Magnetic nanoparticle supported hyperbranched polyglycerol catalysts for synthesis of 4H-benzo[b]pyran

Article abstract of DOI:10.1007/s00706-013-1026-3

A magnetic nanoparticle supported hyperbranched polyglycerol catalyst was prepared readily from inexpensive starting materials in aqueous medium that catalyzed the synthesis of 4H-benzo[b]pyran under solvent-free conditions at room temperature. X-ray diff

Full text of DOI:10.1007/s00706-013-1026-3

Monatsh Chem
DOI 10.1007/s00706-013-1026-3
ORIGINAL PAPER
Magnetic nanoparticle supported hyperbranched polyglycerol
catalysts for synthesis of 4H-benzo[b]pyran
•
Mohammad Ali Nasseri Seyed Mohsen Sadeghzadeh
Received: 7 November 2012 / Accepted: 29 May 2013
Ó The Author(s) 2013. This article is published with open access at Springerlink.com
Abstract A magnetic nanoparticle supported hyper-
branched polyglycerol catalyst was prepared readily from
inexpensive starting materials in aqueous medium that
catalyzed the synthesis of 4H-benzo[b]pyran under solvent-
free conditions at room temperature. X-ray diffraction,
transmission electron microscopy, thermal gravimetric
analysis, vibrating sample magnetometry, and selected-
area electron diffraction were employed to characterize the
properties of the synthesized catalyst. Its high catalytic
activity and ease of recovery from the reaction mixture
using an external magnet, and the possibility of reusing
several times without significant loss of performance are
additional eco-friendly attributes of this catalytic system.
of the multi-component system and even generate new
synergetic properties. Among core–shell structured com-
posites, those with a magnetic core and functional shell
structures have received special attention because of their
potential applications in catalysis, drug storage/release,
selective separation, chromatography, and chemical or
biologic sensors [7–12]. The magnetic core has good
magnetic responsiveness, and can be easily magnetized.
Therefore, composites with magnetic cores can be conve-
niently collected, separated, or fixed using an external
magnet.
4H-Benzopyran derivatives are a major class of het-
erocycles, and 4H-pyran derivatives have attracted strong
interest due to their useful biological and pharmacological
properties such as anticoagulant, spasmolytic, diutretic,
anticancer [13], and antianaphylactin characteristics [14].
4H-Pyrans also occur in various natural products [15] and
some benzopyran derivatives have been reported to have
photochemical activities [16]. Development of 4H-pyran
synthesis has been of considerable interest in organic
synthesis, because of their wide-ranging biological and
pharmaceutical activities. Consequently, numerous meth-
ods for the synthesis of 4H-pyrans have been reported. A
variety of reagents, such as Yb(PFO)3 [17], tetramethyl-
ammonium hydroxide [18], Na2SeO4 [19], LiBr [20], NaBr
[21], MgO [22], SB-DABCO [24], and the use of micro-
wave irradiation [23], were found to catalyze these
reactions. However, some of the reported methods have the
following drawbacks: use of expensive reagents, long
reaction times, low product yields, and use of an additional
microwave oven. Herein we report the fabrication of hy-
perbranched polyglycerol (HPG) incorporated into
mesoporous magnetite nanoparticles (MNP) that catalyze
the synthesis 4H-benzo[b]pyrans under solvent-free con-
ditions at room temperature (Scheme 1).
Keywords Magnetic nanoparticle ꢀ 4H-Benzo[b]pyran ꢀ
Solvent-free ꢀ One-pot synthesis ꢀ Green chemistry
Introduction
In recent years, core–shell multi-components have attracted
intense attention because of their potential applications in
catalysis [1]. Unlike single-components that can supply
only one function, core–shell multi-components can inte-
grate multiple functions into one system for specific
applications [2–6]. Moreover, the interactions between
different components can greatly improve the performance
M. A. Nasseri (&) ꢀ S. M. Sadeghzadeh
Department of Chemistry, College of Sciences,
Birjand University, PO Box 97175-615, Birjand, Iran
e-mail: mohammadali.nasseri@yahoo.com
123

M. A. Nasseri, S. M. Sadeghzadeh
Results and discussion
(XRD). As shown in Fig. 2, the XRD pattern of the syn-
thesized FeNi3/SiO2/HPG nanoparticle displays several
relatively strong reflection peaks in the 2h region of 40°–
80°, which is quite similar to those of FeNi3 nanoparticles
reported by other groups. Three characteristic peaks for
FeNi3 (2h = 44.3°, 51.5°, 75.9°) from (111), (200), and
(220) planes were obtained. In addition, no iron and nickel
oxides or other impurity phases were detected in the XRD
patterns. The sharp and strong diffraction peaks confirm the
good crystallization of the products. The broad band at
2h = 15.0°–30.0° can be assigned to the amorphous SiO2
shell (JCPDS No. 29-0085).
We report the synthesis of a magnetic particle-based solid
polymer with a high density of HPG groups and discuss its
performance as a novel strong and stable solid polymer.
We were intrigued by the possibility of applying anhydrous
dioxane and nanotechnology to the design of a novel,
active, recyclable, and magnetically recoverable HPG
derivative for the first time (Fig. 1).
Normally, N2H4ꢀH2O can serve as either an oxidant or a
reducer in alkaline solution. Ni2? can be reduced easily to
Ni in alkaline solution by N2H4ꢀH2O. However, it is dif-
ficult to reduce Fe2? to Fe directly by N2H4ꢀH2O because
the electromotive force of the oxidation reaction of Fe2? to
Fe3? (0.66 V) is much larger than that of the reduction
reaction from Fe2? to Fe (0.283 V). Thus, Fe2? is more
likely to be oxidized to Fe3? when treated by N2H4ꢀH2O in
alkali solution. In this experiment, however, when Fe2?
and Ni2? coexist in the solution, Fe2? ions can be reduced
easily to Fe under the assistance of Ni2? to form FeNi3
alloy. The reduction reaction can be expressed as follows:
High-resolution transmission electron microscopy
High-resolution
transmission
electron
microscopy
(HRTEM) images of FeNi3, FeNi3/SiO2, and FeNi3/SiO2/
HPG MNPs are shown in Fig. 3. The average size of FeNi3
MNPs is about 15 nm, and the aggregation of the nano-
particles can be discerned clearly (Fig. 3a). After being
coated with a silica layer, the typical core–shell structure of
the FeNi3/SiO2 MNPs can be observed. The dispersity of
FeNi3/SiO2 MNPs is also improved, and the average size
increases to about 20 nm (Fig. 3b). The average size of
FeNi3/SiO2/HPG MNPs is about 60 nm (Fig. 3c), but
aggregation of FeNi3/SiO2/HPG is more evident than that
of FeNi3/SiO2 MNPs.
3Ni2þ þ Fe2þ þ 2N2H4 þ 8OHꢁ ! FeNi3 þ 2N2 þ 8H2O:
X-ray power diffraction
The structural properties of synthesized FeNi3/SiO2/HPG
nanoparticle were analyzed by X-ray power diffraction
Selected-area electron diffraction
The selected-area electron diffraction (SAED) pattern
taken from the prepared FeNi3/SiO2/HPG MNPs consists
of typical polycrystalline rings, suggesting a nanocrystal-
line structure (Fig. 4). The diffraction peaks from (111),
(200), (220), and (311) planes of (FCC)-FeNi3 are in total
agreement with those of XRD.
Scheme 1
R
O
O
O
O
CN
MNP-HPG
r.t.
CN
+
+
H
CN
R
O
4
NH2
Thermogravimetric analysis
1
3
2
O
O
O
O
O
O
The thermal behavior of FeNi3/SiO2/HPG MNPs (Fig. 5)
was evaluated to be 1.5 % according to thermogravimetric
analysis (TGA). The analysis showed two decreasing
peaks. The first peak appears at temperature around
O
1a
1b
1c
OH
Fig. 1 Schematic illustration
of the synthesis for magnetic
nanoparticle supported
hyperbranched polyglycerol
(MNP-HPG)
O
HO
HO
O
Silica Shell
OH
HO
O
O
O
HO
O
Tetraethyoxysilane
OH
O
OH
O
HO
Magnetic NP
O
O
O
O
O
Si
O
Magnetic NP
OH
HO
HO
123

Magnetic nanoparticle supported hyperbranched polyglycerol catalysts
130–150 °C due to desorption of water molecules from the
catalyst surface. This is followed by a second peak at
425–450 °C, corresponding to the loss of the organic
spacer group.
smoothly in solvent-free conditions and gave the desired
product in 97 % yield (Table 1, entry 11).
At this stage, the amount of catalyst necessary to pro-
mote the reaction efficiently was examined. It was
observed that variation of the amount of FeNi3/SiO2/HPG
Magnetic properties of FeNi3/SiO2/HPG MNP
The magnetization curves of FeNi3 and FeNi3/SiO2/HPG
MNPs were further recorded at room temperature (Fig. 6).
The magnetizations were expressed in units of emu per
gram of powder. The two measured samples display a su-
perparamagnetic behavior, as evidenced by
a zero
coercivity and remanence on the magnetization loop. The
saturation magnetization value of the FeNi3/SiO2/HPG
MNP is 25 emu/g, which is lower than that of uncoated
magnetic particles (about 60 emu/g).
Catalytic activity of FeNi3/SiO2/HPG MNPs
The effect of solvent on this reaction was examined and the
results obtained are summarized in Table 1. In n-hexane,
CHCl3, and dioxane (Table 1, entries 12–14), only a trace
of product was observed. On the contrary, moderate yields
could be achieved in other solvents (Table 1, entries 1–10).
More strikingly, we found that the reaction proceeded
Fig. 4 Selected-area electron diffraction (SAED) pattern of FeNi3/
SiO2/HPG MNP
Fig. 5 Thermogravimetric analysis (TGA) of FeNi3/SiO2/HPG MNP
Fig. 2 X-ray power diffraction (XRD) analysis of MNP-HPG
Fig. 3 High-resolution transmission electron microscopy (HRTEM) images of a FeNi3, b FeNi3/SiO2, and c FeNi3/SiO2/HPG
123

M. A. Nasseri, S. M. Sadeghzadeh
100
90
80
70
60
50
40
30
20
10
0
0.0002
0.001
0.0004
0.0006
0.0008
0.0012
Amount of MNP-HPG/g
Fig. 7 Effect of increasing amount of FeNi3/SiO2/HPG MNP on the
preparation of 4H-benzo[b]pyran
Fig. 6 Room temperature magnetization curves of the FeNi3 MNP
and FeNi3/SiO2/HPG MNP
100
90
80
70
60
50
40
30
20
10
0
Table 1 Solvent screening for the reaction between benzaldehyde,
malononitrile, and dimedone
Entry
Solvent
Yield/%a
1
H2O
82
2
EtOH
76
3
CH3CN
THF
57
4
36
0
10
15
20
25
35
5
30
40
5
CH2Cl2
Toluene
EtOAC
MeOH
DMF
39
Time/min
6
17
7
72
Fig. 8 Reaction progress monitored by gas chromatography (GC).
Reaction conditions: dimedone (1 mmol), benzaldehyde (1 mmol),
malononitrile (1 mmol), and 0.001 g FeNi3/SiO2/HPG MNP at room
temperature
8
78
9
63
10
11
12
13
14
DMSO
Solvent free
n-Hexane
CHCl3
Dioxane
67
97
activity of the recycled catalyst was also examined under
the optimized conditions. After completion of the reaction,
the catalyst was separated using an external magnet,
washed with methanol and dried at the pump. The recov-
ered catalyst was reused for eight consecutive cycles
without any significant loss in catalytic activity (Fig. 9).
As can be seen from Table 2, the reaction of aromatic
aldehydes with malononitrile and 1,3-diketones at room
temperature under solvent-free conditions provided the
corresponding 4H-benzo[b]pyran derivatives in good
yields. The results presented in Table 2 indicate that
aldehydes bearing electron-withdrawing groups react more
quickly than their electron-donating aldehyde counter-
parts. For example, aromatic aldehydes such as 4-chloro-,
4-nitro-, and 4-bromobenzaldehydes react quickly with
high product yields in comparison to 4-hydroxy-,
4-methyl-, and 4-methoxybenzaldehyde derivatives. The
yield of 4H-benzo[b]pyrans bearing group at the ortho
position on the aromatic ring is lower than that of the
4H-benzo[b]pyrans bearing group at the para position on
the aromatic ring (Scheme 1; Table 2).
Trace
Trace
Trace
Reaction conditions: malononitrile (1 mmol), dimedone (1 mmol),
benzaldehyde (1 mmol), and 0.001 g FeNi3/SiO2/HPG MNP at room
temperature for 45 min
a
Isolated yields
MNP had an effective influence. The best amount of FeNi3/
SiO2/HPG MNP was 0.001 g, which afforded the desired
product in 97 % yield (Fig. 7).
Progress of the reaction in the presence of 0.001 g
FeNi3/SiO2/HPG MNP was monitored by gas chromatog-
raphy (GC) under optimal conditions (Fig. 8). Using this
catalyst system, excellent yields of 4H-benzo[b]pyran can
be achieved in 30 min. No apparent by-products were
observed by GC in any of the experiments and the cyclic
carbonate was obtained cleanly in 97 % yield.
It is important to note that the magnetic property of
FeNi3/SiO2/HPG MNP facilitates its efficient recovery
from the reaction mixture during work-up procedure. The
123

Magnetic nanoparticle supported hyperbranched polyglycerol catalysts
100
80
On the other hand, when benzyl cyanide was treated as a
substitute for malononitrile in this reaction under similar
conditions, not only was a highly prolonged time required,
but the products were different. The spectroscopic data of
the products confirmed that these structures belong to oc-
tahydroxanthene (Scheme 2).
60
40
20
0
In comparison with other catalysts employed for the
synthesis of 4H-benzo[b]pyran from malononitrile, benz-
aldehyde, and dimedone, FeNi3/SiO2/HPG MNP showed a
much higher catalytic activity in terms of a very much
shorter reaction time and mild conditions (Table 3).
To further explore the potential of this MNP catalyst
for heterocyclic synthesis, we investigated one-pot reac-
tions involving aromatic aldehydes, malononitrile, ethyl
acetoacetate, and hydrazine hydrate and obtained pyrano-
pyrazoles in excellent yields (Scheme 3; Table 4). This
methodology was evaluated using a variety of different
1
2
3
4
5
Reuse
6
7
8
Fig. 9 Reuse performance of the catalyst
Table 2 Synthesis of 4H-benzo[b]pyran derivatives catalyzed by FeNi3/SiO2/HPG MNP
Entry
R
1,3-Diketone
Product
Time/min
Yield/%a,b
M.p. (obs)/°C
M.p. (lit)/°C
1
C6H5
1a
1a
1a
1a
1a
1a
1a
1a
1a
1a
1a
1a
1b
1b
1b
1b
1b
1b
1b
1b
1b
1b
1c
1c
1c
1c
1c
4a
4b
4c
4d
4e
4f
30
30
35
40
30
35
30
35
40
40
35
40
30
30
30
40
35
35
40
40
30
40
35
30
40
40
30
97
96
94
90
94
92
95
93
91
89
97
88
95
97
95
93
95
92
89
88
96
89
96
97
92
91
98
228–230
207–209
210–212
228–230
183–186
217–220
200–202
152–154
201–202
201–204
188–190
199–201
235–237
222–224
213–215
224–226
235–236
191–193
188–190
229–232
217–220
173–175
193–195
173–175
180–182
140–142
183–185
224 [25]
2
4-ClC6H4
2-ClC6H4
4-MeC6H4
4-NO2C6H4
2-NO2C6H4
4-BrC6H4
2-BrC6H4
4-MeOC6H4
4-HOC6H4
4-FC6H4
209–211 [25]
214–215 [25]
223–225 [25]
179–180 [25]
222–223 [26]
203–205 [26]
150–152 [26]
199–201 [25]
206–208 [25]
192–194 [27]
198–200 [25]
239–241 [28]
226–229 [28]
210–212 [28]
223–225 [28]
234–236 [28]
196–198 [28]
193–195 [28]
234–236 [28]
213–215 [28]
168–170 [28]
194–196 [27]
175–177 [27]
177–179 [27]
137–139 [27]
180–183 [27]
3
4
5
6
7
4g
4h
4i
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
a
4j
4k
4l
4-(Me2N)C6H4
C6H5
4m
4n
4o
4p
4q
4r
4s
4-ClC6H4
2-ClC6H4
4-MeC6H4
4-NO2C6H4
2-NO2C6H4
4-MeOC6H4
4-HOC6H4
4-FC6H4
4t
4u
4v
4w
4x
4y
4z
4a0
4-(Me2N)C6H4
C6H5
4-ClC6H4
4-MeC6H4
4-MeOC6H4
4-NO2C6H4
Reaction condition: benzaldehyde derivatives (1 mmol), 1,3-diketones (1 mmol), malononitrile (1 mmol), 0.001 g FeNi3/SiO2/HPG MNP at
room temperature under solvent-free conditions
b
Yield refers to isolated product
123

M. A. Nasseri, S. M. Sadeghzadeh
substituted aromatic aldehydes in the presence of magnetic
nanocatalyst under similar conditions. Aromatic aldehydes,
carrying either electron-withdrawing or electron-donating
substituents, afforded high yields of products with high pur-
ity; the results are presented in Table 4. The four-component
cyclocondensation reaction proceeded smoothly and was
completed in 35–50 min.
Experimental
Chemical materials were purchased from Fluka (Buchs,
Switzerland) and Merck (Darmstadt, Germany) in high
purity. Melting points were determined in open capillar-
ies using an Electrothermal 9100 apparatus (http://www.
electrothermal.com). Morphology was analyzed using high-
resolution transmission electron microscopy (HRTEM) on a
JEOL transmission electron microscope (http://www.jeol.
com) operating at 200 kV. Powder X-ray diffraction data
was obtained using Bruker D8 Advance model with Cu-Ka
radiation. The thermogravimetric analysis (TGA) was car-
ried out on a NETZSCH STA449F3 (http://www.netzsch-
thermal-analysis.com) at a heating rate of 10 °C min-1
under nitrogen. The magnetic measurement was carried out
in a vibrating sample magnetometer (VSM) (4 inch, Dag-
high Meghnatis Kashan, Kashan, Iran) at room temperature.
NMR spectra were recorded in DMSO-d6 on a Bruker
Avance DRX-400 MHz instrument spectrometer (http://
www.bruker.com/) using tetramethylsilane (TMS) as
internal standard. IR spectra were recorded on a Perkin
Elmer 781 (http://www.perkinelmer.com/). Mass spectra
were recorded on Shimadzu GCMS-QP5050 mass spec-
trometer (Shimadzu, Tokyo, Japan). The purity
determination of the products and reaction monitoring were
accomplished by thin layer chromatography (TLC) on silica
gel polygram SILG/UV 254 plates.
Conclusion
In conclusion, we have developed current important areas
in the heterogenization of HPG—a rapidly developing
research area. The main objectives are to develop room-
temperature, solvent-free conditions, a rapid (immediate)
and easy immobilization technique, and low-cost precur-
sors for the preparation of highly active and stable MPs
with high densities of functional groups. Furthermore,
applying the exciting new area of magnetic particles that
are intrinsically not magnetic, but can be magnetized
readily by an external magnet, can have a positive effect on
high activity on the one hand and separation and recycling
on the other.
Scheme 2
O
O
Synthesis of FeNi3 MNPs
O
O
O
5'
CN
FeCl2ꢀ4H2O (1.72 g) and 4.72 g NiCl2ꢀ6H2O were dis-
solved in 80 cm3 deaerated highly purified water contained
in a three-neck flask with vigorous stirring (800 rpm) under
nitrogen. As the temperature was elevated to 80 °C,
10 cm3 ammonium hydroxide was added drop by drop, and
the reaction was maintained for 30 min. The black product
was separated by placing the vessel on a permanent magnet
and the supernatant was decanted. The black precipitate
H
+
+
+
Ph
O
1
2
3'
O
Ph
NH2
O
4'
Table 3 Comparison of the
catalytic efficiency of FeNi3/
SiO2/HPG MNP with that of
other catalysts
Entry Catalyst
Condition Solvent
Amount catalyst/g Time/min Yield/%a
1
2
Yb(PFO)3
60 °C
EtOH
H2O
1.8
300
90 [17]
81 [18]
Tetramethylammonium r.t.
hydroxide
0.09
30–120
3
4
5
6
7
8
9
Na2SeO4
LiBr
Reflux
H2O/EtOH 0.1
60
15
25
30
10
35
30
97 [19]
95 [20]
84 [21]
75 [22]
95 [23]
96 [24]
97
Reflux
20 °C
r.t.
H2O
n-PrOH
H2O
–
8.7
NaBr
0.01
0.02
0.042
0.06
0.001
MgO
a
NaBr
MW
r.t.
Isolated yield, conditions:
malononitrile (1 mmol),
benzaldehyde (1 mmol), and
dimedone (1 mmol)
SB-DABCO
EtOH
None
FeNi3/SiO2/HPG MNP r.t.
123

Magnetic nanoparticle supported hyperbranched polyglycerol catalysts
by the addition of 10 cm3 anhydrous dioxane. Glycidol
(2.0 g) was added dropwise over a period of 15 h. After
vigorous stirring for 2 h, the final suspension was repeat-
edly washed, filtered several times, and air-dried at 60 °C.
Scheme 3
R
O
CN
CN
+
R
MNP-HPG
r.t.
+
+
H2N NH2
HN
N
CN
H
O
NH2
O
O
O
1
2
3
6
5a-5m
General procedure for the synthesis of 4H-
benzo[b]pyran
A mixture of aromatic aldehyde (1 mmol), dimedone
(1 mmol), malononitrile (1 mmol), and 0.001 g FeNi3/
SiO2/HPG MNP was stirred at room temperature under
solvent-free conditions for the appropriate time (Table 2).
Upon completion (the progress of the reaction was moni-
tored by TLC), EtOH was added to the reaction mixture
and the FeNi3/SiO2/HPG MNP was separated by external
magnet. The solvent was then removed from solution under
reduced pressure and the resulting product purified by
recrystallization using ethanol.
Table 4 Synthesis of pyranopyrazoles from various aromatic alde-
hydes, malononitrile, ethyl acetoacetate, and hydrazine hydrate in the
presence of magnetic nanocatalyst at room temperature under solvent-
free conditions
Producta
R
Yield/ Time/ M.p.
b
M.p.
(obs)/°C (lit)/°C
%
min
5a
5b
5c
5d
5e
5f
C6H5
94
95
91
93
92
90
92
88
91
92
88
90
35
35
45
50
35
40
45
50
50
45
45
40
50
244
233
245
197
250
240
249
233
250
212
224
246
220
245–246 [29]
4-ClC6H4
2-ClC6H4
4-MeC6H4
4-NO2C6H4
2-NO2C6H4
4-BrC6H4
3-BrC6H4
2-MeOC6H4
4-MeOC6H4
4-HOC6H4
4-FC6H4
234–235 [30]
245–246 [31]
197–198 [32]
251–252 [29]
242–243 [32]
249–250 [32]
223–224 [29]
252–253 [32]
212–213 [33]
223–224 [33]
247–248 [32]
219–220 [32]
General procedure for the synthesis of pyranopyrazoles
5g
5h
5i
A mixture of ethyl acetoacetate (1 mmol), hydrazine
hydrate (1 mmol), malononitrile (1 mmol), aldehyde
(1 mmol), and 0.001 g FeNi3/SiO2/HPG MNPs was stirred
at room temperature under solvent-free conditions for the
appropriate time (Table 4). Upon completion (the progress
of the reaction was monitored by TLC), EtOH was added to
the reaction mixture and the FeNi3/SiO2/HPG MNPs was
separated by external magnet. The solvent was then
removed from solution under reduced pressure and the
resulting product purified by recrystallization using
ethanol.
5j
5k
5l
5m
4-(Me2N)C6H4 92
a
All products were identified and characterized by comparison with
authentic samples
b
Yield refers to isolated product
was washed six times with highly purified water to remove
unreacted chemicals, then the black product FeNi3 was
dried under vacuum.
Open Access This article is distributed under the terms of the
Creative Commons Attribution License which permits any use, dis-
tribution, and reproduction in any medium, provided the original
author(s) and the source are credited.
Synthesis of FeNi3/SiO2 MNPs
First, a mixture of 100 cm3 ethanol and 20 cm3 distilled
water was added to 1 g magnetite nanoparticles, and the
resulting dispersion was sonicated for 10 min. After adding
2.5 cm3 ammonia water, 2 cm3 tetraethyl orthosilicate
(TEOS) was added to the reaction solution. The resulting
dispersion was mechanically stirred continuously for 20 h
at room temperature. The magnetic FeNi3/SiO2 nanoparti-
cles were collected by magnetic separation and washed
with ethanol and deionized water in sequence.
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