
structure of the Fe3O4 core (Figure 2b). The broad peak at
2q of 22° corresponded to the amorphous nature of the sil-
ica shell. Silica-coated iron oxide NPs still maintain the
magnetization characteristics of the bare Fe3O4 NPs.
Fig. 2. XRD patterns of (a) Fe3O4 and (b) Fe3O4@ SiO2
NPs.
The Fourier Transform Infrared (FTIR) spectrum of
Fe3O4@SiO2 NPs in Figure 3 exhibits an absorption peak at
Fig. 3. FT-IR spectrum of Fe3O4@SiO2 NPs.
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sented the asymmetric stretching and bending of siloxane
groups (Si–O–Si). Vibrations at 3500– 3400 cm–1, 1633
cm–1, and 797 cm–1 assigned to the adsorbed water (H–OH,
stretching vibration), residual intermolecular water (H–
OH, bending) and moisture (H– OH, bending) in the sam-
ples.23
SiO2 NPs was decreased, but the core-shell system exhi-
bited sufficient magnetic response to the external mag-
netic force during magnetically isolation of the catalyst
from the reaction medium.
CONCLUSIONS
The study on the particle size and particle size distribu-
tion (PSD) of Fe3O4 and Fe3O4@SiO2 NPs were performed
using dynamic light scattering (DLS) (Figure 4). The Z-av-
erage particle size of Fe3O4 NPs and Fe3O4@SiO2 NPs in
ethanol were found to be ~174 nm (87 r.nm; radius nano-
meter, PDI = 1.000) and ~306 (153 r.nm; radius nanometer,
PDI = 1.000), respectively. The particle size is defined as an
average hydrodynamic diameter indicating the aggregation
phenomenon within nanoparticles. Moreover, the unifor-
mity and homogeneity in particle size is inferred from nar-
row particle size distribution. A difference between the DLS
and XRD sizes is observed the size calculated by XRD was
related to the size of crystallites, whereas DLS gave the size
of aggregated and agglomerated particles.
The potential application of Fe3O4@SiO2 core-shell
nanocatalysts was studied for the synthesis of pyrano-
pyrazole via a one-pot four-component reaction of hy-
drazine hydrate, ethyl acetoacetate (EAA), malononitrile
and various aromatic aldehydes in aqueous medium. The
corresponding products were synthesized in good to excel-
lent yield in short time. The effect of temperature and sol-
vent polarity on the reactions yield and time were also ob-
served. The advantageous of the current work can be noted:
easy preparation and handling of the environmental benign
catalyst, simplicity in operation of the one-pot reaction,
and mild reaction condition. Furthermore, a simple and fast
recycling of the catalyst from the reaction medium without
any tedious work-up or extensive purification were other
great features of this synthetic method. The catalyst was
durable, and successfully reused for at least five times
without significant loss in catalytic activity. Finally, em-
ploying magnetically recyclable catalyst can avoid solvent
and energy consumption during its recovery, and make it a
cost-effective catalyst.
The morphology of Fe3O4@SiO2 NPs was studied by
Transmission Electron Microscopy (TEM). Figure 5 shows
that the Fe3O4 NPs were roughly spherical with agglomera-
tion within the nanoparticles. The silica layer was then
coated on the surface of the groups of iron oxides nano-
particles. Although upon the formation of silica shell on the
surface of Fe3O4 NPs, the magnetic property of the Fe3O4@
EXPERIMENTAL
Chemicals were purchased from Fluka and Merck chemical
companies. All synthesized products were identified using FTIR
and 1H NMR, and then verified in comparison with reported data
Fig. 4. Particle size distribution of (a) Fe3O4 and (b)
Fe3O4@SiO2 NPs obtained by DLS.
Fig. 5. TEM image of Fe3O4@SiO2 NPs.
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in literature (see Supplimentary data).
in powder form were exposed under the X-ray at room tempera-
ture. Particle size and particle size distribution were determined
by zetasizer nanoparticle analyzer, Malvern Nano ZS series
(Model: ZEN3600) at room temperature. Zetasizer was equipped
with Red Laser (HeNe gas laser, maximum output-power: 4 mW,
wavelength: 632.8 nm) as light source and avalanche photodiode
as detector. Glass cuvette with square aperture was used as a cell.
The samples first dissolved in ethanol with 1 wt.% and then
sonicated at an ultrasonic bath for 30 min. After that, the disper-
sant was filtered to separate agglomerated particles. Ultrasoni-
cation was also used to remove air bubbles and breakup ag-
glomerated particles. The morphological studies were performed
using a TEM (Transmission Electron Microscopy), Philips CM10
operated at 80 KV electron beam accelerating voltage and
equipped with a CCD camera. One drop of the sample solution
was placed on a copper grid, and the solvent (ethanol) was evapo-
rated in an ambient conditions.
Typical procedure for the preparation of Fe3O4 nano-
particles: Fe3O4 nanoparticles (NPs) were synthesized by a
chemical co-precipitation method.20 Aqueous solution of FeCl3
and FeCl2 in a molar ratio of Fe2+/Fe3+ = 1/2 was prepared and
kept at room temperature. For this purpose, 0.036 mol of
FeCl3.6H2O and 0.018 mol of FeCl2.4H2O were dissolved in 20
mL deionized water under nitrogen gas with vigorous stirring.
Then, 25% NH3 was added into the solution until the pH of the so-
lution reached to 11 and the stirring was continued for 1 h at 60
°C. The color of bulk solution turned from orange to black imme-
diately. The magnetite precipitate was separated from the solution
by magnetic decantation, then washed with deionized water and
ethanol several times, and finally dried at air.
Typical procedure for the preparation of core-shell
Fe3O4@SiO2 nancatalyst: An appropriate amount of as-pre-
pared Fe3O4 NPs (45 mg) were initially dispersed in water (16
mL) under ultrasonic irradiation, then an aqueous ammonia solu-
tion (25 wt.%, 2 mL) and ethanol (solvent, 80 mL) were added
into the dispersed magnetite solution. Tetraethylorthosilicate
(TEOS, 0.8 mL) was added dropwise into the solution of Fe3O4
NPs, and the medium was vigorously stirred for 24 h at room tem-
perature. Finally, the core-shell nanocatalyst was collected from
the solution by applying an external magnetic force, washed with
water and ethanol several times, and dried at 50 °C overnight.
Typical procedure for the synthesis of pyranopyrazole
from four components in the presence of Fe3O4@SiO2 nano-
catalyst: In a round-bottomed flask (50 mL), ethyl acetoacetate
(1 mmol) was added to hydrazine hydrate (1 mmol) in 50:50 v:v%
of water and ethanol (1 mL) and the solution was heated at 70 °C
in an oil bath under violent stirring for 15 min. After the formation
of light solution, followed by adding various aromatic aldehydes
(1 mmol) and malononitrile (1 mmol) in the presence of the cata-
lyst (0.2 g), stirring was continued for 20-50 min at 70 °C in the
oil bath. Completion of the reaction was monitored by TLC. The
reaction mass was allowed to cool and then the catalyst was iso-
lated by applying an external magnet. The solvent was evaporated
and product was purified. Furthermore, the recycled catalyst was
reused for several times in the synthesis of pyranopyrazoles under
same reaction conditions.
ACKNOWLEDGEMENTS
The authors are thankful to Razi University and
Universiti Malaysia Sabah for financial supports.
REFERENCES
1. Mecadon, H.; Rohman, M. R.; Rajbangshi, M.; Myrboh, B.
Tetrahedron Lett. 2011, 52, 2523-2525.
2. Kshirsagar, S. W.; Patil, N. R.; Samant, S. D. Synth. Com-
mun. 2011, 41, 1320-1325.
3. Babaie, M.; Sheibani, H. Arab. J. Chem. 2011, 4, 159-162.
4. Chavan, H. V.; Babar, S. B.; Hoval, R. U.; Bandgar, B. P.
Bull. Korean Chem. Soc. 2011, 32, 3963-3966.
5. Azzam, S. H. S.; Pasha, M. A. Tetrahedron Lett. 2012, 53,
6834-6837.
6. Shinde, P. V.; Gujar, J. B.; Shingate, B. B.; Shingare, M. S.
Bull. Korean Chem. Soc. 2012, 33, 1345-1348.
7. Karimi-Jaberi, Z.; Shams, M. M. R.; Pooladian, B. Acta
Chim. Solv. 2013, 60, 105-108.
8. Tekale, S. U.; Kauthale, S. S.; Jadhav, K. M.; Pawar, R. P. J.
Chem. 2013, 840954.
9. Mecadon, H.; Rohman, M. R.; Kharbangar, I.; Laloo, B. M.;
Kharkongor, I.; Rajbangshi, M.; Myrboh, B. Tetrahedron
Lett. 2011, 52, 3228-3231.
10. Kanagaraj, K.; Pitchumani, K. Tetrahedron Lett. 2010, 51,
3312-3316.
Characterization techniques: Melting points were deter-
mined in open capillaries with a Gallen-Kamp melting point ap-
paratus. Infrared spectra were obtained by using a Ray Leigh
Wqf-510 FT-IR spectrophotometer. X-ray diffraction was con-
ducted using Philips x’pert pro X-ray diffractometer (PW 3040),
with monochromatic high-intensity Cu-Ka radiation (k =
1.54056 Å, 40 kV, 30 mA) at 2q range of 10-80°. The dry samples
11. Polshettiwar, V.; Varma, R. S. Green Chem. 2010, 12, 743-
754.
12. Fihri, A.; Bouhara, M.; Nekoueishahraki, B.; Basset, J.-M.;
Polshettiwar, V. Chem. Soc. Rev. 2011, 40, 5181-5203.
13. Narayanan, R.; El-Sayed, M. A. J. Phys. Chem. B 2005, 109,
12663-12676.
14. Iller, R. K. The Chemistry of Silica; John Wiley & Sons: New
J. Chin. Chem. Soc. 2015, 62, 1155-1162
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Soleimani et al.
York, 1979.
497, 221-227.
15. Hench, L. L.; West, J. K. Chem. Rev. 1990, 90, 33-72.
16. Brinker, C. J.; Scherer, G. W. Sol-gel Science: The Physics
and Chemistry of Sol-gel Processing; Academic Press: San
Diego, 1990.
21. Zhang, J.; Li, X.; Rosenholm, J. M.; Gu, H.-C. J. Colloid In-
terface Sci. 2011, 361, 16-24.
22. Zhang, Q.; Su, H.; Luo, J.; Wei, Y. Green Chem. 2012, 14,
201-208.
17. Vansant, E. F.; Voort, P. V. D.; Vrancken, K. C. Character-
ization and Chemical Modification of the Silica Surface;
Elsevier: Amsterdam, 1995.
23. Rahman, I. A.; Jafarzadeh, M.; Sipaut, C. S. J. Sol-Gel Sci.
Technol. 2011, 59, 63-72.
24. Stöber, W.; Fink, A.; Bohn, E. J. Colloid Interface Sci. 1968,
26, 62-69.
18. Sun, S.-N.; Wei, C.; Zhu, Z.-Z.; Hou, Y.-L.; Subbu, S. V.; Xu,
Z.-C. Chin. Phys. B 2014, 23, 037503.
25. Hui, C.; Shen, C.; Tian, J.; Bao, L.; Ding, H.; Li, C.; Tian, Y.;
Shi, X.; Gao, H.-J. Nanoscale 2011, 3, 701-705.
26. Ahmad, S.; Riaz, U.; Kaushik, A.; Alam, J. J. Inorg. Or-
ganomet. Polym. 2009, 19, 355-360.
19. Wang, S.; Cao, H.; Gu, F.; Li, C.; Huang, G. J. Alloy Compd.
2008, 457, 560-564.
20. Chen, L.; Xu, Z.; Dai, H.; Zhang, S. J. Alloy Compd. 2010,
1162
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