Glucose-coated superparamagnetic nanoparticle-catalysed pyrazole synthesis in water

Article abstract of DOI:10.1002/aoc.3641

A green, benign, heterogeneous, superparamagnetic catalyst (Glu.@Fe₃O₄) was synthesized and characterized using Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, scanning electron microscopy and vibrating sample magnetometry. The prepared catalyst was used to achieve a high-efficiency, low-cost, eco-friendly and easy-to-handle protocol for synthesizing substituted pyrazole derivatives from aldehydes, malononitrile and phenylhydrazine. The catalyst was also used in chromene synthesis. Glucose coated on magnetic nanoparticles provided excellent catalytic activity. The catalyst could be recycled for up to four runs without significant loss in catalytic activity.

Full text of DOI:10.1002/aoc.3641

Received: 28 July 2016
DOI 10.1002/aoc.3641
Revised: 20 August 2016
Accepted: 28 August 2016
F U L L PA P E R
Glucose‐coated superparamagnetic nanoparticle‐catalysed
pyrazole synthesis in water†
Naghmeh Esfandiary | Athar Nakisa | Kobra Azizi | Jamshid Azarnia | Iman Radfar |
Akbar Heydari
Tarbiat Modares University, Tehran, PO Box:
A green, benign, heterogeneous, superparamagnetic catalyst (Glu.@Fe3O4) was syn-
thesized and characterized using Fourier transform infrared spectroscopy, X‐ray dif-
fraction, thermogravimetric analysis, scanning electron microscopy and vibrating
sample magnetometry. The prepared catalyst was used to achieve a high‐efficiency,
low‐cost, eco‐friendly and easy‐to‐handle protocol for synthesizing substituted
pyrazole derivatives from aldehydes, malononitrile and phenylhydrazine. The cata-
lyst was also used in chromene synthesis. Glucose coated on magnetic nanoparticles
provided excellent catalytic activity. The catalyst could be recycled for up to four
runs without significant loss in catalytic activity.
14155‐4838, Iran
Correspondence
Akbar Heydari, Tarbiat Modares University, PO
Box: 14155‐4838, Tehran, Iran.
Email: heydar_a@modares.ac.ir
† The article is dedicated to memory of
Muhammad Baqir al‐Sadr.
KEYWORDS
glucose immobilization, green catalyst, hydrogen bond catalysis, magnetic
nanoparticles, pyrazole synthesis
1
|
INTRODUCTION
interesting properties which are different from those of their
bulk state.[8] In this regard, magnetic nanoparticles exhibit ver-
satility and high‐performance capabilities in various fields,[9]
such as medical diagnostics and treatments,[10] chemistry,[11]
wastewater treatment,[12] and so on. In terms of chemistry,
their utilization as recyclable heterogeneous green
nanocatalysts is of significant interest. Therefore, we decided
to cover the surface of magnetic nanoparticles with glucose
to make them more compatible and avoid aggregation and
use the hydroxyl groups of the glucose to catalyse reactions.
Pyrazole, a five‐membered heterocyclic structure, is pres-
ent in many applicable components. This scaffold is found in
various biomolecules with biological and pharmaceutical
properties.[13] Italsohasbeenusedascatalyst[14] andligand.[15]
The first report of pyrazole synthesis was published in
1964, where Dickinson et al. used cyanoethylene and hydra-
zine to obtain aminocyanopyrazoles.[16] Later, much research
has been reported of the synthesis of pyrazole with various
reagents and conditions.[17] Some recent research has
reported pyrazole synthesis with ionic liquid,[18] iodine[19]
and metal oxide[20] as catalysts and with photocatalyst.[21]
So we attempted to use our environmentally friendly catalyst
to synthesize pyrazole derivatives in water at room tempera-
ture with ultrasonic irradiation.
Nowadays, scientists from all branches around the world
attempt to consider their permanent home, Earth. Formulat-
ing the twelve principles of green chemistry in the 1990s
was one of the first efforts in chemistry in this regard.
Towards these concepts, doing reactions in mild and benign
situations with the least hazards and highest synthetic effi-
ciency is admired.[1]
Glucose is the most important monosaccharide in living
organisms and it is known as the human body's key source
of energy,[2] so it can be considered as a natural, biocompat-
ible agent. As a consequence of the polyhydroxyl structure, it
has been used as a green catalyst and provided excellent cat-
alytic activity in chemical reactions[3] such as epoxidation[4]
and enantioselective Michael addition.[5] Also, it has played
the role of a green medium for undertaking reactions.[6]
Recently, glucose‐coated superparamagnetic iron oxide
nanoparticles have been synthesized and used for biological
applications.[7] This allows one to consider glucose‐coated
superparamagnetic iron oxide nanoparticles as recyclable,
heterogeneous green catalysts.
Today, nanoparticles play a key role in various fields
because of their unique surface‐to‐volume ratio that causes
Appl Organometal Chem 2016; 1–9
wileyonlinelibrary.com/journal/aoc
Copyright © 2016 John Wiley & Sons, Ltd.
1

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ESFANDIARY ET AL.
According to the literature, the reaction of
400–4000 cm−1 using a Nicolet IR100 instrument with spec-
troscopic‐grade KBr. The morphology of the catalyst was
studied using scanning electron microscopy (SEM; Philips
XL 30 and S‐4160) with coated gold equipped with disper-
sive X‐ray spectroscopy capability. Powder X‐ray diffraction
(XRD) spectra were recorded at room temperature with a
Philips X‐Pert 1710 diffractometer using Co Kα radiation
(λ = 1.78897 Å) at a voltage of 40 kV and current of
40 mA to define the crystalline structure of the catalyst
nanoparticles. Data were collected from 10° to 90° (2θ) with
phenylhydrazine,aromaticaldehydeandmalononitrileinwater
assolventwithoutcatalystatroom temperature, and evenunder
reflux conditions during 24 h, did not show any product.[20]
2
| EXPERIMENTAL
2.1 | Chemicals, instrumentation and analysis
All solvents and chemicals purchased were of analytical
grade and used without further purification. Fourier trans-
form infrared (FT‐IR) spectra were obtained in the region
SCHEME 1 Catalyst synthetic procedure
FIGURE 2 XRD pattern of Glu.@Fe3O4
FIGURE 3 TGA of Glu.@Fe3O4
SCHEME 2 Synthesis of pyrazoles cayalysed by Glu.@Fe3O4
FIGURE 1 FT‐IR spectra of Fe3O4 and Glu.@Fe3O4
FIGURE 4 SEM image of Glu.@Fe3O4

ESFANDIARY ET AL.
3
a scan speed of 0.02° s−1. The magnetic properties were mea-
sured with a vibrating magnetometer/alternating gradient
force magnetometer (MDCo., Iran, www.mdk‐magnetic.
com). Thermogravimetric analysis (TGA) was performed
using a thermal analyser with a heating rate of 20°C min−1
over the temperature range 25–1100°C under flowing com-
pressed nitrogen.
FeCl3⋅6H2O (10 mmol) and FeCl2⋅4H2O (5 mmol) salts were
dissolved in 40 ml of deionized water and were stirred vigor-
ously (800 rpm) for 2 min at room temperature. Then ammo-
nia solution (25% w/w) was added dropwise to produce an
alkaline medium (pH about 11). The obtained black suspen-
sion was stirred vigorously for 1 h at room temperature and
then was refluxed for 6 h. The synthesized magnetic Fe3O4
nanoparticles were separated from the medium by applying
an external magnet and washed several times with water then
ethanol. Glucose (20 mmol) was dissolved in 40 ml of deion-
ized water and the prepared Fe3O4 nanoparticles were added.
The mixture was exposed to ultrasonic waves for 20 min. The
resulting superparamagnetic nanoparticles (Glu.@Fe3O4)
were first separated from the alkaline medium then washed
several times with deionized water then ethanol and dried at
60°C overnight. The synthesis route is shown in Scheme 1.
2.2 | Preparation of catalyst
Superparamagnetic Fe3O4 nanoparticles were prepared
according to
a conventional co‐precipitation method.
2.3 | General procedure for synthesis of pyrazoles
Benzaldehyde (1 mmol) and malononitrile (1 mmol) were
dissolved in 1 ml of water in a round‐bottom flask, and then
the synthesized catalyst (30 mg) was added. To form
Knoevenagel adduct, the mixture was exposed to ultrasonic
waves for 2 min at room temperature. In the next step,
phenylhydrazine (1 mmol) was added to afford pyrazole.
After completion of the reaction, the mixture was diluted with
hot ethanol, the nanocatalyst was separated from the medium
with an external magnet and cold water was added to separate
FIGURE 5 VSM curve of Glu.@Fe3O4
semi‐solid
products.
Synthesized
products
were
recrystallized from ethanol and then filtered under reduced
pressure. The synthesis route is shown in Scheme 2.
2.4 | General procedure for synthesis of chromenes
Benzaldehyde (1 mmol) and malononitrile (1 mmol) were
SCHEME 3 Design of reaction for optimizing conditions
TABLE 1 Optimization of reaction conditions
dissolved in 1 ml of water in a round‐bottom flask, and
Entry
Catalyst
Solvent
Amount of catalyst (mg)
Temp. (°C)
Time (min)
Yield (%)
1
—
H2O
—
—
—
—
—
20
25
30
40
50
30
30
30
30
30
r.t.
150
20
20
20
20
8
—
24
32
32
32
87
89
95
95
90
87
69
20
15
58
2
—
H2O
60
3
—
H2O
r.t./ultrasonic
45/ ultrasonic
60/ ultrasonic
r.t./ultrasonic
r.t./ultrasonic
r.t./ultrasonic
r.t./ultrasonic
r.t./ultrasonic
r.t./ultrasonic
r.t./ultrasonic
r.t./ultrasonic
r.t./ultrasonic
r.t./ultrasonic
4
—
H2O
5
—
H2O
6
Glu.@Fe3O4
Glu.@Fe3O4
Glu.@Fe3O4
Glu.@Fe3O4
Glu.@Fe3O4
Glu.@Fe3O4
Glu.@Fe3O4
Glu.@Fe3O4
Glu.@Fe3O4
Glu.@Fe3O4
H2O
7
H2O
8
8
H2O
H2O
8
9
8
10
11
12
13
14
15
H2O
8
MeOH
EtOH
Toluene
THF
8
8
15
20
15
MeCN

4
ESFANDIARY ET AL.
TABLE 2 Synthesis of various pyrazole derivatives
Entry
R
Product
Time(min)
Yield (%)
1
8
95
2
3
4
5
6
7
6
7
5
5
7
8
96
90
95
95
92
89
8
9
6
6
92
99
(Continues)

ESFANDIARY ET AL.
5
TABLE 2 (Continued)
Entry
R
Product
Time(min)
Yield (%)
10
11
12
13
14
15
16
6
7
98
95
94
86
93
—
—
10
8
10
—
—
then the synthesized catalyst (30 mg) was added. To form
Knoevenagel adduct, the mixture was exposed to ultrasonic
waves for 2 min at room temperature. In the next step,
β‐naphthol (1 mmol) was added to afford chromene. After
completion of the reaction, the mixture was diluted with
hot ethanol, the nanocatalyst was separated from the

6
ESFANDIARY ET AL.
medium with an external magnet and cold water was added
to separate solid products. Synthesized products were
recrystallized from ethanol and then filtered under reduced
pressure.
3
| RESULTS AND DISCUSSION
To confirm the synthesis of the nanocatalyst, the structure
was characterized using some spectroscopic and microscopic
techniques, namely FT‐IR spectroscopy, XRD, TGA, SEM
and vibrating sample magnetometry (VSM).
SCHEME 4 Proposed mechanism of pyrazole synthesis
3.1 | FT‐IR spectroscopy
The FT‐IR spectra of magnetic nanoparticles (Fe3O4) and
magnetic nanoparticles coated with glucose (Glu.@Fe3O4)
are shown in Figure 1. The broad peak at 3400 cm−1 is
related to ─OH. Peaks at 2923, 2857, 1024 and 560 cm−1
are, respectively, associated with the stretching vibrations of
C(sp3)─H, C(sp2)─H, C─O and Fe─O bonds.
3.2 | XRD analysis
The synthesized Glu.@Fe3O4 was analysed using XRD to
examine the crystalline structure. The XRD pattern is shown
in Figure 2. As seen, the six peaks (2θ = 35°, 43°, 51°, 63°,
67.5° and 75°) are representative of Fe3O4 crystalline struc-
ture. This result proves that glucose coating does not alter
the structure of the magnetic nanoparticles.
FIGURE 6 Recyclability of catalyst
3.3 | Thermogravimetric analysis
The amount of material that covers the surface of the mag-
netic nanoparticles was determined using TGA. As shown in
Figure 3, there is only one step of weight loss, in compliance
SCHEME 5 Synthesis of chromene in the presence of Glu.@Fe3O4
TABLE 3 Optimization of reaction conditions for chromene synthesis
Entry
Catalyst
Solvent
Amount of catalyst (mg)
Temp (°C)
Time (h)
Yield (%)
1
—
H2O
—
20
20
25
30
35
35
40
35
35
35
35
35
35
35
35
80
6
6
6
6
6
6
6
6
1
1
1
6
6
6
6
6
—
23
70
88
90
93
94
93
93
94
94
88
91
27
21
76
2
Glu.@Fe3O4
Glu.@Fe3O4
Glu.@Fe3O4
Glu.@Fe3O4
Glu.@Fe3O4
Glu.@Fe3O4
Glu.@Fe3O4
Glu.@Fe3O4
Glu.@Fe3O4
Glu.@Fe3O4
Glu.@Fe3O4
Glu.@Fe3O4
Glu.@Fe3O4
Glu.@Fe3O4
Glu.@Fe3O4
H2O
r.t
3
H2O
60
4
H2O
80
5
H2O
80
6
H2O
80
7
H2O
100
8
H2O
80
9
H2O
H2O
r.t/ultrasonic
10
11
12
3
60/ultrasonic
H2O
80/ultrasonic
MeOH
EtOH
Toluene
THF
MeCN
80
80
80
80
80
14
15
16

ESFANDIARY ET AL.
7
with our consideration, which begins from under 100°C and
finishes under 400°C. This decomposition appears to corre-
spond to the loss of the organic portion (5% w/w).
the range − 10 000 to +10 000 Oe at room temperature. As
shown in Figure 5, the completely reversible hysteresis loop
indicates the superparamagnetic property of the
nanoparticles. Saturation magnetization of the nanoparticles
is determined as about 52 emu g−1
.
3.4 | SEM analysis
To investigate the surface morphology and the size of the
nanoparticles, we used SEM (Figure 4). The resulting image
shows uniform and minuscule nanoparticles. The approxi-
mate size of particles is determined as about 10–30 nm.
3.6 | Catalyst activity
The multicomponent pyrazole synthesis reaction was opti-
mizedusingbenzaldehyde,malononitrileandphenylhydrazine
(Scheme 3) and all results are summarized in Table 1. In the
first step, we attempted the reaction with no catalyst: the
results are not satisfactory (entries 1–5). For the next step
we tested Glu.@Fe3O4 as heterogeneous catalyst and we get
excellent results. So we persevered in this way to optimize
other factors. We compared different media by changing sol-
vent and observe that water leads to the best results (entries
9–15). By changing the temperature, we find the best yield
is obtained when the reaction occurs at room temperature
together with ultrasonication. For the last step, we find the
optimized amount of catalyst is 30 mg (7 mol%) (entries 6–10).
Using this procedure, we tried to synthesize various
derivatives of pyrazole using different aldehydes with
malononitrile and phenylhydrazine. The achieved products
are listed in Table 2.
3.5 | VSM analysis
To investigate the magnetic properties of the nanoparticles,
we used the VSM technique, applying a magnetic field in
TABLE 4 Synthesis of various chromene derivatives
Entry
Substrate
Product
Yield (%)
1
93
2
3
4
5
6
7
83
92
95
75
75
82
The mechanism of this reaction, as was reported,[18]
includes three steps (Scheme 4). The first step is condensa-
tion of benzaldehyde and malononitrile to obtain white crys-
talline Knoevenagel product. After that, phenylhydrazine is
added to undergo 1,2‐addition reaction, and the last step is
elimination of hydrogen to cause aromaticity.
After accomplishing the reaction, the superparamagnetic
nanocatalyst was separated from the medium, as usual with
application of an external magnet, then washed and dried
and used for another reaction run. The nanocatalyst was re‐
used until the results were not satisfactory. In this way, the
recyclability of our synthesized nanocatalyst was examined
(Figure 6). The catalyst shows excellent result for four repeat
cycles, after which we witness a deterioration in its catalytic
activity.
SCHEME 6 Proposed mechanism of chromene synthesis

8
ESFANDIARY ET AL.
Following the successful pyrazole synthesis, the reaction
νmax, cm−1): 3149, 3126, 3024, 2954, 1743, 1571, 1492,
1278, 1142. 1H NMR (500 MHz, CDCl3, δ, ppm): 8.56
(m, J = 7.1 Hz, 2H), 8.04 (b, 2H), 7.51 (ddd, J = 6.8 Hz,
2H), 7.22–7.33 (t, J = 8 Hz, 2H), 7.10–7.16 (m, J = 6.5 Hz,
2H), 6.93–7.16 (t, J = 7.6 Hz, 1H).
3‐Amino‐1‐(thiophen‐2‐yl)‐1H–benzo[f]chromene‐2‐
carbonitrile (Table 4, entry 5). FT‐IR (KBr, νmax, cm−1):
3442, 3344, 2178, 1640, 1588. 1H NMR (500 MHz, CDCl3,
δ, ppm): 5.70 (s, 1H, CH), 6.87 (dd, 1H, J = 4.8, 3.4 Hz),
7.01 (d, 1H, J = 3.3 Hz), 7.10 (s, 2H), 7.24–7.31 (m, 2H),
7.42–7.53 (m, 2H), 7.93(d, 2H, J = 8.7 Hz), 8.03 (d, 1H,
J = 8.2 Hz).
of benzaldehyde, malononitrile and β‐naphthol was found to
be facilitated, leading to the desired product in high yield
(Scheme 5). The optimal reaction conditions are found to
be arylaldehyde (1 mmol), malononitrile (1 mmol) and
β‐naphthol (1 mmol) at room temperature for 1 h under ultra-
sonic irradiation in water (Table 3, entry 9). Under these opti-
mized conditions, various aldehydes were used as substrates
for the formation of corresponding chromenes (Table 4).
The reaction mechanism consists of three steps. The first
step is Knoevenagel condensation, the same as in the
pyrazole synthesis reaction. The next step is Michael addition
of β‐naphthol to the Knoevenagel product. Finally the
chromene product is formed by intermolecular cyclization
(Scheme 6).
ACKNOWLEDGMENTS
We are grateful to Tarbiat Modares University for financial
support of this work.
4
| CONCLUSIONS
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(2016), Glucose‐coated superparamagnetic nanoparti-
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