Magnetic graphene nanocomposite as an efficient catalyst for hydrogenation of nitroarenes

Article abstract of DOI:10.1016/j.cclet.2013.03.036

Graphene-Fe₃O₄ nanocomposite (G-Fe₃O ₄) was synthesized by a chemical co-precipitation method which was used as an efficient catalyst for the reduction of nitroarenes with hydrazine hydrate. The method has been

Full text of DOI:10.1016/j.cclet.2013.03.036

Chinese Chemical Letters 24 (2013) 539–541
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Chinese Chemical Letters
journal homepage: www.elsevier.com/locate/cclet
Original article
Magnetic graphene nanocomposite as an efficient catalyst for hydrogenation
of nitroarenes
*
Cheng Feng, Hai-Yan Zhang, Ning-Zhao Shang, Shu-Tao Gao, Chun Wang
College of Sciences, Agricultural University of Hebei, Baoding 071001, China
A R T I C L E I N F O
A B S T R A C T
Article history:
Graphene-Fe3O4 nanocomposite (G-Fe3O4) was synthesized by a chemical co-precipitation method
which was used as an efficient catalyst for the reduction of nitroarenes with hydrazine hydrate. The
method has been applied to a broad range of compounds with different properties and the yields were in
the range of 75%–92%. The G-Fe3O4 catalyst can be readily recovered and reused 5 times without
significant loss of the catalytic activity.
Received 21 January 2013
Received in revised form 12 February 2013
Accepted 27 February 2013
Available online 19 April 2013
ß 2013 Chun Wang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Keywords:
Nitroarenes
Magnetic graphene
Reduction
Hydrazine hydrate
1. Introduction
supported on magnetic nanoparticles can be quickly and easily
recovered in the presence of external magnetic field for reuse.
Aromatic amines are central intermediates and key precursors
in the synthesis of dyes, pigments, agrochemicals and pharma-
ceuticals [1,2]. The usual methods for preparation aromatic amines
are reduction using Raney-nickel [2], which is combustible in air
after the use. Pd-carbon [3], or Pt-Ni [4] are used frequently, but
these precious metal complexes are expensive. The use of metals
such as Fe or Zn powder in acidic media for the reduction of
aromatic nitro compounds is also widely used [5,6]. However, the
main drawback of all these methods is the lack of selectivity.
Among other nitro reducing agents, hydrazine hydrate has been
applied successfully [1,7]. This method has following advantages:
mild reaction conditions, simple post-reaction treatments, envi-
ronment-friendly [8]. The catalysts employed in hydrazine hydrate
reduction including iron-compound [9,10], mixed metal com-
pounds [4,11] and zeolite [7] have been reported.
Graphene (G) is a type of novel and interesting carbon material
and has caused wide attention in recent years [12]. The properties
of graphene such as high thermal, chemical, and mechanical
stability as well as high surface area also represent desirable
characteristics as 2D support layers for metallic and bimetallic
nanoparticles in heterogeneous catalysis applications [13]. In
recent years, nanoscale magnetic catalysts have shown great
potentials in catalysis because of their high dispersion, high
reactivity and magnetic to easy phase separation [14,15]. Catalysts
The preparation of graphene-based magnetic nanocomposite
has been reported recently [16]. However, to the best of our
knowledge, there has been no report yet about the use of G-based
magnetic nanocomposite as the catalyst for organic synthesis.
In continuation of our interest in exploring efficient catalysts for
organic transformations [17], in this work, a superparamagnetic
graphene-Fe3O4 nanocomposite (G-Fe3O4) was synthesized by a
co-precipitation method and its catalytic activity was evaluated for
the reduction of aromatic nitro compounds for the first time with
hydrazine hydrate as a hydrogen donor.
2. Experimental
Graphite powder (320 mesh) and hydrazine hydrate (80%) were
provided by the Bohaixin Co., Ltd. (Baoding, China). Nitroaromatic
substrates were purchased from Aladdin Reagent Company. The
size and morphology of the magnetic nanoparticles were measured
by transmission electron microscopy (TEM) using a JEOL model
JEM-2011(HR) at 200 kV The Fe content was determined by means
of visible spectrophotometry with o-phenanthroline. Graphene
and magnetic graphene nanoparticles (G-Fe3O4) were synthesized
and characterized according to the method reported in our
previous work [18]. Fe3O4 was synthesized by the same method
for the preparation of G-Fe3O4 without adding graphene.
The nitroarenes were reduced with hydrazine hydrate cata-
lyzed by G-Fe3O4. Typically, 2.0 mmol of nitroarene, 0.01 g of
G-Fe3O4 and 4.0 mmol of 80% hydrazine hydrate were added
sequentially into a 50 mL round-bottom flask. The mixture was
* Corresponding author.
E-mail address: wangc69@yahoo.com.cn (C. Wang).
1001-8417/$ – see front matter ß 2013 Chun Wang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
http://dx.doi.org/10.1016/j.cclet.2013.03.036

[
C. Feng et al. / Chinese Chemical Letters 24 (2013) 539–541
Fig. 1. TEM image of graphene (a) and G-Fe3O4 composite (b).
stirred at 70 8C for an appropriate time depending upon the nature
of the substrate. Upon completion of the reaction (monitored by
TLC), 5 mL of ethanol was added and a homogeneous solution was
obtained. The mixture was cooled to room temperature and the
catalyst was separated by a magnet for recycling tests. The reaction
mixture was concentrated under reduced pressure. The residue
was subjected to silica-gel column chromatography using petro-
leum ether-ethyl acetate as an eluent to give pure product.
G-Fe3O4. Thus, it seemed to us that the graphene played an
important role in this more efficient catalyst.
To demonstrate the generality of this model reaction, the
reduction of a series of aromatic nitro compounds was studied
under the optimized reaction conditions. As shown in Table 2,
aromatic nitro compounds containing various electron-donating
or electron-withdrawing groups were converted to the corre-
sponding amines in good yields. In all cases, amines were found to
be the only product of the reactions and the usual side products of
nitro reduction were not observed in the final product mixtures.
The present method was highly chemoselective in the presence of
sensitive functional groups such as halogens and –COOH. In some
cases, the catalytic activity was significantly influenced by the
position of the substituents on the aromatic ring. For example, the
presence of a methyl group ortho to the nitro group required a
longer reaction time than the para-analogs due to steric effects.
The reusability and recycling of the G-Fe3O4 were also
investigated under the same condition, except that amount of
catalyst was reduced to 1%. At the end of the reduction, the catalyst
was separated by a magnet, washed with ethanol, dried at 100 8C
for 1 h and reused for the next reaction. The catalytic activity of the
G-Fe3O4 did not show significant decrease even after five runs. The
ferrum content in fresh G-Fe3O4 and used G-Fe3O4 (five times)
3. Results and discussion
The morphology of the G and G-Fe3O4 was determined by TEM.
As shown in Fig. 1(a), G consisted of randomly aggregated and
crumpled sheets to form a disordered solid. It was clear that these
graphenes were essentially transparent and no large graphitic
crystallites were observed. Fig. 1(b) shows that iron oxide
nanoparticles were successfully coated on the surface of the G
to form a G-Fe3O4 nanocomposite and the size of Fe3O4 particles
ranged from 25 nm to 50 nm.
The catalytic activity of G-Fe3O4 was evaluated by the reduction
of aromatic nitro compounds with hydrazine hydrate. In our initial
study, nitrobenzene was chosen as the model reactant in order to
examine the efficiency of different catalysts (i.e. graphene, Fe3O4
and G-Fe3O4). As shown in Table 1, no product was obtained in the
absence of the catalyst (Table 1, entry 1), indicating that the
catalyst was necessary for the reaction. Among the catalysts tested,
G-Fe3O4 was found to be the most effective catalyst since it gave
the highest yield of product (Table 1, entry 5). Similar but lower
yields were obtained when using graphene, Fe3O4 or their hybrid
as the catalyst. The results indicated that the graphene [13] and
Fe3O4 both were catalytically active for this reaction. From Fig. 1,
one can observe that the Fe3O4 was distributed on the graphene
sheets with an average size of 25–50 nm. This shows that the active
sites of the catalyst were stabilized and dispersed on graphene and
there may have a synergistic effect [19] on the catalytic activity of
Table 2
Reduction of nitroarenes by hydrazine hydrate in the presence of G-Fe3O4.a
Entry
Nitro compound
Product
T (8C)
Time
Yield
(%)b
(min)
1
2
70
70
20
85
88.4
89.0
]
[TD$INLE]
NO2
NH2
[DT$INLE]
[DT$INLE]
H C
NO
2
H C
NH
3
3
2
3
CH
70
360
83.9
CH
3
3
[
[TD$INLE]
NH
NO
2
2
4
5
70
70
80
90.5
91.9
]
[TD$INLE]
Br
NH2
Br
NO2
NH
NO
255
2
2
Table 1
[
[TD$INLE]
Reduction of nitrobenzene with different catalysts.a
Entry
Catalyst
Time (min)
Isolated yield (%)b
6
7
8
a
Reflux
Reflux
Reflux
240
300
300
91.4
90.5
82.4
]
[TD$INLE]
EtOOC
NO
EtOOC
NH2
NH2
2
1
2
3
4
5
–
90
90
90
90
90
0.0
85.9
84.9
87.7
93.6
Graphene
Fe3O4
]
[TD$INLE]
HOOC
NO2
HOOC
G+Fe3O4 (1:1 wt)
G-Fe3O4
[DT$INLE]
H2N
NO2
[TD$INLE]
H N
NH
2
2
a
Reaction condition: molar ratio of nitrobenzene to hydrazine hydrate is 1:2,
Reaction condition: molar ratio of nitroarenes to hydrazine hydrate is 1:2,
amount of catalyst is 5%.
amount of catalyst is 5%, reaction temperature is 70 8C.
The products were identified by IR and 1H NMR.
The products were characterized by IR and 1H NMR.
b
b

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541
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