Nanosilica molybdic acid: synthesis, characterization and application as a green and reusable catalyst for the Pechmann condensation

Article abstract of DOI:10.1007/s13738-016-1016-6

Abstract: Nanosilica molybdic acid (SMA NPs) was founded as an efficient and recyclable nanocatalyst for the synthesis of coumarin derivatives in excellent yields with good purity. Nano-SMA as a new solid acid was characterized by X-ray fluorescence, X-ray diffraction, energy-dispersive X-ray analyzer, transmission electron microscopy and Fourier transform infrared spectroscopy. Coumarin derivatives were obtained via the Pechmann condensation reaction of phenols and β-ketoesters at 80?°C under solvent-free conditions. The main advantages of the present procedure are high yields, shorter reaction time and green chemistry procedure, simple work-up and inexpensive and reusability of the catalyst. Graphical Abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s13738-016-1016-6

J IRAN CHEM SOC
DOI 10.1007/s13738-016-1016-6
ORIGINAL PAPER
Nanosilica molybdic acid: synthesis, characterization
and application as a green and reusable catalyst for the Pechmann
condensation
Mahtab Kiani · Bahador Karami2
1
Received: 21 July 2016 / Accepted: 24 November 2016
©
Iranian Chemical Society 2016
Abstract Nanosilica molybdic acid (SMA NPs) was
founded as an efficient and recyclable nanocatalyst for the
synthesis of coumarin derivatives in excellent yields with
good purity. Nano-SMA as a new solid acid was character-
ized by X-ray fluorescence, X-ray diffraction, energy-dis-
persive X-ray analyzer, transmission electron microscopy
and Fourier transform infrared spectroscopy. Coumarin
derivatives were obtained via the Pechmann condensation
reaction of phenols and β-ketoesters at 80 °C under sol-
vent-free conditions. The main advantages of the present
procedure are high yields, shorter reaction time and green
chemistry procedure, simple work-up and inexpensive and
reusability of the catalyst.
Graphical Abstract
Keywords Nanosilica molybdic acid · Coumarins ·
Pechmann condensation · Solvent-free conditions ·
Nanocatalyst
Introduction
In recent years, one of the growing and important fields is
nanotechnology. Because of different physical and chemi-
cal properties of nanosized catalysts compared to bulk
material, they attract interest for different research areas
Electronic supplementary material The online version of this
article (doi:10.1007/s13738-016-1016-6) contains supplementary
material, which is available to authorized users.
[1]. Since the particles are in small size, the surface area
exposed to the reactant is maximized so allowing more
reactions to occur at the same time; hence, the process is
speeded up [2].
Application of heterogeneous catalysts in organic trans-
formations has an important role, because they have many
advantages such as decreased reactor, facile handling, plant
corrosion problems and more environmentally safe dis-
posal [3–6].
*
Mahtab Kiani
mahtabkiani47@yahoo.com
1
2
Young Researchers and Elite Club, Karaj Branch, Islamic
Azad University, Karaj, Iran
Department of Chemistry, Yasouj University, P.O. Box 353,
Yasouj 75918-74831, Iran
1
3

J IRAN CHEM SOC
Fig. 1 Biologically active
coumarin derivatives
O
O
N
N
H
NO2
O
O
O
O
O
O
O
OH
O
HO
O
O
Coumarin derivatives have attracted considerable inter-
est because they exhibit a variety of biological activities
such as antimicrobial, anti-inflammatory, analgesic, anti-
oxidant, antimalarial, anticancer, antituberculosis and anti-
HIV properties, which have been reviewed [7–15]. Some
biologically active anticancer [16] and antituberculosis [17]
agents having coumarin moiety are presented in Fig. 1.
Nowadays, many synthetic methods for preparing cou-
marins have been developed to improve and modify this
reaction. However, in spite of their potential utility, many
of these methods involve expensive reagents, strong acidic
conditions, tedious work-up, low yields and long reaction
times. Pechmann condensation under solvent-free condi-
tions as an eco-friendly strategy since reduces waste pro-
duction and precludes the use of organic solvents [18].
Several acid catalysts have been used in the Pechmann
reaction, including nanocrystalline sulfated tin oxide [19],
mesoporous zirconium phosphate (m-ZrP) [20], BaCl2
TMS as the internal standard. X-ray diffraction (XRD) pat-
tern was obtained by Philips X Pert Pro X diffractometer
operated with a Ni-filtered Cu-Kα radiation source. X-ray
fluorescence (XRF) spectroscopy was recorded by X-ray
Fluorescence Analyzer, Bruker, S4 Pioneer, Germany.
EDAX analyses were carried out on a Philips XL30, oper-
ated at a 20-kV accelerating voltage. Transmission elec-
tron microscopy (TEM) images of the electrocatalyst were
recorded using a Philips CM-10 TEM microscope operated
at 100 kV.
General procedure for the preparation of nanosilica
molybdic acid 2
To an oven-dried (125 °C, vacuum) sample of silica gel 60
(10 g) in a round-bottomed flask (250 ml) equipped with a
condenser and a drying tube, thionyl chloride (40 ml) was
added and the mixture in the presence of CaCl as a drying
2
[
[
21], silica gel-supported zirconyl chloride octahydrate
22], HClO SiO [23], alumina sulfuric acid [24], Zr-TMS-
agent was refluxed for 48 h. The resulting white-grayish
powder was filtered and stored in a tightly capped bottle
[29]. For 30 min, 0.1 g of silica chloride 1 was stirred in
toluene (10 ml). The solution of 0.084 g sodium molyb-
date in 10 ml toluene was added to the first solution and
stirred for 10 min. The resulting mixture was sonicated in
an ultrasonic bath for 1 h at room temperature. The mixture
was transferred to a 70-ml autoclave and heated at 140 °C
for 4 h. White precipitate obtained, washed with distilled
water, then separated by filtration and dried at 30 °C for
4
2
TFA-25 [25], poly (4-vinylpyridine)-supported copper
iodide [26], PEG-SO H [27], zirconium (IV) phosphotung-
state and 12-tungstophosphoric acid supported onto ZrO2
[
3
28].
In this work, a new methodology to obtain coumarins,
via a one-pot Pechmann condensation, is reported. We
introduce nanosilica molybdic acid (SMA NPs) as a novel
and safe catalyst for the synthesis of coumarin derivatives.
2
h. The white powder was stirred in HCl (0.1 N) for 1 h.
The white powder was separated by filtration, washed with
distilled water and dried at 30 °C for 2 h.
Experimental
General
General procedure for the synthesis of coumarin
derivatives 5a–o
The chemicals were purchased from Merck and Aldrich
chemical companies. The silica chloride 1 was synthe-
sized according to the published procedure [29]. The reac-
tions 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 melting points were determined
In a general experimental procedure, β-ketoester 3
(1 mmol) was added to a mixture of substituted phenol
4 (1 mmol) and SMA NPs 2 (5 mol%) in a solvent-free
tube. The reaction mixture was stirred in a preheated oil
bath (80 °C). After the completion of the reaction, the pre-
cipitate obtained was extracted with ethyl acetate, washed
with water (3 × 10 ml) and dried to obtain the product.
The remaining insoluble solid catalyst in aqueous phase
was separated by filtration, washed with ethyl acetate
1
on a KRUSS model instrument. H NMR spectra were
recorded on a Bruker Avance II 400 NMR spectrometer
at 400 MHz, in which DMSO-d was used as solvent and
6
1
3

J IRAN CHEM SOC
(
3 × 10 ml) and reused for further catalytic cycles. The
7‑Methoxy‑4‑methyl‑2H‑chromen‑2‑one (5j)
crude product was recrystallized to afford the pure product.
1
Colorless prisms, mp 161–163 °C; yield 88%. HNMR
Representative spectral data
(400 MHz, CDCl ): δ 7.50 (d, 1H, J = 8.8 Hz), 6.87 (dd,
3
1
H, J = 8.8, 2.4 Hz), 6.83 (d, 1H, J = 2.4 Hz), 6.14 (d,
7
‑Hydroxy‑4‑methyl‑2H‑chromen‑2‑one (5a)
1H, J = 1.2 Hz), 3.88 (s, 3H), 2.40 (d, 3H, J = 1.2 Hz).
1
3
CNMR (100 MHz, CDCl ): δ 162.83, 160.59, 155.24,
3
Colorless prisms, mp 183–185 °C; yield 93%.
153.86, 126.88, 113.56, 112.54, 111.58, 101.16, 56.36,
18.58. IR (KBr, cm ): 3400 (OH), 1705 (C=O).
1
−1
HNMR(400 MHz, DMSO-d ): δ 10.138 (s, 1H), 7.373
6
(
(
m, 5H), 6.722 (s, 1H), 6.470 (s, 1H), 5.957 (s, 1H), 2.292
1
3
s, 3H). CNMR (100 MHz, DMSO-d ):δ 160.09, 156.05,
7,8‑Dihydroxy‑4‑methyl‑2H‑chromen‑2‑one (5n)
6
1
1
55.96, 155.51, 143.93, 139.75, 128.34, 127.92, 127.75,
13.88, 112.52, 108.19, 105.44, 21.65. IR (KBr, cm ):
−1
White solid, mp 235–237 °C; yield 75%. 1HNMR
(
3000–3400), 3050, 2900, 1690, 1615, 1590, 1500, 1080.
‑Hydroxy‑4‑phenyl‑2H‑chromen‑2‑one (5b)
Colorless prisms, mp 246–248 °C; yield 86%. HNMR
(400 MHz, DMSO-d ): δ 10.1 (s, 1H), 9.35(s,1H), 7.07 (d,
6
1
H, J = 8.8 Hz), 6.81 (d, 1H, J = 8.4 Hz), 6.12 (d, 1H,
13
7
J = 1.2 Hz), 2.4 (d, 3H, J = 1.2 Hz). CNMR (100 MHz,
DMSO-d ): δ 160.71, 154.35, 149.81, 143.47, 132.60,
6
1
−1
115.88, 113.23, 112.56, 110.60, 18.63. IR (KBr, cm ):
(
1
400 MHz, CDCl ): δ 5.905 (s, 1H), 6.56 (m, 2H), 7.04 (d,
H), 7.28 (t, 1H), 7.322 (m, 3H), 10.65 (s, 1H). CNMR
3231 (OH), 1668 (C=O).
3
1
3
(
100 MHz, CDCl ): δ 103.12, 110.10, 111.08, 113.68,
7‑Amino‑4‑methyl‑2H‑chromen‑2‑one (5o)
3
1
28.54, 128.79, 129.29, 130.07, 135.52, 155.9. IR (KBr,
−1
1
cm ): 3050, 1690, 1600, 1250, 1150.
Light yellow solid, mp 220–222 °C; yield 94%. HNMR
(
400 MHz, DMSO-d ): δ 7.4 (d, 1H, J = 8.8 Hz), 6.56 (d,
6
5
‑Hydroxy‑4,7‑dimethyl‑2H‑chromen‑2‑one (5d)
1H, J = 7.2 Hz), 6.39 (s, 1H), 6.09 (s, 2H), 5.89 (s, 1H),
13
2
.39 (s, 3H). CNMR (100 MHz, DMSO-d ): δ 160.90,
6
1
Colorless prisms, mp 250–252 °C; yield 96%. HNMR
400 MHz, DMSO-d ): δ 10.52 (s, 1H), 6.62 (d, 1H,
152.80, 151.00, 148.00, 127.60, 113.00, 112.50, 111.10,
106.70, 21.2. IR (KBr, cm ): 3439 (N–H), 1684 (C=O).
−1
(
6
J = 1.2 Hz), 6.57 (d,1H, J = 1.2 Hz), 6.03 (d, 1H,
J = 1.2 Hz), 2.54 (d, 3H, J = 1.2 Hz), 2.27 (s, 3H).
NMR (100 MHz, DMSO-d ): δ 160.29, 156.90, 155.28,
1
3
C
Results and discussion
6
1
2
54.04, 143.18, 112.37, 112.3, 108.15, 106.96, 23.91,
1.56. IR (KBr, cm ): 3393 (OH), 1655 (C=O).
−
1
Nanosilica molybdic acid was synthesized and character-
ized by X-ray fluorescence (XRF), X-ray diffraction pat-
tern (XRD), Fourier transform infrared spectroscopy (FT-
IR), energy-dispersive X-ray spectroscopy (EDAX) and
transmission electron microscopy (TEM).
5
‑Hydroxy‑7‑methyl‑4‑phenyl‑2H‑chromen‑2‑one (5e)
1
Colorless prisms, mp 214–216 °C; yield 88%. HNMR
(
(
(
400 MHz, DMSO-d ): δ 10.14 (s, 1H), 7.35 (m, 5H,), 6.72
s, 1H), 6.47 (s, 1H), 5.96 (s, 1H), 3.01 (s, 3H). CNMR
In continuation of our previous studies on the develop-
ment of various catalysts in the synthesis of organic com-
pounds [30–32], as can be seen in Scheme 1, SMA NPs 2
6
1
3
100 MHz, DMSO-d ): δ 160.09, 156.05, 155.96, 155.51,
6
1
1
43.93, 139.75, 128.34, 127.92, 127.75, 113.88, 112.52,
08.19, 105.44, 21.65. IR (KBr, cm ): 3180 (OH), 1680
−
1
OH
Si
O O O
ONa
O Mo O
O
OH
O Mo O
O
(
C=O).
SOCl2
Reflux
Si
O
Si
O
O
5
,7‑Dihydroxy‑4‑methyl‑2H‑chromen‑2‑one (5g)
SiO2
HCl/ H2O, 1 h
-NaCl
O
O
O
4
8 h
Cl
Si
O O O
SiO2
-
SO2
White solid, mp 279–281 °C; yield 91%. 1HNMR
400 MHz, DMSO-d ): δ 10.51 (1H, s), 10.28 (1H,
-
HCl
SiO2
2
Na2MoO4
(
6
SiO2
Toluene
Reflux, 4 h
s), 6.24 (1H, s), 6.15 (1H, s), 5.83 (1H, s), 2.49 (3H, s).
1
3
CNMR(100 MHz, DMSO-d ): δ 16.51, 160.55, 158.39,
1
-NaCl
6
1
56.96, 155.43, 109.22, 102.55, 99.45, 94.98, 23.88. IR
−1
(
KBr cm ): 3400, 3070, 2940, 1670, 1600, 1480, 1080.
Scheme 1 Synthesis of nanosilica molybdic acid 2
1
3

J IRAN CHEM SOC
Table 1 XRF data of SMA NPs 2
Entry
Compound
Concentration (%)
1
2
3
4
5
6
7
8
9
SiO2
71.14
25.62
1.90
MoO4
Na O
2
Cl
0.460
0.355
0.289
0.046
0.045
0.027
0.023
0.022
0.022
99.95
ZnO
CaO
Fe O
2
3
3
Al O
2
CuO
1
1
1
1
0
1
2
3
GeO2
MnO
TiO2
Total
Fig. 3 XRD pattern for SMA NPs 2
This spectrum shows the characteristic bonds of anhydrous
sodium molybdate and silica chloride.
The successful incorporation of molybdate groups was
also confirmed by EDAX analysis (Fig. 5), which showed
the presence of Mo in addition to Si and O elements.
−1
The adsorption in 3452, 1634, 1086, 800 cm in the
catalyst spectrum reveals both bonds in SiO –Cl and MoO
2
4
+
group. We evaluated that the amount of H was determined
by back titration of the weighed amount of catalyst with
standard 0.01 N NaOH solution and was found to be equal
to 0.25 mmol of the catalyst.
Fig. 2 XRF analysis of SMA NPs 2
was prepared from the reaction of readily available materi-
als such as silica gel, thionyl chloride and silica chloride
The structural information about nanosilica molyb-
dic acid such as particle size and shape was provided by
transmission electron microscopy (TEM). As shown in
Fig. 6, the TEM image revealed the formation of meso-
structured nanoparticles with an average size in the range
of 15–30 nm.
To study the efficiency of SMA NPs 2 for Pechmann
condensation, the reaction of β-ketoesters 3 and phenol
derivatives 4 was selected as the model. The expected cou-
marins 5a–o were obtained as pure products in high yield
by solvent-free stirring (Scheme 2).
1
[33]. Accordingly, we found that anhydrous sodium
molybdate can react with 1 to give nanosilica molybdic
acid (SMA NPs) 2. This reaction is clean and easy. From
the synthetic point of view, the nucleophilic substitution of
+
silicon is also attractive. The amount of H was determined
by back titration of the weighed amount of catalyst with
standard 0.1 N NaOH solution that was found to be equal
to 0.25 mmol/g of the catalyst.
As can be seen in Table 1, XRF data for the SMA NPs
2
show the composition of the catalyst as 71.14 (%W/W)
This reaction was firstly examined in the absence of
catalyst which did not show any appreciable progress even
after 360 min. Silica gel and silica chloride as catalysts
could not show promising catalytic effects. When the reac-
tion was tried with Na MoO and sodium silica molybdate
as catalysts, the product was obtained in low yield in longer
time period. However, when the reaction was tried using
SMA NPs as a catalyst, the results obtained were very sat-
isfactory as good yield of the product (93%) was obtained
at 20 min only (Table 2, entry 1). Upon screening, the
results well showed that the reaction proceeds efficiently
SiO and 25.62 (%W/W) MoO (Fig. 2).
2
4
Figure 3 shows the XRD patterns for the SMA NPs
which exhibits the presence of molybdic acid crystal-
2
line phase supported on amorphous silica as a broad peak
around 23° (2θ) (θ is Bragg’s angle). The three peaks in
the 35°–40° region of the XRD spectrum could be attrib-
2
4
uted to the presence and linking of MoO to the silica gel
3
[
34].
The FT-IR spectra for the anhydrous sodium molyb-
date, silica chloride and SMA NPs 2 are shown in Fig. 4.
1
3

J IRAN CHEM SOC
Fig. 4 FT-IR spectra for
the comparison of SiO Cl,
2
Na MoO , SMA NPs 2 and
2
4
recycled SMA NPs 2
Fig. 5 Energy-dispersive spectroscopy (EDAX) pattern of SMA NPs
2
Fig. 6 TEM image of SMA NPs 2
by adding 5 mol% of SMA NPs. Also, increasing the cata-
lyst amount did not improve the results (Fig. 7).
was characterized by IR, NMR and other spectral data.
Similarly, resorcinol was treated with ethyl 4-chloroace-
toacetate, ethyl benzoylacetate (Table 2, entries 2, 3) to fur-
nish coumarins (5b, 5c), respectively.
Encouraged by the above results, other phenolic sub-
strates were subjected to the Pechmann reaction using SMA
NPs. In all cases, the reactions proceeded successfully to
afford the corresponding coumarins in good-to-excellent
yields. The electron-donating substituents in the meta-
position to the phenolic –OH facilitated the cyclization.
The reactivity of phloroglucinol (1,3,5-trihydroxybenzene)
After optimization of the reaction conditions, as can be
seen in Fig. 7, in order to extend the scope of this reaction,
various phenols such as resorcinol, pyrogallol and phloro-
glucinol were successfully used for the efficient Pechmann
reaction with different β-ketoesters. A wide variety of
coumarins were obtained through this method in good-to-
excellent yield in short reaction times.
Coumarin 5a was synthesized in 93% yield for 20 min
(
monitored by TLC CCl –ethyl acetate 5:1). Coumarin 5a
4
1
3

J IRAN CHEM SOC
O
O
O
O
Ph
OC H5
H C
3
OC H5
2
2
OH
3a
3
b
G
CH3
SMA NPs
SMA NPs
G
4
G
O
O
G =Alkyl, Ar, OH
O
O
Condition:solvent-free
5
5
o
8
0 C
O
O
ClH C
OC H5
SMA NPs
2
2
3
c
CH Cl
2
G
O
O
5
Scheme 2 SMA NPs-catalyzed synthesis of coumarins
Table 2 Synthesis of coumarins via von Pechmann condensation of phenols with β-ketoesters catalyzed by SMA NPs
O
O
R
SiO2
O
O
Si
O
Mo OH
O
O
O
OH
G
R
OC2H5
+
G
O
O
8
0 oC, solvent-free
3
4
5a-o
a
Entry
R
G
Product
Time (min)
Mp. (°C) [lit.]
Yield (%)
1
2
3
4
5
6
7
8
9
Me
Ph
3-OH
3-OH
3-OH
5a
5b
5c
5d
5e
5f
20
90
15
25
50
15
15
20
20
25
20
30
100
40
20
183–185 [31]
246–248 [31]
176–178 [31]
250–252 [31]
214–216 [31]
163–165 [31]
279–281 [31]
243–245 [31]
184–186 [31]
161–163 [31]
177–179 [31]
154–156 [31]
166–168 [31]
235–237 [31]
220–222 [31]
93
86
84
96
88
87
91
76
84
88
85
78
67
75
94
CH Cl
2
Me
Ph
3-Me-5-OH
3-Me-5-OH
3-Me-5-OH
3,5-(OH)2
3,5-(OH)2
3,5-(OH)2
3-MeO
CH Cl
2
Me
Ph
5g
5h
5i
CH Cl
2
10
11
12
13
14
15
Me
5j
CH Cl
3-MeO
5k
5l
2
Me
1-Naphthol
1-Naphthol
2,3-(OH)2
3-NH2
CH Cl
5m
5n
5o
2
Me
Me
a
Yields refer to isolated products
1
3

J IRAN CHEM SOC
Finally, the reactions are remarkably clean, and no chro-
matographic separation is necessary to get the spectra-pure
compounds.
The suggested mechanism for the Pechmann conden-
sation of phenols 4 with β-ketoesters 3 in the presence of
SMA NPs catalyst (Scheme 3) has been described using
condensation as probe reaction. The SMA NPs catalyst
would cause dehydration and produce an olefinic bond; at
the same time, ethyl alcohol would be eliminated with the
formation of coumarin ring.
Comparing this method with other catalysts, the syn-
thesis of 7-hydroxy-4-methyl-2H-chromen-2-one (Table 2,
Entry 1) as a model reaction was performed in the presence
of other catalysts [31]. The results are shown in Table 3.
The data show that our method is suitable and better than
the others to synthesize coumarins with respect to the
amounts of the used catalysts, reaction times and yields of
the products (Table 3).
The design and synthesis of recoverable catalysts
is a highly challenging interdisciplinary field, which
combines chemistry, materials science and engineering
from economic and environmental perspectives. The
main disadvantage for many of the reported methods is
that the catalysts are destroyed in the work-up proce-
dure and cannot be recovered or reused. In this process,
Fig. 7 Optimization of the catalyst amount
(
entry 7) with ethyl acetoacetate was observed to be higher
than pyrogallol (entry 14) due to two hydroxyl groups at
meta-positions in phloroglucinol compared to one hydroxy
group in pyrogallol. Presence of the meta-hydroxy group
strongly activates the substrates due to resonance effect.
m-Methoxyphenol (entry 10) showed no detectable dem-
ethylation under the reaction conditions. Similarly, 1-naph-
thol (entry 12) requires a slightly higher temperature and
longer reaction time. These results show that the reactivity
of phenolic substrates as the catalyst acidity is important.
Scheme 3 The proposed
G
mechanism for the SMA
NPs-catalyzed formation of
coumarins
O
O
OH
O
R
OC H
2 5
HO
R
OC H
2
5
3
4
O
O
SiO2
O
Si
O
Mo OH
O
O
O
O
R
H
OC2H5
R
O
OH
H
G
G
HO
O
O
O
OH
R
OC H
2
5
R
5
a-o
OH
OC H
2
5
OH
G
O
G
O
Mo
O
O
Si
O
O
O
SiO2
1
3

J IRAN CHEM SOC
Table 3 Comparison of our method with other methods for the synthesis of (5a)
Catalyst
Catalyst amount
Condition
Time (min)
Yield (%)
SMA NPs
5 mol%
0.2 g
Solvent-free, 80 °C
Solvent-free, 130 °C
Solvent-free, 120 °C
Solvent-free, 100 °C
Solvent-free, 160 °C
Solvent-free, 80 °C
Solvent-free, 80 °C
Solvent-free, 90 °C
Solvent-free, 120 °C
20
480
240
540
240
10
93
58
95
88
94
98
87
92
78
ZrPW
Nanocrystalline sulfated tin oxide
Zr-TMS-TFA-25
25 wt%
0.1 g
Mesoporous zirconium phosphate (m-ZrP)
ZrOCl ·8H O/SiO
15 wt%
10 mol%
1 mol%
10 mol%
30 wt%
2
2
2
In(OTf)3
32
Y(NO3) ·6H O
45
3
2
H PW O supported on nanoparticle tin oxide
120
3
12 40
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(
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L. Wu, X. Wang, W. Xu, F. Farzaneh, R. Xu, Curr. Med. Chem.
1
6, 4236 (2006)
Fig. 8 Recyclability of SMA NPs as a catalyst for the synthesis of 5a
9. F. Borges, F. Roleira, N. Milhazes, L. Santana, E. Uriarte, Curr.
Med. Chem. 12, 887 (2005)
1
0. X.M. Peng, G.L.V. Damu, C.H. Zhou, Curr. Pharm. Des. 19,
884 (2013)
3
as outlined in Fig. 8, the recycled catalyst can be used
for up to six cycles, during which there are negligible
losses in the catalytic activity. The FT-IR spectra of the
catalyst after six cycles (Fig. 4) showed the same spec-
tral fingerprint of the freshly prepared catalyst indicat-
ing the stability of the catalyst throughout the recycling
experiment.
1
1
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1
5, 2664 (2008)
1
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1
1
4. M.V. Kulkarni, G.M. Kulkarni, C.H. Lin, C.M. Sun, Curr. Med.
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In summary, we found SMA NPs as an effective and envi-
ronmentally safe heterogeneous catalyst which successfully
catalyzed the Pechmann condensation reaction to produce
coumarins of potential synthetic and pharmaceutical inter-
est was presented. The present protocol not only originates
the products with excellent yields in short reaction times
but also avoids some problems such as catalyst cost, pol-
lution, handling and safety. Also, conventional work-up of
products and high recyclability of catalyst are other attrac-
tive features of this procedure.
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