Heterogenization of an imidazolium ionic liquid based on magnetic carbon nanotubes as a novel organocatalyst for the synthesis of 2-amino-chromenes via a microwave-assisted multicomponent strategy

Article abstract of DOI:10.1039/c6nj01631f

Imidazolium ionic liquid functionalized magnetic multiwalled carbon nanotubes (CNTs-Fe₃O₄-IL) were synthesized and the structure, morphology and properties of nanocomposites were investigated using different characterization techniqu

Full text of DOI:10.1039/c6nj01631f

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Heterogenization of an imidazolium ionic liquid
based on magnetic carbon nanotubes as a novel
organocatalyst for the synthesis of 2-amino-
chromenes via a microwave-assisted
Cite this:DOI: 10.1039/c6nj01631f
multicomponent strategy†
Zohre Zarnegar and Javad Safari*
Imidazolium ionic liquid functionalized magnetic multiwalled carbon nanotubes (CNTs–Fe3O4–IL) were
synthesized and the structure, morphology and properties of nanocomposites were investigated using
different characterization techniques such as FT-IR, VSM, SEM, TEM, XRD, TGA and DTA. In order to
synthesize CNT–Fe3O4–IL, magnetite supported on CNTs (CNT–Fe3O4) was modified with 1-methyl-3-
(3-trimethoxysilylpropyl)-1H-imidazol-3-ium chloride. This nanocomposite was found to be an efficient
organocatalyst for the synthesis of 2-amino-chromenes via a microwave-assisted multicomponent strategy
in aqueous media. The attractive features of this simple method include easy isolation of products, milder
and cleaner reaction conditions, higher yields and purity of the product and an easier work-up procedure.
This heterogeneous catalyst was easily separated by simply applying an external magnetic field and the
recyclable organocatalyst was reused several times without any significant loss of activity. A combination of
the advantages of ionic liquids and magnetic solid support nanomaterials provides an environmentally benign
procedure for carrying out catalytic processes.
Received (in Nottingham, UK)
24th May 2016,
Accepted 25th July 2016
DOI: 10.1039/c6nj01631f
www.rsc.org/njc
spectrum of biological activities, including anti-inflammatory,6
antimalarial,7 anticancer8 and pesticide activities.9 Therefore,
1. Introduction
In recent years, multicomponent reactions (MCRs) have gained in recent times, the preparation of this class of O-heterocycles
eminence as a highly valuable synthetic tool for the synthesis is of continuing interest. The most straightforward synthesis of
of organic compounds. The possible structural variations, the these heterocyclic compounds involves the one-pot MCRs of
atom economy and convergent character, the simplicity of a an aldehyde, malononitrile and an activated phenol in the
one-pot procedure, conducting the reaction without isolation of presence of homogeneous and heterogeneous catalysts.10–20
intermediates, the accessible complexity of the molecules, Moreover, many green MCR methods have been designed to
and the very large number of accessible compounds and the synthesize chromenes via a three-component reaction using an
formation of new C–C, C–O bonds are the main advantages of organocatalyst prepared from renewable materials,18 enzyme
MCRs compared with traditional reactions.1,2 Various hetero- lipase19 and a supported ionic liquid catalyst.20 However, some
cycles can be synthesized by applying the MCR strategy.
of these methods show varying degrees of success as well as
On the other hand, chromene derivatives are one of the most limitations, including the use of toxic or expensive catalytic
important classes of pharmaceutical heterocyclic scaffolds in systems, high catalytic loading and difficulty in catalyst separation,
medicinal chemistry, such as spasmolytic, diuretic, anti-coagulant, high temperatures, environmentally hazardous solvents, tedious
anticancer, and anti-anaphylactic activity.3 Chromenes and their purification of catalysts or reaction solvents, reagents in stoichio-
derivatives are often used in the fields of cosmetics, pigments,4 metric amounts, harsh reaction conditions, and low yields.1 Thus,
and potential biodegradable agrochemicals5 and exhibit a wide exploring novel, recyclable catalytic systems for the clean chemical
synthesis of chromenes is still highly desirable. In this context,
ionic liquids are ideal catalysts for chemical reactions.
Ionic liquids with the properties of a wide liquid range, high
catalytic activity and good selectivity, high ionic conductivity,
Laboratory of Organic Compound Research, Department of Organic Chemistry,
College of Chemistry and Biochemistry, University of Kashan, P.O. Box: 87317-51167,
Kashan, I.R., Iran. E-mail: Safari@kashanu.ac.ir, safari_jav@yahoo.com;
low vapour pressure, good thermal stability, and adjustable
Fax: +98 31 55912397; Tel: +98 31 5591 2320
† Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nj01631f physical and chemical properties, have attracted considerable
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interest in catalysis as solvents, catalysts and catalyst carriers efficiency’’ are two key principles of relevance in chemical syntheses
during the past decade.21 Notably, the wide range of ionic liquids and processes. Microwave-assisted synthesis is one of the most
especially imidazolium salts have been applied for the preparation important fields of green chemistry in chemical processes. Micro-
of heterocyclic scaffolds such as nitration,22 N-alkylation wave energy is an efficient approach in order to improve reaction
reaction,23 Diels–Alder,24 dehydration,21 esterification,25 Michael efficiencies, in terms of the product quality and reaction rate and
addition,26 and MCRs.27 Despite the wide use of ionic liquids in time. This green chemistry method has received great attention in
homogeneous catalytic processes, limitations such as difficulty in recent years due to its capability to design alternative, safer, energy
the separation of organic products from the ionic phase, catalyst efficient, and clean routes towards synthesis. In addition, ionic
recovery, and high cost for the use of relatively large amounts of liquids have also been employed as solvents, co-solvents and/or
ionic liquids still exist. To overcome the disadvantages, ionic catalysts in combination with environmentally beneficial heating
liquids are immobilized onto the surface of different materials technologies such as microwave energy and ultrasound to carry out
to prepare supported IL catalysts.21 Carbon nanotubes (CNTs),28 the synthesis of heterocycles.38
magnetic materials,29 silica,21b graphene nanosheets,30 polymers,31
Continuing with our interest in the development of environ-
and inorganic materials32 have been employed as carriers for mentally friendly, efficient, and new catalytic systems and the
immobilizing ionic liquids. Immobilized ionic liquids in catalysis conditions for the preparation of various valuable heterocyclic
combine the advantages of homogeneous and heterogeneous compounds, such as 3,4-dihydropyrimidin-2(1H)-ones/thiones,35a
catalysts with the properties of high activity and selectivity, high polyhydroquinolines,35b substituted imidazoles,29 and chromenes,12
system stability, easy separation, good recyclability, etc.21b,28–32
we report herein the first MCR leading to 2-amino-chromene
Recently, ionic liquids supported on the CNTs have been promoted imidazolium ionic liquid-modified magnetic carbon
developed in modern chemistry to unite the diverse properties nanotubes as novel organo-catalysts under microwave irradiation
of ILs and CNTs.33,34 CNTs as supports for catalytic species and an aqueous reaction medium (Scheme 1).
have been widely studied because of their important properties
such as high surface areas, high tensile strengths, unique
mesoporous structures, ultra-light weight and excellent chemical
2. Results and discussion
2.1. The purpose of the investigation
and thermal stabilities.35 Moreover, magnetic nanoparticles are
another reinforcing nanostructure used in CNT-based nano-
hybrids in numerous applications. Magnetically supported In recent times, the development of microwave irradiation has
ionic liquids can be recovered using a conventional magnet also opened up new avenues for the synthesis of bioactive
without the need for a tedious separation procedure.36 Recently, compounds with various biological activities. For example, the
magnetic CNT-based nanohybrids especially CNT–ionic liquid microwave-assisted synthesis of compounds with potent anti-
nanocomposites for separation processes have been obtained mycobacterial activity, with antimicrobial activity, as adenosine
and developed, as the magnetic separation technique has receptors, and with anticancer activity has been reported. In this
useful properties, such as simplicity, high efficiency and cost- context, the application of the microwave-assisted synthesis of
effectiveness.37
Nowadays, green chemists are constantly challenged to consider medicinal chemistry and pharmacology.39
bioactive heterocycles has been found to be particularly useful in
more eco-friendly procedures for the design of chemical products
As part of our continuous interest in developing efficient
and industrial processes. From a green chemistry perspective, and environmentally benign protocols for the synthesis
the desires for utilizing ‘‘safer solvents’’ and to ‘‘design for energy of various heterocyclic compounds,36 we recently succeeded
Scheme 1 Microwave-assisted synthesis of 2-amino-chromenes catalyzed by CNT–Fe3O4–IL in aqueous medium.
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in developing a novel class of magnetic catalysts based on
carbon nanotubes and applied them to MCRs.29,35,36 Encour-
aged by these successful efforts and aiming to demonstrate the
efficiency and generality of these nanocatalysts, we fixed our
recent attention on employing CNT–Fe3O4–IL for the one-pot
synthesis of 2-amino-chromenes under microwave irradiation.
This microwave accelerated multicomponent reaction in the
presence of a magnetically supported ionic liquid is a benign
alternate for the preparation of a large number of heterocycles.
2.2. Characterization of catalysts
Fig. 1 The FT-IR spectrum of CNT–Fe3O4–IL.
The synthesis process of CNT–Fe3O4–IL magnetic nanohybrids
is shown in Scheme 2. First, Fe3O4 nanoparticles were immo-
bilized on the surface of CNTs. Next, CNT–Fe3O4 was modified The absorbance bands at 2916 and 1646 cmÀ1 are related to
with an ionic liquid to obtain magnetic CNT supported imida- CH2 and CQC stretching vibrations, respectively. The band at
zolium cation-based ionic liquids. CNT–Fe3O4–IL is expected to 1558 cmÀ1 is assigned to CQN stretching vibrations and that of
have various properties, as each component would contribute 1042 cmÀ1 to Si–O stretching of the imidazolium ionic liquid.
different physical and chemical properties. In fact, an efficient In addition, the intense peak at 575 cmÀ1 is the stretching
improvement is the combination of ionic liquids with magnetic vibration of Fe–O.
carbon-based supports for the easy separation of catalysts using
The particle size and surface morphologies of CNTs–Fe3O4
a conventional magnet and CNTs because of good mechanical and CNT–Fe3O4–IL nanocomposites were examined using SEM.
properties, a high chemical stability and a large surface area-to- Fig. 2(a) shows the uniform distribution of Fe3O4 nanoparticles
volume ratio in the catalytic process. CNT–Fe3O4–IL nano- on the surface of the CNTs. The micrograph obtained for the
composites were characterized using FTIR, XRD, SEM, TEM, CNT–Fe3O4–IL nanohybrids showed a considerable change in
EDS, TGA, DTA, and VSM techniques.
the surface of the CNT–Fe3O4 after modification by the ionic
Fig. 1 shows the FT-IR spectra of CNT–Fe3O4–IL. The broad liquid (Fig. 2(b)). Fig. 3 shows TEM images of the CNT–COOH,
band at 3443 cmÀ1 corresponds to the stretching vibrations of CNT–Fe3O4, and CNT–Fe3O4–IL nanocomposites. As shown
hydroxyl groups on the surface of CNTs and Fe3O4 nanoparticles. in Fig. 3(b), TEM confirms that CNT–COOH is decorated
Scheme 2 The procedure for the preparation of CNT–Fe3O4–IL nanocomposites.
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Fig. 2 SEM micrographs of (a) CNTs–Fe3O4, and (b) CNT–Fe3O4–IL nanocomposites.
Fig. 3 TEM images of (a) CNT–COOH, (b) CNTs–Fe3O4, and (c) CNT–Fe3O4–IL nanocomposites.
successfully with many well-dispersed Fe3O4 nanoparticles.
Fig. 3(c) shows a TEM image of CNT–Fe3O4–IL. There is no
detectable outer shell within the sensitivity limit of TEM.
A reasonable explanation might be that silanization of CNTs–
Fe3O4 with the imidazolium ionic liquid results in the formation
of a monolayer Si–O network which is too thin to be recognized.
The energy dispersive X-ray (EDX) spectrum in Fig. 4 shows the
presence of carbon, iron, oxygen and silicon in magnetic CNT–
Fe3O4–IL. The carbon, iron and oxygen signals originated from
Fe3O4 and CNTs, while the silicon signal came from the ionic
liquid, which confirms the existence of an organic shell.
X-ray powder diffraction (XRD) patterns of CNT–COOH,
Fe3O4 nanoparticles, CNT–Fe3O4, and CNT–Fe3O4–IL are shown
Fig. 4 EDX of CNT–Fe3O4–IL nanocomposites.
in Fig. 5. The characteristic sharp peak at 2y = 261 representing
(0 0 2) was attributed to the plane of the CNTs.41 This diffraction
peak was observed in the other nanocomposites. XRD patterns of
CNTs–Fe3O4 displayed characteristic peaks (2y = 26.31, 30.51, an organosilane shell, showing that the crystalline structure of
35.91, 43.61, 54.01, 57.51 and 63.11), which were consistent with the magnetite nanoparticles was retained.
those found in the JCPDS database (PDF No. 01-1111). The (3 1 1)
The magnetic hysteresis loops of the synthesized nano-
peak at 2y = 35.91 indicates the presence of a magnetite composites are depicted in Fig. 6. The saturation magnetization
component in the magnetic samples. The same characteristic (Ms) value is found to be 32.0 and 24.30 electromagnetic
peaks also have been presented in Fig. 5(d), which illustrated units per gram (emu gÀ1) for CNTs–Fe3O4 and CNT–Fe3O4–IL
that the characteristic peaks did not change after coating with nanohybrids, respectively. The reduction in the Ms values of
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Fig. 7 TGA-DTA diagram of CNT–Fe3O4–IL nanohybrids.
nanocomposites, there are two steps of mass losses at tem-
peratures of 50–200 and 200–420 1C. In the first step, adsorbed
water or solvent is removed; in the second step, the decom-
position of organic layers on the surface of the modified CNTs
ocurs. The DTA diagram indicates that CNT–Fe3O4–IL was
decomposed in two steps at 50 and 348 1C which are followed
by an exothermic process. The first region, which occurred
below 50 1C, displayed a mass loss that was attributable to the
loss of adsorbed solvent or trapped water from the magnetic
nanohybrids. The exothermic process at 348 1C could be mainly
attributed to the decomposition of ionic liquids. The tempera-
tures above confirm the previous results of TGA.
Fig. 8 shows the TGA-DTA curves of CNTs–Fe3O4. There was
a weight loss in the temperature range of 20–100 1C that can be
assigned to the loss of adsorbed water on the surface of
the Fe3O4@CNT nanocomposites. A weight loss occurring in
the temperature interval of 100–320 1C was attributed to the
decomposition of labile oxygen functional groups from CNT
layers. In the temperature range from 320–600 1C, the weight
loss was ascribed to the thermal decomposition of stable
oxygen functional groups from the CNT layer.40 As a result,
the DTA curve was quite consistent with what was shown in the
TGA diagram. The DTA curve indicates that CNT–Fe3O4 was
decomposed in three stages at 45, 295 and 566 1C which are
followed by an exothermic and two endothermic processes. The
exothermic process, which occurred below 50 1C, displayed a
mass loss that was attributable to the loss of adsorbed trapped
Fig. 5 XRD analysis of (a) CNT–COOH, (b) Fe3O4, (c) CNTs–Fe3O4, and
(d) CNT–Fe3O4–IL.
CNT–Fe3O4–IL is attributed to the nonmagnetic organic layer
coating on the surface of CNTs–Fe3O4. However, the Ms value of
CNT–Fe3O4–IL is lower than CNT—Fe3O4 composites, it could
be rapidly separated from the reaction mixture via a conven-
tional magnet, which is displayed in the nether inset of Fig. 6.
However it is still enough for the magnetic separation of the
catalyst.
The TGA-DTA curves of the CNT–Fe3O4–IL nanohybrids were
obtained under a N2 atmosphere (Fig. 7). For the CNT–Fe3O4–IL
Fig. 6 VSM magnetization curves for CNT–COOH, CNTs–Fe3O4, and
CNT–Fe3O4–IL at room temperature.
Fig. 8 TGA-DTA diagram of CNT–Fe3O4 nanohybrids.
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water from CNT–Fe3O4. The endothermic processes could be
mainly attributed to the decomposition of oxygen functional
groups.
After the synthesis and characterization of CNT–Fe3O4–IL,
we studied the catalytic activity of this heterogeneous catalyst
for the preparation of chromene derivatives.
2.3. Evaluation of the catalytic activity of CNT–Fe3O4–IL in the
synthesis of 2-amino-chromenes
Initially, in order to optimize the reaction parameters and test
the performance of CNT–Fe3O4–IL as a magnetic nanocatalyst
for the synthesis of 2-amino-chromenes, we selected the three-
component reaction of benzaldehyde, resorcinol and malono-
nitrile as the model reaction under different conditions such
as the amount of magnetic nanocatalyst, temperature, power of
the microwave irradiation, and reaction time. As presented
in Table 1, the best result was obtained with benzaldehyde
(1 mmol), resorcinol (1 mmol), malononitrile (1 mmol) and
CNT–Fe3O4–IL (0.020 g) as a catalyst at 70 1C for 5 min in
aqueous media under microwave irradiation using a power of
100 W. Owing to their high ionic charges, high polarities and
high dielectric constants, ionic liquids have the ability to
absorb microwave energy and convert it into fast and homo-
geneous heat, and this can increase the rate of this organic
condensation.38 The desired product 6a was not obtained when
the reaction was carried out in H2O at 70 1C for 5 min under
microwave irradiation and catalyst free conditions.
To survey the generality and scope of the catalyst, we extended
our study on CNT–Fe3O4–IL (0.020 g) in aqueous media at 70 1C
using a variety of aromatic aldehyde and phenol derivatives
to prepare a series of 2-amino-4H-chromenes and 2-amino-2-
chromenes. The obtained results presented in Table 2 indicate
that various aromatic aldehydes containing electron-withdrawing
and electron-releasing substituents were utilized successfully in
Table 1 Optimization of reaction conditions for the synthesis of 6a under
microwave irradiation
Entry Catalyst (g) Temp. (1C) Time (min) Power (W) Yield (%)
1
2
3
4
5
6
7
8
0.008
0.009
0.010
0.015
0.020
0.025
0.030
0.020
0.020
0.020
0.020
0.020
0.020
0.020
0.020
0.020
0.025
0.020
0.020
0.020
—
50
50
50
50
50
50
50
60
70
80
90
60
70
70
70
90
70
30
40
50
70
10
8
8
7
7
7
7
6
6
6
6
5
5
5
5
5
5
7
6
6
5
90
90
90
90
90
90
90
90
90
45
50
55
65
70
70
68
75
80
80
75
85
97
96
96
95
97
35
45
65
—
9
10
11
12
13
14
15
16
17
18
19
20
21
90
90
100
100
110
120
100
100
100
100
100
100
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Table 3 Comparison of CNT–Fe3O4–IL with other catalysts reported in the literature for the preparation of 6a
Entry
Catalyst
Amount; condition
Time
Yield (%)
Ref.
1
2
3
4
5
6
7
8
9
Glycine
15 mol%; water and ultrasound, 28–30 1C
0.1 mmol; refluxed in MeCN
30 mg; H2O, 100 1C
Refluxed in 2,2,2-trifluoroethanol
7 mol%; water and r.t
0.04 g; EtOH : H2O (5 : 2), 30 1C
10 mol%; solvent-free, 67.5 1C
5 mol%; water and reflux
9 min
4 h
12 h
5 h
25
10 min
27
15
5
5 h
94
83
86
90
98
95
92
92
97
87
41
42
43
44
12a
12b
45
13
Fe(HSO4)3
Tungstic acid–SBA-15
—
Fe3O4
MNPs–NH2
[2-Eim] OAc
POPINO
CNT–Fe3O4–IL
TPOP-2
0.02 g, water and 70 1C
40 mg; solvent-free, 80 1C
This work
46
10
this MCR, and furnished the desired products in excellent yields addition reaction with A to afford the product (B). The Michael
and in short reaction times. Moreover, both 1-naphthol and addition product (B) undergoes intra-molecular cyclization
2-naphthol are suitable for the synthesis of 2-amino-2-chromenes through nucleophilic attack of the phenoxide group on the
using microwave technology. As the results show this novel cyano moiety and is subsequently tautomerized to yield the
organocatalyst has excellent catalytic activity for the synthesis of 2-amino-chromenes (C).12
various 2-amino-chromene derivatives in very high yields and with
The reusability and recoverability of the heterogeneous
a short reaction time. The combined merits of microwave energy catalyst was investigated using the model reaction under the
and supported ionic liquids on magnetic CNTs provide this optimized conditions. To test the reusability of the catalyst,
organic reaction with low pollution, safe operation, and rapid after completion of the reaction, the catalyst was easily removed
access to products with a simple workup.
from the reaction medium using a normal magnet. After being
A comparison of the catalytic efficiency of CNT–Fe3O4–IL washed with ethyl acetate several times and drying at 60 1C, the
with other catalysts reported in the literature to prepare the organocatalyst can be easily reused without any deactivation
product of the model reaction (6a) is shown in Table 3. even after five successive cycles of the synthesis of product
The present method offers a lot of advantages over most of the 6a (Fig. 9).
reported methods, such as facility of scale up, clean, simple and
straightforward work up, savings in energy consumption, a short
reaction time, high to quantitative yields of products and
enhancement in the reaction rate. Therefore, the combination
of a magnetic nanocatalyst and microwave technology was found
to be an efficient reaction medium for this three-component
condensation.
The proposed mechanism for the synthesis of chromenes is
shown in Scheme 3. As the initiation step (1), the aldehyde is
activated by the imidazolium cation of CNT–Fe3O4–IL. Sub-
sequently Knoevenagel condensation occurs with malononitrile
to afford a-cyanocinnamonitrile derivative (A) using the ionic
liquid anion (ClÀ). The activated phenol endures a Michael
Fig. 9 Reusability of CNT–Fe3O4–IL for the synthesis of 6a.
Scheme 3 Proposed mechanism for the synthesis of chromenes using CNT–Fe3O4–IL.
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The present method is an interesting, clean and novel proce- the mixture (CNTs–COOH) was centrifuged and washed several
dure for the preparation of 2-amino-chromenes. In the field of times with deionized water and dried at 100 1C. Then, Fe3O4
synthetic chemistry, the use of microwave technology and an supported on the surface of the CNTs was performed using
immobilized ionic liquid significantly increased the reaction chemical coprecipitation by following the reported procedure.35a
yield and shortened the reaction times. In addition, the use of FeCl2Á4H2O and FeCl3Á6H2O (2 : 1; molar ratio) were dissolved in
water as a green solvent combined with the exploitation of the 100 mL of deionized water and stirred at 90 1C for 30 min. Next,
multicomponent strategy as an environmentally benign and 10 mL of 0.4 g of CNTs–COOH and ammonium hydroxide (25%)
powerful tool open to this process suggests good prospects for were dispersed in 50 mL of distilled water, which was added
the rapid construction of target molecules.
rapidly and the mixture was stirred at 90 1C for 30 minutes under
an Ar atmosphere. The obtained nanocomposite (Fe3O4–CNTs)
was magnetically recovered and washed with distilled water and
dried at 50 1C.
3. Conclusions
In this research, we have reported that magnetically ionic
liquids based on carbon nanotubes are excellent heterogeneous
catalysts for the preparation of a wide range of 2-amino-
chromenes, which are often encountered in pharmacologically
and biologically active compounds. The salient features of the
novel synthetic method include good yields and a short reaction
time, high atom-economy, reusability of the magnetic catalyst, no
need for column chromatographic separation, and its adaptability
for the synthesis of a diverse set of 2-amino-chromene derivatives.
Moreover, the use of water as a green solvent combined with the
exploitation of the multicomponent strategy open to this process
suggests good prospects for its industrial applicability.
4.3. Preparation of CNT–Fe3O4–IL nanocomposites
1-Methyl-3-(3-trimethoxysilylpropyl) imidazolium chloride was
prepared from the reaction of N-methyl imidazole with
(3-chloropropyl) trimethoxysilane at 80 1C under solvent-free
conditions.36 In order to prepare CNT–Fe3O4–IL nanocompo-
sites, 0.60 g of CNT–Fe3O4 was fully dispersed in 20.0 mL of
anhydrous toluene by ultrasonication. Then, 20 mmol (5.60 g)
1-methyl-3-(3-trimethoxysilylpropyl)-1H-imidazol-3-ium chloride
and 0.60 ml 28% NH4OH were added dropwise at room tem-
perature and stirred for another 36 h. The resultant products
were magnetically collected and washed multiple times with
ethanol, diethyl ether and double-distilled water to remove
unreacted ionic liquids. The obtained magnetic CNT–Fe3O4–IL
was dried again in an oven at 70 1C for 5 hours.
4. Experimental
4.1. Chemicals and apparatus
4.4. General procedure for the preparation of 2-amino-
chromenes
Most of the reagents used were purchased from the Merck,
Aldrich and Sigma Chemical Companies. Multi walled carbon
nanotubes with a surface area of 136 m2 gÀ1 and 10–20 nm in
diameter were supplied from Neutrino Company, Iran. Melting
points were determined on an Electrothermal MK3 apparatus
using an open-glass capillary and are uncorrected. FT-IR spectra
were recorded on a Perkin-Elmer 550 instrument in the range
400–4000 cmÀ1. NMR spectra were recorded on a Bruker DRX-
400 spectrometer. Elemental analysis was obtained from a Carlo
ERBA Model EA 1108 analyzer carried out on a Perkin-Elmer
240c analyzer. Magnetic nanohybrids were characterized using a
Holland Philips Xpert X-ray diffraction (XRD) diffractometer
(CuK, radiation, l = 0.154056 nm), at a scanning speed of 21
minÀ1 from 101 to 1001 (2y). The surface morphology of the
samples was characterized by scanning electron microscopy
(SEM; EM3200) and transmission electron microscopy (TEM;
Philips CM10). Thermogravimetric analysis (TGA) profiles were
obtained using a PL-STA 1500 thermal analyzer at a uniform
heating rate of 15 1C minÀ1 under N2 flow. The magnetic
measurements of the samples were carried out using a vibrating
sample magnetometer (VSM) (4 inch, Daghigh Meghnatis Kashan
Co., Kashan, Iran) at room temperature.
A mixture of aldehyde (1 mmol), resorcinol (1-naphtol or
2-naphtol) (1 mmol) and malononitrile (1 mmol) was placed
in a 10 mL initiator reaction vial, followed by the addition of
0.02 g CNT–Fe3O4–IL and distilled water (5 mL). The reaction
vial was then sealed and prestirred for 20 s before being
irradiated in the microwave at 70 1C until TLC (petroleum
ether–ethyl acetate 7 : 3) revealed complete consumption of
the starting materials. The reaction mixture was then cooled to
room temperature and the magnetic organocatalyst was magneti-
cally recovered. Then, the residue was purified by recrystallization
from EtOH to afford the pure product in high yield.
Acknowledgements
We gratefully acknowledge financial support from the Research
Council of the University of Kashan for supporting this work by
Grant No. (363022/14).
References
4.2. Synthesis of CNT–Fe3O4 nanocomposites
1 (a) G. Brahmachari and B. Banerjee, ACS Sustainable Chem.
Eng., 2014, 2, 411–422; (b) A. Solhy, A. Elmakssoudi,
R. Tahir, M. ed Karkouri, M. Larzek, M. Bousmina and
M. Zahouily, Green Chem., 2010, 12, 2261–2267.
A mixture of nitric acid and sulphuric acid (10 mL/20 mL) was
added to a flask containing 0.5 g of CNTs and was heated
to 50 1C under ultrasonic irradiation for six hours. After that,
New J. Chem.
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2 M. Boominathan, M. Nagaraj, S. Muthusubramanian and
R. V. Krishnakumar, Tetrahedron, 2011, 67, 6057–6064.
A: Chem., 2012, 359, 74–80; (b) S. Nemouchi, R. Boulcina,
B. Carboni and A. Debache, C. R. Chim., 2012, 15, 394–397.
3 (a) W. O. Foye, Principi Di Chimica Farmaceutica, Piccin, 18 R. Sangsuwan, S. Sangher, T. Aree, C. Mahidol, S. Ruchirawat
Padova, Italy, 1991, p. 416; (b) L. L. Andreani and E. Lapi, and P. Kittakoop, RSC Adv., 2014, 4, 13708–13718.
Boll. Chim. Farm., 1960, 99, 583–586; (c) Y. L. Zhang, 19 F. Yang, Z. Wang, H. Wang, H. Zhang, H. Yue and L. Wang,
B. Z. Chen, K. Q. Zheng, M. L. Xu and X. H. Lei, Yaoxue RSC Adv., 2014, 4, 25633–25636.
Xuebao, 1982, 17, 17–22 (Chem. Abstr., 1982, 96, 135383e); 20 P. Sharma, M. Gupta, R. Kant and V. K. Gupta, RSC Adv.,
(d) L. Bonsignore, G. Loy, D. Secci and A. Calignano, Eur. 2016, 6, 32052–32059.
J. Med. Chem., 1993, 28, 517–520; (e) E. C. Witte, P. Neubert 21 (a) H. Xu, H. Zhao, H. Song, Z. Miao, J. Yang, J. Zhao,
and A. Roesch, Ger. Offen DE., 3427985, 1986 (Chem.
Abstr.1986, 104, 224915f).
4 G. P. Ellis, in The Chemistry of Heterocyclic Compounds
N. Liang and L. Chou, J. Mol. Catal. A: Chem., 2015, 410,
235–241; (b) H. Li, P. S. Bhadury, B. Song and S. Yang, RSC
Adv., 2012, 2, 12525–12551.
Chromenes, Chromanes and Chromones, ed. A. Weissberger 22 G. Aridoss and K. K. Laali, J. Org. Chem., 2011, 76,
and E. C. Taylor, John Wiley, New York, NY, USA, 1977,
ch. II, pp. 11–139.
5 E. A. Hafez, M. H. Elnagdi, A. G. A. Elagemey and F. M. A. A.
El-Taweel, Heterocycles, 1987, 26, 903–907.
6 D. O. Moon, Y. H. Choi, N. D. Kim, Y. M. Park and G. Y. Kim,
Int. Immunopharmacol., 2007, 7, 506–514.
8088–8094.
:
¨
23 S. Demir, Y. Damarhan and I Ozdemir, J. Mol. Liq., 2015,
204, 210–215.
24 J. K. Park, P. Sreekanth and B. M. Kim, Adv. Synth. Catal.,
2004, 346, 49–52.
25 Y. A. Elsheikh, Ind. Crops Prod., 2013, 49, 822–829.
7 (a) V. F. De Andrade-Neto, M. O. F. Goulart, J. F. Da Silva 26 B. C. Ranu, S. Banerjee and R. Jana, Tetrahedron, 2007, 63,
Filho, M. J. Da Silva, M. D. C. F. R. Pinto, A. V. Pinto, 776–782.
M. G. Zalis, L. H. Carvalho and A. U. Krettli, Bioorg. Med. 27 J. Safari and Z. Zarnegar, Ultrason. Sonochem., 2014, 21,
Chem. Lett., 2004, 14, 1145–1149; (b) P. S. Elisa, E. B. Ana, 1132–1139.
A. G. Ravelo, D. J. Yapu and A. G. Turba, Chem. Biodiversity, 28 Y. Ai, M. Wu, L. Li, F. Zhao and B. Zeng, J. Chromatogr. A,
2005, 2, 264–274. 2016, 1437, 1–7.
8 (a) C. J. Li and Y. L. Li, U.S. Pat., U.S. 005222246 A1 29 J. Safari and Z. Zarnegar, C. R. Chim., 2013, 16, 920–928;
20,051,006, 2005; (b) M. Ough, A. Lewis, E. A. Bey, J. Gao,
J. M. Ritchie, W. Bornmann, D. A. Boothman, L. W. Oberley
and J. J. Cullen, Cancer Biol. Ther., 2005, 4, 95–102.
9 A. M. Shestopalov, Y. M. Emelianova and V. N. Nesterov,
Russ. Chem. Bull., 2003, 52, 1164–1171.
10 A. T. Khan, M. Lal, S. AliKhan and M. Musawwer Khan,
Tetrahedron Lett., 2011, 52, 5327–5332.
11 A. R. Moosavi-Zare, M. A. Zolfigol, O. Khaledian,
A. Pourjavadi, S. H. Hosseini, M. Doulabi, S. M. Fakoorpoor
and F. Seidi, ACS Catal., 2012, 2, 1259–1266.
30 J. Xu, Z. Sheng, X. Wang, X. Liu, J. Xia, P. Xiong and B. He,
Bioresour. Technol., 2016, 200, 1060–1064.
31 W. Dai, Y. Zhang, Y. Tan, X. Luo and X. Tu, Appl. Catal., A,
2016, 514, 43–50.
32 X. Xing, P. H. Chang, G. Lv, W. T. Jiang, J. S. Jean, L. Liao
and Z. Li, J. Taiwan Inst. Chem. Eng., 2016, 59, 237–243.
V. Khakyzadeh, M. Darestani farahani, M. H. Beyzavi and 33 Y. Ai, M. Wu, L. Li, F. Zhao and B. Zeng, J. Chromatogr. A,
H. Gerhardus Kruger, Chem. Eng. J., 2014, 248, 122–127. 2016, 1437, 1–7.
12 (a) J. Safari, Z. Zarnegar and M. Heydarian, Bull. Chem. Soc. 34 A. Abo-Hamad, M. A. H. Al Saadi, M. Hayyan, I. Juneidi and
Jpn., 2012, 85, 1332–1338; (b) J. Safari and Z. Zarnegar,
J. Mol. Struct., 2014, 1072, 53–60.
13 M. G. Dekamin, M. Eslami and A. Maleki, Tetrahedron, 2013,
69, 1074–1085.
M. A. Hashim, Electrochim. Acta, 2016, 193, 321–343.
35 (a) Z. Zarnegar and J. Safari, RSC Adv., 2013, 3, 17962–17967;
(b) Z. Zarnegar, J. Safari and Z. Mansouri Kafroudi, New
J. Chem., 2015, 39, 1445–1451.
14 (a) D. Kumar, V. B. Reddy, B. G. Mishra, R. K. Rana, M. N. 36 Z. Zarnegar and J. Safari, RSC Adv., 2013, 3, 26094–26101.
Nadagouda and R. S. Varma, Tetrahedron, 2007, 63, 37 C. Wu, J. Fan, J. Jiang and J. Wang, RSC Adv., 2015, 5,
3093–3097; (b) K. Gong, H. L. Wang, D. Fang and Z. L. Liu,
Catal. Commun., 2008, 9, 650–653.
47165–47173.
38 (a) H. Duan, D. Wang and Y. Li, Chem. Soc. Rev., 2015, 44,
´
15 (a) A. R. Moosavi-Zare, M. A. Zolfigol, O. Khaledian,
V. Khakyzadeh, M. Darestani farahani, Mo. H. Beyzavi and
5778–5792; (b) I. T. Horvath and P. T. Anastas, Chem. Rev.,
2007, 107, 2167–2168.
H. G. Kruger, Chem. Eng. J., 2014, 248, 122–127; (b) I. A. 39 (a) D. U. Ganihigama, S. Sureram, S. Sangher, P. Hongmanee,
Azath, P. Puthiaraj and K. Pitchumani, ACS Sustainable
Chem. Eng., 2013, 1, 174–179.
T. Aree, C. Mahidol, S. Ruchirawat and P. Kittakoop, Eur.
J. Med. Chem., 2015, 89, 1–12; (b) D. N. Pansare, N. A. Mulla,
C. D. Pawar, V. R. Shende and D. B. Shinde, Bioorg. Med. Chem.
Lett., 2014, 24, 3569–3573; (c) M. Costa, F. Areias, M. Castro,
J. Brea, M. I. Loza and F. Proença, Org. Biomol. Chem., 2011,
16 (a) A. Pourjavadi, S. H. Hosseini and S. S. Amin, Chem. Eng.
J., 2014, 247, 85–92; (b) Y. Essamlali, O. Amadine, H. Maati,
K. Abdelouahdi, A. Fihri, M. Zahouily, R. S. Varma and
A. Solhy, ACS Sustainable Chem. Eng., 2013, 1, 1154–1159.
17 (a) M. Khoobi, L. Ma’mani, F. Rezazadeh, Z. Zareie,
A. Foroumadi, A. Ramazani and A. Shafiee, J. Mol. Catal.
´
9, 4242–4249; (d) J. Ferreira da Costa, X. Garcıa-Mera,
˜
O. Caamano, J. M. Brea and M. I. Loza, Eur. J. Med. Chem.,
2015, 98, 212–220.
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Paper
NJC
40 G. Gao, Q. Zhang, X. B. Cheng, J. G. Shapter, T. Yin, R. Sun 43 S. K. Kundu, J. Mondal and A. Bhaumik, Dalton Trans., 2013,
and D. Cui, Sci. Rep., 2015, 5, 17553, DOI: 10.1038/
srep17553.
41 B. Datta and M. A. Pasha, Ultrason. Sonochem., 2012, 19,
725–728.
42 H. Eshghi, S. Damavandi and G. H. Zohuri, Synth. React.
Inorg. Met.-Org. Chem., 2011, 41, 1067–1073.
42, 10515–10524.
44 S. Khaksar, A. Rouhollahpour and S. Mohammadzadeh
Talesh, J. Fluorine Chem., 2012, 141, 11–15.
45 M. Ghorbani, S. Noura, M. Oftadeh, M. A. Zolfigol, M. H.
Soleimani and K. Behbodi, J. Mol. Liq., 2015, 212, 291–300.
46 S. K. Kundu and A. Bhaumik, RSC Adv., 2015, 5, 32730–32739.
New J. Chem.
This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2016