Cobalt Vanadium Oxide Supported on Reduced Graphene Oxide for the Oxidation of Styrene Derivatives to Aldehydes with Hydrogen Peroxide as Oxidant

Article abstract of DOI:10.1055/s-0037-1610630

Cobalt vanadium oxide supported on reduced graphene oxide showed excellent performance in the oxidation of styrene derivatives to the corresponding aldehydes with hydrogen peroxide as oxidant. An electron-donating group at the para -position of the aromatic ring facilitates the formation of the corresponding aldehyde. Compared with conventional methods, the newly designed heterogeneous catalytic system offers a promising prospect because of its economic applicability and environmental friendliness.

Full text of DOI:10.1055/s-0037-1610630

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Georg Thieme Verlag Stuttgart · New York
2018, 29, A–D
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Synlett
H. Zou et al.
Letter
Cobalt Vanadium Oxide Supported on Reduced Graphene Oxide
for the Oxidation of Styrene Derivatives to Aldehydes with Hydro-
gen Peroxide as Oxidant
Hui Zou
Chuanfeng Hu
Kaihao Chen
O
O
Guansheng Xiao
Xinhua Peng*
CoV/rGO
R2
R1
R1
O
School of Chemical Engineering, Nanjing University
of Science and Technology, Nanjing 210094,
P. R. of China
catalyst (0.02 g), 65 °C, MeCN (5 mL)
H2O2 (30 wt%, 3 equiv), 6 h
recyclable metal complex
oxide catalyst
xhpeng@mail.njust.edu.cn
R1 = aryl
up to 96% yield
R2 = H, NO2, Ph
16 examples
Received: 20.06.2018
Accepted after revision: 06.08.2018
Published online: 30.08.2018
The key to the success of this reaction is to use an effi-
cient catalyst that activates H O to oxidize styrene. In re-
2
2
DOI: 10.1055/s-0037-1610630; Art ID: st-2018-u0384-l
cent years, tremendous efforts have been dedicated to solv-
ing this problem, and many researches have been reported
in this field. The catalysts are generally divided into two
Abstract Cobalt vanadium oxide supported on reduced graphene ox-
ide showed excellent performance in the oxidation of styrene deriva-
tives to the corresponding aldehydes with hydrogen peroxide as oxi-
dant. An electron-donating group at the para-position of the aromatic
ring facilitates the formation of the corresponding aldehyde. Compared
with conventional methods, the newly designed heterogeneous cata-
lytic system offers a promising prospect because of its economic appli-
cability and environmental friendliness.
4
broad categories: homogeneous catalysts and heteroge-
5
neous catalysts. Homogeneous catalysts are less attractive
on account of difficulties in separating them from their re-
action mixtures. Compared with homogeneous catalysts,
heterogeneous catalysts can be easily isolated from the re-
action mixture. Therefore, considerable attention has been
devoted to the use of heterogeneous catalysts for the green
oxidation of styrene. Various heterogeneous catalysts have
Key words cobalt vanadium oxide, reduced graphene oxide, styrene
oxidation, hydrogen peroxide, styrene derivatives, aldehydes
6
been applied to the oxidation of styrene, including hetero-
The oxidation of olefins occupies an important position
in academic research and industrial utilization. Numerous
fine chemicals such as epoxides, diols, carbonyl com-
pounds, and aldehydes can be synthesized through this oxi-
dation reaction. Benzaldehyde, as a versatile fine chemical,
has attracted great interest due to its widespread applica-
tion in the manufacture of perfumes, dyestuffs, pharma-
poly acids, cerium-doped cobalt ferrites, molecular sieves,
A: Pankaj’s oxidation using a heterogeneous catalyst
H3PMo12O40⋅nH2O
O
80 °C, 48 h, H2O2
1
ceuticals, and agrochemicals. Benzaldehyde is usually pro-
B: Tong’s oxidation using a heterogeneous catalyst
duced by hydrolysis of (dichloromethyl)benzene, and it can
be also prepared through oxidation of toluene. However,
2
Ce0.3Co0.7Fe2O4
O
90 °C, 9 h, H2O2
both processes can cause serious pollution, which does not
satisfy the desire for environmentally friendly chemistry.
Traces of chlorine-containing contaminants, which are of-
ten present after the hydrolysis of (dichloromethyl)ben-
zene, are unacceptable in commodity chemicals; further-
more, copious waste is generated in this process. Oxidation
of toluene is usually carried out in organic solvents, which
C: Gao’s oxidation using a heterogeneous catalyst
CoVSB-5
O
70 °C, 6 h, H2O2
D: Liu’s oxidation using a heterogeneous catalyst
3
are environmentally undesirable. In view of producing
Ag-VPO
O
benzaldehyde by a green method, increasing attention has
been paid to the green oxidation of styrene to benzalde-
hyde.
8
2 °C, 3 h, TBHP
Scheme 1 Examples from the literature of the use of heterogeneous
catalysts
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Georg Thieme Verlag Stuttgart · New York — Synlett 2018, 29, A–D

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Synlett
H. Zou et al.
Letter
and silver-doped vanadium phosphorus oxides (Scheme 1).
Some catalysts are not sufficiently active to catalyze the
transformation of styrene into benzaldehyde, or they can-
not be reused with comparable properties to the fresh cata-
lyst. Hence, finding a better heterogeneous catalyst is still a
serious challenge and there is an urgent need to improve
both the performance and reusability of catalysts.
Table 1 Optimization of the Reaction Conditionsa
CoV/rGO, 65 °C
H2O2, MeCN
O
b
b
Entry
Catalyst
H
2
O
2
(equiv) Conversion (%) Yield (%)
1
2
3
4
5
6
7
8
9c
rGO
CoV
CoO
NiO
3
3
3
3
3
3
3
3
3
3
3
3
2
4
3
3
trace
81
21
18
70
77
98
90
20
53
84
97
67
99
<63
9
trace
71
19
13
42
60
91
82
15
36
67
74g
61
89
<49
3
2
Graphene, a honeycomb-like planar sheet of sp carbon
atoms in a hexagonal array, exhibits outstanding properties
in terms of its electrical conductivity, thermal conductivity,
7
and thermostability. Graphene oxide (GO) is usually
2 5
V O
prepared by chemical treatment of graphene with
KMnO /H SO according to the modified method of Hum-
NiV
4
2
4
8
mers and Offeman. The surface of GO contains an abun-
dance of oxygen-containing groups (hydroxy, carboxy, car-
bonyl, and epoxide functional groups). As a result, GO is hy-
drophilic and can be readily exfoliated in water to form a
stable colloidal suspension. GO can be reduced to give re-
CoV/rGO
NiV/rGO
CoV/rGO
CoV/rGO
CoV/rGO
CoV/rGO
CoV/rGO
CoV/rGO
CoV/rGO
rGO
1
1
0d
9
1e
duced GO (rGO), which has comparable properties to pure
10
12f
graphene, but which retains functional groups. These re-
maining groups on the surface of rGO can act as anchoring
sites for metals, providing rGO with promising performance
in the catalytic field. Although various metal nanoparticles
supported on rGO have been studied in the field of cataly-
1
1
1
3
4
5h
11
16i
sis, few researches on metal complex oxides have been re-
12
a
ported.
Reaction conditions: styrene (1 mmol, 0.10 g), catalyst
(0.02 g), MeCN (5 mL), 65 °C, 6 h.
Inspired by previous reports,5c,6b,e,f we designed
CoV/rGO and NiV/rGO composites that we prepared by us-
ing a mild and environmentally friendly hydrothermal
method. Surprisingly, these composites efficiently cata-
lyzed the oxidation of styrene to benzaldehyde. In addition,
a wide range of olefins could be transformed into aldehydes
by using CoV/rGO as catalyst. The heterogeneous catalyst
could be recycled seven times without a significant de-
crease in its catalytic performance.
b
determined by GC.
At 25 °C.
At 50 °C.
At 60 °C.
c
d
e
f
At 70 °C.
g
h
i
21% of benzoic acid was detected.
Solvents: EtOH, CH
At 80 °C.
2 2 2
Cl , EtOAc, HOAc, or H O.
the most effective catalyst for the reaction, it was impera-
tive to investigate the effect of temperature. The yield of
benzaldehyde improved on raising the temperature from
25 °C to 65 °C (entries 7, 9–11). However, when the tem-
perature was increased further to 70 °C, the yield decreased
as a result of overoxidation of benzaldehyde to benzoic acid
(entry 12). The use of three equivalents of hydrogen perox-
ide was found to be most suitable for the current catalytic
system (entry 7); further increases in the amount of hydro-
gen peroxide did not show any positive effect (entry 14),
whereas reducing the amount of hydrogen peroxide to two
equivalents led to a drop in the yield (entry 13). Subse-
quently, a series of experiments were carried out in various
solvents (entries 7, 15). The results showed that acetonitrile
was the optimal solvent for this reaction and that other sol-
vents produced inferior yields. This might be because the
high dielectric constant of acetonitrile permits the various
reaction phases to exist in a uniform condition, thereby in-
creasing the efficiency of mass transfer.13 The conversion of
styrene and the yield of benzaldehyde were lower than ex-
pected when water, the solvent with the highest dielectric
In our preliminary experiments, we selected styrene as
a model substrate to optimize the reaction conditions (Ta-
ble 1). To identify the active components that actually in-
fluence the oxidation reaction, styrene was initially treated
with various catalysts (Table 1, entries 1–8). The results re-
vealed that rGO alone did not catalyze this oxidation (entry
1). The conversion of styrene and the yield of benzaldehyde
were 81% and 71%, respectively, in the presence of cobalt
vanadium oxide alone (entry 2), which were better results
than those obtained with cobalt oxide or vanadium oxide
alone (entries 3 and 5). This suggested that there was a syn-
ergistic effect between cobalt and vanadium. A similar ten-
dency was observed with nickel vanadium oxide (entries 4–
6). Interestingly, when we used rGO as a support, CoV/rGO
and NiV/rGO showed better catalytic activities (entries 7
and 8) giving benzaldehyde in yields of 91% and 82%, re-
spectively. This was attributed to the dispersion of active
components on the rGO support, as confirmed by TEM
analysis (Fig S5; Supporting Information). After identifying
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H. Zou et al.
Letter
constant, was used. This is because the insolubility of sty-
rene in water hinders contact between the substrate and
oxidant.
Table 2 (continued)
b
Entry
9
Substrate
Product
Yield (%)
89
The oxidation of various styrene derivatives over the
solid CoV/rGO catalyst was studied under the optimal con-
ditions, and the results are shown in Table 2. Surprisingly,
we found that the position of substituent groups had a sig-
nificant effect on the yield of the desired product. When the
substituent groups were in the para-position, substrates
were easily transformed, and more of the desired product
was obtained (Table 2, entries 3, 5, and 7). However, when
substituent groups were in the ortho- or meta-position, a
lower yield was obtained (entries 1, 2, 4, and 6), especially
when the substituents were in the ortho-position (entries 1
and 4). Furthermore, the nature of the substituent group
also influenced the results of the oxidation. An electron-do-
nating group was beneficial for the transformation of the
substrate into the desire product, whereas an electron-
withdrawing group decreased the conversion of the substi-
tuted styrene (entries 3, 5, and 7–13). Conjugation of the
aromatic ring with an exocyclic double bond also increased
the yield of the target product (entry 14).
O
Br
Br
1
0
92
O
11
93
O
1
2
3
67
34
O
O2N
O2N
1
NO2
O
O
14
96
1
5
6
46
91
O
Table 2 Extension of the Substrate Scopea
1
R2
CoV/rGO (0.02 g), 65 °C, 6 h
H2O2 (3 equiv), CH3CN (5 mL)
O
O
R1
R1
a
Reaction conditions: substrate (1 mmol), MeCN (5 mL), CoV/rGO (0.02 g),
(3 equiv), 65 °C, 6 h.
Isolated yield.
b
Entry
1
Substrate
Product
Yield (%)
2 2
H O
b
Cl
Cl
55
O
In consideration of pursuing practical applications, we
investigated the stability and reusability of the CoV/rGO
catalyst. After each experiment, the catalyst was separated
from the products by centrifugation, washed twice with
ethanol and deionized water, and dried at 60 °C before re-
use in the next experimental run. The results of a recycling
test performed under the optimal conditions for styrene
oxidation are shown in Figure 1. It was clear that there were
only marginal decreases in the conversion of styrene and in
the yield of benzaldehyde after seven cycles of catalyst re-
use. This demonstrated that the catalyst exhibited an out-
standing performance in terms of its stability and reusability.
On the basis of a previous report,14 we propose a plausi-
ble mechanism for the CoV/rGO-catalyzed oxidation of ole-
fins with H O (Scheme 2). Cobalt vanadium peroxide (I) is
2
3
4
Cl
Cl
Cl
78
85
63
O
O
Cl
O
O
O
5
92
O
O
O
6
7
8
84
89
84
2
2
O
O
formed by the oxidation of H O (Step 1). The active perox-
2
2
ide species then attacks the double bond of styrene and
generates an intermediate species II (Step 2) that rapidly
breaks down to give styrene oxide with regeneration of co-
balt vanadium oxide (Step 3). Finally, the styrene oxide re-
acts with hydrogen peroxide to generate benzaldehyde
O
F
F
(Step 4).
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H. Zou et al.
Letter
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4
24.
15
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Supporting Information
Supporting information for this article is available online at
https://doi.org/10.1055/s-0037-1610630.
(
15) Typical Procedure
S
u
p
p
ortioIgnfrm oaitn
S
u
p
p
ortioIgnfrm oaitn
The oxidation of styrene derivatives was carried out in a 50 mL
two-necked round-bottomed flask. Substrate (1 mmol) was
stirred with the CoV catalyst (0.02 g) in MeCN (5.0 mL). 30 wt%
H O (0.34 g) was added slowly to the mixture, the temperature
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extracted with EtOAc and sat. aq NaCl. The organic phase was
dried (Na SO ) and purified by column chromatography.
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2) (a) Yadav, G. D.; Mistry, C. K. J. Mol. Catal. A: Chem. 1995, 102,
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67. (b) Yadav, G. D.; Haldavanekar, B. V. J. Phys. Chem. A 1997,
colorless liquid; yield: 91 mg (91%). H NMR (500 MHz, CDCl );
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δ = 10.08 (s, 1 H), 7.98–7.91 (m, 2 H), 7.69 (t, J = 7.4 Hz, 1 H),
13
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7.59 (t, J = 7.6 Hz, 2 H). C NMR (126 MHz, CDCl ); δ = 191.87,
3
135.96, 133.98, 129.24, 128.53.
©
Georg Thieme Verlag Stuttgart · New York — Synlett 2018, 29, A–D