Facile synthesis of imidazoles by an efficient and eco-friendly heterogeneous catalytic system constructed of Fe3O4 and Cu2O nanoparticles, and guarana as a natural basis

Article abstract of DOI:10.1016/j.inoche.2021.108465

In this study, an efficient hybrid nanocatalyst made of guar gum (guarana, as a natural basis), magnetic iron oxide nanoparticles, and copper(I) oxide nanoparticles (Cu₂O NPs) is fabricated and suitably applied for catalyzing the multicomponent (three- and four-component) synthesis reactions of imidazole derivatives. Here, an easy preparation strategy for this novel catalytic system (Cu₂O/Fe₃O₄@guarana) is presented. Then, the application of this catalytic system for the synthesis of imidazole derivatives is precisely investigated. For this purpose, ultrasonication is introduced as an efficient and fast method. In summary, the high catalytic efficiency of Cu₂O/Fe₃O₄@guarana nanocomposite is well demonstrated by high reaction yields obtained in the presence of a small amount of this nanocomposite, under mild conditions. Wide active surface area, substantial magnetic behavior, excellent heterogeneity, suitable stability, well reusability, and etc. have distinguished this catalytic system as an instrumental tool for facilitating the complex synthetic reactions.

Full text of DOI:10.1016/j.inoche.2021.108465

Inorganic Chemistry Communications 125 (2021) 108465
Contents lists available at ScienceDirect
Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Short communication
Facile synthesis of imidazoles by an efficient and eco-friendly
heterogeneous catalytic system constructed of Fe O and Cu O
3
4
2
nanoparticles, and guarana as a natural basis
1
*
Zahra Varzi, Mir Saeed Esmaeili , Reza Taheri-Ledari, Ali Maleki
Catalysts and Organic Synthesis Research Laboratory, Department of Chemistry, Iran University of Science and Technology, Tehran 16846-13114, Iran
A R T I C L E I N F O
A B S T R A C T
Keywords:
In this study, an efficient hybrid nanocatalyst made of guar gum (guarana, as a natural basis), magnetic iron
Copper nanoparticles
Guarana
oxide nanoparticles, and copper(I) oxide nanoparticles (Cu
lyzing the multicomponent (three- and four-component) synthesis reactions of imidazole derivatives. Here, an
easy preparation strategy for this novel catalytic system (Cu O/Fe @guarana) is presented. Then, the appli-
cation of this catalytic system for the synthesis of imidazole derivatives is precisely investigated. For this purpose,
ultrasonication is introduced as an efficient and fast method. In summary, the high catalytic efficiency of Cu O/
Fe @guarana nanocomposite is well demonstrated by high reaction yields obtained in the presence of a small
2
O NPs) is fabricated and suitably applied for cata-
Organometallic nanocomposite
Heterogeneous nanocatalyst
Biopolymer texture
Imidazole reaction
2
3 4
O
2
3 4
O
amount of this nanocomposite, under mild conditions. Wide active surface area, substantial magnetic behavior,
excellent heterogeneity, suitable stability, well reusability, and etc. have distinguished this catalytic system as an
instrumental tool for facilitating the complex synthetic reactions.
1
. Introduction
In two recent decades, attentions to heterogeneous nanoscale sys-
separation processes like antisolvent, column chromatography, recrys-
tallization and etc. are practically removed from the procedures [15,16].
Providing wide surface active areas (through nano scaling), shortening
the reaction times (through high performances), and high biocompati-
bility and biodegradability (through involving the natural resources for
designing a catalytic system), could also be referred as additional ad-
vantages for this newly emerged generation of the catalytic systems
[17,18]. Recently, magnetic property has also been added to the het-
erogeneous catalytic systems through the composition of the magnetic
tems have been amazingly increased due to their substantial effective-
ness on various types of the scientific studies. For instance, in medicine,
they are extremely used for targeted drug delivery, in which the desired
medication is delivered to the target tissue with high selectivity [1–3]. In
the field of the natural energies, they have been widely applied for
fabrication of the novel devices (like solar cells) with higher efficiencies.
For this purpose, the internal layers of a device is manipulated via re-
composition of the heterogeneous nanoscale materials [4]. In fact,
nano scaling affects the band gap of the ingredients that are involved in
an electronic device [5,6]. Moreover, the nanoscale heterogeneous
materials have been used for catalytic aims. So far, numerous nano-
catalysts with high performances as great alternatives for traditional
homogeneous catalytic systems have been designed and introduced to
the science world [7–14]. In other words, the ancient generation of the
catalytic systems (organocatalyst) is being replaced by next generation
3 4
ingredients like iron oxide nanoparticles (Fe O NPs), which creates
more convenience in the separation processes. In this regard, several
magnetic catalytic systems have been designed and suitably applied for
various catalytic applications [19–22]. Furthermore, the catalytic ac-
tivity of these heterogeneous particles could be enhanced through
simultaneously applying other energy resources like ultrasound waves
[23,24]. Thus, in this study, we try to design an efficient heterogeneous
3 4
system, in which Fe O NPs are well composed with other components
to make a magnetic catalytic system.
(
heterogeneous nanocatalyst), which includes several excellences. The
For immobilization of the NPs in the composited form, polymeric and
fibrous matrices are usually used [25]. In this case, polymeric textures
with natural resources are typically preferred due to their
first and foremost advantage is heterogeneity that leads to convenient
separation and purification processes. In fact, complex conventional
*
Corresponding author.
E-mail address: maleki@iust.ac.ir (A. Maleki).
Co-first author.
1
https://doi.org/10.1016/j.inoche.2021.108465
Received 22 November 2020; Received in revised form 9 January 2021; Accepted 9 January 2021
Available online 15 January 2021
1
387-7003/© 2021 Elsevier B.V. All rights reserved.

Z. Varzi et al.
Inorganic Chemistry Communications 125 (2021) 108465
Fig. 1. The chemical structure of the guarana natural polymeric strand.
biocompatibility and biodegradability, and also nontoxicity that well
meet the principles of the green chemistry [26]. As well, the polymer’s
textures could be chemically functionalized through the existence of the
functional groups (like hydroxyl) [27]. In this regard, we chose “Gua-
rana” (also called guar gum) that is considered as an appropriate addi-
tive in many processed foods [28]. From chemical aspect, there are
several hydroxyl groups in the guarana’s structure that provide a suit-
able substrate for the composition of the other essential components
(
Fig. 1). From biological aspect, guarana is extracted from a plant
resource and not only produces no toxic substances, but also adds high
biocompatibility to our catalytic system.
However, in this work, we have made an effort to suitably employ
guarana (as a natural substrate) for immobilization of the Fe
copper(I) oxide (Cu O) NPs. For this purpose, a convenient in situ pro-
cess has been applied, through which guarana textures are well
magnetized with the composed Fe NPs. Then, Cu O NPs are formed
and well immobilized between the textures of guarana. In fact, Cu O NPs
are the main active catalytic sites of our designed system (Cu O/
Fe @guarana), which provide constructive electronic interactions
3 4
O NPs and
2
3
O
4
2
2
2
3 4
O
between the involved components in three- and four-component syn-
thesis reactions of imidazole derivatives. Herein, precise optimization
2 3 4
Fig. 2. Preparation route of Cu O/Fe O @guarana nanocomposite.
Fig. 3. (a) FT-IR spectra of the neat guarana (I), Fe
3
O
4
@guarana nanocomposite (II), and Cu
2
O/Fe
3 4
O @guarana nanocomposite (III), and (b) EDX spectra and the
elemental quantitative ratios tables of Fe
3
O
4
2 3 4
@guarana nanocomposite (I), and Cu O/Fe O @guarana nanocomposite (II).
2

Z. Varzi et al.
Inorganic Chemistry Communications 125 (2021) 108465
Fig. 4. (a) TGA curves of the neat guarana (I), Fe
3
O
4
@guarana nanocomposite (II), and Cu
2
O/Fe
3
O
4
@guarana nanocomposite (III), and VSM Mꢀ H curves of
3 4 2 3 4
Fe O @guarana nanocomposite (I), and Cu O/Fe O @guarana nanocomposite (II) (recorded at room temperature).
and comparisons have been made to highlight the performance of the
fabricated Cu O/Fe @guarana. In this study, ultrasonication is
introduced as the best applicable conditions for the synthesis of imid-
an in situ co-deposition process. For this purpose, the chloride salts of
iron(II) and iron(III) have been used in basic conditions (pH ~ 12),
provided by ammonia solution [29,30]. Then, the reaction medium is
neutralized by HCl (0.1 M) and the chloride salt of copper(II) in the
presence of ascorbic acid [31]. After completion of the preparation re-
action, the fabricated final product has been conveniently separated (by
using an external magnet at the bottom of the flask), and well washed to
remove the excess ions.
2
3 4
O
2 3 4
azoles in the presence of Cu O/Fe O @guarana heterogeneous catalytic
system.
2
. Results and discussion
2
.1. Preparation of the Cu O/Fe O @guarana nanocomposite
2
3 4
2
2 3 4
.2. Characterization of the Cu O/Fe O @guarana nanocomposite
The schematic of the preparation route of Cu
nanocomposite is presented in Fig. 2. As a fast and concise review, it is
observed that guarana textures are well magnetized with Fe NPs via
2 3 4
O/Fe O @guarana
As the first identification method, Fourier-transform infrared (FT-IR)
spectroscopy was used (Fig. 3a). As can be seen in the spectra, the peak
3 4
O
2 3 4
Fig. 5. XRD pattern of the fabricated Cu O/Fe O @guarana nanocomposite.
3

Z. Varzi et al.
Inorganic Chemistry Communications 125 (2021) 108465
Fig. 6. (a,b) FESEM images, and (c) TEM image of the fabricated Cu
2
O/Fe
3
O
4
@guarana nanocomposite and size distribution diagram of metal oxide NPs.
intensity of the O
been appeared at ~3400 cm , was decreased through the composition
with Fe and Cu O NPs. Also, the peaks related to Fe O and Cu
–
H groups (in the guarana’s structure), which has
vibrating-sample magnetometer (VSM) analysis (Fig. 4b). The S-shape
curves prove super-paramagnetic behavior of the samples. As it can be
ꢀ 1
3
O
4
2
–
–
O
seen in the Mꢀ H curves I and II, the magnetic feature of Fe
3
O
4
@guarana
O NPs.
ꢀ 1
bands have been appeared at ~600 cm that prove the formation of the
metal oxide NPs [31]. The existence of the essential elements in the
samples was also proven by energy-dispersive X-ray (EDX) spectroscopy
is a bit reduced (~5 emu/g) through the addition of the Cu
2
However, from the VSM curves (recorded at room temperature) this is
well revealed that the fabricated catalytic system is quickly isolated
from the mixture through applying a magnetic field.
[
32]. As demonstrated in Fig. 3(b), 13.0 and 8.8% of the total weight in
the fabricated Cu O/Fe @guarana nanocomposite belong to iron and
2
3
O
4
2 3 4
The XRD pattern of the fabricated Cu O/Fe O @guarana nano-
copper elements, respectively. In the EDX spectra, high similarity is
composite is shown in Fig. 5. As can be observed, the obtained diffrac-
tion pattern has been compared with the original patterns of the neat
observed, only copper’s peak has been added in the spectrum (II), which
is related to the fabricated Cu
2
O/Fe
3
O
4
@guarana nanocomposite.
Fe
3 4 2
O , Cu O NPs, and guarana. It was clearly verified that the NPs have
Thermal resistance of the neat guarana (curve I), Fe
curve II), and the fabricated Cu O/Fe @guarana nanocomposite
curve III) has been studied by thermogravimetric analysis (TGA). As
3 4
O @guarana
been well prepared and composited with guarana matrix. Accordingly,
◦
◦
◦
◦
(
(
2
3
O
4
the peaks appeared at the angles 2θ = 18.51 , 31.64 , 33.91 , 36.56 ,
◦
◦
◦
◦
◦
◦
43.15 , 46.96 , 58.65 , 63.25 , 68.25 and 74.85 are attributed to the
formed Fe and Cu O NPs [29,31]. Also, the broad beak initiated from
demonstrated in Fig. 4(a), the first shoulder is observed when guarana is
3
O
4
2
◦
2θ = 22◦ and ended by ca. 48 and a peak appeared at ca. 72 are
◦
◦
dehydrated proportional to the increase in temperature until ca. 150 C.
Almost 7% of the weight has been lost at this stage. Then, the second
shoulder, in which ~50% of the weight has been lost, is observed in a
thermal range of 150–410 ◦C. At this stage, all the hydroxyl groups of
guarana are removed as water molecules. As can be seen, the main
decomposition is started after this stage. Considering the thermal
attributed to guarana matrix [33].
3 4 2
Morphology and particle size of the produced Fe O and Cu O NPs
were studied by field-emission scanning electron microscopy (FESEM)
and transmission-electron microscopic (TEM) imaging methods (Fig. 6).
3 4 2
As illustrated in image (a), the spherical-shaped Fe O and Cu O NPs
resistance behaviors of the Fe
3
O
4
@guarana and Cu
2
O/Fe
3
O
4
@guarana,
have been nicely distributed onto the guarana surfaces and formed a
cluster-shaped nanocomposite. Moreover, the average size of the
spherical NPs is obtained ~40 nm diameter that confirms the obtained
results from XRD analysis (image b). TEM was used for better discern of
this is clearly indicated that the thermal stability of guarana is enhanced
through composition with the heterogeneous NPs. As can be seen in the
TGA curves II and III, both main shoulders have shifted to higher tem-
peratures. Magnetic property of the fabricated Fe
3
O
4
@guarana and
Fe
3 4 2
O and Cu O NPs (image c). As expected, some particles are rela-
Cu O/Fe @guarana nanocomposite has also been studied by
2
3 4
O
tively darker than the others in TEM image that are attributed to the
4

Z. Varzi et al.
Inorganic Chemistry Communications 125 (2021) 108465
Cu
2
O NPs due to more electron density of copper.
Table 1
Optimization of the reaction condition for the synthesis of 2-(4-chlorophenyl)-
,5-diphenyl-1H-imidazole.
4
3
. Experimental section
a
Entry
Cat. system
Cat.
Solvent
Temp.
Time
Yield
(%)
◦
3
.1. Materials and equipment
weight
( C)
(min)
(
g)
All the used materials and equipment in this work have been listed in
1
2
3
4
Fe
Guarana
Fe @guarana
Cu O/
3
O
4
0.01
0.01
0.01
0.005
EtOH
EtOH
EtOH
EtOH
25
25
25
25
20
20
20
20
35
53
74
83
Table S1 (in the SI section).
3 4
O
2
3
3
.2. Methods
Fe
3
O
4
@guarana
b
5
6
7
8
9
Cu
2
O/
0.01
EtOH
EtOH
THF
25
25
25
25
25
50
70
20
20
20
20
20
20
20
97*
97
92
95
88
97
97
.2.1. Preparation of Cu
2
O/Fe
3
O
4
@guarana nanocomposite
Fe
O
3 4
@guarana
Cu
2
O/
0.02
0.01
0.01
0.01
0.01
0.01
In a three-necked round-bottom flask (100 mL), 3.0 g of guarana was
Fe
O
3 4
@guarana
placed and well dissolved in deionized water (25 mL) via ultra-
Cu
2
O/
◦
sonication, at 50 C. After resulting a relative homogen mixture,
Fe O @guarana
3
4
FeCl
2
⋅4H
2
O (0.3 g, 1.5 mmol) and FeCl
3
⋅6H
2
O (0.5 g, 1.84 mmol) were
Cu
Fe
Cu
2
O/
DMF
Water
EtOH
EtOH
O
3 4
@guarana
O/
@guarana
O/
added to the flask and the content were vigorously stirred for 60 min, at
the same temperature. After 60 min stirring, an orange opaque solution
is obtained. Afterward, the atmosphere of the flask was neutralized by
2
3 4
Fe O
1
0
Cu
2
N
2
gas and a solution of ammonia (10 mL, 1 M) was added drop by drop,
Fe O @guarana
3
4
◦
during the stirring. The temperature was maintained at 50 C during the
addition of the ammonia. After completion of addition, the mixture were
stirred for additional 2 h, at room temperature. Next, the reaction
11
Cu
Fe
2
O/
O
3 4
@guarana
a
Isolated yield.
b
environment was neutralized by HCl (0.1 M) and CuCl
.92 mmol) was added into the flask. During the stirring at room tem-
perature, ascorbic acid (1.13 mmol) was added. After 1 h stirring, the
2
⋅2H
2
O (0.5 g,
Based on the EDX data, 1.4 mol% of Cu is used in the catalyzed reactions (see
2
the SI file, page S13).
*
Optimum conditions. All reactions were carried out in an ultrasound cleaner
ꢀ 1
ꢀ 1
bath (50 KHz, 150 W L ). 4-Chlorobenzaldehyde (1.0 mmol), benzyl (1.0
mmol), and ammonium acetate (2.0 mmol) were used in 3.0 mL of solvent.
content was ultrasonicated in a cleaner bath (50 KHz, 150 W L ) for 10
min, and the resulting product (Cu O/Fe @guarana) was magneti-
2
3 4
O
cally separated (by holding a magnet at the bottom of the flask) and
washed for several times with deionized water and finally dried.
1
1
2
2
27.2, 127.0, 126.5, 48.7; HNMR (300 MHz, CDCl
3
): δ (ppm) = 7.80 (d,
H), 7.42–7.40 (m, 3H), 7.29–7.30 (m, 2H), 7.20–7.13 (m, 6H), 6.76 (d,
H), 5.20 (s, 2H).
3
.2.2. General procedure for catalyzed synthesis of 2,4,5-triaryl-1H-
imidazoles
An integration of substituted 4-chlorobenzaldehyde (0.14 g, 1
mmol), ammonium acetate (0.3 g, 4 mmol), benzyl (0.21 g, 1 mmol) and
Cu O/Fe @guarana nanocatalyst (0.01 g) was ultrasonicated in a
1
-Benzyl-2-(3-methoxyphenyl)-4,5-diphenyl-1H-imidazole 21. MP:
29–130 ◦C; CNMR (75 MHz, CDCl
): δ (ppm) = 160, 147.8, 138.3,
13
1
1
3
37.8, 135.4, 132.9, 131.7, 131.4, 131.2, 130.5, 129.8, 129.7, 129.4,
28.9, 128.0, 127.1, 127.0, 126.5, 121.7, 115.6, 114.6, 55.9, 48.6, 41.1.
1
1
2
3 4
O
ꢀ 1
HNMR (300 MHz, CDCl ): δ (ppm) = 7.48–7.46 (m, 2H), 7.41–7.40 (m,
cleaner bath (50 KHz, 150 W L ) in ethanol (3.0 mL) for 20 min. The
reaction progress was monitored by thin layer chromatography (TLC)
and after completion of the reaction, the catalyst was magnetically
separated and washed with deionized water and dried. Flash-column
chromatography was applied for purification of the desired products.
3
3
H), 7.32–7.30 (m, 3H), 7.21–7.20 (m, 5H), 7.19–7.15 (m, 3H),
.15–6.81 (m, 1H), 6.80 (d, 2H), 5.16 (d, 2H), 3.70 (s, 3H).
7
2 3 4
3.3. Application of the Cu O/Fe O @guarana nanocomposite for
catalyzing three- and four-component synthesis reactions of imidazole
derivatives
3
.2.3. General procedure for catalyzed synthesis of 1,2,4,5-tetraryl-1H-
imidazoles
An integration of benzyl (1 mmol), 4-chlorobenzaldehyde (1 mmol),
benzyl amine (1 mmol) ammonium acetate (4 mmol), and Cu O/
Fe @guarana nanocatalyst (0.01 g) was ultrasonicated in a cleaner
3.3.1. Optimization of the catalytic conditions for synthesis of the three
component imidazole
2
3
O
4
In order to determine the best reaction conditions (solvent, tem-
ꢀ 1
bath (50 KHz, 150 W L ) in ethanol (3.0 mL) for 20 min. The reaction
progress was monitored by thin layer chromatography (TLC) (elusion
solvent: ethyl acetate/n-hexane 1:3). After completion of the reaction,
the catalyst was magnetically separated and washed with deionized
water and dried. Anti-solvent technique and in many cases flash-column
chromatography was applied for purification of the desired products.
2 3 4
perature, and catalytic ratio of Cu O/Fe O @guarana), a model reaction
was carried out using 4-chlorobenzaldehyde (1.0 mmol), benzyl (1.0
mmol), and ammonium acetate (2.0 mmol) in various solvents and
different temperatures. Also, different amounts of the catalytic system
were applied. A comparison was made between the performances of the
2 3 4
Cu O/Fe O @guarana nanocomposite and the individual components
as well. Table 1 summarize the obtained results from the optimization
section.
3
.2.4. Spectral data for selected compounds
-(4-Hydroxyphenyl)-4,5-diphenyl-1H-imidazole 6. MP: 257–259 ◦C;
C NMR (75 MHz, CDCl (ppm); 170.5, 154.4, 135.0, 133.0, 132.0,
): δ
29.9, 129.8, 129.1, 128.8, 128.7, 128.6, 128.5, 128.2, 127.6, 126.5,
2
1
3
3
C
3.3.2. Synthesis of the various derivatives of three component imidazole,
under optimum catalytic conditions
1
1
1
1
25.1; H NMR (300 MHz, CDCl
4H), 4.44 (s, 1H).
3
): δ
H
(ppm); 9.72 (s, 1H), 8.00–7.25 (m,
After optimization of the reaction conditions, various derivatives of
three component imidazole were constructed by using various de-
2
,4,5-Triphenyl-1H-imidazole 11. Mp: 275–277 ◦C; 1H NMR (300
2 3 4
rivatives of benzaldehyde, in the presence of Cu O/Fe O @guarana
MHz, DMSO‑d
6
): δ
.00–7.30 (m, 13H).
-Benzyl-2-(4-cholorophenyl)-4,5-diphenyl-1H-imidazole 18. MP:
H
(ppm); 11.27 (s, 1H,), 8.10 (d, 2H), 8.11 (d, 2H),
nanocomposite. Thin-layer chromatography (TLC) was used to monitor
the reaction progress. After completion of the reactions, the magnetic
heterogeneous nanocatalyst were removed through holding an external
magnet at the bottom of the reaction flask. The, flash-column chroma-
tography was applied for further purification of the resulted products.
8
1
◦
13
1
60–163 C; C NMR (75 MHz, CDCl
3
): δ (ppm) = 146.8, 138.0, 135.3,
1
34.5, 131.7, 131.5, 131.3, 131.0, 130.5, 129.8, 129.5, 129.0, 128.1,
5

Z. Varzi et al.
Inorganic Chemistry Communications 125 (2021) 108465
Table 2
2 3 4
Synthesis of various derivatives of 2,4,5-triaryl-1H-imidazoles in the presence of Cu O/Fe O @guarana nanocomposite.
a
◦
Entry
1
Product structure
Product No.
Yield (%)
MP ( C)
Lit. ref.
[34]
Found
Lit.
1
89
264–266
265–266
2
2
86
230–231
230–231
[35]
3
4
5
6
3
4
5
6
85
87
81
83
199–201
259–260
298–299
257–259
200–201
258–260
296–299
257–258
[36]
[37]
[38]
[36]
7
8
9
7
87
75
88
97
197–199
229–231
229–231
258–260
196–198
230–231
230–231
259–262
[39]
[34]
[35]
[40]
8
9
1
0
10
(
continued on next page)
6

Z. Varzi et al.
Inorganic Chemistry Communications 125 (2021) 108465
Table 2 (continued)
a
◦
Entry
Product structure
Product No.
Yield (%)
MP ( C)
Lit. ref.
Found
Lit.
1
1
11
85
275–277
273–275
[37]
1
2
12
80
210–211
210–212
[41]
1
3
13
84
266
264–265
[34]
a
Isolated Yield.
3
.3.3. Optimization of the catalytic conditions for the synthesis of the four
Table 3
component imidazole
Optimization of the reaction condition for the synthesis of 1-benzyl-2-(4-chlor-
In order to extend the catalytic scope of the magnetic nanocatalyst,
synthesis of the four component imidazole derivatives, with different
parameters including temperature, solvent and amount of nanocatalyst
was evaluated to determine the optimized reaction condition (Table 3,
entries 1–11). For this purpose, a reaction mixture consists of benzyl (1
mmol), 4-chlorobenzaldehyde (1 mmol), benzyl amine (1 mmol)
ammonium acetate (4 mmol) was considered as a model reaction. As
shown in Table 3, entry 4–6 various amounts of catalyst loading are
investigated and the 0.02 g was the highest yield percentage of the
product. Also, increasing temperature was effectless to the yield of the
ophenyl)-4,5-diphenyl-1H-imidazole.
a
Entry
Cat. system
Cat.
Solvent
Temp.
Time
Yield
(%)
◦
weight
( C)
(min)
(
g)
1
2
3
4
Fe
Guarana
Fe @guarana
Cu O/
3
O
4
0.02
0.02
0.02
0.01
EtOH
EtOH
EtOH
EtOH
25
25
25
25
20
20
20
20
28
39
70
83
3 4
O
2
Fe
3
O
4
@guarana
5
6
7
8
9
Cu
2
O/
0.02
0.03
0.02
0.02
0.02
0.02
0.02
EtOH
EtOH
THF
25
25
25
25
25
50
70
20
20
20
20
20
20
20
95*
95
90
93
88
95
95
Fe
3
O
4
@guarana
◦
reaction and the 25 C was the best chosen (Table 3, entries 10 and 11).
Cu
2
O/
Fe
3
O
4
@guarana
Furthermore, it was found that ethanol solvent is the best solvent in
Cu
2
O/
yield percentage of the product (Table 3, entries 7–9).
Fe
3
O
4
@guarana
Cu
2
O/
DMF
Water
EtOH
EtOH
3
.3.4. Synthesis of the various derivatives of 1,2,4,5-tetraryl-1H-imidazoles
Fe
3
O
4
@guarana
under optimum catalytic conditions
Cu
2
O/
Fe
3
O
4
@guarana
Having the optimized conditions, with purpose study performance of
1
1
0
1
Cu
2
O/
2 3 4
the Cu O/Fe O @guarana nanocomposite in the 1,2,4,5-tetraryl-1H-
Fe
3
O
4
@guarana
imidazoles reactions various derivatives as electron withdrawing and
electron releasing was investigated. As be seen in Table 4, electron-
withdrawing derivatives better than electron releasing derivatives con-
verted to the desired product.
2
Cu O/
3 4
Fe O @guarana
a
*
Isolated yield.
Optimum conditions. All reactions were carried out in an ultrasound cleaner
ꢀ 1
bath (50 KHz, 150 W L ). 4-Chlorobenzaldehyde (1.0 mmol), benzyl amine (1
mmol), benzyl (1.0 mmol), and ammonium acetate (2.0 mmol) were used in 3.0
mL of solvent.
3
2 3 4
.3.5. Comparison of the catalytic performance of Cu O/Fe O @guarana
nanocomposite in the 2,4,5-triaryl-1H-imidazoles and 1,2,4,5-tetraryl-1H-
imidazoles reactions with previously reported systems
A brief survey on recently reported catalytic systems, which have
been applied for the synthesis of the imidazole derivatives, was also
Melting points of the obtained products were precisely compared with
the literature. Some of them were also selected for more identification
2 3 4
done to highlight the efficiency of the fabricated Cu O/Fe O @guarana
1
13
by HNMR and CNMR spectroscopy. However, Table 2 marks the
synthesized imidazole products under optimal catalytic conditions, with
more details.
catalytic system. As seen in Table 5, higher reaction yield was obtained
in shorter reaction time, for 2-(4-chlorophenyl)-4,5-diphenyl-1H-
7

Z. Varzi et al.
Inorganic Chemistry Communications 125 (2021) 108465
Table 4
2 3 4
Synthesis of various derivatives of 1,2,4,5-tetraryl-1H-imidazoles in the presence of Cu O/Fe O @guarana nanocomposite.
a
◦
Entry
1
Product structure
Product No.
Yield (%)
MP ( C)
Lit. ref.
[42]
Found
Lit.
14
71
151–152
152–155
2
3
4
5
6
7
8
15
16
17
18
19
20
21
81
89
87
95
88
82
86
163–165
173–175
163–164
160–163
144–148
134–137
129–130
165
[43]
[44]
[36]
[42]
[45]
[36]
175–178
163–165
162–165
146–148
135–137
129–131
[36]
(
continued on next page)
8

Z. Varzi et al.
Inorganic Chemistry Communications 125 (2021) 108465
Table 4 (continued)
a
◦
Entry
Product structure
Product No.
Yield (%)
MP ( C)
Lit. ref.
Found
Lit.
9
22
83
138–141
140–142
[45]
a
Isolated Yield.
Table 5
Comparison of the different catalytic systems applied for the synthesis of 2-(4-chlorophenyl)-4,5-diphenyl-1H-imidazole (10) and 1-benzyl-2-(4-chlorophenyl)-4,5-
diphenyl-1H-imidazole (18).
Entry
Cat. System
Conditions
Time (min)
Yield (%)
Ref.
Three component Four component
◦
1
2
3
4
5
6
7
8
9
Yb(OPf)
3
–
Perflurodecalin/80
C
360
95
83
75
90
75
78
69
94
80
97
[46]
[47]
[48]
[49]
[50]
[51]
[52]
[53]
–
Montmorilonite K10
–
EtOH/reflux
a
◦
SBSSA
–
Solvent free/130
C
30
b
DBSA
–
H
2
O/reflux
240
300
180
120
420
20
◦
–
–
–
–
4-(1-Imidazolium) butane sulfonate
Acetic acid
Solvent free/80
EtOH/reflux
C
◦
[bmim]
OAc-HPro@Fe
Cu O/Fe
3
[GdCl
6
]
Solvent free/120
C
◦
3
O
4
EtOH/60
C
Cu
2
O/Fe
3
4
O @guarana
2
3
4
O @guarana
EtOH/ultrasonic/r.t.
a
Silica-bonded S-Sulfonic Acid.
Dodecylbenzenesulfonic acid.
b
imidazole 10 and 1-benzyl-2-(4-chlorophenyl)-4,5-diphenyl-1H-imid-
azole 18, through using our catalytic system. In addition, it is clear that a
milder reaction conditions was applied in this work.
Fe
3 4
O @guarana nanocomposite. The TGA estimations related to the
fresh and recovered catalyst have been given in the SI file, on page S12.
4
. Conclusions
3
.3.6. Suggested mechanism
From mechanistic aspect, initially, the present Cu atoms in the
Following the extensive research on the novel heterogeneous cata-
structure of the catalyst activate the carbonyl group of aldehyde. Then,
this activated form is converted to a diamine by ammonium acetate
lytic systems, we intended to prepare a nature-based hybrid nano-
composite with high magnetic property in nano scale and apply it in the
organic synthesis reactions. In this regard, we chose “guarana” as a
natural polymeric basis, which includes excellent biocompatibility.
(
stage 1 and 2). The benzyl groups is also activated by copper through
the electronic interaction (stage 3) and reacts with the formed diamine,
and a water molecule is removed (stage 4). During stage 5 the product is
obtained and the catalytic system is separated and recycled [54,55]. A
schematic of this plausible mechanism is illustrated in Fig. 7.
3 4 2
Fe O and Cu O NPs have been further well immobilized into this nat-
ural matrix to add well magnetic behavior and promising catalytic ef-
ficiency to this catalytic system, respectively. Afterward, the application
of this catalyst was precisely investigated in multicomponent (three- and
four-component) synthesis reactions of imidazole derivatives. Concisely,
it has been well shown that pure products with high reaction yields (97%
and 95%) are obtained in a short reaction time (20 min) through
applying this catalytic system under ultrasound wave irradiation with a
specific frequency and power density. In summary, all of the distin-
3
.3.7. Catalyst reusability
2 3 4
The catalytic efficiency of the fabricated Cu O/Fe O @guarana
nanocomposite was monitored in the model reaction after six times
recycling. For this aim, after run 1, the Cu O/Fe @guarana NPs were
2
3 4
O
isolated from the reaction mixture and washed with ethanol for several
times and reused for further running the process. In Fig. 8 it is observed
that the nanocatalyst could be re-applied for additional five times
without any considerable reduction in the catalytic performance. The
FT-IR spectrum of the recovered nanocatalyst after six times usages has
been shown in supporting information section (Fig. S9). From the TGA
curve of the recovered catalyst (Fig. S10, in the SI file), it has been
revealed that only 0.0092 mmol/g of guarana is lost after six times
2 3 4
guished properties of our novel designed product (Cu O/Fe O @guar-
ana nanocomposite) such as high heterogeneity, excellent magnetic
behavior, nano scale and cluster-shaped morphology, great thermal
stability, well composition, and etc. have been studied by various
analytical methods. Moreover, noticeable recyclability of this catalyst
has been studied in this report. As well the characterization of the
1
13
imidazole products have been done by HNMR and
CNMR
recycling, which confirms high stability of the prepared Cu
2
O/
spectroscopy.
9

Z. Varzi et al.
Inorganic Chemistry Communications 125 (2021) 108465
2 3 4
Fig. 7. The plausible mechanism for the synthesis of imidazole derivatives assisted by Cu O/Fe O @guarana nanocomposite.
Acknowledgements
The authors gratefully acknowledge the partial support from the
Research Council of the Iran University of Science and Technology.
Appendix A. Supplementary material
The SI file includes the NMR (H and C) of selected imidazole products
and also FT-IR results of the recovered nanocatalyst. The brand and
purity of used materials are also listed in this section. This section can be
found in the online version Supplementary data to this article can be
found online at https://doi.org/10.1016/j.inoche.2021.108465.
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