Highly efficient oxidation of alcohols to carboxylic acids using a polyoxometalate-supported chromium(iii) catalyst and CO2

Article abstract of DOI:10.1039/d0gc00388c

Direct catalytic oxidation of alcohols to carboxylic acids is very attractive, but economical catalysis systems have not yet been well established. Here, we show that a pure inorganic ligand-supported chromium compound, (NH₄)₃[CrMo₆O₁₈(OH)₆] (simplified as CrMo₆), could be used to effectively promote this type of reaction in the presence of CO₂. In almost all cases, oxidation of various alcohols (aromatic and aliphatic) could be achieved under mild conditions, and the corresponding carboxylic acids can be achieved in high yield. The chromium catalyst 1 can be reused several times with little loss of activity. Mechanism study and control reactions demonstrate that the acidification proceeds via the key oxidative immediate of aldehydes.

Full text of DOI:10.1039/d0gc00388c

View Article Online
View Journal
Green
Chemistry
Cutting-edge research for a greener sustainable future
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: Y. Wang, Z. Wu, H.
Yu, S. Han and Y. Wei, Green Chem., 2020, DOI: 10.1039/D0GC00388C.
Volume 20
This is an Accepted Manuscript, which has been through the
Number
May 2018
Pages 1919-2160
9
7
Royal Society of Chemistry peer review process and has been
accepted for publication.
Green
Chemistry
Cutting-edge research for a greener sustainable future
rsc.li/greenchem
Accepted Manuscripts are published online shortly after acceptance,
before technical editing, formatting and proof reading. Using this free
service, authors can make their results available to the community, in
citable form, before we publish the edited article. We will replace this
Accepted Manuscript with the edited and formatted Advance Article as
soon as it is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes to the
text and/or graphics, which may alter content. The journal’s standard
Terms & Conditions and the Ethical guidelines still apply. In no event
shall the Royal Society of Chemistry be held responsible for any errors
or omissions in this Accepted Manuscript or any consequences arising
from the use of any information it contains.
ISSN 1463-9262
PAPER
Paul T. Anastas et al.
The Green ChemisTREE: 20 years after taking root with the 12
principles
rsc.li/greenchem

Please do not adjust margins
Page 1 of 5
Green Chemistry
View Article Online
DOI: 10.1039/D0GC00388C
Journal Name
ARTICLE
Highly Efficient Oxidation of Alcohols to Carboxylic Acids Using
Polyoxometalate-supported Chromium(III) Catalyst and CO2
Ying Wang,a‡ZhiKang Wu,a‡Han Yu,abc*Sheng Hana*and Yongge Weibc*
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
Direct catalytic oxidation of alcohols to carboxylic acidsis very attractive, but the economical-friendly catalysis systems
have not yet well established. Here, we show that
a pure inorganic ligand-supported chromiumcompound,
www.rsc.org/
(NH4)3[CrMo6O18(OH)6] (simplified as CrMo6), could be used to effectively promote this type of reaction in the presence of
CO2.In almost all cases, the oxidation of various alcohols (aromatic and aliphatic) could be achieved under mild conditions,
and corresponding carboxylic acids can be achieved in high yield.The chromium catalyst 1 can be reused for several times
with little loss of the activity. Mechanism study and control reactions demonstrate that the acidification proceedsvia the
key oxidative immediate of aldehydes.
chemistry.15
Polyoxometalates (POMs)16,17, as a class of metal-oxide clusters
with unmatched structural diversity and functionality, are
Introduction
Selective oxidation of alcohols to carboxylic acids is an important
process for the synthesis of various fine chemicals in the chemical
industry, and has been kept a difficult task in the field of green
organic synthesis.1Traditionally, stoichiometric, toxic and expensive
considered to be an inorganic alternative to classical transition-
metal complexes. The catalytic function of POMs has attracted
much attention because their ability to design catalytically active
sites allows for ‘fine-tuning’ of their redox and acidic properties at
the atomic or molecular levels18. Recently, our group reported that
Anderson-typePOMs19 can be used as the inorganic ligand-
supported metal catalysts20 for the highly efficient aerobic oxidation
of aldehydes to carboxylic acids, amines to imines or formamides,
and alcohols to aldehydes/ ketones. These types of inorganic ligand-
supported metal catalysts possess a unique structure with a single
central metal atom supported by an inorganic ring made up of six
edge-sharing MoVIO6 octahedral scaffolds; this greatly enhances the
Lewis acidity of catalytically active sites, as well as enables the
edge-sharing MoO6 unit to act as ligand analogues to those used in
traditional organometallic complexes. Inspired by this, the versatile
tunability of Anderson-type POMs prompts us to further extend
the scope of this type of catalysts for other catalytic oxidative
transformations.
2
3
oxidants, such as KMnO4 and CrO3 , have often been used to
complete this conversion, resulting in significant waste. Therefore,
it is highly desirable to develop an environmentally friendly new
oxidation scheme. Compared with traditional oxidants, the cheap,
abundant and non-toxic nature of CO2 has brought great interest to
its use as an accelerator in oxidation reactions, including the
oxidative dehydrogenation of alkanes, the oxidation of CH4,alkyl
aromatics, C-C bond formation between aldehydes and the
like.4Although metal-ligand complexes have become a mature
technology for the selective catalytic oxidation of alcohols to
aldehydes,5 there are few reports on the oxidation of alcohols
directly to carboxylic acids. In that case, the preparation of
carboxylic acids still remains a fundamental challenge. Even with
the use of precious metal catalysts, the success or scope of
preparation is quite limited.6-14In addition, a common feature of
these catalytic systems is that they use complex and unavailable
organic ligands to increase catalytic activity and selectivity. Due to
the sensitivity of organic ligands to oxidative self-degradation, the
durability and recyclability of organometallic catalysts under mild
conditions remain a major challenge in industrial and synthetic
O
O
Mo
O
(NH4)3
O
O
O
O
Mo
O
O
O
O
O
O
O
O
Cat. 1
Cr
Mo
Mo
+
CO2(1.0 bar)
R
OH
O
R
OH
O
O
O
O
O
Mo
O
Mo
O
O
O
1
: (NH4)3[CrMo6O18(OH)6]
Scheme 1Oxidation of alcohols into carboxylic acid
a. School of Chemical and Environmental Engineering Shanghai Institute of
Technology, No. 100 Haiquan Road, Shanghai 201418 (P.R. China) E-mail:
hansheng654321@sina.com
Herein, we report that an inorganic-ligand supported chromium
catalyst 1, (NH4)3[CrMo6O18(OH)6]21 (Scheme1), which possess the
chromium(III) ion core and can be readily synthesized in one pot in
aqueous solution (see supporting information, Figure S1), can
efficiently catalyse the oxidation of various alcohols into
carboxylic acids in the presence of CO2withhigh catalytic activity
and good selectivity. More importantly, 1 could be recycled and
reused for at least six times with negligible loss of activity due to
high stability. One of the main advantages of this catalytic system is
b. Key Lab of Organic Optoelectronics & Molecular Engineering of Ministry of
Education, Department of Chemistry, Tsinghua University, Beijing 100084, P.R.
China. E-mail: yonggewei@tsinghua.edu.cn
c. State Key Laboratory of Natural and Biomimetic Drugs, Peking University, Beijing
100191 (P. R. China),E-mail: ygwei@pku.edu.cn
‡These authors contributed equally to this work.
*All correspondences should be addressed.
†Electronic Supplementary Information (ESI) available: experimental conditions,
supplementary table and NMR spectra. See DOI: 10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 2 of 5
ARTICLE
Journal Name
that it can avoid the use of complicated/sensitive organic ligands. example, entries 5 and 6).The superior oxidation efficiency of the
View Article Online
Mechanistic insight based on the observation of key intermediate combined catalyst platform indicates that every constituent plays a
DOI: 10.1039/D0GC00388C
and control reactions will be also presented.
vital role in the inorganic-ligand supported chromium catalysis.
Table 2 CO2and POM-CrIII-catalyzed oxidation of various alcohols ab
A. Reaction condition
2 Results and discussion
Standed Conditions
Cl
O
O
1
Cat. (1.0 mol %)
Initially, our studies began with the oxidation of salicyl alcoholas
a model substrate using one atmospheric pressureCO2at 80 °Cin a
solution of DMSO for 24h to assess the catalyst 1. And the efficiency
of the transformation is clearly strongly affected by the presence of
inorganic salt(Table 1, entries 1 and 2). The reaction with the
presence catalyst1 resulted in the formation of salicyl acid in 85%
yield after 24h. In contrast, we found that replacing the centric
chromium atom with other metals such as iron and nickel, a very
low and not that high yield (< 10%) was obtained under the same
conditions, being indicative of the key role of chromium in catalysis.
When the reaction was carried out with N2orO2instead of CO2, a
very low and not that high yield was obtained (entries5 and 6),
reflecting a stoichiometric alcohol oxidation. Since we have
conducted several reactions with different additives, such as KCl,
NaCl, ZnCl2 and so on, the results showed that only K3PO4 gave the
optimized yield under the same reaction conditions (see in SI, Table
S1).We propose that CO2 promoted the oxidation of alcohol to acid
in the presence of a base. And considering that the phosphate
provides a relatively large number of oxidizing products which is
most likely attributed to the PO43−acted as an electron-transfer
mediator to improve the electron transfer efficiency. Thus,
Potassium phosphate was selected as the salt for optimizing the
conditions.
O
OH
K3PO4 (0.1 equiv.)
OH
CO2 (1.0 bar)
(balloon)
R
OH +
R
OH
DMSO (2.0 ml), 24 h, 80 o
C
Br
13
14
, 86%(80%)
, 88%(81%)
O
B. Aliphatic Acids
O
O
H3CO
O
OH
OH
OH
OH
R
OCH3
R
2
3
4
5
6
7
8
9
, R=H, 92% (89%)
, R=CH3, 91% (87%)
, R=CH(CH3)2, 91% (87%)
, R=OCH3, 91% (85%)
, R=Br, 89% (85%)
, R=CI, 91% (85%)
, R=F, 91% (86%)
, R=CF3, 90% (82%)
12
, 91%(82%)
17
, R=H, 88% (84%)
18
19, R=OCH3, 86% (82%)
20
21
22
23
11
, 91% (84%)
O
, R=CH3, 86% (81%)
O
, R=Br, 87% (81%)
, R=CI, 86% (80%)
, R=F, 87% (81%)
, R=CF3, 85% (78%)
OH
OH
OH
HO
15, 84%(79%)
O
10
16, 85%(79%)
, R=NO2, 90% (84%)
C. Heterocyclic compounds
O
O
O
O
O
S
S
OH
N
OH
OH
OH
N
24
25
26
27
, 74%(70%)
, 83%(77%)
, 82%(75%)
, 79%(72%)
D. Aromatic Acids
O
OH
O
O
OH
O
O
OH
(
)
2
OH
OH
28
29
30
31
, 93%(89%)
, 95%(90%)
, 93%(91%)
O
, 94%(90%)
O
32
, 82%(78%)
O
OH
OH
OH
Cl
O
33
34
35
, 92%(89%)
, 86%(81%)
, 91%(87%)
aUnless otherwise stated, all reactions were carried out under
following conditions: Cat. 1 (1.0 mol %), alcohols (1.0 mmol),
CO2 (1.0 bar), K3PO4 (0.1 equiv.), and DMSO (2.0mL) at 80oCfor
Table 1 Optimization of reaction conditionsa
b
24 h. Yields were determined by GC-MS and1H NMR, values in
Standed Conditions
O
1
Cat. (1.0 mol %)
parentheses are the isolated yields.
OH
K3PO4 (0.1 equiv.)
OH
OH
CO2(1.0 bar)
(balloon)
+
DMSO (2.0 ml), 24 h, 80 o
C
OH
With the optimized reaction conditions in hand, the scope of
alcohols was investigated (Table2). To our delight, various
substituted aromatic and aliphatic alcohols could be smoothly
converted to the corresponding acids in remarkably high yields.
Aromatic alcohols bearing a hydrocarbon R group (benzyl alcohol,
p-toluic alcohol, 4-isopropylbenzyl alcohol, 2,4,6-trimethylbenzyl
alcohol, naphthalene methanol) were all oxidized in quantitative
yields (2-4, 11and 13). Halogen-substituted alcohols such as 4-
bromobenzyl alcohol, 4-chlorobenzyl alcohol,4-fluorobenzyl alcohol,
4-(trifluoromethyl) benzyl alcohol and 4-bromo-2-chlorobenzyl
alcohol were tolerated under the optimized reaction conditions,
and the corresponding carboxylic acids were obtained in
quantitative yields regardless of the location of the substituent (6-9
and 14). Electron-poor aromatic alcohols, for example 4-
nitrosubstituted benzyl alcohol, were highly amenable to the
reaction conditions and were oxidized to the corresponding
products with near quantitative yield (10). The electron-rich
aromatic alcohols, mono- and di-methoxy-substituted benzyl
alcohols, were also oxidized in quantitative yields (5 and 12). It is
worth noting that 4-hydroxy-3-methoxybenzyl alcohol and 2-
hydroxybenzyl alcohol undergo near quantitative conversion into
their respective carboxylic acids, without the need for carboxyl and
hydroxyl protection (15-16). All aryl-substituted conjugated
cinnamyl alcohols bearing electron-donating and electron-
withdrawing groups were oxidized quantitatively, irrespective of
the position of the substituent on the aryl ring (17-23). Various
aliphatic alcohols were also tested and gave the corresponding
Variation from the standard
conditions
Yield
Entry
(%)a
85(79)
-
1
2
3
4
5
6
7
8
None
Without cat. 1
N2(1.0 bar) instead of CO2 (1.0 bar)
O2 (1.0 bar) instead of CO2 (1.0 bar)
Cr(NO3)3.6H2O instead of cat. 1
(NH4)6Mo7O24.4H2O instead of cat. 1
Cr(NO3)3.6H2O+ (NH4)6Mo7O24.4H2O
Without K3PO4
<5
53
Trace
Trace
<10
37
aYields were determined by GC-MS analysis of the crude
reaction mixtures, values in parentheses are the isolated
yields.
We then tested different loading amount of catalyst,
temperature, also including the effect of solvent and time(Table
S1),and found that the best results being obtained in 85% yield and
99% conversion of the desired product with 1.0 mol% of chromium
catalyst in DMSO at 80 °C for 24 h. As a control experiment, only
atrace amount of the product was detected in the absence of the
chromium catalyst(entry 2).It should be noted that when Cr(NO)3,
or (NH4)6Mo7O24 also considered to be an isomerized Anderson-
structured POM with an Mo core instead of Cr as the central atom
was used as the catalyst alone, no product was provided(for
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 3 of 5
Green Chemistry
Please do not adjust margins
Journal Name
ARTICLE
products in quantitative yield (28-32). Similarly,2-chloro-2- D was determined to be 5.26 (Figure 2c). Taken together, these
propanolandcyclohexanemethanol also gave quantitative yields (34- experimental results suggested that the cleavage oVfietwheArtibcleenOznylilniec
DOI: 10.1039/D0GC00388C
35). Heterocyclic aromatic alcohols such as 3-(hydroxymethyl) C(sp3)–H bond would be the rate-determining step in the oxidation
pyridine, furfuryl alcohol, 2-thiophenemethanol and 4-methyl-5- process.
1
thiazoleethanolwere also oxidized with essentially quantitative
The H NMR studies that the progress of the oxidation of benzyl
yields of products (24-27). Finally, a gram-scale reaction was alcohol in the presence of K3PO4as an additive was also carried out
conducted with 1.0 mol% of catalyst and1.34 grams (10.0 mmol) as shown in Figure 3. To our delight, the production of benzoic acid
alcohol in 20.0mL DMSO. Analytically pure benzoic acid was isolated (12.89 ppm) was detected after 16h, and benzaldehyde as the only
in 88% yield after 24 hours (Figure S4).
intermediate product, was also observed (10.03 ppm). The
characteristic peaks of benzyl alcohol and benzaldehyde in the
The catalyst-recycling experiments were also performed. The reaction system gradually decreased, and benzyl alcohol almost
solid catalyst was isolated by filtration and was used directly for disappeared completely when the reaction time was prolonged to
subsequent oxidation of alcohols without further purification (other 24h. And also a significant proportion of benzoic acid can be
than the addition of ether to remove the hydrophobic organic detected in the system then.
products). The catalyst could be used at least five times without any
On the basis of the above experiments, polyoxometalate
degradation in catalyst performance during the reaction. Since POM catalysts reported,23,24we proposed the mechanism in
has several unique properties because of its structure, certain polar Figure4.Firstly, the formation of carbonate ester is required to
molecules (such as alcohols and amines) can freely enter and exit transform the hydroxyl group into a better leaving group. And we
the body phase of POM at room temperature, making it have a find that the key features are the formation of an intermediate
liquid phase-like reaction characteristic, which is called "pseudo- carbonate ester followed by nucleophilic substitution by DMSO and
liquid-phase behavior".22The catalyst we used is soluble in DMSO at finally deprotonation and proton shift which leads to the aldehyde
80°C. As a result, after the reaction completed, we need to get it intermediate.4eAnd then the chromium catalyst 1 activates the
filtrated from the system by simply adding ethyl acetate to the intermediate to be further oxidized to carboxylic acid.
reaction system after the oxidative experiments and the solid
catalyst was reused for next run. For the 6th run of the recycling
experiment, the yield of the acid was 78% which implied the
robustness and good stability of the catalyst (Figure S5). To confirm
the high stability of the catalyst and its associated performance, the
structure and morphology of the catalyst were further investigated
using FTIR and XRD spectroscopy. The structure and morphology of
the recycled catalyst remains unchanged from its initial state
(Figures S6 and S7).
Control experiments
Cat. 1
(1.0 mol %)
CO2 (1.0 bar, balloon)
K3PO4 (0.1 equiv)
TEMPO(0.1equiv)
or
BHT(0.1equiv)
(a)
(b)
PhCO2H
trace
PhCH2OH
1.0 mmol
+
DMSO, 24 h, 80 o
C
Cat. 1
(1.0 mol %)
CO2 (1.0 bar, balloon)
K3PO4 (0.1 equiv)
-or-
-or-
PhCO2H
PhCO2D
PhCH2OH
1.0 mmol
PhCH2OD
DMSO, 24 h, 80 o
C
1.0 mmol
KIE=KH/KD = 1.06
Cat. 1
(1.0 mol %)
CO2 (1.0 bar, balloon)
K3PO4 (0.1equiv)
PhCH2OH
PhCH2OD
0.5 mmol
+
(c)
+
PhCO2H
PhCO2D
DMSO, 24 h, 80 o
C
0.5 mmol
KIE=KH/KD = 5.36
Figure 2 Control experiments
To investigate the mechanism, several control experiments were
conducted (Figure 2). When 0.1 mmol Cr-catalyst 1 is used under an
CO2 atmosphere at 80oC for 6 hours, according to Das group's
outstanding resaerch,4eweproposed that key features were the
formation of an intermediate carbonate ester followed by
nucleophilic substitution by DMSO and finally deprotonation and
proton shift which led to the benzaldehyde formation. And then the
chromium catalyst 1 activates the further combination of the
product. The presence of trapping agents (such as BHT or TEMPO)
strongly suppressed the carbonyl compound formation, which
indicated that a free radical pathway may be involved in the present
oxidation reaction (Figure 2a).The kinetic isotope effect (KIE) was
investigated with respect to both alcoholic O–H/D bonds and
benzylic C(sp3)–H/D bonds. A clear kH/kD value of 1.02 was
determined bytwo independent reactions using benzyl alcohol-H
and benzyl alcohol-D as the substrates (Figure 2b). The
intermolecular kH/kD value for benzyl alcohol-H and benzyl alcohol-
Figure 31H NMR studies of the oxidation of benzyl alcohol.
H
H
O
CO2
O
S
O
S
DMSO
R
O
OH
R
OH

B
S
H2O
+ CO2
BH
+
HCO3
HCO3
B(base)
O
H
O
POM-CrIII
DMSO
R
H
R
O
S
R
OH
Figure 4 Proposed mechanism for POM-Cr(III)-catalyzedoxidation of
alcohols.
4 Conclusions
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 4 of 5
ARTICLE
Journal Name
In summary, we described here that the pure inorganic ligand 12. A. Itoh, S. Hashimoto, K. Kuwabara, T. Kodama, Y. Masaki.
View Article Online
supported chromium catalyst 1 can promote the direct oxidative
acidification of a variety of alcohols in the presence ofCO2 as green 13. T. Iwahama, Y. Yoshino, T. Keitoku, S. Sakaguchi, Y. Ishii. J.Org.
promoter. Both oxidation of aromatic and aliphatic alcohols Chem. 2000, 65, 6502.
proceed quite smoothly under mild conditions, affording the 14. Y. M. A. Yamada, T. Arakawa, H. Hocke, Y. Uozumi. Angew.
corresponding carboxylic acid products very efficiently. The Chem., Int. Ed. 2007, 46, 704-706.
chromium catalyst is stable and recyclable, and can be easily 15. X. Jiang, J. Zhang and S. Ma, J. Am. Chem. Soc.,2016, 138, 8344-
prepared by a simple one-step synthesis from simple inorganic 8347.
metal salts. Furthermore, the catalysis is achieved high efficiently in 16. a) N. Mizuno, K.Kamata. Coord. Chem. Rev. 2011, 255,2358-
Green Chem. 2005, 7, 830.
DOI: 10.1039/D0GC00388C
the absence of any organic ligands. We envision that this simple,
effective and environmentally benign methodology can be
potentially used for various synthetic procedures.
2370. b) D.L.Long, R.Tsunashima, L.Cronin, Angew. Chem.
Int.Ed. 2010, 49, 1736-1739. c) C. L.Hill, In Comprehensive
Coordination Chemistry-II: From Biology to Nanotechnology;
Wedd, A. G., Ed., Elsevier Ltd.: Oxford, UK, 2004, 4, 679-759. d)
A.Müller, P.Kögerler, A. W. M.Dress,Coord.Chem.Rev.2001,
222, 193-218. e) J. T.Rhule,C. L. Hill, D. A.Judd,Chem. Rev.1998,
98, 327-357. f) M. T.Pope, A.Müller,Angew. Chem. Int.
Ed.1991,30, 34-48.
Conflicts of interest
There are no conflicts of interest to declare.
Acknowledgements
17. a)Y.Kikukawa, K.Yamaguchi, N.Mizuno, Angew. Chem. Int. Ed.
2010, 49, 6096-6100.b)R.Ben-Daniel, P.Alsters, R.Neumann, J.
Org. Chem.2001,66, 8650-8653. c) I. A.Weinstock, E.
M.G.Barbuzzi, M. W.Wemple, J. J.Cowan, R. S. Reiner, D.
M.Sonnen, R. A.Heintz, J. S.Bond, C. L.Hill, Nature. 2001, 414,
191-195.
18. a)Y. Liu, S.-F. Zhao, S.-X. Guo, A. M. Bond, J. Zhang, J. Am.
Chem. Soc.2016, 138, 2617-2628.b)S.S.Wang, G.Y.Yang, Chem.
Rev.2015,115, 4893–4962. c)B. B.Sarma, I.Efremenko, R.
Neumann, J. Am. Chem. Soc.2015, 137, 5916−5922. d)C. Zou, Z.
Zhang, X. Xu, Q. Gong, J. Li, C. Wu, J. Am. Chem. Soc.2012, 134,
87−90. e)K.Kamata, K.Yonehara, Y. Nakagawa, K. Uehara, N.
Mizuno, Nat. Chem.2010, 2, 478-483.
This work was supported by the National Natural Science
Foundation of China (Nos. 21871183, 21971134, 21631007,
21471087, and 21225103), Doctoral Fund of Ministry of Education
of China No. 20130002110042, Tsinghua University Initiative
Foundation Research Program No. 20131089204 and the State Key
Laboratory of Natural and Biomimetic Drugs K20160202. The start-
up fund of the Shanghai Institute of Technology is also gratefully
acknowledged.
Notes and references
1. E.Balaraman, E. Khaskin, G. Leitus, D. Milstein. Nat. Chem. 2013,
5, 122-125.
2. A. Abiko, J. C. Roberts, T.Takemasa, S. Masamune,Tetrahedron
Lett.1986, 27, 4537-4540.
3. J. K.Thottathil, J. L.Moniot, R. H.Mueller, M. K. Y. Wong; T. P.
Kissick.J. Org. Chem.1986, 51, 3140-3143.
4. a) L. Zhang,Z.Wu,N. C.Nelson, A. D.Sadow, I. I.Slowing, S.
H.Overbury.ACSCatal. 2015, 5, 6426−6435. b) M. B.Ansari, S.-
E.Park.Energy Environ. Sci. 2012, 5, 9419−9437. c) P.Hirapara,
D.Riemer, N.Hazra, J.Gajera, M.Finger, S.Das.Green Chem.
2017, 19, 5356−5360. d) Y.Sugawara, W.Yamada, S.Yoshida,
T.Ikeno, T.Yamada.J. Am. Chem. Soc. 2007, 129, 12902−12903.
e)D. Riemer, B. Mandaviya, W. Schilling, A. C. Götz, Torben
Kühl,M. Finger, S. Das. ACS Catal. 2018, 8, 3030−3034.
5. a) B. L. Ryland, S .S. Stahl. Angew. Chem., Int. Ed. 2014,53,
8824-8832; b) Q. Cao, L. M. Dornan, L. Rogan, N. L. Hughes, M.
L. Muldoon. Chem. Commun. 2014, 50, 4524-4543. c) J. Piera, J.
E. Bäckvall. Angew. Chem. Int. Ed. 2008, 47, 3506. d) A. E. J. de
Nooy, A. C. Besemer; H. van Bekkum. Synthesis.1996, 1996,
1153 and references therein. e) R. A. Sheldon, I. W. C. E.
Arends. Adv. Synth. Catal. 2004, 346, 1051-1071.
19. a) Jr. H. T. Evans, J. Am. Chem. Soc.1948, 70, 1291-1292. b) J.
S.Anderson, Nature. 1937, 140, 850.
20. a)Z.Wei,S.Ru,Q.Zhao, H. Yu, G. Zhang; Y. Wei, Green Chem.,
2019, 21, 4069–4075.b) M. Zhang, Y. Zhai, S. Ru, D. Zang, S.
Han, H. Yu, Y. Wei, Chem. Commun.2018, 54, 10164-10167. c)
H. Yu, S. Ru, G. Y. Dai, Y. Y. Zhai, H. L. Lin, S. Han, Y. G. Wei,
Angew. Chem. Int. Ed. 2017, 56, 3867-3871.d) H. Yu, Y. Zhai, G.
Dai, S. Ru, S. Han, Y. Wei, Chem. - Eur. J. 2017, 23, 13883-
13887.
21. H. Yu, Z. Wu, Z. Wei, Y. Zhai, S. Ru, Q. Zhao, J. Wang, S. Han Y.
Wei, Commun. Chem. 2019,2,15.
22. N.Mizuno, M.Misono, Y. Nishiyama, Y. Seki, I.Kiyoto, C. Nozaki.
Res. Chem. Intermed. 2000, 26, 193.
23. F. A. Cotton, G. Wilkinson, C. A. Murillo, Advanced Inorganic
Chemistry 6thEd.JohnWiley,NewYork,1999.
24. a) I. Bauer, H. J. Knölker, Chem. Rev. 2015, 115, 3170-3387. b)
J. I. Padrón, V. S. Martín, Iron Catalysis. Springer Berlin
Heidelberg, 2011, 1-26. c) C. Bolm, J. Legros, P. J. Le, L. Zani,
Chem. Rev. 2005,36, 6217-6254. d) P. K. Sharma, R.
Kevorkiants, S. P. Visser, D. Kumar, S. Shaik,Angew. Chem. Int.
Ed. 2004, 43, 1129-1132.
6. a) O. Dalmer, K. Heyns. U.S. Pat. 1940, 2 (190), 377. b) K. Heyns.
Lieb. Ann. Chem. 1947, 558, 177.
7. L. Han, P. Xing, B. Jiang. Org. Lett. 2014, 16, 3428-3433.
8. B. N. Zope, D. D. Hibbitts, M. Neurock, R. J. Davis. Science. 2010,
330, 74-78.
9. B. P. Buffin, J. P. Clarkson, N. L. Belitz, A. J. Mol. Kundu. Catal. A:
Chem. 2005, 225, 111-116.
10. Z. H. Zhang, J. D. Zhen, B. Liu, K. L. Lv, K. J. Deng. Green Chem.
2015, 17, 1308-1311.
11. F. Kerdi, H. A. Rass, C. Pinel, M. Besson, G. Peru, B. Leger, S. Rio,
E. Monflier, A. Ponchel. Appl. Catal. 2015, 506, 206.
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 5 of 5
Green Chemistry
View Article Online
DOI: 10.1039/D0GC00388C
O
O
(NH4)3
O
O
O
Mo Mo
O
O
O
Mo
O
O
O
O
O
O
O
O
O
Cr
O
O
Mo
O
O
O
Mo Mo
O
O
1
: (NH4)3[CrMo6O18(OH)6]
Cat.1(1.0 mol %)
K3PO4 (0.1 equiv.)
O
CO2
34 examples
up to 95% yield
+
R
OH
R
OH
DMSO (2.0 ml),
24 h, 80 oC
1.0 bar
(balloon)
A green and highly efficient oxidation of alcohols to carboxylic acids using
polyoxometalate-supported chromium(III) catalyst and CO2