[Fe3O4@SiO2@(C3H6)2-(Imidazolium)2-Butyl][MnCl42-] as a novel nanomagnetic catalyst for the one-pot synthesis of tetrahydrobenzo[b]pyran derivatives

Article abstract of DOI:10.4314/bcse.v32i2.10

In this article a convenient method for the synthesis of tetrahydrobenzo[b]pyran derivatives using imidazolium-based ionic liquid-stabilized on magnetic nanoparticles [Fe3O4@SiO2@(C3H6)2-(Imidazolium)2-Butyl][MnCl4^2-] as a new heterogeneous cat

Full text of DOI:10.4314/bcse.v32i2.10

Bull. Chem. Soc. Ethiop. 2018, 32(2), 309-321.
 2018 Chemical Society of Ethiopia and The Authors
DOI: https://dx.doi.org/10.4314/bcse.v32i2.10
ISSN 1011-3924
Printed in Ethiopia
[Fe3O4@SiO2@(C3H6)2-(IMIDAZOLIUM)2-BUTYL][MnCl42-] AS A NOVEL
NANOMAGNETIC CATALYST FOR THE ONE-POT SYNTHESIS OF
TETRAHYDROBENZO[b]PYRAN DERIVATIVES
Zahra Hormozinezhad1, Maryam Gorjizadeh2, Narges Taheri1 and Soheil Sayyahi1*
1Department of Chemistry, Mahshahr Branch, Islamic Azad University, Mahshahr, Iran
2Department of Chemistry, Shoushtar Branch, Islamic Azad University, Shoushtar, Iran
(Received February 9, 2018; Revised March 22, 2018; Accepted April 3, 2018)
ABSTRACT. In this article a convenient method for the synthesis of tetrahydrobenzo[b]pyran derivatives using
imidazolium-based ionic liquid-stabilized on magnetic nanoparticles [Fe3O4@SiO2@(C3H6)2-(Imidazolium)2-
Butyl][MnCl42-] as a new heterogeneous catalyst has been described. These compounds were synthesized via one-
pot three component condensation reaction between several aromatic aldehydes, malononitrile, and dimedone in
water under reflux condition. The magnetic nanoparticle catalyst was fully characterized by Fourier transform
infrared, scanning electron microscopy, energy dispersive X-ray spectroscopy, and vibrating sample
magnetometer. Furthermore, the solid catalyst could be recovered and reused conveniently several times with
satisfactory yields.
KEY WORDS: Chromene derivatives, Magnetic nanoparticles, Dicationic ionic liquid, Reusability, One-pot
synthesis
INTRODUCTION
Tetrahydrobenzo[b]pyrans known as 4H-chromenes are present in many pharmaceuticals and
exhibit remarkable biological activities such as anticoagulant, anti-tumor, antibacterial,
anticoagulant and antiallergic [1, 2]. Also, 4H-chromenes have been widely used as cosmetics,
pigments, and importantly biodegradable agrochemicals [3]. Thus, the attractive biological
profiles of this group of compounds stimulate chemists to explore efficient methods for the
synthesis of 4H-chromenes and their structural analogues [4-10].
In recent years, ionic liquids (ILs) have attracted a considerable attention in catalytic
systems because they can dissolve a wide variety of organic, organometallic, and inorganic
compounds [11, 12]. Also, they have low vapor pressure, low melting point and are relatively
thermal stable [13]. Although ILs possess some advantages but the properties of high viscosity,
some difficulties in recovery and homogeneity of ILs limit their practical applications in
chemical processes [14]. These problems can be overcome by immobilization of ILs onto solid
supports and functional groups to obtain heterogeneous catalysts [15, 16]. One of the most
attractive alternatives to stabilize ILs is the magnetic nanoparticles support [17, 18].
Magnetite nanoparticles (MNPs) are inorganic materials with metal-based configuration.
These nanoparticles have received increasing consideration because they can be easily
manipulated using alternating current magnetic field and subsequently employed in various
fields including environmental science, analytical, medicine and importantly, catalysis [19-22].
MNPs exhibit inherent and unique properties, such as high surface area, less toxicity, high
saturation magnetization, and catalyst loading capacity [23-25].
In view of the advantages of magnetic nanoparticles and ILs, some magnetic ILs composites
have been developed [26, 27]. Following our ongoing efforts for the development of more
benign and efficient nanocatalysts [28-31], herein, we present the design and preparation and
use of [Fe3O4@SiO2@(C3H6)2-(Imidazolium)2-Butyl][MnCl42-] or MNPs@Dicationic-IL as a
__________
*Corresponding author. E-mail: sayyahi.soheil@gmail.com
This work is licensed under the Creative Commons Attribution 4.0 International License

310
Zahra Hormozinezhad et al.
nanosized ionic liquid catalyst for the synthesis of tetrahydrobenzo[b]pyran derivatives (Scheme
1).
Scheme 1
EXPERIMENTAL
Materials and apparatus
Chemical reagents in high purity were purchased from Merck and Aldrich and were used
without further purification. Fe3O4 and Fe3O4@SiO2 were prepared according to reported
methods [29-30]. Purity of the synthesized compounds was monitored by TLC, visualizing with
ultraviolet light and all yields refer to isolated products. Melting points were determined using a
Stuart scientific apparatus. SEM images were obtained from a Zeiss-Vp-500 instrument. IR
spectra of synthesized compounds were recorded on KBr pellets on a Bomem MB-1998
spectrophotometer. Magnetism analysis was performed on a vibrating sample magnetometer (4
in., Daghigh Meghnatis Kashan Company, Kashan, Iran) at room temperature. SEM-EDX
analyses were carried out using a Philips XL30 instrument.
Preparation of [Fe3O4@SiO2@(C3H6)2-(Imidazolium)2-Butyl][MnCl42-] as a heterogeneous
catalyst
At first, dicationic-IL [(C3H6)2-(Imidazolium)2-Butyl][Cl-]2 was produced by adding 1,4-
bis(imidazol-1-yl)-butane (0.237 g, 1.25 mmol), 3-chloropropyl-trimethoxysilane (0.497 g, 2.5
mmol) and DMF (5 mL) into a 50 mL round-bottom flask. The mixture was refluxed for 72 h.
The obtained white solid material was filtered, washed with methanol and dried under reduced
pressure. Next, SiO2@Fe3O4 (0.5 g) was dispersed in 10 mL of dry toluene and, sonicated for 15
min using an ultrasonic bath. Then, dicationic-IL (1.0 g) was added to the mixture. The mixture
was stirred and refluxed for 24 h. The treated [Fe3O4@SiO2@(C3H6)2-(Imidazolium)2-Butyl]
[Cl-]2 was removed by using an external magnet and washed twice with ethanol, and dried.
Finally, a solution of MnCl2 (0.25 g) in methanol (5 mL) was added to the suspension of
Fe3O4@SiO2@(C3H6)2-(Imidazolium)2-Butyl] [Cl-]2 (0.5 g) and the reaction mixture was stirred
for 24 h. The imidazolium-based ionic liquid-stabilized on silica coated Fe3O4 magnetic
2-
nanoparticles [Fe3O4@SiO2@(C3H6)2-(Imidazolium)2-Butyl][MnCl4
filtering, washing and drying.
]
was obtained after
General procedure for the synthesis of 4H-chromene derivatives
In a round bottom flask, to a mixture of aromatic aldehyde (1 mmol), dimedone (1 mmol),
malononitrile (1.2 mmol), and H2O (5 mL), [Fe3O4@SiO2@(C3H6)2-(Imidazolium)2-
o
Butyl][MnCl42-] (0.05 g) was added. Then, the reaction mixture was refluxed at 80 C for the
corresponding time, as indexed in Table 2. After completion of the reaction as monitored by
TLC (n-hexane/ethyl acetate, 4:1), the reaction mixture was diluted with ethyl acetate and
stirred for 5 min. Then, the catalyst was separated by using an external magnet and the
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[Fe3O4@SiO2@(C3H6)2-(imidazolium)2-butyl][MnCl42-] as a novel nanomagnetic catalyst
remaining supernatant was diluted with water and stirred for 5 min. The precipitated product
was filtered, washed with water, and dried in an oven. The residue was purified by
recrystallization in ethanol.
SiO2
TEOS, H2O
Fe3O4
Fe3O4
NH3, EtOH
Si
Cl
N
2
+
N
N
DMF, 72h, 90oC
N
N
N
N
N
Cl
Si
Si
Cl
SiO2
SiO2
N
N
N
Fe O
Fe3 O4
Si
N
+
3
4
Si
Cl
Cl
THF, Reflux, 24h
SiO
SiO
N
2
SiO
2
2
SiO2
SiO2
N
N
N
Si
Fe O
Fe33O4 4
Si
Fe O
Fe O
Cl
3
3
4
4
Cl
MnCl2, MeOH, 24h, r.t
SiO2
SSiOiO
N
22
SiO
SiO
SiO
2
2
2
N
N
N
Si
Fe O
F3e O
2
4
Si
3
4
Fe O
Fe33O44
MnCl4
Scheme 2. Synthesis of imidazolium-based ionic liquid-stabilized on silica coated Fe3O4
magnetic nano particles.
RESULTS AND DISCUSSION
Synthesis and characterization of [Fe3O4@SiO2@(C3H6)2-(Imidazolium)2-Butyl][MnCl42-] as a
heterogeneous catalyst
We report the synthesis of imidazolium-based ionic liquid-stabilized on silica coated Fe3O4
magnetic nano particles and discuss its performance as a novel strong and recyclable catalyst
(Scheme 2). The structure of catalyst was studied and characterized by FT-IR, EDX, SEM and
VSM analysis.
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The FT-IR spectrum of the bare Fe3O4 MNPs (Figure 1) presents a characteristic absorption
peak of Fe–O bond at about 623 cm-1. The absorption peaks of the silica shell in MNPs around
1104 and 801 cm-1 are attributed to the asymmetric and symmetric stretching vibrations of Si–
O–Si, respectively. The absorption peak at 2923 cm-1 is related to the stretching vibration of C–
H groups. Also, the absorption peaks at 3200 and 1618 cm-1 are associated with the stretching
vibrations of aromatic C–H groups and C=N bond on imidazolium ring. Moreover, the
absorption band at 3412 cm-1 is attributed to the stretching vibration of O–H in the Si-OH group.
Figure 1. FT-IR spectrum of the bare Fe3O4 MNPs.
Figure 2. SEM image of the MNP catalyst.
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[Fe3O4@SiO2@(C3H6)2-(imidazolium)2-butyl][MnCl42-] as a novel nanomagnetic catalyst
To determine the morphology and the size of the MNP catalyst, SEM was used. The image
of the MNP catalyst shows that these particles have nearly spherical shape with sizes of between
about 19-28 nm.
The magnetic properties of Fe3O4 and MNPs@Dicationic-IL were evaluated by vibrating
sample magnetometry (VSM) at room temperature. The magnetic saturation values were 60
emu/g and 32 emu/g for Fe3O4 and [Fe3O4@SiO2@(C3H6)2-(Imidazolium)2-Butyl][MnCl42-],
respectively. Compared with the uncoated Fe3O4 particles, the saturation magnetization of the
2-
[Fe3O4@SiO2@(C3H6)2-(Imidazolium)2-Butyl][MnCl4
] obviously decreased because the
contribution of the thick SiO2 and organic matter resulted in a low mass fraction of the Fe3O4
magnetic substance. The results show that even with the lower magnetic saturation, catalyst can
still be effectively separated from the solution by an external magnet.
Figure 3. Results of vibrating sample magnetometry of Fe3O4 and [Fe3O4@SiO2@(C3H6)2-
(Imidazolium)2-Butyl][MnCl42-], respectively.
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The elemental composition of [Fe3O4@SiO2@(C3H6)2-(Imidazolium)2-Butyl][MnCl42-] was
analyzed by energy dispersive X-ray (EDX) spectroscopy and the result (Figure 4) clearly
indicates the expected elemental composition (N, O, Si, Cl, Mn, Fe).
Figure 4. Energy dispersive X-ray spectrum of [Fe3O4@SiO2@(C3H6)2-(Imidazolium)2-
2-
Butyl][MnCl4
]
Application of MNPs@Dicationic-IL as heterogeneous catalyst for the synthesis of chromene
derivatives in water
In order to optimize the reaction conditions, the reaction between benzaldehyde, malononitrile,
and dimedone was chosen as a simple model reaction and different reaction parameters such as
solvent, catalyst amount and reaction temperature were investigated (Table 1). As can be seen
from the results, 50 mg of MNPs catalyst was found to be the optimum amount of the catalyst
(Table 1, entries 1-5). Increasing the amount of MNPs catalyst did not change significantly the
yield and the reaction time (Table 1, entries 4 and 5). To examine the effect of the solvent on the
catalytic reaction, the model reaction in the presence of 50 mg of nano magnetic catalyst was
performed in various solvents and under solvent-free condition (Table 1, entries 6-9). According
to the experimental results, the best results in terms of the reaction rates and yields were
achieved in MeOH and H2O for 10 min and 15 min respectively (Table 1, entries 3 and 8).
However, with regard to environmental considerations, H2O was chosen as the solvent for the
reaction. Additionally, at room temperature, only 55% yield was obtained after 120 min (Table
1, entry 10). The slight increase in malononitrile was favorable, and therefore, the molar ratio of
benzaldehyde and dimedone to malononitrile was obtained at 1:1:1.2. To compare the effect of
the supported catalyst in comparison with non-supported catalyst, the model reaction was
studied in the presence of 50 mg pure dicationic-IL [(C3H6)2-(Imidazolium)2-Butyl][Cl-]2 under
reflux condition. The result showed that the reaction did not give the desired product (Table 1,
entry 11). It is worth mentioning that in the absence of catalyst, the product was produced in
trace amount after 120 min (Table 1, entry 12).
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[Fe3O4@SiO2@(C3H6)2-(imidazolium)2-butyl][MnCl42-] as a novel nanomagnetic catalyst
Table 1. Optimization of reaction conditions.
Catalyst
amount (mg)
Time
(min)
60
60
15
15
15
15
15
10
15
120
15
120
No
Catalyst
Solvent
Condition
Yielda (%)
1
2
3
4
5
6
7
8
9
MNPs@Dicationic-IL
MNPs@Dicationic-IL
MNPs@Dicationic-IL
MNPs@Dicationic-IL
MNPs@Dicationic-IL
MNPs@Dicationic-IL
MNPs@Dicationic-IL
MNPs@Dicationic-IL
MNPs@Dicationic-IL
MNPs@Dicationic-IL
Dicationic-IL
30
40
50
60
70
50
50
50
50
50
50
-
H2O
H2O
H2O
H2O
H2O
CHCl3
CH3CN
MeOH
-
H2O
H2O
reflux
reflux
reflux
reflux
reflux
reflux
reflux
reflux
reflux
r.t.
45
70
90
90
92
75
85
92
65
10
11
12
55
75
Trace
reflux
reflux
None
H2O
aIsolated yields.
After optimizing the reaction conditions, the scope and generality for the developed protocol
were explored by using different substituted aryl aldehydes. The reaction of malononitrile and
dimedone with a variety of arylaldehydes bearing electron withdrawing as well as electron
donating groups provided the corresponding 4H-chromenes in 85–92% yield in short reaction
times (Table 2, entries 1-11). It should be mentioned that the present method is compatible with
a wide range of functional groups such as methoxy, methyl, halogens and nitro at the ortho,
meta or para position of arene moiety, and functional group nature does not significantly effect
on the yield of the reaction.
Table 2. Formation of 4H-chromene derivatives catalyzed by MNPs@Dicationic-IL.
No.
Substrate
Product
Time (min)
Yielda (%)
90
M.P. (oC) [Ref.]
235-237 [32]
1
15
Br
O
2
3
10
10
92
87
265-267 [33]
211-213 [34]
CN
O
NH2
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Cl
O
4
15
90
209-210 [35]
CN
O
NH2
5
35
91
199-202 [36]
6
7
8
20
20
30
90
85
90
213-215 [36]
208-210 [8]
178-180 [8]
NO2
O
CN
O
NH2
9
10
88
227-229 [37]
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[Fe3O4@SiO2@(C3H6)2-(imidazolium)2-butyl][MnCl42-] as a novel nanomagnetic catalyst
10
20
20
85
88
223-225 [8]
221-223 [8]
11
aIsolated yields.
We proposed the plausible reaction mechanism on the basis of the literature reports [38] and
the above mentioned results. Firstly, the MNP catalyst activates the carbonyl group of the
aromatic aldehyde and tautomerizes malononitrile. The Knoevenagel condensation of aromatic
aldehyde and malononitrile forms the arylidene malononitrile. Subsequently, dimedone is
tautomerized and reacts with arylidene malononitrile to give Michael adduct. Finally,
intramolecular cyclization and tautomerization of Michael adduct provided the corresponding
4H-chromene (Scheme 3).
2-
To compare the reactivity of the [Fe3O4@SiO2@(C3H6)2-(Imidazolium)2-Butyl][MnCl4
]
with previously reported catalysts a comparative chart is presented in Table 3. The reaction
times and product yields showed that our novel catalyst is equal or more effective than those
reported for other catalytic systems.
Table 3. Comparison of the efficiency of MNPs@Dicationic-IL with some of catalyst reported in the
literature.
No
1
2
3
4
5
6
7
8
Catalyst
Sodium selenate
SO42-/MCM-41
TBAF
Solvent
EtOH/H2O
EtOH
H2O
EtOH/H2O
H2O
H2O
EtOH
Solvent free
H2O
Condition
Reflux
Reflux
Reflux
Reflux
Time (min) Yield (%)
Ref.
39
40
41
42
43
44
45
46
47
180
60
30
30
25
15
15
30
30
90
80
97
84
92
95
94
88
95
Phenylboronic acid
Fe3O4@SiO2@NH-NH2PW
LiBr
Nano titania sulfuric acid
NH4H2PO4/Al2O3
TBAB
Reflux
Reflux
Ultrasonic/40 oC
80 oC
9
Reflux
We have examined the recyclability of [Fe3O4@SiO2@(C3H6)2-(Imidazolium)2-
Butyl][MnCl42-] catalyst for the model reaction, because it is crucial to approve that the highly
active catalyst is recyclable. The study indicated that the catalyst can be reused up to the 5th
cycle (Table 4) under optimized reaction conditions without important loss of its catalytic
activity. At the end of each repeated reaction, the catalyst was separated by using a magnet and
then washed with deionized water followed by ethyl acetate, dried at 100 oC and reused for the
next cycle.
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Scheme 3
Table 4. Reusability of MNPs@Dicationic-IL in the synthesisof 4H-chromenes.
Run
1
2
3
4
5
Time (min)
Yield (%)
15
90
15
88
18
88
20
85
22
82
CONCLUSION
In the present work, a novel imidazolium based dicationic ionic liquid was produced and
successfully grafted on magnetite nanoparticles and its efficiency as heterogeneous and reusable
catalyst for synthesis of 4H-chromenes in water was also investigated. The MNPs@Dicationic-
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[Fe3O4@SiO2@(C3H6)2-(imidazolium)2-butyl][MnCl42-] as a novel nanomagnetic catalyst
IL promotes both the reaction rate and simplify the work-up procedure. In addition, the catalyst
was reused for five times with no considerable decrease in its catalytic activity. Simple
operation, eco-friendly benign, high yields of products and short reaction times are other
advantages of this new catalytic system.
ACKNOWLEDGMENTS
We gratefully acknowledge the financial support of the Mahshahr Branch, Islamic Azad
University.
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