Synthesis of graphene oxide supported copper–cobalt ferrite material functionalized by arginine amino acid as a new high–performance catalyst

Article abstract of DOI:10.1002/aoc.3965

A novel Cu_0.5Co_0.5Fe₂O₄@Arg–GO catalytic system was successfully prepared by immobilization of copper substituted cobalt ferrite nanoparticles on arginine–grafted graphene oxide nanosheets, in which ferrite moiety acts as an oxidation catalyst and arginine has the role of base catalyst. Also, arginine amino acid was used to modify the surface of graphene oxide nanosheets which the prepared support can improve dispersion and uniform loading of nanoparticles. The prepared nanocomposite was characterized by flame atomic absorption spectroscopy (FAAS), inductively coupled plasma optical emission spectrometer (ICP–OES), energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FT–IR), ultraviolet–visible spectroscopy (UV–vis), Raman spectroscopy, thermogravimetric analysis (TGA), x–ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) analysis. The prepared Cu_0.5Co_0.5Fe₂O₄@Arg–GO nanocomposite was used as an efficient catalyst for one–pot tandem oxidative synthesis of 2–phenylbenzimidazole derivatives in good yields.

Full text of DOI:10.1002/aoc.3965

Received: 11 April 2017
DOI: 10.1002/aoc.3965
Revised: 15 May 2017
Accepted: 17 June 2017
F U L L P A P E R
Synthesis of graphene oxide supported copper–cobalt ferrite
material functionalized by arginine amino acid as a new
high–performance catalyst
Rahim Ghadari1
| Hassan Namazi1 | Mohammad Aghazadeh2
1 Department of Organic and
A novel Cu0.5Co0.5Fe2O4@Arg–GO catalytic system was successfully prepared
by immobilization of copper substituted cobalt ferrite nanoparticles on argi-
nine–grafted graphene oxide nanosheets, in which ferrite moiety acts as an oxi-
dation catalyst and arginine has the role of base catalyst. Also, arginine amino
acid was used to modify the surface of graphene oxide nanosheets which the
prepared support can improve dispersion and uniform loading of nanoparticles.
The prepared nanocomposite was characterized by flame atomic absorption
spectroscopy (FAAS), inductively coupled plasma optical emission spectrome-
ter (ICP–OES), energy dispersive spectroscopy (EDS), Fourier transform infra-
red spectroscopy (FT–IR), ultraviolet–visible spectroscopy (UV–vis), Raman
spectroscopy, thermogravimetric analysis (TGA), x–ray diffraction (XRD), scan-
ning electron microscopy (SEM), and transmission electron microscopy (TEM)
analysis. The prepared Cu0.5Co0.5Fe2O4@Arg–GO nanocomposite was used as
an efficient catalyst for one–pot tandem oxidative synthesis of 2–
phenylbenzimidazole derivatives in good yields.
Biochemistry, Faculty of Chemistry,
University of Tabriz, 5166616471 Tabriz,
Iran
2 Microbiology Department, Faculty of
Medicine, Tabriz University of Medical
Sciences, Tabriz, Iran
Correspondence
Rahim Ghadari, Department of Organic
and Biochemistry, Faculty of Chemistry,
University of Tabriz, 5166616471 Tabriz,
Iran.
Email: r‐ghadari@tabrizu.ac.ir
Funding information
Iran National Science Foundation (INSF),
Grant/Award Number: 94011834
KEYWORDS
arginine, copper substituted cobalt ferrite nanoparticles, graphene oxide, oxidative synthesis
[6–8]
1 | INTRODUCTION
(CoFe2O4)
(CuFe2O4)
and copper substituted spinel ferrite
are two groups of important magnetic
[9–11]
Fe3O4 ferrite (it occurs in nature as the mineral magnetite
as one of the major iron ores found in the earth's crust)
was made from iron and oxygen via chemical combina-
tion of iron(II) oxide with iron(III) oxide. Spinel ferrites
can chemically modify with different transition metal ions
to produce metal ferrites with variable application. Fer-
rites as attractive inorganic materials with excellent phys-
ical and chemical properties can catalyze various kinds of
the organic transformation. Several kinds of ferrites
nanomaterials have been utilized in different catalytic
processes based on their transition metal.[1–5] Spinel fer-
rite nanoparticles such as cobalt substituted spinel ferrite
materials in catalysis applications due to their excellent
chemical stability, high thermal stability, and high cata-
lytic activity. It is reported that the catalytic activity of spi-
nel ferrites containing transition metal ions is often
enhanced by means of rapid electron exchange between
their tetrahedral and octahedral sites.[12] The catalytic
performance of spinel ferrite nanoparticles will be
increased by keeping the size of the nanoparticles as small
as possible.[13] The use of suitable supports with high
surface area can provide high loading, uniform disper-
sion, and keeping the size of ferrite nanoparticles.
Graphene, the one–atom–thick two–dimensional (2D)
Appl Organometal Chem. 2017;e3965.
wileyonlinelibrary.com/journal/aoc
Copyright © 2017 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.3965

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GHADARI ET AL.
layer of sp2–bonded carbon, has become the focus of
considerable interest for this purpose due to its unique
electronic properties and large specific surface area.[14,15]
Graphene oxide (GO), as one of the most important
derivatives of graphene, contains a large number of
oxygen–containing functional groups (hydroxyl, carboxyl,
epoxy group, etc.) bearing on its basal planes and
edges.[16–19] The large specific surface area and the
oxygen–containing functional groups of GO provide it
suitable for the immobilization of large amount of catalyt-
ically active nanoparticles with uniform dispersion.[20] In
recent years, modified graphene oxide nanosheets have
received a lot of attention as support for immobilization
of catalytic nanoparticles. The surface of graphene oxide
nanosheets coated by a suitable modifier has a strong
interaction with nanoparticles which modified GO
inhibits the aggregation of nanoparticles in liquid and
increases the chemical stability of them. Therefore, com-
bining nanometer–sized and nanostructured graphene
oxide with suitable modifier can produce the appropriate
support for catalytic applications.[17] The large number
of oxygenated functional groups of graphene oxide can
act as favorable anchoring centers and nucleation sites
for chemical modifiers.[21] Because of oxygen–containing
functional groups on the basal planes and edges of GO,
it can easily functionalized with small molecules chemi-
cally by using the nucleophilic substitution reactions. So,
some α–amino acids contain free –NH2 functional groups
can be used as green, biodegradable, renewable modifiers
for chemical modification of GO.[22]
Amino acids, as biologically important organic com-
pounds, are green, inexpensive, and nontoxic materials
containing amine and carboxyl functional groups along
with a side–chain specific to each amino acid. Amino acids
with free –NH2 functional groups can be used as good can-
didates to improve the nanoparticle loading property of
GO.[22] The basic groups (primary amines) on side–chain
of amino acids also provide an active base–catalyst for an
enormous variety of synthetic applications.
Nitrogen containing five membered heterocyclic
aromatic compounds, as important structures in pharma-
cological researches, are found in natural and synthetic
compounds. Among nitrogenous five membered
heteroaromatics, benzazoles are crucial core structures
with significant biological and pharmacological activities.
Benzimidazoles, as nitrogen containing benzazoles, are
considered as important building blocks for pharmaceuti-
cals and bioactive molecules in the field of medicinal
chemistry. Traditionally, benzimidazoles were prepared
using condensation of carboxylic acid derivatives such as
acids, acyl chlorides, esters, nitriles, and amides with o–
phenylenediamines.[23] Due to harsh conditions (high
temperatures, strong dehydrating reagents, etc.) needed
for the mentioned methods, oxidative condensation of
aldehydes with o–phenylenediamines were developed
later.[23] Oxidative condensation of aldehydes with o–
phenylenediamines had inherent drawbacks such as the
utilization of reactive and toxic reagents and transition–
metal catalysts, therefore, improved methods have been
developed for the synthesis of benzimidazoles using
greener, cheaper, and more readily available substrates
and catalysts. Alcohols are readily available chemicals
feedstock which are used for the preparation of benzimid-
azoles using various catalysts or reagents, recently.[23–29]
In order to the developing new heterogeneous catalyst
for organic transformations, the synthesis and catalytic
application of copper substituted cobalt ferrite nanoparti-
cles supported on arginine–grafted graphene oxide nano-
sheets (Cu0.5Co0.5Fe2O4@Arg–GO) are investigated. The
activity of the obtained Cu0.5Co0.5Fe2O4@Arg–GO cata-
lyst was studied in the one–pot tandem oxidative synthe-
sis of 2–phenylbenzimidazole derivatives. The prepared
novel Cu0.5Co0.5Fe2O4@Arg–GO nanocomposite has both
Cu0.5Co0.5Fe2O4 and arginine moieties which can be not
only used to oxidation reactions but also applied in
organic base catalysis.
2 | EXPERIMENTAL
Arginine was used to modify the graphene oxide nano-
sheets surfaces due to inertness property of graphene
oxide for immobilization of ferrite nanoparticles and good
coordination interaction between –NH2 group of arginine
and ferrite nanoparticles. Use of Cu0.5Co0.5Fe2O4 ferrite
nanoparticles and arginine for the synthesis of
Cu0.5Co0.5Fe2O4@Arg–GO nanocatalyst gave double
nature to the prepared nanocomposite because of oxida-
tion capability of ferrite moiety and basic property of argi-
nine moiety. The mentioned double nature of the
Cu0.5Co0.5Fe2O4@Arg–GO nanocomposite made it usable
in the both oxidation and synthetic sections of the one–
pot tandem oxidative synthesis of 2–phenylbenzimidazole
derivatives. Cu0.5Co0.5Fe2O4@Arg–GO nanocatalyst was
prepared as Figure 1.
2.1 | Synthesis of arginine–grafted
graphene oxide nanosheets (Arg–GO)
The modified Hummers method was used to synthesize
the graphene oxide.[30,31] The graphite powder (2.0 g)
was treated with 1.0 g of K2S2O8 and 1.0 g of P2O5 in the
6.0 ml of concentrated sulfuric acid. The reaction media
was magnetically stirred at 80 °C for 6 h. In continue,
the mixture of reaction was cooled to room temperature
and diluted with deionized water (DI water, 200 ml) and

GHADARI ET AL.
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FIGURE 1 Preparation of Cu0.5Co0.5Fe2O4@Arg–GO nanocomposite
left overnight. After that, the mixture was filtered and the
residue was washed with DI water to remove the residual
acid. The obtained product was dried under ambient con-
ditions overnight to give the preoxidized graphite. The
obtained preoxidized graphite powder was put into cold
concentrated H2SO4 (50 ml) at 0 °C. The KMnO4 (6.0 g)
was added gradually under stirring while keeping the
temperature at 0 °C. The mixture was stirred at room tem-
perature for 4 h. In continue, the mixture was diluted with
DI water in two steps (at first, 100 ml and after 2 h,
300 ml) while the reaction vessel was kept in the ice bath.
After adding all of the 400 ml DI water, the mixture was
stirred at room temperature for 2 h. Finally, hydrogen per-
oxide (30%) was drop–wise added to the mixture until the
color of the reaction media was changed from black to the
golden yellow. The mixture was filtered and washed by
HCl (0.1 M, 300 ml) and DI water to remove metal ions
and residual acid. The resulting GO solid was dried in
air, at room temperature. To synthesize the acylated
graphene oxide, 0.3 g of as–synthesized GO was added
into the solution containing 20 ml of thionyl chloride
and 0.5 ml of dimethylformamide, and then treated at
70 °C for 24 h under nitrogen atmosphere. Then, the reac-
tion solvent was evaporated. After evaporation of the
excess solvent from the reaction mixture at 100 °C, the
residue was washed with dry tetrahydrofuran at least five
times. The obtained acylated GO, arginine (2.0 mmol,
0.1 g), and dry DMF (20 ml) were added to the round flask
and the reaction mixture was stirred at 90 °C. After mag-
netic stirring for 12 h, the obtained product was centri-
fuged and washed with DI water and ethanol
successively and dried at 50 °C under vacuum. Finally,
the arginine attached graphene oxide product was
obtained as a black powder.
2.2 | Copper substituted cobalt ferrite
nanoparticles supported on arginine–
grafted graphene oxide nanosheets
(Cu0.5Co0.5Fe2O4@Arg–GO)
The as–prepared Arg–GO (1.0 g) was added to DI water
(200 ml) and sonicated until a dispersed mixture was
obtained. To a magnetically stirred mixture of as–pre-
pared dispersed Arg–GO, FeCl3.6H2O (1.6 mmol),
CoCl2.6H2O (0.4 mmol), and CuCl2.2H2O (0.4 mmol)
were added at room temperature. The prepared mixture
was sonicated for 1 h and then, the temperature is raised
to 80 °C. The stirring of reaction media is continued at
this temperature for about 30 minutes. NaOH solution
(0.1 M) was drop–wise added to the reaction media during
20 minutes until the pH of the mixture solution was raised
to 10. The obtained mixture was magnetically stirred for
30 minutes and then, the temperature of mixture was
decreased to room temperature and stirred for 6 h.
Finally, the mixture was centrifuged and the
Cu0.5Co0.5Fe2O4@Arg–GO nanocomposite was washed
with DI water and EtOH in sequence and dried at room
temperature.
2.3 | General procedure for catalytic test
A mixture of diamine (1.0 mmol), alcohol (1.2 mmol), and
dispersed Cu0.5Co0.5Fe2O4@Arg–GO (0.07 g) in 7.0 ml of
acetonitrile was prepared in a two–necked flask equipped
with an air bubbling tube and reflux condenser. The mix-
ture of the reaction was stirred under reflux conditions (at
80 °C) while air was bubbled into the reaction mixture at
a rate of 5 ml min−1. The reaction progress was monitored
by thin–layer chromatography (TLC) and gas

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GHADARI ET AL.
chromatography (GC) methods. After that, the mixture
was cooled to room temperature. After separation of
Cu0.5Co0.5Fe2O4@Arg–GO nanocomposite and evapora-
tion of the filtrate solvent under vacuum, the crude
product was separated on a silica gel column to give 2–
phenylbenzimidazole derivatives. (The final products
1
were identified using H NMR spectroscopy and quanti-
fied by isolated yield; selected 1H NMR spectra are
included in the supporting information.)
3 | RESULTS AND DISCUSSION
The prepared Cu0.5Co0.5Fe2O4@Arg–GO nanocomposite
was characterized by flame atomic absorption spectros-
copy (FAAS), inductively coupled plasma optical emission
spectrometer (ICP–OES), energy dispersive spectroscopy
(EDS), Fourier transform infrared spectroscopy (FT–IR),
ultraviolet–visible spectroscopy (UV–vis), Raman spec-
troscopy, thermogravimetric analysis (TGA), x–ray dif-
fraction (XRD), scanning electron microscopy (SEM),
and transmission electron microscopy (TEM) analysis.
The FAAS method has been applied to determine the ele-
ments of Cu0.5Co0.5Fe2O4@Arg–GO nanocomposite
including copper, cobalt, and iron metals. The determina-
tion of copper, cobalt, and iron contents of the
Cu0.5Co0.5Fe2O4@Arg–GO nanocomposite using FAAS
method showed that the amount of Cu0.5Co0.5Fe2O4 in
the Cu0.5Co0.5Fe2O4@Arg–GO catalyst is 8.21 weight per-
cent. ICP–AES, an analytical technique used for the detec-
tion of trace metals, was used to provide the data about
Cu0.5Co0.5Fe2O4 content in the Cu0.5Co0.5Fe2O4@Arg–
GO nanocomposite. The analysis of elements of
Cu0.5Co0.5Fe2O4@Arg–GO using ICP–AES method cor-
roborates the previously determined amount of copper,
cobalt, and iron in the mentioned nanocomposite which
the determined composition of the prepared specimen
was conformed within the composition of predicted
Cu0.5Co0.5Fe2O4@Arg–GO product. The EDS analytical
technique was applied for the elemental analysis and
chemical characterization of Cu0.5Co0.5Fe2O4@Arg–GO
nanocomposite which the obtained results proves the
presence of carbon, nitrogen, oxygen, copper, cobalt, and
iron in the mentioned nanocomposite (Figure 2).
FIGURE
nanocomposite
2
SEM–EDS result for Cu0.5Co0.5Fe2O4@Arg–GO
band due to the presence of ferrite moiety. The maximum
ultraviolet absorbance of Cu0.5Co0.5Fe2O4@Arg–GO
nanocomposite was found to be approximately 335 nm.
Two main peaks in the Raman spectrum of graphene–
based materials is observable due to the first order E2g
mode from sp2 carbon domains (G–band) and characteris-
tic of a breathing mode for k–point (D–band). Therefore,
Raman spectroscopy was used for investigating the
electronic and phonon structure of the prepared GO and
Cu0.5Co0.5Fe2O4@Arg–GO. The Raman spectra of
prepared GO and Cu0.5Co0.5Fe2O4@Arg–GO are shown in
Figure 3. The characteristic D and G bands of GO are
observed around 1308 and 1584 cm−1, respectively. Also,
Raman spectrum of Cu0.5Co0.5Fe2O4@Arg–GO nanocom-
posite in Figure 3 shows two prominent peaks at 1585 and
1313 cm−1 related to G–band and D–band, respectively.
The XRD patterns of graphite, GO and
Cu0.5Co0.5Fe2O4@Arg–GO nanocomposite were employed
to further investigate the structure of the synthetic
materials (Figure 4). The XRD patterns of graphite, GO,
and Cu0.5Co0.5Fe2O4@Arg–GO nanocomposite are shown
The UV–vis analysis of GO, Arg–GO, and
Cu0.5Co0.5Fe2O4@Arg–GO nanocomposite is carried out
in the solution of the mentioned specimens dissolved in
the concentrated HCl and diluted with DI water. The
obtained results are presented in the Figure 1S (see Elec-
tronic Supplementary Material). As can be seen, GO and
Arg–GO does not show significant characteristic bands
in the region 200–800 nm. The UV–visible spectrum of
Cu0.5Co0.5Fe2O4@Arg–GO nanocomposite shows a broad
FIGURE 3 Raman spectra of GO (I) and Cu0.5Co0.5Fe2O4@Arg–
GO (II)

GHADARI ET AL.
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1624 cm−1 and 1408 cm−1 corresponds to the –C = N
and –C–N stretches, respectively, due to the chemical
attachment of arginine to the GO.[22] The characteristic
bands at 621 cm−1 and 428 cm−1 (attributed to stretching
vibrations of tetrahedral and octahedral complexes,
respectively) in the Cu0.5Co0.5Fe2O4@Arg–GO nanocom-
posite also is appeared due to the metal − O stretching
vibrations.[33]
The morphological characterization of the obtained
GO, Arg–GO, and Cu0.5Co0.5Fe2O4@Arg–GO nanocom-
posite was conducted by SEM. SEM images of GO, Arg–
GO, and Cu0.5Co0.5Fe2O4@Arg–GO nanocomposite are
shown in Figure 5. The SEM image of Arg–GO comparing
to the SEM image of GO was confirmed that the forma-
tion of arginine–grafted graphene oxide nanosheets was
done without a large change in the morphology of GO.
SEM images of Cu0.5Co0.5Fe2O4@Arg–GO show it to be
a nanocomposite structure having the uniform dispersion
of Cu0.5Co0.5Fe2O4 nanoparticles on the arginine–grafted
graphene oxide nanosheets surfaces.
The microstructure and morphology of the
Cu0.5Co0.5Fe2O4@Arg–GO nanocomposite is character-
ized by means of TEM, as well. As is seen in representative
TEM micrographs, Figure 6a,b compares the morphologies
of GO and Arg–GO. The micrographs of GO and Arg–GO
possess similar sheet morphology which confirmed that
arginine was grafted on GO surface without a large change
in the morphology of GO. TEM image of copper substituted
cobalt ferrite nanoparticles on arginine–grafted graphene
oxide nanosheets shows the uniform dispersion and the
size distribution of the supported Cu0.5Co0.5Fe2O4
nanoparticles on the Arg–GO (Figure 6c). As Figure 6c
shows, the surface of Arg–GO is covered with good
dispersion of Cu0.5Co0.5Fe2O4 nanoparticles.
In order to achieve suitable reaction conditions for the
oxidative synthesis of 2–phenylbenzimidazole derivatives,
a mixture of o–phenylenediamine (1a) and benzyl alcohol
(2a) in acetonitrile was stirred at 80 °C for 24 h under air
blowing. The obtained result showed that the formation
of 2–phenylbenzimidazole (3a) product was not observed
in the absence of catalyst (Table 1, Entry 1). Also, the
mentioned reaction did not proceed in the presence of
the Arg–GO (Entry 2), which excluded the contribution
of arginine–grafted graphene oxide itself as a catalyst.
Another reaction carried out to test the possibility of the
oxidative synthesis of 2–phenylbenzimidazole derivatives
by Cu0.5Co0.5Fe2O4 nanoparticles (Entry 3). Therefore,
Cu0.5Co0.5Fe2O4 nanoparticles as catalytic system was
added to the reaction media. To our surprise, 2–
phenylbenzimidazole product was obtained in 32% yield
(Entry 3) which confirmed the role of Cu0.5Co0.5Fe2O4
nanoparticles in the oxidative synthesis of 2–
phenylbenzimidazole derivatives. Since the π–π
FIGURE
Cu0.5Co0.5Fe2O4@Arg–GO (III)
4
XRD patterns of graphite (I), GO (II), and
in Figure 4. The parent graphite exhibits a characteristic
sharp peak at 26.7° related to the plane with an interlayer
spacing equal to 0.33 nm. After oxidation of graphite to
graphene oxide, the obtained GO shows the diffraction
peak at 2θ = 11.3° with an interlayer spacing value at
0.78 nm which has been assigned to the intercalation of
the large amount of oxygen containing functional groups
between the layers of the graphite. The completely oxida-
tion of the parent graphite to graphene oxide nanosheets
is confirmed by the disappearance of the graphite peak at
26.7° in the XRD pattern of GO. The diffraction character-
istic peaks related to the Cu0.5Co0.5Fe2O4 is observable at
2θ = 30.3°, 32.6°, 35.6°, 43.3°, 57.3°, and 62.8° which
corroborate to the reported ones in the literature[32–34]
and confirm the successful preparation of the
Cu0.5Co0.5Fe2O4@Arg–GO catalytic system.
The
TGA
thermograms
of
GO
and
Cu0.5Co0.5Fe2O4@Arg–GO catalytic system are showed
in Figure 2S (see Electronic Supplementary Material).
The relatively high thermal stability of the GO and
Cu0.5Co0.5Fe2O4@Arg–GO in air is observable from
Figure 2S (see Electronic Supplementary Material). As it
is clear from Figure 2S (see Electronic Supplementary
Material), in the TGA curve of Cu0.5Co0.5Fe2O4@Arg–
GO nanocomposite, three stages could be observed. In
the low temperature range, removal of adsorbed water
on the surface of the mentioned catalyst is occurred. In
the range of 148–499 °C and 499–715 °C, a large weight
loss was occurred in two stages related to the decomposi-
tion of GO and arginine.
FT–IR spectroscopy was used to confirm the chemical
attachment of arginine to the graphene oxide nanosheets
and immobilization of the Cu0.5Co0.5Fe2O4 on arginine–
grafted graphene oxide nanosheets (Figure3S, Electronic
Supplementary Material). The GO exhibits various prom-
inent bands at 3408, 1713, 1600, 1391, 1229, and 1093 cm
−1 which have been assigned to: –OH, −C = O present in
COOH, aromatic –C = C–, carboxyl –C–O, epoxy –C–O,
and alkoxy –C–O functional groups, respectively.[35] In
the IR spectrum of Arg–GO, the new bands appeared at

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GHADARI ET AL.
FIGURE
6
TEM images of GO (a), Arg–GO (b), and
Cu0.5Co0.5Fe2O4@Arg–GO (c)
interaction between graphene support and benzene skele-
ton of the reactants can enhance the efficiency of
graphene–supported nanoparticles compared to unsup-
ported ones,[36,37] Cu0.5Co0.5Fe2O4@Arg–GO as catalyst
was added to the reaction media for the oxidative synthe-
sis of 2–phenylbenzimidazole product. The obtained
result showed that Cu0.5Co0.5Fe2O4@Arg–GO has higher
catalytic activity than unsupported Cu0.5Co0.5Fe2O4
which confirmed the adsorption of aromatic reactants
on the surface of Cu0.5Co0.5Fe2O4@Arg–GO nanocompos-
ite (Entry 4). The mentioned data proves the role of the
arginine–grafted graphene oxide nanosheets as support
FIGURE
Cu0.5Co0.5Fe2O4@Arg–GO (c,d)
5
SEM images of GO (a), Arg–GO (b), and

GHADARI ET AL.
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TABLE 1 Optimization of the reaction conditions for the oxidative synthesis of 2–phenylbenzimidazole derivatives by
Cu0.5Co0.5Fe2O4@Arg–GO nanocompositea
Entry
Catalyst
Amount of catalyst
Solvent
Time (h)
Temperature (°C)
Yield (%)b
1
–
–
CH3CN
24
80
trace
2
Arg–GO
0.07
0.01
0.07
0.07
0.06
0.05
0.07
0.07
0.07
0.07
0.07
0.07
0.07
0.09
0.08
0.07
0.07
0.07
0.07
0.07
0.07
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
toluene
o–xylene
DMF
24
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
80
80
80
80
80
80
60
40
r.t.
80
80
80
80
80
80
80
80
80
80
80
80
trace
32
3
Cu0.5Co0.5Fe2O4
4
5c
Cu0.5Co0.5Fe2O4@Arg–GO
Cu0.5Co0.5Fe2O4@Arg–GO
Cu0.5Co0.5Fe2O4@Arg–GO
Cu0.5Co0.5Fe2O4@Arg–GO
Cu0.5Co0.5Fe2O4@Arg–GO
Cu0.5Co0.5Fe2O4@Arg–GO
Cu0.5Co0.5Fe2O4@Arg–GO
Cu0.5Co0.5Fe2O4@Arg–GO
Cu0.5Co0.5Fe2O4@Arg–GO
Cu0.5Co0.5Fe2O4@Arg–GO
Cu0.5Co0.5Fe2O4@GO
82
trace
49
6
7
42
8
54
9
36
10
11
12
13
14
15
16
17
18
19
20
21
22
13
49
75
20
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
35
Cu0.5Co0.5Fe2O4@Arg–GO
Cu0.5Co0.5Fe2O4@Arg–GO
CuFe2O4@Arg–GO
84
84
53
CoFe2O4@Arg–GO
61
Cu0.2Co0.8Fe2O4@Arg–GO
Cu0.4Co0.6Fe2O4@Arg–GO
Cu0.6Co0.4Fe2O4@Arg–GO
Cu0.8Co0.2Fe2O4@Arg–GO
78
83
89
70
aReaction conditions: o–phenylenediamine (1.0 mmol), benzyl alcohol (1.2 mmol), solvent (7.0 ml), air as oxidant.
bIsolated yield.
cThe reaction in the absence of air oxidant.
for immobilization of Cu0.5Co0.5Fe2O4 nanoparticles in
the oxidative synthesis of 2–phenylbenzimidazole product
(Entries 3, 4). Not surprisingly, without air blowing, the
2–phenylbenzimidazole product 3a was not detected
(Entry 5). In continue, the effect of various amounts of
Cu0.5Co0.5Fe2O4@Arg–GO nanocomposite was investi-
was also tested in other solvents, e.g. toluene, o–xylene,
and DMF (Entries 11–13), but all gave inferior results
compared to that in acetonitrile. Therefore, acetonitrile
was selected as preferred solvent for the oxidative synthe-
sis
of
2–phenylbenzimidazole
derivatives
by
Cu0.5Co0.5Fe2O4@Arg–GO
nanocomposite.
Since
gated in the mentioned reaction. 0.07
g
of
Cu0.5Co0.5Fe2O4@Arg–GO has double nature due to oxi-
dation capability of ferrite moiety and basic property of
arginine moiety, the role of arginine in the synthesis of
product 3a was examined. For this purpose, copper
substituted cobalt ferrite nanoparticles supported on
graphene oxide nanosheets without use of arginine
(Cu0.5Co0.5Fe2O4@GO) was applied in the same reaction
conditions compared to Entry 4. The obtained result con-
firmed that arginine enhances the catalytic activity of the
prepared Cu0.5Co0.5Fe2O4@Arg–GO for the synthesis of
product (Entries 4, 14) because of the basic property of
the prepared catalytic system. As it is clear from the pre-
sented data in Table 1 (Entries 2–4, 14), double nature
Cu0.5Co0.5Fe2O4@Arg–GO catalyst gave better yield
(82%) as compared with lowering the amount of the cata-
lyst which afforded the target molecule in <50% yield
(Entries 4,6,7). Although the use of 60 °C, 40 °C, and
room
temperature
of
reaction
resulted
2–
phenylbenzimidazole product in 54%, 36%, and 13%,
respectively (Entries 8–10), but improvement of the reac-
tion yield was observed at 80 °C (Entry 4, 82%). The
obtained results confirmed that heating at 80 °C is neces-
sary to form the 3a product in good yield. The reaction of
o–phenylenediamine (1a) and benzyl alcohol (2a) in the
presence of 0.07 g of Cu0.5Co0.5Fe2O4@Arg–GO catalyst

8 of 10
GHADARI ET AL.
of Cu0.5Co0.5Fe2O4@Arg–GO promotes the catalytic activ-
ity of prepared nanocomposite because ferrite and argi-
nine moieties of Cu0.5Co0.5Fe2O4@Arg–GO can catalyze
aerobic oxidation and synthetic sections of the one–pot
tandem oxidative synthesis of 2–phenylbenzimidazole
product, as it has been designed. The effect of more
amounts of Cu0.5Co0.5Fe2O4@Arg–GO catalyst than
0.07 g was tested in the oxidative synthesis of 2–
phenylbenzimidazole product (Entries 15, 16). The
obtained data are showing that increase of amount of cat-
alyst will have no significant effect on its catalytic activity.
Six CuxCo1‐xFe2O4@Arg–GO (x = 0, 0.2, 0.4, 0.6, 0.8, 1)
nanocomposites with different Cu/Co ratio were prepared
to compare their activities with Cu0.5Co0.5Fe2O4@Arg–
GO nanocomposite (Entries 17–22). The obtained results
showed that the order of the catalytic activity of CuxCo1‐
xFe2O4@Arg–GO nanocomposites can be regarded as
Cu0.6Co0.4Fe2O4@Arg–GO > Cu0.4Co0.6Fe2O4@Arg–GO
> Cu0.2Co0.8Fe2O4@Arg–GO > Cu0.8Co0.2Fe2O4@Arg–
GO > CoFe2O4@Arg–GO > CuFe2O4@Arg–GO.
After examining the reaction profiles, the conditions
of Entry 4 (0.07 g of Cu0.5Co0.5Fe2O4@Arg–GO catalyst
in acetonitrile at 80 °C under air blowing) was selected
as the optimal conditions for further investigations of
the substrate scope of the mentioned tandem oxidative
reaction. Results for the reaction of o–phenylenediamine
(1a) with a number of benzyl alcohols (2) using
Cu0.5Co0.5Fe2O4@Arg–GO nanocomposite and air
TABLE 2 Oxidative synthesis of 2–phenylbenzimidazole derivatives by Cu0.5Co0.5Fe2O4@Arg–GO nanocompositea
Melting point
Yield
(%)b
Entry
Diamine
Alcohol
Product
3a
Found
Reported
[38]
1
o–Phenylenediamine
Benzyl alcohol
82
85
91
92
78
84
92
88
90
90
94
95
82
86
292–295
292–293
223–224
156–158
232–235
231–232
223–224
275–276
255–256
218–219
287–289
260–261
181–182
243–245
106–108
[38]
[39]
[40]
[38]
[38]
[38]
[38]
[38]
[41]
[38]
[38]
[41]
[42]
2
o–Phenylenediamine
o–Phenylenediamine
o–Phenylenediamine
o–Phenylenediamine
o–Phenylenediamine
o–Phenylenediamine
o–Phenylenediamine
o–Phenylenediamine
o–Phenylenediamine
o–Phenylenediamine
o–Phenylenediamine
4–Methyl–o–phenylenediamine
4–Methyl–o–phenylenediamine
2–Methylbenzyl alcohol
2–Methoxybenzyl alcohol
2–Nitrobenzyl alcohol
3–Methylbenzyl alcohol
3–Bromobenzyl alcohol
4–Methylbenzyl alcohol
4–Bromobenzyl alcohol
4–Methoxybenzyl alcohol
4–Chlorobenzyl alcohol
4–Nitrobenzyl alcohol
3,4–Dimethoxybenzyl alcohol
Benzyl alcohol
3b
3c
223–225
157–158
234–235
231–233
222–223
276–277
256–257
219–220
288–290
259–260
183–184
243–244
107–109
3
4
3d
3e
5
6
3f
7
3 g
3 h
3i
8
9
10
11
12
13
14
3j
3 k
3 l
3 m
3n
2–Chlorobenzyl alcohol
aReaction conditions: diamine (1.0 mmol), alcohol (1.2 mmol), Cu0.5Co0.5Fe2O4@Arg–GO (0.07 g), CH3CN (7.0 ml), air as oxidant, 80 °C, 5 h.
bIsolated yield.
TABLE 3 Comparison of the results obtained using Cu0.5Co0.5Fe2O4@Arg–GO nanocomposite and some other catalysts for the oxidative
synthesis of 2–phenylbenzimidazole from o–phenylenediamine and benzyl alcohol
Molar ratio
substrate
Yield
Entry Catalyst
Reagent
Conditions
to catalyst (%)
Reference
[24]
1
2
3
4
5
6
7
8
Pt@TiO2
‐
s.f./hν/N2/30 °C/24 h
1:0.080
89
90
84
95
93
88
89
82
[25]
[26]
[27]
[28]
[29]
[23]
‐
Propylphosphonic anhydride DMSO/EtOAc/0–25 °C/4 h
‐
FePc
‐
‐
‐
‐
‐
‐
Toluene/N2/NaOtBu/120 °C/36 h 1:0.010
CuCl
s.f./Bpy/TEMPO/Air/RT/12 h
Toluene/KOH/120 °C/24 h
s.f./TEMPO/Air/110 °C/24 h
xylene/O2/130 °C/24 h
1:0.050
1:0.005
1:0.100
1:0.050
1:0.020
[RuCl(CO)(PPh3)(PNS‐Me)]
Fe2(SO4)3
tBuONa
Cu0.5Co0.5Fe2O4@Arg–GO
CH3CN/Air/80 °C/5 h
This work

GHADARI ET AL.
9 of 10
Cu0.5Co0.5Fe2O4@Arg–GO catalyst due to its double
nature of oxidation capability and basic property.
ACKNOWLEDGEMENTS
The financial support from the Iran National Science
Foundation (INSF), project number 94011834, is grate-
fully acknowledged. The partial support from the research
council of the University of Tabriz is gratefully
acknowledged.
FIGURE
7
Successive use of the Cu0.5Co0.5Fe2O4@Arg–GO
nanocomposite for the oxidative synthesis of 2–phenylbenzimidazole
compound
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