High-performance sono/nano-catalytic system: CTSN/Fe3O4-Cu nanocomposite, a promising heterogeneous catalyst for the synthesis of: N -arylimidazoles

Article abstract of DOI:10.1039/c9ra08062g

Herein, a promising heterogeneous nanoscale catalytic system constructed of chitosan (CTSN, as a polymeric basis), iron oxide nanoparticles (Fe₃O₄ NPs, as the magnetic agent), and copper oxide nanoparticles (CuO NPs, as the main cata

Full text of DOI:10.1039/c9ra08062g

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High-performance sono/nano-catalytic system:
CTSN/Fe3O4–Cu nanocomposite, a promising
heterogeneous catalyst for the synthesis of N-
arylimidazoles†
Cite this: RSC Adv., 2019, 9, 40348
*
Reza Taheri-Ledari, Seyed Masoud Hashemi and Ali Maleki
Herein, a promising heterogeneous nanoscale catalytic system constructed of chitosan (CTSN, as
a polymeric basis), iron oxide nanoparticles (Fe3O4 NPs, as the magnetic agent), and copper oxide
nanoparticles (CuO NPs, as the main catalytic active site) is presented. Firstly, a convenient synthetic
route for preparation of this novel nanocatalyst (CTSN/Fe3O4–Cu) is presented. Further, the synergistic
catalytic effect between the novel-designed catalyst and ultrasound waves (USW) in N-arylation coupling
reactions of the imidazole derivatives (using various aryl halides) is precisely discussed. Concisely, high
reaction yields (98%) have been obtained in short reaction time (10 min) through applying a partial
amount (0.01 g) of this nanocatalyst. As the main reason for high catalytic activity of CTSN/Fe3O4–Cu,
nanosized cluster-shaped morphology, which provides a wide surface active area, can be expressed.
However, as the most distinguished properties of CTSN/Fe3O4–Cu catalytic system, high convenience in
separation and excellent reusability could be mentioned. CTSN/Fe3O4–Cu nanocomposite can be easily
recovered by using an external magnet and reused at least for eight times with no significant decline in
the catalytic activity. Structural characterizations of this novel system have been done by various
analytical methods and the obtained results have been well interpreted in the context.
Received 4th October 2019
Accepted 29th November 2019
DOI: 10.1039/c9ra08062g
rsc.li/rsc-advances
heterogeneous catalytic systems will not be damaged under
USW irradiation. Concisely, USW irradiation is more conve-
nient, fast, safe and simple than traditional heating sources.5–7
1. Introduction
Recently, science and technology are shiing more toward
design and development of the novel safe energy resources to
create a healthier world. Thus, using clean and nonhazardous
materials and executing the green methods have attracted so
much attentions in different research elds. In chemical
catalysis scope, numerous efforts have been made to design and
fabricate efficient catalytic systems that include nontoxic
materials in their structures and do not need any hazardous
reagent for running the catalytic process.1,2 In recent decade,
ultrasound wave (USW) irradiation has been introduced as one
of the most effective strategies that can also be considered as
a great co-catalyst agent for chemical reactions.3,4 From both
physical and chemical aspects, USW irradiation activates the
catalytic sites of the chemicals to enhance the performance of
the catalytic systems. Also, USW irradiation leads to obtain high
reaction yields in short reaction times, with the least amount of
the wasted materials. Moreover, the structure of the
Therefore, diverse organic reactions can efficiently be carried
out under USW irradiation. As the main reasons, acoustic
cavitation and cage effect through microject bubbles (micro-
bubbles) that create high temperatures and microscopic pres-
sures within few seconds lead to acceleration of the chemical
reactions.8 As a result, USW irradiation is classied as a green,
powerful, economical and environmentally-friendly approach
in chemical reactions. In this study, we try to show the syner-
gistic catalytic effect between USW (using an US cleaner bath)
with a novel nanoscale catalytic system for facilitating the
chemical synthesis reactions.
Proportional to the impressive and fast progress in nano-
technology, several nanoscale heterogeneous catalytic systems
have been introduced by researchers to perform the complex
chemical reactions with more convenience.9–12 Among various
species of the reported heterogeneous catalytic systems,
magnetic nanocatalysts have attracted more attentions due to
including high convenience in separation and recycling
processes. For instance, we recently reported some novel
magnetic nanoparticles (NPs) that have been functionalized and
applied for different catalytic aims such as facilitating peptide
couplings and multicomponent synthesis reactions of
Catalysts and Organic Synthesis Research Laboratory, Department of Chemistry, Iran
University of Science and Technology, Tehran 16846-13114, Iran. E-mail: maleki@
iust.ac.ir; Fax: +98 21 73021584; Tel: +98 21 73228313
† Electronic supplementary information (ESI) available: The ESI le includes the
NMR (H and C) of selected N-aryimidazole products and also SEM and EDX results
of recovered nanocatalyst. See DOI: 10.1039/c9ra08062g
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pharmaceutical compounds.13,14 However, wide surface active efficient route for the synthesis of N-aryl or heteroarylamines
area, great functionalization capability, nontoxicity, excellent remains highly desirable.
stability and thermal resistance, and etc. could also be mentioned
In this work, we try to facilitate the N-arylation of imidazoles
as the additional important reasons for employing the magnetic and its derivatives by using a novel designed CTSN/Fe3O4–Cu
NPs for catalytic purposes. Among all of the different categories nanocomposite, as an inexpensive magnetic nanocatalyst,
of magnetic NPs, iron oxide NPs species (Fe3O4, g-Fe2O3, and etc.) under ‘ligand-free’ conditions. Firstly, a convenient route is
are extremely used due to their easy preparation and super- introduced for preparation of this novel catalytic system. Then,
paramagnetic behavior.15–17 In this work, we report a novel as the distinguished advantages, high magnetic behavior that
magnetic nanocatalyst that is constructed of copper nano- leads to easily separation aer completion of the synthetic
particles (Cu NPs) as the main catalytic active sites, iron oxide reactions with no need to some complex purication processes.
nanoparticles (Fe3O4 NPs) as the magnetic agent, and chitosan Moreover, high stability of this heterogeneous catalytic system
(CTSN) as the natural polymeric matrix for composition and provides a great opportunity to reuse this system for several
stabilization of the nanoscale ingredients (CTSN/Fe3O4–Cu).
times without any decline in the catalytic performance. High
In recent decades, N-arylated azoles e.g., arylpyrroles, aryl- performance of this catalytic system origins from a synergistic
pyrazoles, arylimidazoles, aryltriazoles, arylindoles, arylcarba- catalytic effect between the fabricated nanocomposite (CTSN/
zoles, and etc. have attracted so much attentions because of Fe3O4–Cu) and ultrasound waves, which is considered as
their important applications in medicinal and materials elds. a faster and safer method in comparison with other methods.23
Some of these scaffolds are also found in many bioactive natural For this purpose, all of the synthetic reactions have been carried
products.18 Among all of the heterocyclic compounds, study on out in an ultrasound cleaner bath with 50 kHz frequency and
the N-aryl imidazoles is very intensive because of its famous 200 W Lꢀ1 power density. From physical aspect, well-known
biomedical properties such as receptor antagonists and cluster shape of the composite provide an extreme surface
thromboxane synthase inhibitors.19,20 In this regard, some active area for catalytic aims. In addition of the mentioned
ligand-free copper-catalyzed N-arylation reactions have been excellences, substantial biocompatibility and biodegradability
reported. For instance, Son et al. have prepared coated-CuO is obtained for this catalytic system, through applying a natural
nanoparticles by thermal decomposition using copper acetyla- basis (CTSN) in the structure of the catalyst. As a result, a fast
cetonate.21 Choudary et al. have designed a catalyst for N-ary- and safe strategy for the synthesis of the N-arylated imidazole
lation of imidazoles via the cation exchange of uorapatite and derivatives is presented in this study, through which high
tert-butoxyapatite with copper.22 Thus, designing a simple and reaction yields (98%) are obtained in short reaction time (10
min) with high safety and convenience.
Scheme 1 Preparation route of CTSN/Fe3O4–Cu nanocomposite.
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Fig. 1 FT-IR spectra of CTSN, Fe3O4, and CTSN/Fe3O4–Cu nanocomposite.
2.2. Practical methods
2. Experimental
2.2.1. Synthesis of CTSN/Fe3O4 nanocomposite. In
a round-bottom ask (100 mL), CTSN (high purity, 180 kDa)
(0.5 g) was dissolved in a mix of dilute acidic deionized water
(4.0 mL, pH ¼ 5.5 by HCl) and ethanol (4.0 mL), at 80 ꢁC under
N2 atmosphere. Then, two aqueous solutions (0.1 M) of
FeCl2$4H2O and FeCl3$6H2O were simultaneously added to
the ask. Next, concentrate NH3 was slowly added to the
mixture, until pH ¼ 12 was obtained. The dark particles of the
Fe3O4 were produced via co-deposition method and compos-
ited with CTSN during an in situ process. Aer completion of
the addition, the magnetized CTSN was collected by an
external magnet and washed with distilled water and ethanol,
and dried in a vacuum oven.
2.2.2. Synthesis of CTSN/Fe3O4–Cu nanocomposite. In
a round-bottom ask (50 mL), CTSN/Fe3O4 (0.1 g) was placed and
well dispersed in deionized water (3.0 mL), via ultrasonication (10
min). Next, Cu(OAc)2 aqueous solution (5% wt, 2.0 mL) was
added drop by drop to the aqueous mixture of CTSN/Fe3O4, and
the mixture were ultrasonicated into an US bath (50 kHz, 200 W
2.1. Materials and equipment
All the solvents, chemicals and reagents were purchased from
Merck, Sigma and Aldrich. Melting points were measured on
an Electrothermal 9100 apparatus and are uncorrected. FT-IR
spectra were recorded on a Shimadzu IR-470 spectrometer by
the method of KBr pellet. 1H and 13C Nuclear Magnetic
Resonance (NMR) spectra were recorded on a Bruker DRX-500
Avance spectrometer at 500, 300, 75 and 125 MHz, respec-
tively. Thermal analysis (TGA) was also done by using of Bahr-
STA 504 instrument under argon atmosphere. FESEM images
were taken by Sigma-Zeiss microscope with attached camera.
Magnetic measurements of the solid samples were performed
using Lakeshore 7407 and Meghnatis Kavir Kashan Co., Iran
vibrating sample magnetometers (VSMs). Elemental analysis
of the nanocatalyst was carried out by energy-dispersive X-ray
(EDX) analysis which was recorded on a Numerix DXP-X10P.
XRD measurements were carried out by using a DRON-8 X-
ray diffractometer.
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Fig. 2 (a) FE-SEM image of CTSN/Fe3O4, and (b) the prepared CTSN/Fe3O4–Cu nanocomposite. (c) EDX analysis results of the prepared CTSN/
Fe3O4–Cu nanocomposite [Y-axis: count, X-axis: energy (keV)].
Lꢀ1) for 1 h, at 80 ꢁC. Finally, the fabricated CTSN/Fe3O4–Cu
nanocomposite were magnetically separated and washed with
3. Results and discussion
3.1. Preparation of CTSN/Fe3O4–Cu nanocatalyst
deionized water and ethanol and dried at room temperature.
2.2.3. General procedure for N-arylation of imidazoles by
CTSN/Fe3O4–Cu nanocatalyst via USW irradiation. In a glass
tube (Threaded Test Tube with Phenolic Cap, 13 ꢂ 100 mm),
aryl halide (1.0 mmol), imidazole (2.0 mmol), CTSN/Fe3O4–Cu
(0.01 mg), CTAB (0.5 mmol) and K2CO3 (1.5 mmol) were added
in deionized water (4.0 mL). The mixture was sonicated for
10 min, at room temperature in an ultrasonic bath (50 kHz, 200
W). Aer completion of the reaction, the mixture was diluted
with H2O (5.0 mL) and extracted with EtOAc (4 ꢂ 10 mL). The
combined organic phases was washed with water and brine,
dried over anhydrous Na2SO4, and concentrated in vacuum. The
residue was puried by ash column chromatograph on silica
gel (ethyl acetate/n-hexane, 2 : 1) to afford the target pure
product. As same as excellent results were obtained in gram
scale of the reaction by starting these ratio of raw materials and
reagents.
Initially, CTSN was dissolved in a mix of dilute acidic water (pH
¼ 5.5) and ethanol with equal ratios, at 80 C under N2 atmo-
ꢁ
sphere. When a clear and homogeneous mixture was obtained,
two aqueous solutions of FeCl2$4H2O and FeCl3$6H2O were
added drop by drop to into the ask. Next, ammonia was slowly
added to the mixture, until pH ¼ 12 was obtained. The dark
particles of the Fe3O4 were synthesized via an in situ co-
deposition method and composited with CTSN. Aer comple-
tion of the addition, the magnetized CTSN was collected by an
external magnet and washed with distilled water and ethanol,
and dried in a vacuum oven. Aerward, copper(II) acetate
aqueous solution (5% wt) was added drop by drop to a dispersed
aqueous mixture of CTSN/Fe3O4, and the mixture were ultra-
sonicated into an US bath (with frequency: 50 kHz and power
density: 200 W Lꢀ1) for 1 h, at 80 ꢁC. Finally, the CTSN/Fe3O4–Cu
nanocomposite was magnetically separated and washed with
deionized water and ethanol and dried at room temperature
(Scheme 1).
2.2.4. Spectral data for selected products
1-Phenyl-1H-imidazole 3a. 1H NMR (DMSO-d6, 300 MHz),
d (ppm): 7.14 (s, 1H), 7.37 (t, 1H, J ¼ 7.2 Hz), 7.53 (t, 2H, J ¼ 7.4
Hz), 7.67–7.78 (m, 3H), 8.3 (s, 1H). 13C NMR (DMSO-d6, 75
MHz): d (ppm): 118.5, 121.5, 127.8, 130.1, 130.8, 135.7, 137.7.
1-p-Tolyl-1H-imidazole 3b. 1H NMR (CDCl3, 500 MHz),
3.2. Characterization of CTSN/Fe3O4–Cu nanocatalyst
Aer preparation of the nanocomposite, various conventional
instrumental techniques were used for the characterization of
the structure and morphology. The comparative FT-IR spectra
of the synthesized CTSN/Fe3O4–Cu nanocomposite and its
individual components are shown in Fig. 1. In the spectrum of
d (ppm): 7.79 (s, 1H), 7.22 (m, 5H), 7.17 (s, 1H), 2.37 (s, 3H). 13
C
NMR (CDCl3, 125 MHz): d (ppm): 137.7, 135.8, 135.4, 130.7,
130.4, 121.6, 118.6, 21.2.
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Table 1 Optimization of the reaction conditions of the synthesis of
phenyl imidazole as the pilot experiment under USW irradiation
Entry Solvent
Cat. (g) Temp. (ꢁC) Time (min) Yielda (%)
1
2
3
4
5
6
7
8
9
10
DMF
DCM
0.01
0.01
0.01
0.01
0.01
0.01
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
50
10
10
10
10
10
10
10
10
10
30
88
85
76
96
91
98b
98
97
97
98
Water
EtOH
MeOH
Water
Water/EtOH 0.05
Water/EtOH 0.01
Water/EtOH 0.01
Water/EtOH 0.01
80
r.t.
Fig.
3 XRD pattern of the fabricated CTSN/Fe3O4–Cu
a
nanocomposite.
Isolated yield for product 3a, via coupling reaction between
bromobenzene (1.0 mmol) and imidazole (2.0 mmol), CTAB (0.5
mmol), in the presence of K2CO3 (1.5 mmol), and the solvent (4.0
mL), in the USW bath (50 kHz, 200 W). b Optimum conditions.
CTSN, The absorption band at 3443 cmꢀ1 is related to the
vibrational stretching of the N–H and O–H groups. The
absorption band that is appeared at 2922 cmꢀ1 coming from the
stretching vibrations of aliphatic C–H groups, and the appeared
peak at 1155 cmꢀ1 origins from the stretching vibrations of
C–O–C bond. The absorption band at 1602 cmꢀ1 indicates the
presence of N–H of amide groups. The absorption bands
appeared at 1423 and 1384 cmꢀ1 refer to C–N vibrations. The
absorption bands at ca. 598 cmꢀ1 can be seen in the spectrum of
Fe3O4 NPs, corresponds to the stretching vibrations of Fe–O
band. The intensive broad absorption at 3425 cmꢀ1 represented
the stretching mode of H2O molecules and –OH groups. In the
spectrum of CTSN/Fe3O4–Cu nanocomposite, absorption band
at 3431 cmꢀ1 refers to the stretching vibrations of O–H and N–H
groups of chitosan that bonded to the copper ferrite nano
particles and shi to lower frequency. It also refers to O–H
groups of nanoparticles. The absorption band at ca. 1059 cmꢀ1
shows the stretch vibrations of C–O bond and the 598 cmꢀ1
band represented the Fe–O group of Fe3O4 NPs. Therefore, the
FT-IR analysis conrmed the supporting of Fe3O4 and Cu NPs
on the surface and matrix of chitosan. EDX analysis was also
performed for determination of the elements constitutes cata-
lyst.24 EDX spectra shows that there are C, Fe, Cu and O atoms in
the structure of the fabricated nanocomposite. The EDX spec-
trum of the fabricated CTSN/Fe3O4–Cu nanocomposite and also
the quantitative results have been exhibited in Fig. 2(c).
Field-emission scanning electron microscopy (FE-SEM)
images were used to investigate shape and size of the
prepared nanocomposite (Fig. 2). As seen in Fig. 2(a), suitable
distribution of the spherical Fe3O4 NPs on the chitosan
surfaces has formed a cluster-shaped nanocomposite. This
morphology provides more extreme active areas for catalytic
applications. Moreover, the size of the spherical Fe3O4 NPs is
in a range of 40–60 nm diameter. Most likely, these regular
cluster-shaped structures are produced via the in situ co-
deposition process (described in preparation section).
Then, the uniform spherical Cu NPs have been incorporated
into the CTSN polymeric network, as can be observed in
Fig. 2(b). Overall, this is clearly seen that an extreme catalytic
active area is provided by the nanosized CTSN/Fe3O4–Cu
nanocomposite.
The XRD pattern of the CTSN/Fe3O4–Cu nanocomposite has
been demonstrated in Fig. 3, and the average size of the parti-
cles is calculated by the Scherrer equation; D ¼ kl/b cos q.
According to the gure, the resulted diffraction pattern has
been precisely compared with the reference patterns of the
Fe3O4 and CuO NPs and it was strongly conrmed that they have
been thoroughly produced and distributed onto the textures of
Fig. 4 (a) TGA of the fabricated CTSN/Fe3O4–Cu nanocomposite, and (b) VSM analysis of (i) Fe3O4 NPs and (ii) CTSN/Fe3O4–Cu nanocomposite.
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Scheme 2 Schematic of the synthesis of aryl imidazole derivatives by CTSN/Fe3O4–Cu nanocatalyst, in US bath.
CTSN matrix. Accordingly, the peaks at the dispersion angles 2q are attributed to the formed Fe3O4 and CuO NPs. There are
¼ 19.11ꢁ, 31.64ꢁ, 33.91ꢁ, 36.56ꢁ, 38.42ꢁ, 45.15ꢁ, 58.65ꢁ, 63.25ꢁ, strong correlations between the obtained XRD pattern and the
64.25ꢁ and 78.65ꢁ, which have been marked with miller indices, reported references.13,25
Table 2 Synthesis of various aryl imidazole derivatives using CTSN/Fe3O4–Cu nanocatalyst
R–Ar–X
Entry
R
X
Product structure
Product no.
Yielda (%)
98
1
H
Br
3a
2
3
4
5
6
Me
Me
OMe
OH
Cl
Br
I
3b
3c
3d
3e
3f
92
90
85
82
93
I
Br
I
7
COMe
CN
Br
I
3g
3h
92
98
8
9
NO2
NO2
Br
I
3i
3j
96
97
10
a
Isolated yield.
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decomposition of the CTSN is started abꢁove 420 ꢁC.26 Further,
the second shoulder is observed at 620 C, which is ascribed
to the decomposition of the NPs. Totally, from the TGA, this
is well proven that the degradation and decomposition of
CTSN polysaccharide is greatly inhibited by the composited
Cu and Fe3O4 NPs. Magnetic property of the fabricated CTSN/
Fe3O4–Cu nanocomposite has also been investigated by
vibrating-sample magnetometer (VSM) analysis and related
spectra are shown in Fig. 4(b). As it can be seen in the spectra,
the magnetic feature of the neat Fe3O4 NPs is reduced
proportional to more core coating by various layers. Graph (i)
that belongs to the neat Fe3O4 NPs exhibits a typical super-
paramagnetic behavior (55 emu gꢀ1) through applying the
magnetic eld, as presented in the gure. This property was
ꢃ20 emu gꢀ1 decreased through subsequent coating by CTSN
(graph ii). However, this is clearly seen that super-
paramagnetic behavior of the produced CTSN/Fe3O4–Cu
nanocomposite is adequate for easily separation of the cata-
lyst from the reaction mixture.
Fig. 5 Reusability diagram of CTSN/Fe3O4–Cu nanocomposite.
Thermal resistance of the fabricated CTSN/Fe3O4–Cu
nanocomposite has also been studied by thermogravimetric
analysis (TGA). As shown in Fig. 4(a), initially a partial
increase in the weight was observed that is attributed to the
physical adsorption of the moisture of the air onto the hot
surfaces of NPs. Then, the weight percentage was decreased
to ca. 98% due to removal of the water molecules. In
continue, by increasing the temperature to around 420 ꢁC,
the rst important shoulder was appeared that coming from
the weight loss of CTSN. According to the literature,
3.3. Catalytic activity of CTSN/Fe3O4–Cu nanocatalyst
3.3.1. Optimization of the catalyzed-reaction conditions &
catalytic performance screening. In order to obtain the
optimum conditions for the synthesis reactions by novel
prepared heterogeneous CTSN/Fe3O4–Cu nanocatalyst,
control reaction was carried out using imidazole 1 (2.0
mmol),
bromobenzene
2
(1.0
mmol),
cetyl-
trimethylammonium bromide (CTAB, 0.5 mmol), and
Fig. 6 The plausible mechanism for N-arylation of imidazole derivatives assisted by CTSN/Fe3O4–Cu nanocomposite.
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different amounts of CTSN/Fe3O4–Cu in various conditions presented as an instrumental tool for facilitating the synthesis
(Scheme 2 and Table 1). Accordingly, the same reaction of N-arylimidazole derivatives. There are several advantages for
conditions were applied for all of the control reactions. applying this nanoscale system. The rst and foremost excel-
Different amounts of the magnetic nanocatalyst, different lence, well execution of synthesis reactions under mild condi-
reaction times, and the synergistic effect between the tions (98% yielded in 10 min at room temperature) through
magnetic nanocomposite and USW were precisely investi- using a partial amount (0.01 g) of this heterogeneous catalytic
gated. As reported in Table 1, the best result was observed system can be referred. This high catalytic performance is due
when 0.01 g of CTSN/Fe3O4–Cu was used in deionized water, to a synergistic catalytic effect between the fabricated nano-
under 10 min ultrasonication (50 kHz frequency and 200 W composite (CTSN/Fe3O4–Cu) and the ultrasound waves with 50
power density), at room temperature. The reaction progress kHz frequency and 200 W Lꢀ1 power density. In addition, the
was screened using thin-layer chromatography (TLC). Aer nanocatalyst is conveniently separated from the reaction
completion of the reaction, the heterogeneous nanocatalyst mixture and recovered by an external magnetic eld and reused
were conveniently collected using an external magnet, then efficiently for additional seven times without signicant
resulted aryl imidazole was immediately separated and decrease in its catalytic activity. Moreover, there are several
puried via ash column chromatography and identied advantages for the presented catalytic system such as high
1
with H-NMR and 13C-NMR (see the ESI section†). However, heterogeneity, great biocompatibility and biodegradability
in order to evaluate the scope and generality of this approach, (through applying CTSN as a natural basis), economic advan-
the optimized reaction condition was applied for the tages, excellent structural stability due to assisting by ultra-
synthesis reactions of the diverse aryl imidazole derivatives, sound waves, and no need to another chemical additive or
as summarized in Table 2. The N-arylation of imidazoles with applying intense reaction conditions to provide the required
aryl iodides and aryl bromides bearing both electron- driving force. Thus, this catalytic system could be suggested for
donating and electron-withdrawing groups was done effec- scaling up and using in industry.
tively and gave good yields. As same as excellent results were
obtained in gram scale of the reaction by starting these ratio
of raw materials and reagents.
Conflicts of interest
3.3.2. Catalyst reusability. Another important advantage of
this active, non-toxic, and environmentally-benign heterogeneous
There are no conicts to declare.
catalyst is its well recyclability. In this regard, the nanocatalyst
performance was carefully monitored in the model reaction Acknowledgements
(product 3a) aer eight times recycling. For this purpose, aer
The authors gratefully acknowledge the partial support from the
Research Council of the Iran University of Science and Tech-
nology and Iran National Science Foundation (INSF).
completion of the reaction, the CTSN/Fe3O4–Cu nanocomposite
were magnetically isolated from the mixture and washed with
ethanol, then dried and reused in subsequent reactions. It is
observed that the nanocatalyst can be reused at least for eight
successive times without any signicant reduction in coupling
reaction yield (Fig. 5). The observed reduction in catalytic activity
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A plausible mechanism for this catalytic reaction has been
depicted in Fig. 6. As can be seen, at the rst stage, an oxidative
addition is occurred through which Cu inserts into the Ar–X
bond. Then, the resulted complex reacts with imidazole that
was activated by potassium carbonate, at stage 2. In the
following step (stage 3), a reductive elimination is occurred and
the desirable product is obtained.27
4. Conclusion
In summary, a novel catalytic system constructed of chitosan,
iron oxide NPs, and copper NPs has been designed and
5 A. Maleki, H. Movahed, P. Ravaghi and T. Kari, Facile in situ
synthesis and characterization of a novel PANI/Fe3O4/Ag
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40356 | RSC Adv., 2019, 9, 40348–40356
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