Ammonium Tungstate as an Effective Catalyst for Selective Oxidation of Alcohols to Aldehydes or Ketones with Hydrogen Peroxide under Water - A Synergy of Graphene Oxide

Article abstract of DOI:10.1055/s-0036-1590949

Ammonium tungstate was found to be a facile and efficient catalyst for selective oxidation of alcohols to the corresponding carbonyl compounds with hydrogen peroxide as oxidant. Heterogeneous graphene oxide as acid effectively intensified the transformations and resulted in excellent yields. The use of water as solvent rendered the reactions promising both economically and environmentally.

Full text of DOI:10.1055/s-0036-1590949

SYNLETT
0
9
3
6
-
5
2
1
4
1
4
3
7
-
2
0
9
6
©
Georg Thieme Verlag Stuttgart · New York
2017, 28, A–E
letter
A
en
Synlett
H. Fu et al.
Letter
Ammonium Tungstate as an Effective Catalyst for Selective Oxida-
tion of Alcohols to Aldehydes or Ketones with Hydrogen Peroxide
under Water – A Synergy of Graphene Oxide
Huihui Fu
Chuanfeng Hu
(
NH4)5H5[H2(WO4)6]
Zhida Huang
Jianhao Zhou
Xinhua Peng*
OH
H2O2
H2O
R1
R2
O
School of Chemical Engineering, Nanjing University of Science
and Technology, Nanjing 210094, P. R. of China
xhpeng@mail.njust.edu.cn
HOOC
OH
1
6 examples
R1
R2
O
COOH
COOH
up to 98% yield
mild conditions
O
O
OH
O
HOOC
HOOC
COOH
HO
graphene oxide
Received: 17.08.2017
Accepted after revision: 15.10.2017
Published online: 17.11.2017
molybdenum and tungsten have been proposed. Unfortu-
nately, most of these methods still have some disadvantages
such as the use of phase-transfer agents, employment of
flammable organic solvents, or difficulties in preparing the
polyoxometalate. Therefore, exploring a facile and efficient
catalytic system that can be performed in water remains a
crucial challenge.
DOI: 10.1055/s-0036-1590949; Art ID: st-2017-w0628-l
Abstract Ammonium tungstate was found to be a facile and efficient
catalyst for selective oxidation of alcohols to the corresponding carbon-
yl compounds with hydrogen peroxide as oxidant. Heterogeneous
graphene oxide as acid effectively intensified the transformations and
resulted in excellent yields. The use of water as solvent rendered the re-
actions promising both economically and environmentally.
In addition, the presence of acid would normally pro-
mote the oxidation of alcohols and result in satisfactory
yield. Some reports demonstrated that graphene oxide (GO)
could be used as heterogeneous acid in chemistry transfor-
mations.14 As a readily available and inexpensive material,
GO has drawn increasing attention because of the fast
charge mobility, high surface area etc.15 GO with carboxyl
groups at the edges of the sheet are conventionally ob-
tained by modified Hummers method. Especially, due to the
oxygen-containing groups, GO shows better hydrophilicity
than graphene. GO could easily disperse in water to produce
stable colloidal suspensions under a mild ultrasonic treat-
ment.16 GO was also applied for the oxidation reaction as an
Key words alcohol oxidation, hydrogen peroxide, ammonium tung-
state, graphene oxide, water
Selective oxidation of alcohols to the corresponding car-
bonyl compounds is an important organic transformation
in laboratory reactions and industry procedures. Tradition-
ally, the oxidation of alcohols generally requires stoichio-
metric amounts of inorganic oxidants such as chromi-
um(VI) and manganese(VII) reagents. These reagents are
1
2
usually toxic and hazardous, and deliver a large quantity of
heavy-metal waste. In recent years, hydrogen peroxide as
an ideal oxidant has attracted wide attention because it is
cheap, mild, atom-efficient and generates water as the only
17
oxidizing agent in several reports (Scheme 1). Hence, the
oxidation properties of GO should be considered.
3
A: Dreyer's oxidation using GO
by-product. Many catalytic systems involving transition-
OH
O
metal complexes with hydrogen peroxide have been inves-
tigated, such as cobalt, copper, palladium, ruthenium,7
4
5
6
GO (200 wt%)
00 °C, 24 h
8
9
10
iron, titanium or other complexes, typically in organic
solvents. In particular, tungsten and molybdenum com-
pounds appear to be efficient catalysts for the oxidation of
1
B: Mirza-Aghayan's oxidation using GO
1
1
alcohols by hydrogen peroxide. In 1986, DiFuria and co-
OH
O
12
workers first reported the tungstate-catalyzed oxidation
of alcohols by using hydrogen peroxide in coordination
with a phase-transfer agent. Afterwards, Noyori and co-
GO (200 wt%)
toluene, 80 °C, 2 h
ultrasonic bath
13
workers optimized the system by operating under strong-
ly acidic conditions with phase-transfer agents. Subse-
quently, a series of systems involving polyoxometalate of
Scheme 1 Examples from the literature for GO as an oxidant
©
Georg Thieme Verlag Stuttgart · New York — Synlett 2017, 28, A–E

B
Synlett
H. Fu et al.
Letter
Inspired by these previous results, we developed an effi-
cient and simple catalytic system for the transformation of
alcohols into carbonyl compounds under mild conditions.
Specifically, this method utilized hydrogen peroxide as the
oxidant in the presence of ammonium tungstate as catalyst
by a synergic effect from GO under water. Additionally, the
described method could be applied to a wide range of alco-
hols with excellent yields. GO as heterogeneous acid could
be efficiently reused in at least seven cycles without loss of
activity.
Table 1 Optimization of Reaction Conditionsa
OH
O
(NH4)5H5[H2(WO4)6]
H2O2, GO, H2O
2 2
H O
(equiv.) Conv. (%)b Yield (%)b
Entry Cat. (mmol%) Synergists
1
–
2
3
2
2
2
2
3
3
3
3
3
3
3
3
3
3
3
-
GO
GO
GO
GO
GO
GO
GO
–
4
4
4
4
4
4
4
4
4
4
4
4
4
2
3
4
4
4
–
–
trace
96
trace
94
2
3
100
83
97
Initial experiments were carried out with cyclohexanol
as the model compound to investigate the optimized condi-
tions (Table 1). Cyclohexanol was first treated with various
catalytic systems under the same conditions. In the absence
of the catalyst, only trace amounts of cyclohexanone could
be detected (entry 1). Raising the amount of ammonium
tungstate increased the conversion (entries 2–3). The re-
sults showed that the use of 0.03 mmol ammonium tung-
state was the most conducive to the synthesis of cyclohexa-
none, with a yield of 97% (entry 3). To gain insight into the
difference of catalysts, cyclohexanol was used in combina-
tion with four other catalysts (entries 4–7). In comparison
with ammonium tungstate, the other four catalysts ap-
peared to be poor in activity. Subsequently, to evaluate the
synergic performance of GO, various acids were placed in
the alcohol oxidation under water and the results are sum-
marized in entries 8–13. In the absence of acid, the yield of
cyclohexanone was disappointing. It is noted that acids
could promote alcohol oxidation to improve the selectivity.
The results revealed that different homogeneous acids
could also benefit the oxidation of alcohols. However, the
best conversion and yield were observed when GO was
used as the acid under identical reaction conditions. Fur-
thermore, GO could be separated and recycled easily from
the reaction mixture. Thus, among these acids, GO as a
promising and recyclable synergist was found to be the
most profitable to the reaction with water as the solvent. It
was found that raising the amount of hydrogen peroxide
from 2 equivalents to 4 equivalents improved the yield of
cyclohexanone (entries 3, 14, and 15). Table 1 shows that
the use of 4 equivalents of hydrogen peroxide resulted in
the best yield of 97%. A comparison of different reaction
temperatures showed that the highest yield was observed at
4c
5d
80
49
32
6e
54
39
7f
52
52
8
95
23
9g
HCOOH
92
90
1
0g
CH
SO
H PO
3
COOH
90
89
11g
H
93
91
2
4
g
12
3
4
86
82
3g
1
1
1
1
H
2
C
2
O
4
87
76
4
GO
GO
GO
GO
GO
GO
GO
91
91
5
94
92
6h
95
95
17i
100
<50
trace
trace
81
8j
1
1
<50
trace
trace
9
0
2
3
a
Reaction conditions: cyclohexanol (2 mmol, 0.2 g), GO (0.01 g), water (3
[H (WO ] (0.03 mmol, 0.05 g), 70 ℃, 11 h.
Determined by GC.
mL), (NH
4
)
5
H
5
2
4 6
)
b
c
d
e
f
(
NH
4
4 6 7 24
) Mo O .
NH
VO
3
.
H
3
PW12
O
40
.
Na
2
WO
Synergists (70 wt%, 0.1 equiv).
5 ℃.
4
.
g
h
i
6
75 ℃.
j
Solvents: ethyl acetate, dichloromethane, tetrahydrofuran, ethanol.
Table 2 A Comparison with Reported Methods
Entry Catalyst
Synergists Oxi-
dant
Temp. Time
Yield
(%)
(°C)
(h)
7
0 °C (entries 3, 16, and 17). Complete conversion of the sub-
1a
(NH
4
)
5
H
5
[H
2
(WO
4
)
6
]
GO
–
H
2
O
2
70
11
97
strate could be achieved by catalytic action of 11 hours.
Moreover, several solvents were examined in the subsequent
experiments (entries 3, 18).
2b
–
GO
GO
100
80
24
2
>98
98
3c
–
–
a
Reaction conditions: cyclohexanol (2 mmol, 0.2 g), GO (0.01 g), water (3
[H (WO (0.03 mmol, 0.05 g). Determined by GC
Reaction conditions: 200 wt% GO, Conversion of cyclohexanol into cyclo-
mL), (NH
4
)
5
H
5
2
4
)
6
]
.
b
1
hexanone was monitored by H NMR spectroscopy.
c
Reaction conditions: Conversion of cyclohexanol into cyclohexanone, 200
wt% GO, toluene, ultrasonic bath.
©
Georg Thieme Verlag Stuttgart · New York — Synlett 2017, 28, A–E

C
Synlett
H. Fu et al.
Letter
The results showed that the use of the other solvents
gave inferior yields. It was easier for GO to disperse in water
to form stable colloidal suspensions under mild ultrasonic
treatment, which could then be used for the oxidation of al-
cohol with high selectivity and yield. Alcohol oxidations
that can be conducted in water are considerably safer,
cheaper, and more sustainable. Hence, compared with oth-
er solvents, water is a green and desirable solvent. The oxi-
dative properties of GO have been investigated in several
studies; however, to our knowledge, no results have shown
that GO can be used as an oxidizing agent under these reac-
tion conditions (entries 19 and 20).
Yield (%)b
Entry
5
Substrate
Product
OH
O
92
OH
OH
O
O
6
7
93
A comparison of our work with the reported methods is
92
90
17
shown in Table 2. These methods were all treated with cy-
clohexanol to investigate the oxidation reaction. Table 2 in-
dicates that these transformations occurred under various
conditions, including catalyst loading, temperature, and re-
action time.
OH
O
8
9
Following the optimization study, various substrates
were scoped with respect to the catalytic oxidation with
hydrogen peroxide over ammonium tungstate promoted by
GO (Table 3). To our delight, secondary alcohols including
cyclic alcohols, linear alcohols, and aromatic alcohols were
effectively converted into the corresponding ketones with
satisfactory yields. For example, the isolated yields of cyclo-
hexanone, 2-octanone, and acetophenone were 93, 90, and
OH
O
Cl
Cl
89
90
96
1
0
1
OH
O
OH
OH
O
O
96%, respectively (entries 1, 10, and 11). Unsurprisingly, the
1
aromatic primary alcohols could be oxidized to the corre-
sponding aldehydes in excellent yields.
Table 3 Substrate Scope of the Alcohol Oxidation Reactiona
12
94
(
NH4)5H5[H2(WO4)6] (0.03 mmol)
OH
R2
O
GO (0.01 g)
R1
H2O2 (4 equiv)
H2O (3 mL)
R1
R2
OH
O
70 °C
1
3
4
93
98
Entry
1
Substrate
Product
Yield (%)b
93
OH
O
Cl
Cl
OH
OH
O
O
1
OH
OH
O
2
3
89
95
1
5
6
96
91
O
OH
O
1
OCH3
OH
OCH3
O
a
Reaction conditions: alcohol (2 mmol), GO (0.01 g), water (3 mL),
(NH ) H [H (WO ) ] (0.03 mmol, 0.05 g), 30% H O (8 mmol, 0.92 g), 11 h,
4
5
5
2
4
6
2
2
7
0 °C.
Isolated yield.
4
94
b
©
Georg Thieme Verlag Stuttgart · New York — Synlett 2017, 28, A–E

D
Synlett
H. Fu et al.
Letter
Furthermore, selective oxidation of cyclohexanol was
used as the model reaction to test the reusability of GO (Fig-
ure 1). After completing the reaction, GO could be readily
separated from the mixtures by centrifugation. The conver-
sion was 99% and the yield was 97% even after seven recy-
cling runs. The results also showed that GO was suitable for
the catalytic system.
–
HO
O
2–
R1
HO
O
O
O
W
O
R2
H
O
O
H
W
O
O
GO-H
step 1
O
OH
O
OH
H
H2O
step 4
step 2
H2O
H2O
H2O2
–
–
HO
O
HO
O
H2O2
+
NH4)5H5[H2(WO4)6]
H
O
O
O
W
O
W
O
(
R1
R2
O
H
O
O
H
O
H
O
R1
step 3
R2
H
O –
O
W
O
HO
H
O
Figure 1 Recycling of GO in the cyclohexanol oxidation reaction
R1
O
O
R2
On the basis of previous reports,18 we proposed a plau-
sible catalytic mechanism for the ammonium tungstate cat-
alyzed transformation of alcohols with hydrogen peroxide
in the synergy of GO (Scheme 2). A diperoxo active species
was generated from the action of ammonium tungstate and
hydrogen peroxide. The acid groups on GO promoted the
proton transfer to the diperoxotungstate to form the reac-
tive species (step 1) that acted on alcohols (step 2). After-
wards, the corresponding carbonyl compound was generat-
ed from a six-membered transition state to dehydrogenate
Scheme 2 A plausible mechanism for the ammonium tungstate cata-
lyzed selective oxidation of alcohols
References and Notes
(
1) (a) Enache, D. I.; Edwards, J. K.; Landon, P.; Solsona-Espriu, B.;
Carley, A. F.; Herzing, A. A.; Watanabe, M.; Kiely, C. J.; Knight, D.
W.; Hutchings, G. J. Science 2006, 311, 362. (b) Lin, X.; Nie, Z. Z.;
Zhang, L. Y.; Mei, S. C.; Chen, Y.; Zhang, B. S.; Zhang, R. L.; Liu, Z.
G. Green Chem. 2017, 19, 2164.
(step 3) followed by the re-oxidization of monoperoxotung-
state species to the diperoxotungstate species (step 4).
In conclusion, a clean, economical, and efficient catalyt-
ic system for selective oxidation of alcohols has been devel-
oped. The ammonium tungstate catalyst in the synergy of
GO could be effective for the preparation of carbonyl com-
pounds with high yield and with excellent selectivity. The
new method exhibits promising potential for industrial ap-
plications.
(2) (a) ten, Brink. G. J.; Arends, I. W. C. E.; Sheldon, R. A. Science
2000, 287, 1636. (b) Lee, D. G.; Spitzer, U. A. J. Org. Chem. 1970,
35, 3589. (c) Parmeggiani, C.; Matassini, C.; Cardona, F. Green
Chem. 2017, 19, 2030.
19
(
3) (a) Guo, M. L.; Li, H. Z. Green Chem. 2007, 9, 421. (b) Chen, L.;
Zhou, T.; Chen, L. F.; Ye, Y. M.; Qi, Z. W.; Frenud, H.;
Sundmacher, K. Chem. Commun. 2011, 9354. (c) Jiang, N.;
Ragauskas, A. J. Tetrahedron Lett. 2005, 46, 3323. (d) Ma, Q. G.;
Xing, W. Z.; Xu, J. H.; Peng, X. H. Catal. Commun. 2014, 53, 5.
4) (a) Sharma, R. K.; Gulati, S.; Pandey, A. J. Porous Mater. 2013, 20,
(
937. (b) Li, M.; Wu, S.; Yang, X.; Hu, J.; Peng, L.; Bai, L.; Huo, Q.;
Supporting Information
Guan, J. Appl. Catal., A 2017, 543, 61.
(
5) (a) Kato, C. N.; Hasegawa, M.; Sato, T.; Yoshizawa, A.; Inoue, T.;
Mori, W. J. Catal. 2005, 230, 226. (b) Sun, N.; Zhang, X.; Jin, L.;
Hu, B.; Shen, Z.; Hu, X. Catal. Commun. 2017, 101, 5.
Supporting information for this article is available online at
https://doi.org/10.1055/s-0036-1590949.
S
u
p
p
ortioIgnfrm oaitn
S
u
p
p
ortioIgnfrm oaitn
(6) Liu, J. H.; Wang, F.; Sun, K. P.; Xu, X. L. Catal. Commun. 2008, 9,
3
86.
7) (a) Barak, G.; Dakka, J.; Sasson, Y. J. Org. Chem. 1988, 53, 3553.
b) Shimoyama, Y.; Ishizuka, T.; Kotani, H.; Shiota, Y.;
(
(
Yoshizawa, K.; Mieda, K.; Ogura, T.; Okajima, T.; Nozawa, S.;
Kojima, T. Angew. Chem. 2016, 128, 14247.
©
Georg Thieme Verlag Stuttgart · New York — Synlett 2017, 28, A–E

E
Synlett
H. Fu et al.
Letter
(
8) (a) Bhat, P. B.; Bhat, B. R. New J. Chem. 2015, 39, 273. (b) Martin,
(17) (a) Dreyer, D. R.; Jia, H. P.; Bielawski, C. W. Angew. Chem. 2010,
122, 6965. (b) Mirza-Aghayan, M.; Boukherroub, R.; Nemati, M.;
Rahimifard, M. Tetrahedron Lett. 2012, 53, 2473. (c) Mirza-
Aghayan, M.; Kashef-Azar, E.; Boukherroub, R. Tetrahedron Lett.
2012, 53, 4962. (d) Dreyer, D. R.; Bielawski, C. W. Chem. Sci.
2011, 2, 1233.
S. E.; Garrone, A. Tetrahedron Lett. 2003, 44, 549.
(9) Zhang, X. M.; Zhang, Z. R.; Suo, J. S.; Li, S. B. Catal. Lett. 2000, 66,
1
75.
10) (a) Espenson, J. H.; Zhu, Z.; Zauche, T. H. J. Org. Chem. 1999, 64,
191. (b) Sharma, R. K.; Yadav, M.; Monga, Y.; Gaur, R.;
(
1
Adholeya, A.; Zboril, R.; Varma, R. S.; Gawande, M. B. ACS Sus-
tainable Chem. Eng. 2016, 4, 1123. (c) Prakash, S.; Charan, C.;
Singh, A. K.; Shahi, V. K. Appl. Catal., B 2013, 132, 62. (d) Malan,
F. P.; Singleton, E.; Bulling, B. W.; Cukrowski, I.; Rooyen, P. H.;
Landman, M. Mol. Catal. 2017, 432, 47. (e) Ren, F.; Tian, X.; Ren,
Y. L.; Zhao, S.; Wang, J.; Zhao, B. Catal. Commun. 2017, 101, 98.
(18) (a) Sheldon, R. A.; Arends, I.; Dijksman, A. Catal. Today 2000, 57,
157. (b) Zhan, B. Z.; Thompson, A. Tetrahedron 2004, 60, 2917.
(c) Li, X.; Cao, R.; Lin, Q. Catal. Commun. 2015, 69, 5. (d) Ma, Q.
G.; Xing, W. Z.; Xu, J. H.; Peng, X. H. Chem. Lett. 2014, 43, 941.
(e) Xia, X. M.; Gao, X.; Xu, J. H.; Hu, C. F.; Peng, X. H. Synlett 2016,
28, 607.
(
f) Hu, Y. L.; Fang, D. C. R. Chim. 2015, 18, 614.
11) (a) Maurya, M. R.; Saini, N.; Avecilla, F. Inorg. Chim. Acta 2015,
38, 168. (b) Choi, J. H.; Kim, J. K.; Park, D. R.; Kang, T. H.; Song, J.
(19) Experimental procedures: GO (0.01 g) was added into water (3
mL) to generate a stable colloidal suspension under mild ultra-
sonic treatment. Afterwards, the alcohol (2 mmol) and
(NH ) H [H (WO ) ] (0.03 mmol, M = 1602) were added. The
(
4
H.; Song, I. K. J. Mol. Catal. A: Chem. 2013, 371, 111.
4
5
5
2
4 6
(
12) Bortolini, O.; Conte, V.; DiFuria, F.; Modena, G. J. Org. Chem.
mixture was stirred for 15 min at room temperature. Subse-
quently, hydrogen peroxide (30 wt%, 8 mmol) was added drop-
wise and the mixture was heated to 70 °C until the reaction was
complete (monitored by TLC). GO could then be readily sepa-
rated from the mixtures by centrifugation, and then ethyl
acetate was added to the mixture to extract organic constitu-
ents. Finally, the organic extracts were concentrated under
reduced pressure and purified by column chromatography.
1
986, 51, 2661.
13) (a) Sato, K.; Aoki, M.; Takagi, J.; Noyori, R. J. Am. Chem. Soc. 1997,
19, 12386. (b) Sato, K.; Takagi, J.; Aoki, M.; Noyori, R. Tetrahe-
(
1
dron Lett. 1998, 39, 7549.
(
14) (a) Dhakshinamoorthy, A.; Alvaro, M.; Concepción, P. Chem.
Commun. 2012, 5443. (b) Wang, H. L.; Deng, T. S.; Wang, Y. X.;
Cui, X. J.; Qi, Y. Q.; Mu, X. D.; Hou, X. L.; Zhu, Y. L. Green Chem.
2
013, 15, 2379.
15) Stankovich, S.; Piner, R. D.; Nguyen, S. B. T.; Ruoff, R. S. Carbon
006, 44, 3342.
Cyclohexanone (Table 2, entry 1): Yield: 0.18 g (93%); colorless
1
(
(
liquid. H NMR (500 MHz, CDCl ): δ = 2.37 (t, J = 6.7 Hz, 4 H),
3
13
2
2.07–1.82 (m, 4 H), 1.82–1.62 (m, 2 H). C NMR (126 MHz,
16) Mirza-Aghayan, M.; Kashef-Azar, E.; Boukherroub, R. Tetrahe-
dron Lett. 2012, 53, 4962.
CDCl ): δ = 211.98, 41.92, 26.99, 24.94
3
©
Georg Thieme Verlag Stuttgart · New York — Synlett 2017, 28, A–E