Preparation and characterization of copper chloride supported on citric acid-modified magnetite nanoparticles (Cu2+-CA@Fe3O4) and evaluation of its catalytic activity in the reduction of nitroarene compounds

Article abstract of DOI:10.1002/aoc.3822

A new, powerful and recyclable copper catalyst were prepared by heterogenization of copper chloride using of Fe₃O₄ nano particles modified with citric acid as a linker. This system can catalyze reduction of nitroaren compound to aniline derivatives in the presence of Sodium borohydride as a reduction agent in moderate to good yields. In addition, easy separation and recoverable with an external permanent magnet is the dominant properties of this catalyst (Cu²⁺-CA@Fe₃O₄).

Full text of DOI:10.1002/aoc.3822

Received: 10 October 2016
DOI: 10.1002/aoc.3822
Revised: 6 December 2016
Accepted: 4 March 2017
F U L L PA P E R
Preparation and characterization of copper chloride supported on
2
+
citric acid‐modified magnetite nanoparticles (Cu ‐CA@Fe O )
3
4
and evaluation of its catalytic activity in the reduction of
nitroarene compounds
1
1
2
1
1
Ehsan Ghonchepour
| Elahe Yazdani | Dariush Saberi
| Marzban Arefi | Akbar Heydari
1
Chemistry Department, Tarbiat Modares
University, Tehran, P.O. Box 14155‐4838,
Iran
A new, powerful and recyclable copper catalyst were prepared by heterogenization
of copper chloride using of Fe O nano particles modified with citric acid as a
3
4
2
Fisheries and Aquaculture Department,
linker. This system can catalyze reduction of nitroaren compound to aniline deriva-
tives in the presence of Sodium borohydride as a reduction agent in moderate to
good yields. In addition, easy separation and recoverable with an external permanent
College of Agriculture and Natural
Resources, Persian Gulf University, Bushehr
7
5169, Iran
2+
magnet is the dominant properties of this catalyst (Cu ‐CA@Fe O ).
3
4
Correspondence
Akbar Heydari, Chemistry Department,
Tarbiat Modares University, Tehran, P.O.
Box 14155‐4838, Iran.
KEYWORDS
copper chloride, c‐c coupling, green catalyst, heterogenization, magnetic nanoparticles, nitro reduction
Email: heydar_a@modares.ac.ir
[
4]
1
| INTRODUCTION
manufacture of many analgesic and antipyretic drugs.
One way to prepare amines is reduction of nitro compounds
in the presence of various reductant reagents such as
With the entrance of magnetic nanoparticles into the catalyst
field, the difficulty in separation of catalyst from the reaction
mixture was greatly improved. Magnetic separation of cata-
lysts, by using an external magnet, could be a popular alter-
native to the tedious filtration process. In recent years,
magnetic nanoparticles have found use in abundance as both
catalyst and support since they offer advantages over homo-
geneous catalysts such as longer lives, and minimizing the
change in activity and selectivity, aside from their easy mag-
netic separation.
Citric acid is a weak organic acid with the formula
C H O and water soluble solid. It is a natural preservative
which is present in citrus fruits. Its carboxylate groups can
join to iron oxide surface. Citric acid has the ability to ‘con-
[
5]
[6]
[7]
[8]
[9]
NH Cl,
MeOH,
HCl,
H ,
NH NH ,
formic acid,
4
2
2
2
[
10]
[11]
[12]
[13]
NaHSO3,
NaBH4,
LiAlH4.
Among them,
NaBH is the most popular reductive agent because it is
commercially available and inexpensive. The only disadvan-
tage of NaBH is its low reactivity, which requires activa-
tion. Different catalytic systems have been reported for the
4
4
[
14]
activation of NaBH such as Fe O @EDTA‐Pd,
CeO2,
Pt‐
4
3 4
[
15]
[16]
Au/CeO , Au/Al O , Pt/Al O , and Au/Fe O .
2 2 3 2 3 2 3
[
1]
Although satisfactory results have been obtained in terms
of reaction efficiency, conditions, and catalyst recyclabil-
[
17]
ity,
however, in some procedures, there are disadvantages
6
8 7
[
18]
such as long reaction times,
tedious work‐up and poor
As part of our on‐going
research towards the development of eco‐friendly and green
organic transformations, we attempted to join the high cata-
lytic activity of supported catalysts with the advantages of
easy separation of magnetic nanoparticle. Herein, we report
the preparation of citric acid‐copper complex stabilized on
[
19]
recyclability of the catalyst.
2
+
2+ [2]
fiscate’ metal ions such as Pd and Cu .
Amines are one of the most important functional groups
in nature, constitute versatile building blocks in synthetic
organic chemistry, and also exhibit a wide range of indus-
[3]
trial applications and pharmacological interest. Specially
‐aminophenol is an industrially important raw material
which has been widely used as the intermediate for the
2+
4
the surface of magnetite nanoparticles (Cu ‐CA@Fe O )
3
4
and study of its catalytic properties for the activation of
Appl Organometal Chem. 2017;e3822.
wileyonlinelibrary.com/journal/aoc
Copyright © 2017 John Wiley & Sons, Ltd.
1 of 8
https://doi.org/10.1002/aoc.3822

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GHONCHEPOUR ET AL.
2
+
NaBH4 for reduction of different nitroarenes to amine
groups.
properties of Cu ‐CA@Fe O nanoparticles were obtained
3
4
with a vibrating magnetometer/alternating gradient force
magnetometer (MDK Co., Iran, www.mdk‐magnetic.com).
2
2
| EXPERIMENTAL
2
.2 | Preparation of magnetic nanoparticles
2+
.1 | Chemicals, instrumentation and analysis
(Cu ‐CA@Fe O )
3
4
2+
All chemicals and solvents purchased were of analytical
grade and used without further purification. FT‐IR spectra
were obtained in the area 400–4000 cm‐ using a Nicolet
IR100 instrument with spectroscopic grade KBr. TGA was
performed on a Thermal Analyzer with a heating rate of
The magnetic nano catalyst (Cu ‐CA@Fe O ) was prepared
by dissolving a mixture of 0.994 g (5 mmol) FeCl .4H O and
2.7 g (10 mmol) FeCl .6H O salts in 100 ml of deionized
water under vigorous stirring. 30 ml of an aqueous ammonia
solution (25% w/w) was then added to the stirring mixture to
maintain the reaction pH about 11. Simultaneously, 0.2 M
solution of citric acid (10 ml) was added to this black suspen-
sion. The resulting black dispersion was continuously stirred
for 1 h at room temperature and then refluxed for 1 h.
Fe O nanoparticles were separated from the aqueous solu-
3
4
2
2
1
3
2
‐
1
2
0°C min over a temperature region of 25–1000°C under
flowing compressed nitrogen gas. Powder X‐ray diffraction
XRD) spectra were recorded at room temperature by a
(
Philips X‐Pert 1710 diffractometer using Co Kα(λ=1.78897 Å)
at a voltage of 40 kV and current of 40 mA and data were col-
lected from 10° to 90° (2θ) with a scan speed of 0.02° s .
3
4
‐
1
tion using magnetic decantation, and washed with water
The images of the catalyst were observed using Philips XL
several times. After that 2 mmol (0.269 g) of CuCl and
2
30 and S‐4160instruments with coated gold equipped with
3 mmol (0.317 g) of Na CO were added with stirring at
2
3
dispersive X‐ray spectroscopy capability. The magnetic
40°C for 6 h. The suspension was refluxed for 2 h. Finally,
NH3(eq)
OH
CuCl2
Na2CO3
CA@Fe3O4
Cu+2-CA@Fe3O4
FeCl3.6H2O
FeCl2.4H2O
O
O
O
SCHEME 1 Pathway to synthesis of
Cu ‐CA@Fe O nanoparticles.
3 4
(Citric acid)
HO
OH
2+
OH
2
+
2+
FIGURE 1 FT‐IR spectra of a) Fe
3
O
4
, b) CA@Fe
3
O
4
, c) Cu ‐CA@Fe
3
O
4
, d) Cu ‐CA@Fe
3
O
4
(after fifth run)

GHONCHEPOUR ET AL.
3 of 8
nanoparticles were separated from the aqueous solution by
magnetic decantation, washed several times with water,
ethanol and diethyl ether respectively, before being dried
in an oven overnight.
the reaction mixture and extracted with EtOAc (2 ×20
ml) and dried over Na SO . The solvent was removed
under reduced pressure to give the crude product. The res-
idue was subjected to silica‐gel plate chromatography using
n‐hexane‐ethyl acetate as an eluent to afford pure product.
2
4
2
.3 | General procedure for reduction of
2+
Nitroarenes in the Presence of Cu ‐CA@Fe O
3 | RESULTS AND DISCUSSION
3
4
2+
To a solution of nitroarene compound (1 mmol) in EtOH/H O
Scheme 1 shows the synthetic pathway for Cu ‐CA@Fe O
nanoparticles.
2
3
4
2
+
(
3:1, 4 ml), was added NaBH 5 mmol (0.189 g) and Cu ‐
4
CA@Fe O (20 mg). The reaction vessel was heated at
Prepared catalyst was then characterized using various
microscopic and spectroscopic techniques such as FT‐IR,
XRD, TGA, VSM, ICP, and SEM‐EDX.
3
4
45°C in an oil bath for 5–10 min. The progress of the reac-
tion was scanned by TLC. After completion of the reaction,
the nanoparticles were collected with an external magnet
from the reaction mixture and washed with distilled water
and CH Cl repeatedly. Water (50 ml) was then added to
2+
The FT‐IR spectra of Fe O , CA@Fe O and Cu ‐
3
4
3 4
CA@Fe O are showed in Figure 1 (a‐c). The spectrum in
3
4
Figure 1(a) related to the raw Fe O , shows a band around
2
2
3 4
2+
FIGURE 2 XRD spectrum of a) CA@Fe
3
O
4
3 4
, b) Cu ‐CA@Fe O

4
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GHONCHEPOUR ET AL.
42 cm‐ which is ascribed to stretching vibration of Fe–O.
1
The XRD pattern of two different stepwise synthetic
pathway for the preparation of the catalyst is shown in
Figure 2 and the XRD data of the prepared catalyst inserted
in a Table 1. The XRD pattern of CA@Fe O Figure 2(a)
5
The FT‐IR spectrum of CA@Fe O is shown in Figure 1(b).
Typical bands assigned to the Fe‐O stretching vibration
appeared at around 400–600 cm and the strong band around
583‐1630 cm is consistent with the C=O stretching vibra-
3
4
‐1
3
4
‐1
2+
1
and Cu ‐CA@Fe O4 Figure 2(b) have similar Diffraction
3
tion confirming that citric acid is well coated on the Fe O4
peaks at around 21.38, 35.27, 41.62, 50.71, 63.28, 67.64
and 74.60 correspond to the (111), (220), (311), (400),
(422), (511) and (440) reflections, respectively. These XRD
peaks match well with peaks the magnetic, which is in agree-
ment with the standard pattern for crystalline magnetite
3
nanoparticles. In the FT‐IR spectrum for CuCl ‐functionalized
2
CA@Fe O (Figure 1(c)), it is worth mentioning that in Cu‐
3
4
anchored mesoporous CA@Fe O material, the C=O
3
4
stretching frequency is shifted to a lower wavelength at
‐1
[20]
~
1583 cm indicating that C=O bond is coordinated to copper.
According to the measurements catalyst activity after five
(Fe O ) with an inverse spinel structure.
3
4
The amount of citric acid loaded on the surface of mag-
netic nanoparticles was performed utilizing TGA (Figure 3).
The TGA was recorded by heating the sample at a rate of
run were not observed any change in its activity. But we
recorded FT‐IR spectrum after the fifth run to determine
any change in the catalyst structure (Figure 1(d)). The results
indicate that the catalyst shows no change in its FT‐IR spec-
trum after this run.
‐
1
10°C min , and showed that an endothermic peak at a low
temperature (lower than 150°C) due to water elimination
and exothermic signal over 550°C.
2+
3 4
TABLE 1 The XRD data of Cu ‐CA@Fe O
Pos.[°2Th.]
FWHM [°2Th.]
d‐spacing[Å]
Height[cts]
Rel.Int.[%]
Backgr.[cts]
Area [cps*°2Th.]
2
3
4
5
6
6
7
1.3857
5.2791
1.6229
0.7159
3.2777
7.6413
4.6070
1.6308
0.9626
1.0283
1.0748
1.0455
1.0897
1.2020
4.82098
2.95189
2.51765
2.08864
1.70524
1.60710
1.47599
16.73
133.78
421.76
84.74
3.97
31.72
100.00
20.09
7.61
23.00
37.00
36.00
22.00
21.00
25.00
24.00
29.90
136.53
464.26
98.04
35.93
112.35
190
32.10
94.96
22.52
34.36
144.94
2
+
3 4
FIGURE 3 Thermogravimetric and differential thermogravimetric of Cu ‐CA@Fe O

GHONCHEPOUR ET AL.
5 of 8
1
[21]
2+
7
3.7 emu g‐ at room temperature
which in Cu ‐
‐1
CA@Fe O catalyst decreases to 52 emu g for. Zero rema-
3
4
nence and coercivity of the magnetization curve demonstrate
that these nanoparticles have superparamagnetic properties.
Saturation magnetization decreases as the particle size is
reduced due to enhancement of surface spin effects, and as
particle size decreases the coercivity vanishes and becomes
a superparamagnetic state. The prepared catalyst dispersed
in solvent and subjected to an external magnetic field can
immediately gather nanoparticles, then with slight shaking
can be promptly re‐dispersed. These results indicate that the
particles display good magnetic characteristics that could be
useful when they are applied as a magnetic catalyst. The
nanoparticles exhibit high permeability in magnetization,
which was sufficient for magnetic separation using a conven-
tional magnet.
2
+
3 4
FIGURE 4 Vibrating sample magnetometry of Cu ‐CA@Fe O
2+
The second step within the temperature range 150–375°C
is associated with an exothermic DTA peak in this range. The
broad exotherm is due to the presence of a complex citric acid
moiety in the matrix. There are two peaks accompanied by
The morphology of nano Cu ‐CA@Fe O was evalu-
3
4
ated using scanning electron microscopy (SEM) and they
have a spherical shape with a rough surface and a range diam-
eter of 25‐35 nm (Figure 5).
5
.8% weight loss at 150–375°C in differential thermo gravi-
The EDX spectrum of the Cu‐incorporated catalyst is
outlined in Figure 6. Atoms such as Fe, Cu, C and O, related
to the catalyst structure, are seen in this spectrum. The copper
metric curve can be attributed to decomposition of organic
ligands. Major weight loss at high temperatures is character-
istic of chemisorbed materials and confirms that the citric
acid group is chemically bound to the surface of the mag-
netic nano particles. The TGA and DTA results reveal
‐
1
content of the catalyst was found to be 1.58 mmol g based
on the EDX spectrum. Also, the amount of the copper sup-
ported onto the CA@Fe O measured by induced coupled
3
4
2
+
that the thermal stability of synthesized Cu ‐CA@Fe O
catalyst is maintained at higher temperature.
plasma (ICP) analysis and was 0.24 g of Cu per g of catalyst
3
4
‐
1
(3.8 mmol.g ).
2
+
The hysteresis loop was studied for the Cu ‐CA@Fe O
After characterization, activity of the catalyst was exam-
ined in the reduction of nitroarene compounds. First, we
examined the reduction of p‐hydroxy nitro benzene with
sodium borohydride to p‐hydroxy aniline under various
3
4
in an applied magnetic field at ambient temperatures with the
field sweeping from ‐8000 to +8000 Oersted (Figure 4). Bare
nanocrystals of Fe O have high saturation magnetization of
3
4
2+
3 4
FIGURE 5 SEM image of Fe O @CA‐Cu

6
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GHONCHEPOUR ET AL.
2+
3 4
FIGURE 6 EDX analyze of Fe O @CA‐Cu
a
TABLE 2 Optimization of reaction conditions of reduction of p‐hydroxy nitro benzene
b
Entry
Cat (mg)
Solv (EtOH:H
2
O)
NaBH
4
(mmol)
Yield (%)
1
2
3
4
5
6
7
8
9
10
20
30
20
20
20
20
20
‐
3:1
3:1
3:1
0:4
2:2
1:3
3:1
3:1
3:1
3:1
3:1
5
5
5
5
5
5
4
6
5
5
5
52
95
95
80
72
68
75
95
0
c
1
0
1
10
0
d
1
10
0
a
2+
3 4
Reaction conditions: p‐hydroxy nitro benzene (1 mmol, 0.139 g), Solvent (4 ml), 45 °C, 10 min Cu −CA@Fe O as catalyst, under an air atmosphere.
b
c
Isolated yield,
nanoparticles as catalyst,
CA@Fe as catalyst
3 4
Fe O
d
3 4
O
conditions in order to establish the optimal conditions. The
results are summarized in Table 2.
catalyst to 30 mg, efficiency did not change (Table 2,
entry 3). The yield was reduced in pure water as well as
The first reaction was performed under the following
conditions: p‐hydroxy nitro benzene 1 mmol (0.139 g),
sodium borohydride 5 mmol (0.189 g), and a mixture of
EtOH‐H O system with equal or 1:3 ratio (Table 2, entries
4‐6). In the next step, the effect of amount of the NaBH4
2
was examined. Reducing the amount of the NaBH led to a
4
EtOH/H O (3:1, 4 mL) as the solvent in the presence of
2
2
+
Cu ‐CA@Fe O (10 mg, 3.8 mol% of Cu) at 45°C under
3
4
NO2
10 mg Cat
mmol NaBH4
NH2
air atmosphere. After 1 h of reaction time the desired ani-
line was formed in 52% yield (Table 2, entry 1). Owing to
the improved yield, first the effect of catalyst loading on
the efficiency of the reaction was considered. Interestingly,
the yield was increased up to 95% when 20 mg of catalyst
was used (Table 2, entry 2). With further increase of the
5
R
EtOH:H2O 3:1 (4 ml)
45 °C, 10 min
R
cat: Cu2+-CA@Fe3O4
SCHEME 2 Reduction of nitroarene compound in optimal condition

GHONCHEPOUR ET AL.
7 of 8
2
+
a
3 4
TABLE 3 Reduction of nitroarene compounds catalyzed by Cu ‐CA@Fe O
b
Entry
1
Substrate
Product
Time(min)
90
Yield (%)
82
Ref
[19]
[
14]
2
3
4
120
10
90
95
93
[
[
17]
22]
10
[23]
5
80
60
[
[
24]
25]
6
7
5
5
98
96
[
[
23]
14]
8
9
80
5
92
98
a
2+
Reaction conditions: nitroarene (1 mmol), NaBH
4
3 4 2
5 mmol (0.189 g), 20 mg Cu ‐CA@Fe O , EtOH:H O (3:1, 4 mL), 45 °C, under air atmosphere;
b
Isolated yield
decreased yield, while increasing it showed no effect
Table 2, entries 7 and 8). Formation of no product in the
absence of catalyst or in the presence of CA@Fe O or
(
3
4
Fe O nanoparticles showed that the copper stabilized on
3
4
the surface of magnetic‐modified citric acid play a vital role
for this transformation (Table 2, entries 9‐11).
With the optimal conditions in hand (Scheme 2), we next
studied the substrates scope of this reaction by screening the
nitroarenes. To this end a variety of nitroarenes were sub-
jected under optimal conditions and the result are depicted in
Table 3.
All of the nitroarenes were converted to the correspond-
ing aniline in high yields. All the products were known and
characterized by IR, H and C NMR data as well as by
1
13
FIGURE 7 Reusability of Cu2+‐CA@Fe O in the model reaction
3
4

8
of 8
GHONCHEPOUR ET AL.
comparison of their physical data with those of known
compounds.
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[
3,22,23,26]
Reusability of the catalyst was tested in the model reac-
tion. After completion of the reaction in the first run, the cat-
alyst was easily separated from the reaction mixture by using
an external magnet; it was washed twice with ethyl acetate,
dried at ambient temperature and immediately used in the
next step. The reaction was repeated for up to eight consecu-
tive runs without significant change in the efficiency of the
reaction (Figure 7).
[
[
[
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4
| CONCLUSIONS
2+
In this study Cu ‐CA@Fe O was prepared and character-
3
4
ized as a heterogeneous and magnetically separable
2+
nanocatalyst. Catalytic activity of the prepared Cu ‐
[17] H. Woo, K. H. Park, Cat. Com. 2014, 46, 133.
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3
4
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2
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4
[
[
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4
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