Magnetic nanoparticles functionalized ethane sulfonic acid (MNESA): as an efficient catalyst in the synthesis of coumarin derivatives using Pechmann condensation under mild condition

Article abstract of DOI:10.1007/s11164-016-2447-5

This paper reports an efficient heterogeneous catalyst based on sulfonic acid functionalization of magnetic nanoparticles. This new catalyst was prepared using the reaction between magnetic nanoparticles and sodium 2-bromoethane-1-sulfonate. Magnetic nanoparticles functionalized ethane sulfonic acid (MNESA) was found as efficient catalyst for the synthesis of coumarin derivatives using Pechmann condensation under mild condition. This reaction was catalyzed by MNESA under solvent-free condition at 90?°C, to give the corresponding products in excellent yields. The catalyst is easily separated from the reaction condition and can be reused for several times with consistence in the activity.

Full text of DOI:10.1007/s11164-016-2447-5

Res Chem Intermed
DOI 10.1007/s11164-016-2447-5
Magnetic nanoparticles functionalized ethane sulfonic
acid (MNESA): as an efficient catalyst in the synthesis
of coumarin derivatives using Pechmann condensation
under mild condition
Marjaneh Samadizadeh1 Saeed Nouri1
•
•
Faeze Kiani Moghadam2
Received: 14 September 2015 / Accepted: 16 January 2016
Ó Springer Science+Business Media Dordrecht 2016
Abstract This paper reports an efficient heterogeneous catalyst based on sulfonic
acid functionalization of magnetic nanoparticles. This new catalyst was prepared
using the reaction between magnetic nanoparticles and sodium 2-bromoethane-1-
sulfonate. Magnetic nanoparticles functionalized ethane sulfonic acid (MNESA)
was found as efficient catalyst for the synthesis of coumarin derivatives using
Pechmann condensation under mild condition. This reaction was catalyzed by
MNESA under solvent-free condition at 90 °C, to give the corresponding products
in excellent yields. The catalyst is easily separated from the reaction condition and
can be reused for several times with consistence in the activity.
Keywords Heterogeneous catalyst Á Coumarin Á Pechmann reaction Á Magnetic
nanoparticles
Introduction
There are widespread interests in the preparation of heterogeneous acid catalyst for
application in acid catalyzed organic transformations [1–4]. In recent years, magnetic
nanoparticles (MNPs) have been used as an efficient support for synthesis of
heterogeneous catalyst. This material is an abundantly available and highly stable sub-
strate, mainly characterized by the fact that organic groups can be linked to its surface
Electronic supplementary material The online version of this article (doi:10.1007/s11164-016-2447-5)
contains supplementary material, which is available to authorized users.
&
Marjaneh Samadizadeh
mar.samadizadeh@iauctb.ac.ir
1
2
Department of Chemistry, Islamic Azad University, Central Tehran Branch,
19379-58814 Tehran, Iran
Department of Chemistry, Faculty of Science, Ferdowsi University of Mashhad, Mashhad, Iran
123

M. Samadizadeh et al.
with strong bonding to generate catalytic sites [5–7]. Development of magnetic
reusable catalysts for organic synthesis based on solid acids has become an
environmental chemical procedure for academic and industrial applications [8].
Several types of magnetic nanoparticle sulfonic acids have been prepared and applied
in chemical transformations in recent years [9–11]. All of these magnetic nanoparticles
based on sulfonic acid catalyst are suitable for some acid catalyzed organic
transformations, but such preparation often suffers from some deficiency such as
expensive starting reagents and requires more than two steps for the preparation [9–14].
Our aim was to have magnetic nanoparticles react directly with sodium
2-bromoethane-1-sulfonate to generate SO3H groups on the surface of the magnetic
nanoparticles. In this way, we introduced a new solid acid catalyst based on
magnetic nanoparticles. However, to the best of our knowledge, there are no
examples of silica-based ethane-1-sulfonic acid catalysts that have been prepared
according to our approach.
In this study, we wished to evaluate the catalytic performance of this new catalyst
in the ‘‘Pechmann reaction’’ as an acid catalyzed process. Although various methods
have been reported for this reaction, they suffer from disadvantages such as long
reaction time, using expensive and/or nonstable catalyst and using heterogeneous
catalysts [15–21]. There is widespread interest in the synthesis of new coumarin
derivatives, because of their applications in organic synthesis, biology, medicine,
perfumes and cosmetics fields [22, 23]. Also some of the coumarin derivatives are
known as antioxidant compounds, due to their radical scavenging properties [24]. In
material science, they have been used as fluorescence dyes in composite with other
heterocyclic moieties [24]. Furthermore, for DNA and RNA labeling, some
fluorescent materials containing a coumarin moiety have been reported [25]. Due to
these properties, coumarins have been given attention by chemists, and a range of
methods have been reported for their synthesis [26–39].
Among them, the Pechmann reaction is a simple protocol for the synthesis of
coumarin rings using a two-component coupling reaction between phenol and b-
ketoester under acid catalyst condition. This reaction has been studied with different
homogeneous, heterogeneous and Lewis acid catalysts [16, 40–51]. Although these
methods are suitable for this process, they often suffer from one or more
deficiencies such as low yield, prolonged reaction time, tedious work-up processes,
expensive reagents and hazardous reaction conditions [52–54]. Considering the
above reports, it seems that preparation of a new catalyst to replace these catalyst
procedures with environmentally more acceptable protocols, based on improved
solvent toxicity and recoverable catalysts, is reasonable.
Experimental
Chemicals were purchased from Fluka and Aldrich chemical companies and were
used without further purification. The known products were characterized by the
comparison of their spectral and physical data with those reported in the literature.
1H and 13C NMR spectra were recorded on a Bruker Avance 250 MHz spectrometer
in CDCl3 solution with tetramethylsilane (TMS) as an internal standard. FT-IR
spectroscopy (Shimadzu FT-IR 8300 spectrophotometer), was employed for
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Magnetic nanoparticles functionalized ethane sulfonic…
characterization of the catalyst and products. The scanning electron micrograph
(SEM) for the MNESA catalyst was obtained by SEM instrumentation (SEM, XL-
30 FEG SEM, Philips, at 20 kV). Transmission electron microscopy (TEM) was
obtained using a TEM apparatus (CM-10-Philips, 100 kV) for characterization of
the catalyst. X-ray diffraction (XRD, D8, Advance, Bruker, axs) was also used to
characterize the catalyst. Elemental analyses for C, H, N and S were performed
using a Heraeus CHNS Rapid analyzer. Melting points were determined in open
capillary tubes in a Barnstead Electro-thermal 9100 BZ circulating oil melting point
apparatus. The reaction monitoring was accomplished by TLC on silica gel
PolyGram SILG/UV254 plates.
Preparation of catalyst
Synthesis of Fe3O4 nano particles
Fe3O4nanoparticles were synthesized byusinga coprecipitation process [55]. Briefly,
FeCl3Á6H2O and FeCl2Á4H2O (2:1 molar ratio) were loaded into a three-neck flask
and dissolved in 100 mL Millipore water. Ammonia hydroxide was then added drop-
wise into the vigorously stirred solution at 40 °C. After ammonia ran out, an additional
15 min was required to form stable nanoparticles. Then the Fe3O4 nanoparticles were
collected by permanent magnetic field and washed with water to remove unreacted
ammonia. Tetramethylammonium hydroxide (TMAOH) solution (25 wt% in water)
was added into the collected Fe3O4 and stirred for 30 min to form stable colloid.
Nitrogen was used in the whole process to prevent the particles from oxidation.
Synthesis of Fe3O4@SiO2 nano particles
The silica coated magnetic nanoparticles were prepared based on the literature with
some modifications [56]. In a conical flask, 250 mL of heptanes, 50 mL of i-PrOH,
40 mL of PEG-300 and 20 mL of water and 4 g of Fe3O4 were added. Then, the
mixture was stirred by mechanical stirrer under nitrogen gas for 45 min. Then,
40 mL of tetraethyl orthosilicate (TEOS) was added to the mixture, and the solution
was stirred for 12 h at 35 °C. Afterward, 20 mL of ammonia was added, and the
solution was stirred continuously for another 12 h. The precipitates were washed
with ethanol (3 9 10 mL) and collected by an external magnetic field. The obtained
Fe3O4@SiO2 nanoparticles were dried in an oven under vacuum overnight.
Synthesis of Fe3O4@SiO2@EtSO3H (MNESA) catalyst
In a conical flask (100 mL), a mixture of Fe3O4@SiO2 (4.0 g) in dry toluene
(50 mL), TBAB (0.5 g), K2CO3 (8 mmol, 1.1 g) and sodium 2-bromoethane-1-
sulfonate (1.7 g, 8 mmol), was mechanically stirred at 110 °C for 24 h. Then, the
mixture was cooled down to room temperature, and filtered and washed with EtOH
(2 9 10 mL) and water (3 9 10 mL). After the dark solid was dried in an oven, it
was stirred in a HCl solution (0.1 M) for 6 h in order to exchange protons to obtain
the desired catalyst.
123

M. Samadizadeh et al.
General procedure for Pechmann reaction in the presence of MNESA catalyst
A mixture of phenol (1.0 mmol), b-ketoester (1.5 mmol) and MNESA (0.075 g)
was stirred at 90 °C in a round-bottomed flask for the appreciated time. After
completion of the reaction as confirmed by TLC, the reaction mixture was cooled
down to room temperature and the catalyst was separated from the reaction mixture
using an external magnetic field. Some water was then added to the reaction mixture
and the product was extracted using EtOAc (2 9 10 mL). The combined organic
layers were dried over anhydrous Na2SO4, filtered and concentrated under vacuum
to yield the crude product. For more purification, the crude product was purified by
recrystallization in ethanol to obtain the desired purity.
Results and discussion
Catalyst preparation and characterization
We prepared the MNESA catalyst based on the following operation (Scheme 1).
First, magnetic nanoparticles (Fe3O4) were synthesized according to the
procedure in the literature [55]. Then Fe3O4 nanoparticles were coated with a
silica layer in order to prevent their aggregation [28]. Finally, silica-coated magnetic
TEOS
Fe O
Fe O
3
4
4
Fe(II)+Fe(III)
Fe3O4
3
SiO2
Fe3O4
Fe3O4@SiO2
SO3Na
Br
H
SO3
H
SO3
NaO3S
H
SO3
SO3Na
H
Fe3O4
SiO2
Fe3O4
SiO2
H
SO3
SO3Na
H
SO3
NaO3S
H
SO3
SO3Na
H
SO3
NaO3S
Fe3O4@SiO2@EtSO3Na
Fe3O4@SiO2@EtSO3H
MNESA
Scheme 1 Our synthetic method for the synthesis of MNESA catalyst
123

Magnetic nanoparticles functionalized ethane sulfonic…
Fig. 1 A comparison between the FT-IR spectra of Fe3O4@SiO2 (a), sodium 2-bromoethane-1-sulfonate
(b) and MNESA (c)
nanoparticles were allowed to react with sodium 2-bromoethane-1-sulfonate in
toluene at 110 °C to produce MNESA catalyst.
We next characterized the MNESA catalyst using some different microscopic
and spectroscopic techniques such as FT-IR, TEM, SEM, XRD and elemental
analysis.
The FT-IR spectra of the Fe3O4@SiO2 (a), sodium 2-bromoethane-1-sulfonate
(b) and MNESA (c) are shown in Fig. 1.
A comparison between the FT-IR spectra of Fe3O4@SiO2, sodium 2-bromoethane-
1-sulfonate and MNESA shows the existence of ethane sulfonic acid moiety on the
surface of magnetic nanoparticles, which clarifies the efficiency of our methodology
123

M. Samadizadeh et al.
for synthesis of this heterogeneous catalyst system. The FT-IR transmission spectrum
of the MNESA (Fig. 1c) shows the following peaks: characteristic absorption at
3444.8 cm-1 that is associated with the free –OH site on magnetic nanoparticles
and –OH of –SO3OH group [60], stretching frequency in 2850 cm-1 related to C–C
and C–H bond vibrations [58] (this peak confirms the presence of alkyl chain on the
magnetic nanoparticles), the medium bond in 624 cm-1 presumably is due to the
stretching frequency of S–O bond [60], and two peaks at 1085.5 and 1185.5 cm-1
related to asymmetric and symmetric stretching of O–S–O bond, respectively [57].
The observed peak at 586 cm-1 is related to Fe–O or Fe–O–Fe bond [59]. Also, the
strong peak at 1088 cm-1 corresponds to Si–O–Si bond, which confirms the existence
of an SiO2 layer around magnetic nanoparticles [60].
The TEM images of the MNESA catalyst (Fig. 2) show that nanoparticles of the
catalyst with near spherical morphology are assembled with relatively good
monodispersity. It seems that nanoparticles formed in the range of 20–30 nm are
suitable in view point of catalytic activity.
According to the SEM image (Fig. 3), it is clear that the catalyst particles are
regular in shape and are arranged in an approximately good orderly manner. The
SEM image has also confirmed the point that the MNESA nanoparticles are
produced with near spherical morphology.
The bare magnetic nanoparticles and final catalyst were analyzed using x-ray
diffraction (XRD) technique, and their XRD patterns are shown in Figs. 4 and 5,
respectively.
The peak at 2h = 18.5° corresponds to the SiO2 shell and the peaks indexed as
(220), (311), (400), (422), (511), and (440) are the planes of the Fe3O4 nanoparticles
[61].
The presence of these peaks in the XRD pattern of catalyst shows the successful
synthesis of magnetic base of this catalyst and indicates that the structure of bare
magnetic nanoparticles remained after the surface modification.
According to vibrational sampling magnetometer (VSM) analysis, the catalyst
exhibits a superparamagnetic property. After structural characterization of MNESA
Fig. 2 The TEM image of MNESA catalyst
123

Magnetic nanoparticles functionalized ethane sulfonic…
Fig. 3 The SEM image of
MNESA catalyst
Fig. 4 The XRD pattern of bare Fe3O4@SiO2
catalyst, it was analyzed with elemental analysis in order to estimate the –SO3H
content of this material for the determination of catalyst loading. The obtained
sulfur content of the catalyst was 4.8 %. It is possible to calculate the mmol
of ––SO3H group per 1 g of catalyst, which is equal to 1.5 mmol per 1 g of catalyst.
Thus the catalyst loading is equal to 1.5 mmol/g (Fig. 6).
Pechmann condensation using MNESA catalyst
After characterization of the catalyst, its catalytic activity was evaluated in the
Pechmann condensation for one-pot synthesis of coumarin derivatives. The reaction
123

M. Samadizadeh et al.
Fig. 5 The XRD pattern of MNESA catalyst
Fig. 6 The VSM of MNESA catalyst
between p-cresol (p-methyl phenol) and ethyl acetoacetate was chosen as a model
reaction to find optimization conditions for preparation of the coumarins. The
results are summarized in Table 1.
As shown in Table 1, in the absence of catalyst, no product was observed. In the
presence of magnetic nanoparticles, only 20 % of product was produced. The results
of the optimization study show that the MNESA catalyst is an efficient catalyst for
the Pechmann condensation for one-pot synthesis of coumarins. Some solvents were
tested and under solvent-free condition, maximum yield of product was observed.
Also, 0.075 g of catalyst (11 mol%) was optimal for this reaction. A temperature of
90 °C was recognized to be the best condition to obtain maximum yield of product.
Overall, the optimized conditions for this reaction are shown in Scheme 2.
123

Magnetic nanoparticles functionalized ethane sulfonic…
Table 1 Optimization of the reaction condition for synthesis of coumarins using Pechmann condensation
in the presence of MNESA catalysta
Entry
Catalyst (catalyst loading)
Solvent
T (°C)
Time (h)
Yield (%)b
1
–
–
100
100
100
Reflux
110
Reflux
Reflux
100
100
100
rt
6
6
0
2
Fe3O4@SiO2 (0.1 g)
MNESA (0.1 g)
MNESA (0.1 g)
MNESA (0.1 g)
MNESA (0.1 g)
MNESA (0.1 g)
MNESA (0.05 g)
MNESA (0.075 g)
MNESA (0.025 g)
MNESA (0.075 g)
MNESA (0.075 g)
MNESA (0.075 g)
MNESA (0.075 g)
MNESA (0.075 g)
MNESA (0.075 g)
–
20
3
–
1
90
4
EtOH
6
55
5
Toluene
6
60
6
H2O
12
6
Trace
50
7
CH2Cl2
8
–
–
–
–
–
–
–
–
–
1
82
9
1
89
10
11
12
13
14
15
16
a
2
75
12
1
Trace
86
80
50
1
54
90
1
90
90
1
91c
83d
90
1
Reaction conditions: p-cresol (1 mmol), ethyl acetoacetate (1.5 mmol) and solvent (3 mL), catalyst
(11 mol%)
b
Isolated yield
c
2 mmol of 2a was used
d
1.2 mmol of 2a was used
O
O
OH
O
O
Et
MNESA (0.075 g)
O
+
H
3C
H
3C
solvent-free
90 oC
1a
2a
1.5 mmol
CH3
1 mmol
3a
1h, 90%
Scheme 2 Optimized conditions for synthesis of coumarins using Pechmann condensation in the
presence of MNESA catalyst
123

M. Samadizadeh et al.
Table 2 Diversity of the reaction for the synthesis of coumarins using Pechmann
Entry Starting materials
Products
Time (h)
1
Yield (%)a,b
1
90
91
93
3a
2
3
1
3b
3c
1.5
4
5
6
1
1
3
90
92
88
3d
3e
3f
123

Magnetic nanoparticles functionalized ethane sulfonic…
Table 2 continued
Entry Starting materials
Products
Time (h)
Yield (%)a,b
7
2
90
3g
8
9
5
3
91
89
3h
3i
10
2
92
3j
11
12
4
2
87
90
3k
3l
13
10
75
3m
123

M. Samadizadeh et al.
Table 2 continued
Entry Starting materials
Products
Time (h)
Yield (%)a,b
14
15
5
85
90
3n
3o
3
a
Isolated yield
b
Reaction conditions: phenol (1 mmol), b-ketoester (1.5 mmol), MNESA (0.075 g), temperature 90 °C
H
SO3
R2
O
R2
O
O
H
SO3
O
O
R1
H
O
R1
R
O
1
2
4
R2
H
O
R2
H
O
-
H
2O
O
O
O
R1
R1
5
3
Scheme 3 Mechanism for the synthesis of coumarins using Pechmann condensation in the presence of
MNESA catalyst
To determine the scope of the designed protocol for preparation of coumarin
derivatives, a number of commercially available phenols were condensed with some
b-ketoesters under optimized reaction conditions, and the results are depicted in
Table 2.
Table 2 clearly demonstrates that the MNESA is effective for the synthesis of
coumarin derivatives under solvent-free conditions at 90 °C temperature. As clearly
shown in Table 2, catalytic activity of MNESA depended on both phenol and b-
ketoester substrates, and all phenols were rapidly converted to the corresponding
products in good to excellent yields.
123

Magnetic nanoparticles functionalized ethane sulfonic…
Table 3 The reusability of
catalyst
Entry
Catalyst (g)
Time (h)
Yield (%)a,b
1
2
3
4
5
0.150
0.143
0.140
0.138
0.132
1
1
2
2
5
90
89
88
87
85
a
Isolated yield
b
Reaction conditions: phenol
(1 mmol), b-ketoester
(1.5 mmol), MNESA (0.075 g),
temperature 90 °C
A plausible mechanism of Pechmann condensation reactions for the synthesis of
coumarins between b-ketoester compounds and phenols has been proposed
according to literature (Scheme 3) [15–21]. At first, esterification reaction of
phenol 1 and b-ketoester compound 2 in the presence of catalyst lead to
intermediate 4. Then, Friedel–Crafts reaction between carbonyl group of ketone
and benzene ring and dehydration lead to coumarin 3.
For practical applications of MNESA catalyst, the level of reusability was
evaluated. The possibility of recycling the catalyst was tested using the reaction of
p-cresol with ethyl acetoacetate under optimized reaction conditions. When the
reaction was complete, the reaction mixture was washed with hot ethanol three
times (3 9 5 mL). Then, the filtered solid acid was dried and reused for subsequent
runs. The recycled catalyst could be reused five times. No observation of any
appreciable loss in the catalytic activity of the MNESA was observed (Table 3).
After being reused five times, the S content of catalyst was analyzed by elemental
analysis, and it was shown that the amount of sulfur is 4.58 %. This experiment
revealed that our introduced catalyst is heterogeneous in nature.
To examine whether there was any leaching and if the catalyst completely acts as
a heterogeneous catalyst, we removed the catalyst by external magnet 5 min after
the beginning of the reactions. We observed that the reaction did not reach
completion even after 48 h. This clearly confirmed that the acidic function did not
leach into the solvent and that the catalyst acts as a heterogeneous catalyst.
Conclusion
In summary, a magnetic nanoparticles supported sulfonic acid was successfully
prepared and utilized as effective catalyst for preparation of coumarin derivatives
using Pechmann condensation under solvent free condition. This new catalyst
system efficiently catalyzed this reaction and a range of coumarins were produced in
good to excellent yields. The catalyst system can be reusable using an external
magnetic field. It can therefore be concluded that the reusability (the catalyst was
reusable for at least five times) and easy workup are the main advantages of this
catalyst system. This catalyst can also be useful for applications in other organic
transformations in the future.
Acknowledgments We are thankful to Islamic Azad University central Tehran branch for partial
support of this work.
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M. Samadizadeh et al.
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