Synthesis and characterization of novel nanosilica molybdic acid and its first catalytic application in the synthesis of new and known pyranocoumarins

Article abstract of DOI:10.1039/c5nj01302j

Nanosilica molybdic acid (nano-SMA) was prepared and employed as a novel, recyclable and safe catalyst for the one-pot, three-component condensation of 4-hydroxycoumarin with aldehydes and malononitrile to produce new and known pyrano[2,3-c]chromenes as p

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Synthesis and characterization of novel nanosilica molybdic acid
and its first catalytic application in synthesis of new and known
pyranocoumarins
Received 00th January 20xx,
Accepted 00th January 20xx
Bahador Karami,* Mahtab Kiani, S. Jafar Hosseini and Mehrangiz Bahrami
DOI: 10.1039/x0xx00000x
Nanosilica molybdic acid (nano-SMA) was prepared and employed as a novel, recyclable and safe catalyst for the one-pot,
three-component condensation of 4-hydroxycoumarin with aldehydes and malononitrile to produce new and known
pyrano[2,3-c]chromenes as potent biologically active compounds. This novel method has many advantages, such as the
high product yield and a simple work-up procedure.
www.rsc.org/
recent studies, the synthesis of pyrano[2,3-c]chromenes via a
three-component reaction has been described using various
reagents, such as Ca(OTf)2,10 Bi(OTf)3,11 meglumine,12 Mohr's
Introduction
It is well known in the protocol of green chemistry that its
main objective is to perform reactions using heterogeneous
catalysts, in order to generate environmentally friendly
chemical transformations.1 In this context, substantial research
efforts have been devoted to develop catalysts with high
efficacy. In the case of heterogeneous catalysis, the catalytic
ability of materials mainly depends on their microscopic
structure which directly impacts the activity, selectivity and
thermal or chemical stability of the catalyst.2 Use of efficient
nanocatalysts plays a promising role towards achieving these
objectives of green chemistry.3
The recent emergence of nanocatalysis has received a lot
of attention because it opens new perspectives for the mild
catalysis of important reactions with lower environmental
impact.4 Nanocatalysts have distinguishing features than bulk
case. For example, nano sized systems dramatically increase
the contact between reactants and catalyst.5
Multicomponent reactions (MCRs) are special types of
synthetically useful organic reactions in which three or more
various substrates react to give a final product in a one-pot
procedure.6 These reactions are valuable assets in the organic
synthesis and pharmaceutical chemistry due to their wide
range of usage in the preparation of various structural
scaffolds and discovery of new drugs.7
salt,13 Cu(OTf)2,14 [BMIm]BF4,15 [2-aemim][PF6],16 sodium
dodecyl
sulfate
(SDS),17
H6P2W18O62.18H2O,18
cetyltrimethylammonium chloride/bromide,19,02 Titanium
dioxide nanowires,02 tetrabutylammonium bromide (TBAB),00
triethylbenzylammonium chloride (TEBA),02 chitosan,02
K3PO4,25 Na2CO3 under grinding,26 Mg/Al hydrotalcite,27 DBU28
and piperidine under microwave irradiation.29 However, some
proposed methods suffer from disadvantages including relying
on multi-step conditions, the use of toxic organic solvents or
catalysts containing transition metals, tedious work-up
procedure, troublesome waste discarding, high reaction time,
and low yields.22
In this work,
pyrano[2,3-c]chromene, via
a
new methodology to obtain some
one-pot three-component
a
condensation, is reported. In this paper, we introduce nano
silica molybdic acid (nano-SMA) as a novel and safe catalyst for
the synthesis of novel and known pyranocoumarin derivatives.
Experimental
Methods and materials
The chemicals were purchased from Merck and Aldrich
chemical companies. The silica chloride
1 was synthesized
according to the published procedure.22 The reactions were
monitored by TLC (silica–gel 60 F 254 , hexane: EtOAc). Fourier
transform infrared (FT-IR) spectroscopy spectra were recorded
on a Shimadzu-470 spectrometer, using KBr pellets and the
Pyranocoumarins are well recognized due to their
importance in biological and pharmaceutical researches.8
A
considerable effort has been made for the synthesis of pyran-
annulated heterocycles due to their wide applications.9
Several methods have been reported for the synthesis of
pyrano[2,3-c]coumarin as biologically active compounds. In
melting points were determined on
a KRUSS model
instrument. 1H NMR spectra were recorded on a Bruker
Avance II 400 NMR spectrometer at 400 MHz, in which DMSO-
d6 was used as solvent and TMS as the internal standard. X-ray
diffraction (XRD) pattern was obtained by Philips X Pert Pro X
diffractometer operated with a Ni filtered Cu-Kα radiation
Department of Chemistry, Yasouj University, P. O. Box 353, Yasouj, 75918-74831,
Iran. E-mail: karami@mail.yu.ac.ir; Fax: +98 7412242167; Tel:+98 7412223048
This journal is © The Royal Society of Chemistry 20xx
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source. X-ray fluorescence (XRF) spectroscopy was recorded by Calcd. for C19H10ClFN2O3: C, 61.89; H, 2.73; N, 7.60%. Found: C,
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DOI: 10.1039/C5NJ01302J
X-Ray Fluorescence Analyzer, Bruker, S4 Pioneer, Germany. The 61.90; H, 2.55; N, 7.72%.
varioEl CHNS Isfahan Industrial University was used for
Compound 6k. IR (KBr): 3391, 3180, 2196, 1712, 1674,
1
elemental analysis. Transmission electron microscopy (TEM) 1608, 1381, 1240, 1054 cm-1. H NMR (DMSO, 400 MHz): δ
images of the electrocatalyst were recorded using a Philips 7.90 (dd, 1H, J = 8.0 Hz), 7.73–7.69 (m, 1H), 7.44–7.38 (m, 7H),
CM-10 TEM microscope operated at 100 kV.
7.18 (d, 2H, J = 8.8 Hz), 6.95 (d, 2H, J = 8.8 Hz), 5.06 (s, 2H),
4.40 (s, 1H). 13C NMR (DMSO, 100 MHz): δ 159.51, 157.87,
General procedure for the preparation of nanosilica molybdic 157.45, 153.09, 152.06, 137.05, 135.60, 132.83, 128.76,
acid 2 128.40, 127.79, 127.64, 124.63, 122.41, 119.30, 116.53,
To an oven-dried (125 °C, vacuum) sample of silica–gel 60 (10 114.61, 112.97, 104.19, 69.17, 58.09, 36.13 ppm. Anal. Calcd.
g) in a round bottomed flask (250 mL) equipped with a for C26H18N2O4: C, 73.92; H, 4.29; N, 6.63%. Found: C, 74.15; H,
condenser and a drying tube, thionyl chloride (40 mL) was 4.15; N, 6.79%.
added and the mixture in the presence of CaCl2 as a drying
Compound 6l. IR (KBr): 3340, 3312, 2188, 1697, 1669,
1
agent was refluxed for 48 h. The resulting white-grayish 1598, 1379, 1066 cm-1. H NMR (DMSO, 400 MHz): δ 8.44(d,
powder was filtered and stored in a tightly capped bottle.22 1H, J = 6.4 Hz), 7.96 (d, 2H, J = 8.0 Hz), 7.83 (d, 1H, J = 8.0 Hz),
0.1g of silica chloride
1
was dissolved in toluene (10 ml) and 7.76–7.33 (m, 8H), 5.48 (s, 1H). 13C NMR (DMSO, 100 MHz): δ
stirred for 30 min. The solution of 0.084 g sodium molybdate 159.55, 157.83, 153.80, 152.07, 133.26, 132.93, 130.93,
in 10 ml toluene was added to the first solution and stirred for 128.47, 127.43, 126.10, 126.00, 125.85, 125.75, 124.74,
10 min. The resulting mixture was sonicated in ultrasonic bath 123.43, 122.43, 119.15, 116.61, 112.96, 104.65, 58.49 ppm.
for 1h at room temperature. The mixture was transferred to a Anal. Calcd. for C23H14N2O3: C, 75.40; H, 3.85; N, 7.65%. Found:
70 ml autoclave, heated at 140 °C for 4 h. White precipitate C, 75.65; H, 3.70; N, 7.53%.
obtained, washed with distilled water and then separated by
Compound 6m. IR (KBr): 3389, 3310, 2201, 1713, 1671,
filtration, dried at 22 ˚C for 0 h. The white powder was 1606, 1374, 1049 cm-1. 1H NMR (DMSO, 400 MHz): δ 7.90 (dd,
dissolved in HCl (0.1 N) and stirred for 1h. The white powder 1H, J = 6.5, 1.3 Hz), 7.73–7.69 (m, 1H), 7.51–7.44 (m, 2H), 7.38
was separated by filtration, washed with distilled water and (s, 2H), 7.19–7.15 (m, 4H), 4.41 (s, 1H), 2.84 (m, 1H, 6.92 Hz),
dried at 22 ˚C for 0 h.
1.17 (d, 6H, 6.92 Hz). 13C NMR (DMSO, 100 MHz): δ 159.54,
158.00, 157.95, 153.28, 152.08, 147.11, 140.70, 132.88,
General procedure for the preparation of pyrano[2,3- 127.45, 126.42, 124.65, 122.41, 119.29, 116.54, 112.95,
c]coumarin derivatives 6
Malononitrile (1.1 mmol), aromatic aldehyde
hydroxycoumarin (1 mmol), and SMA
added to a 10 mL mixture EtOH/H2O (50/50) in a 25-mL pyrex
104.18, 58.03, 38.85, 36.50, 33.23, 23.79 ppm. Anal. Calcd. for
(1 mmol), 4- C22H18N2O3: C, 73.74; H, 5.03; N, 7.82%. Found: C, 73.45; H,
(5 mol %) were 5.12; N, 7.74%.
Compound 6n. IR (KBr): 3427, 3280, 2188, 1720, 1669,
3
4
5
2
flask and refluxed for an appropriate time (Table 3). The 1594, 1389, 1048 cm-1. 1H NMR (DMSO, 400 MHz): δ 7.82 (dd,
reaction progress was controlled by thin layer chromatography 1H, J = 6.44, 1.36 Hz), 7.72–7.67 (m, 1H), 7.48–7.43 (m, 2H),
(TLC) using hexane/EtOAc (1:1). After completion of the 7.35 (s, 2H), 4.43 (s, 1H), 1.74 (m, 1H), 1.63-1.57 (m, 4H), 1.38-
reaction, the solvent was removed under vacuum, the crude 1.32 (m, 2H), 1.18-0.94 (m, 4H). 13C NMR (DMSO, 100 MHz): δ
products
6
were obtained after recrystalization from EtOH.
160.64, 160.06, 154.63, 152.02, 132.67, 124.56, 122.05,
116.53, 116.00, 113.00, 104.60, 52.48, 43.18, 36.66, 30.51,
27.52, 26.11, 25.85, 25.52 ppm. Anal. Calcd. for C19H18N2O3: C,
Spectral data
Compound 6i. IR (KBr): 3396, 3321, 3195, 2202, 1706, 70.80; H, 5.59; N, 8.69%. Found: C, 70.53; H, 5.22; N, 8.38%.
1
1671, 1607, 1381, 1053 cm-1. H NMR (DMSO, 400 MHz): δ
7.90 (dd, 1H, J = 7.8, 1.2 Hz), 7.75–7.70 (m, 1H), 7.52–7.43 (m,
6H), 7.30–7.28 (m, 2H), 4.50 (s, 1H) ppm. 13C NMR (DMSO, 100
MHz): δ 159.55, 157.94, 153.70, 152.18, 146.02, 132.99,
130.69, 130.39, 130.05, 126.94, 124.65, 122.54, 121.68,
119.05, 116.57, 112.98, 103.15, 57.31, 36.59 ppm. Anal. Calcd.
for C19H11BrN2O3: C, 57.74; H, 2.81; N, 7.09%. Found: C, 58.05;
H, 2.68; N, 7.16%.
Results and discussion
Nanosilica molybdic acid was synthesized and characterized by
X-ray fluorescence (XRF), X-ray diffraction pattern (XRD),
Fourier transform infrared spectroscopy (FT-IR) and
transmission electron microscopy (TEM).
In continuation of our previous studies on the
development of various catalysts in synthesis of organic
compounds,20-22 as can be seen in Scheme 1, from the reaction
of readily available materials such as silica gel and thionyl
Compound 6j. IR (KBr): 3408, 3280, 3175, 2203, 1705,
1
1674, 1602, 1381, 1055 cm-1. H NMR (DMSO, 400 MHz): δ
7.90 (dd, 1H, J = 7.8, 1.2 Hz), 7.76–7.72 (m, 1H), 7.55–7.48 (m,
4H), 7.55–7.19 (m, 3H), 5.19 (d, 1H, J = 1.6 Hz). 13C NMR
(DMSO, 100 MHz): δ 159.38, 158.77, 152.11, 133.14 (d, J = 8.9
Hz), 129.88 (d, J = 10.4 Hz), 124.84, 124.68 (d, J = 4.2 Hz),
122.29, 118.73, 116.68, 115.25, 112.56, 38.83 ppm. Anal.
chloride, silica chloride
found that anhydrous sodium molybdate can react with
give silica molybdic acid (and subsequently nano SMA) . From
1
has been prepared.35 Accordingly, we
to
1
2
the synthetic point of view, the nucleophilic substitution at
silicon is also attractive.
2 | J. Name., 2012, 00, 1-3
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ONa
O Mo
O
OH
OH
O Mo
O
O
Si
O
O
O
O
O
SOCl2
Si
O
Si
O
O
SiO2
Reflux
48 h
-SO2
- HCl
O
O
HCl/ H2O, 1 h
Cl
SiO2
-NaCl
Si
O
SiO2
O
O
Na2MoO4
pH= 6.26
2
SiO2
Toluene
Reflux, 4 h
-NaCl
pH= 4.36
1
Scheme 1. Preparation of nano silica molybdic acid
2.
As can be seen in Table 1, the XRF data for the nano-SMA
2
show the composition of catalyst as 71.14 (%W/W) SiO2 and
25.62 (%W/W) MoO4 (Fig. 1).
Fig. 2. XRD pattern for nano-SMA 2.
Table 1. XRF data of nano-SMA 2.
Concentration (%W/W)
The FT-IR spectra for the anhydrous sodium molybdate,
silicachloride, and silica molybdic acid are shown in Fig. 3.
Compound
2
SiO2
MoO4
Na2O
Cl
ZnO
CaO
Fe2O3
Al2O3
CuO
GeO2
MnO
TiO2
71.14
25.62
1.90
This spectrum shows the characteristic bonds of anhydrous
sodium molybdate and silica chloride.
0.460
0.355
0.289
0.046
0.045
0.027
0.023
0.022
0.022
99.95
Total
Fig. 3. FT-IR spectra for the comparison of SiO2Cl, Na2MoO4 and
nano-SMA 2.
Fig. 1. XRF analysis of nano-SMA 2.
The adsorption in 3452, 1634, 1086, 800 cm−1 in the
catalyst spectrum reveals both bonds in SiO2–Cl and MoO4
group. We evaluated the amounts of molybdic acid supported
on SiO2 using two methods, including (a) titration with 0.1 N
NaOH (neutralization reaction) and (b) calculating the weight
difference between primary solid acid loosed chloride and new
Fig. 2 shows the XRD patterns for the silica molybdic acid 2
which exhibits the presence of molybdic acid crystalline phase
supported on amorphous silica as a broad peak around 23° (2
θ) (θ is the Bragg's angle). The three peaks in the 35–40°
region of the XRD spectrum could be attributed to the
presence and linking of MoO3 to the silica gel.36
silica molybdic acid 2. After these experiments, we found that
1 g catalyst includes 0.04 g –OMoO3H. Regarding to the
molecular weight of MoO4H (161 g), therefore, 1 g of catalyst
is equal to 0.25 mmol.
The structural information about nanosilica molybdic acid
such as particle size and shape was provided by transmission
electron microscopy (TEM). As shown in Fig. 4., the TEM image
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revealed the formation of mesostructured nanoparticles with
an average size in the range of 15-30 nm.
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DOI: 10.1039/C5NJ01302J
Fig. 5. Optimization of the catalyst amount.
After optimization of the reaction conditions, in order to
extend the scope of this reaction, a wide range of aromatic
aldehydes were used with
3 and 5 (Table 2). All the products
were characterized by comparison of their spectra and
physical data with those reported in the literature.22-22
Fig. 4. TEM image of nano-SMA 2.
Table 2. Synthesis of pyrano[2,3-c]coumarin derivatives using
In continuation of our previous studies on the
development of green synthetic methodologies for the
preparation of organic compounds,37-22 herein, we report a
new green condition for the synthesis of some pyrano[2,3-
nano-SMA
2.
Entry
Ar
Time (min) Yielda (%)
Mp (°C)
262-264
240-242
260-262
255-257
248-250
250-252
258-260
234-236
272-274
288-290
6a
6b
6c
6d
6e
6f
C6H5
30
18
25
35
75
70
50
75
20
30
96
92
78
81
73
87
90
70
91
95
c]coumarins
malononitrile
6
3
from the condensation reaction of
, aromatic aldehydes , and 4-hydroxycoumarin
(Scheme
4-MeO-C6H4
2-Cl-C6H4
3-NO2-C6H4
4-NO2-C6H4
4-Me-C6H4
4-Cl-C6H4
4
5
in the presence of catalytic amount of nano-SMA
2
2).
Scheme. 2 Synthesis of pyrano[2,3-c]chromenes using nano-
O
Ar
CN
NH2
CN
CN
3
O
O
Ar
H
SMA NPs
4
+
O
6g
6h
6i
EtOH: H2O (1:1)
OH
thiophene-2-yl
3-Br-C6H4
6
O
O
6j
2-Cl-6-F-C6H3
4-benzyloxy-
C6H4
5
SMA 2.
6k
450
84
275-277
From the perspective of green chemistry, equal mixture of
H2O/EtOH (1:1) was opted as reaction medium. It should be
noted that the reaction progress in absolute water and/or
absolute ethanol was not better than mixture of these
solvents. From different ratio of H2O/EtOH mixtures, equal
mixture H2O/EtOH (1:1) was considered as the most effective
ratio. Initially, the model reaction was established under reflux
in an equal mixture of H2O/EtOH (1:1) in the presence of
various amounts of nano-SMA. This reaction was firstly
examined in the absence of catalyst which did not show any
appreciable progress even after 360 min. Upon screening, the
results well showed that the this reaction proceeds efficiently
by adding 5 mol% of nano-SMA. Also, increasing the catalyst
amount did not improve the results (Figure 5).
6l
6m
6n
1-Naphthyl
90
40
25
90
92
86
260-262
239-241b
265-267b
4-isopropyl-C6H4
cyclohexyl
aIsolated yield.
bNovel compounds.
Table 3 demonstrates the merit of this method for the
synthesis of pyrano[2,3-c]coumarins in comparison with
previously reported results. As it can be seen from Table 3,
piperidine was employed as a basic catalyst under refluxing
EtOH, but this method could not afford good yields (entry 1).
In the case of (S)-proline (entry 4), the product was obtained in
low yield in a long time. Using some catalysts, such as DAHP
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(entry 3), KF–Al2O3(entry 5), and TEBA (entry 6) needs too long recyclability up to four cycles, during which there are a little
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reaction times. We believe that these reactions can be losses in the catalytic activity.
efficiently carried out under our suggested conditions with
respect to reaction times and product yield.
Table 3. Comparison of the present work with other methods
reported in the literature.a
Time
(min)
120
420
30
180
240
240
30
Yield
(%)Ref.
8517
9602
7022
8145
7245
9046
96b
Catalyst/amount
Conditions
SDS/20 mol%
TEBA/0.07 g
Piperidine/0.5 mL
DAHP/10 mol%
H2O/60 °C
H2O/90 °C
EtOH /reflux
H2O:EtOH /r.t
H2O:EtOH/reflux
EtOH /reflux
H2O:EtOH/reflux
(S)-Proline/10 mol%
KF–Al2O3/0.125 g
nano-SMA/5 mol%
a Synthesis of 6a.
b Present work.
Fig. 6. Recyclability of nano-SMA
2 in the synthesis of 6a
(reaction time = 30 min).
A
mechanistic rationale for the formation of
pyranochromenes is suggested in Scheme 3. It seems that
the reaction takes place in three steps. It is reasonable to
assume that the initial event involves the generation of the In summary, we found nanosilica molybdic acid as an effective
arylmethylene via Knoevenagel condensation of the and environmentally safe heterogeneous catalyst which
aldehyde and malononitrile catalyzed by nano-SMA
next steps, a Michael-type addition to the arylmethylene and hydroxycoumarin,
6
Conclusions
a
2
. In the successfully
catalyzed
the
reaction
aromatic
between
aldehydes
4-
and
various
subsequent heterocyclization promoted by nano-SMA
2
gives malononitrile to produce new and known pyrano[2,3-
c]chromens of potential synthetic and pharmaceutical interest.
The present protocol not only originates the products with
excellent yields in short reaction times, but also avoids some
problems such as catalyst cost, pollution, handling, and safety.
Also, conventional product work-up and high recyclability of
catalyst are other attractive features of this procedure.
the corresponding products
6
.
O
S
i
O
O
Mo
O
O
Si
2
OH
H
O
+
H
H
Ar
O
S
NC
CN
Ar
H
O
i
O
O
Mo
O
O
Si
2
3
4
Acknowledgements
Financial support for this work by Yasouj University (Iran) and
the Iranian Nanotechnology Initiative Council is gratefully
acknowledged.
N
H
O
S
HO
i
O
N
Mo OH
O
2
Ar
NH2
CN
Ar
O
N
N
Notes and references
O
O
6
1
2
A. Corma and H. Garcia, Catal. Today., 1997, 38, 257-308.
V. Polshettiwar and R. S. Varma, Green Chem., 2010, 12, 743-
754.
Ar
H
O
NH2
HN
O
3
4
5
6
D. Astruc, F. Lu and J. R. Aranzaes, Angew. Chem. Int. Ed.,
2005, 44, 7852-7872.
L. Hui, X. Hui-Gang, Y. Jie and O. Jinping, Composites Part B:
Eng., 2003, 35, 185–189.
E. Rafiee, A. Ataei, Sh. Nadri, M. Joshaghani and S. Eavani,
Inorg. Chim. Acta., 2014, 409, 302–309.
C
CN
Ar
CN
H
O
O
O
O
O
O
O
5
Ar
H
O
O
O
O
O
O
O
S
iO2
O
S
O
i
O
O
Mo OH
O
2
G. Evano, N. Blanchard and M. Toumi, Chem. Rev. 2008, 108
3054–3131.
,
SiO2
Scheme
3
A
plausible mechanism for the formation of
catalyzed by nano-SMA
7
8
M. Syamala, Org. Prep. Proced. Int., 2009, 41, 1–68.
pyranocoumarins
6
2.
A. Shaabani, A. Rahmati, A. H. Rezayan and H. R. Khavasi, J.
Iran. Chem. Soc., 2001, 8, 24.
9
J.M. Khurana, B. Nand and P. Saluja, Tetrahedron, 2010, 66,
The main disadvantage of many reported methods for
these reactions is that the catalysts are destroyed in the work-
up procedure and cannot be recovered or reused. In these
5637-5641.
10 S. Yaragorla, P. L. Saini and G. Singh, Tetrahedron Lett., 2015,
56, 1649–1653.
processes, as outlined in Fig. 6, the nano-SMA
2 showed
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New Journal of Chemistry
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DOI: 10.1039/C5NJ01302J
Table of Content (ToC)
Nanosilica molybdic acid as an effective and environmentally safe heterogeneous catalyst has been
developed for the synthesis of pyranocoumarins

New Journal of Chemistry
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DOI: 10.1039/C5NJ01302J