Selective oxidation of alcohols to esters using heterogeneous Co 3O4-N@C catalysts under mild conditions

Article abstract of DOI:10.1021/ja403615c

Novel cobalt-based heterogeneous catalysts have been developed for the direct oxidative esterification of alcohols using molecular oxygen as benign oxidant. Pyrolysis of nitrogen-ligated cobalt(II) acetate supported on commercial carbon transforms typical homogeneous complexes to highly active and selective heterogeneous Co₃O₄-N@C materials. By applying these catalysts in the presence of oxygen, the cross and self-esterification of alcohols to esters proceeds in good to excellent yields.

Full text of DOI:10.1021/ja403615c

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Article
Selective Oxidation of Alcohols to Esters Using
Heterogeneous Co3O4-N@C Catalysts under mild Conditions
Rajenahally V. Jagadeesh, Henrik Junge, Marga-Martina
Pohl, Jörg Radnik, Angelika Brückner, and Matthias Beller
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/ja403615c • Publication Date (Web): 13 May 2013
Downloaded from http://pubs.acs.org on May 31, 2013
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Selective Oxidation of Alcohols to Esters Using Heterogeneous
Co O -N@C Catalysts under mild Conditions
3
4
Rajenahally V. Jagadeesh, Henrik Junge, Marga-Martina Pohl, Jörg Radnik, Angelika Brückner, and Matthias Beller*
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Leibniz-Institut für Katalyse e. V. an der Universität Rostock, Albert-Einstein-Str. 29a, 18059 Rostock, Germany
ABSTRACT: Novel cobalt-based heterogeneous catalysts have been developed for the direct oxidative esterification of
alcohols using molecular oxygen as benign oxidant. Pyrolysis of nitrogen-ligated cobalt(II) acetate supported on commercial
carbon transforms typical homogeneous complexes to highly active and selective heterogeneous Co O -N@C materials.
3 4
Applying these catalysts in the presence of oxygen the cross and self-esterification of alcohols to esters proceeds in good to
excellent yields.
1
2
13-14
15
INTRODUCTION
metals, such as iron, cobalt,
and copper. In addition,
the use of heterogeneous catalysts would be beneficial with
respect to catalyst recycling and engineering. In this regard,
we herein introduce novel reusable Co O -based
3 4
heterogeneous catalysts for the direct oxidative esterification
of alcohols. Advantageously, the inexpensive and easily
reusable catalyst as well as the use of oxygen as final oxidant
makes this process cost-effective and environmentally
benign.
Esters represent an abundant class of compounds in
organic synthesis. Moreover, they are used as important
building blocks for the fine and bulk chemical industry.
Hence, this structural motif is found in numerous
1
pharmaceuticals, agrochemicals, fragrances, and polymers.
Both in industry as well as in academic laboratories esters are
commonly prepared by the reaction of carboxylic acids or
activated acid derivatives, e.g. acid chlorides or anhydrides,
1
,2
with alcohols. In addition, Reppe-type carbonylations are
used in the chemical industry for the preparation of aliphatic
Based on our general objective to develop sustainable
catalysts for selective organic transformations, recently we
started a program to design and apply novel carbon-supported
metal-nitrogen catalyst systems, especially based on iron and
3
esters. Regarding (hetero)aromatic esters, palladium-
catalyzed carbonylations of aryl halides with alcohols are of
4
16
increasing interest in organic synthesis. Moreover, special
cobalt. In our previous work, we showed that carbon-
methods such as the catalytic esterifications of aldehydes
with alcohols are known.
supported Fe- and Co-nitrogen materials constitute active
catalysts for the selective reduction of variety of
5
a
nitroarenes. Here, we demonstrate that Co O -based particles
3
4
Despite all these well-established methodologies, the
development of environmentally benign and cost-effective
procedures for the synthesis of esters continues to attract
significant interest. In this respect, the direct transformation
of alcohols to esters constitutes an interesting alternative,
which does not make use of the corresponding acids or acid
derivatives (Scheme 1).
supported on carbon-nitrogen materials represent excellent
heterogeneous catalysts for the selective oxidation of alcohols
1
7
2
to esters using benign O as the final oxidant. Notably, these
6
-11
catalysts are easily recycled and can be conveniently reused,
which is an important aspect in the development of practical
and cost-effective catalytic oxidation processes.
RESULTS AND DISCUSSION
1
. Development of the Co O -N@C catalyst system. At
3 4
3 4
the start of our work, the supported Co O catalysts were
prepared by impregnating in situ generated amino-ligated
cobalt(II)acetate complexes on commercially available
Vulcan XC72R carbon powder and subsequent pyrolysis at
800°C for 2 h (Scheme 2).
Scheme 1. Direct synthesis of esters from alcohols
Exploratory catalytic experiments with the different
catalytic materials were performed using the oxidative cross
esterification of methanol and benzyl alcohol to give methyl
benzoate. Typically, this model reaction was performed at
60°C using simply 1 bar of molecular oxygen in presence of
Notably, the required alcohols are of increasing
importance as renewable feedstock. So far, most of the
known catalysts for the synthesis of esters from alcohols
under mild conditions are based on precious metals such as
palladium, gold, ruthenium, and iridium. Because of the
limited availability and high price of noble metals, it is
desirable to search for more economical and environmentally
friendly alternatives. A possible solution of this problem can
be the increased utilization of catalysts based on bio-relevant
6
7
8
9
catalytic amounts of K
the homogeneous Co(OAc)
2
CO
3
as base. As expected applying
with or without added ligand L1
2
no activity towards ester formation is observed (Table 1,
entries 2-3). Similarly, the carbon-supported catalysts based
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Journal of the American Chemical Society
Page 2 of 8
on simple hydrated Co(OAc)
Table 1, entries 4-5).
2
showed no desired activity
catalyst (Co
significant loss of activity (Figure 1).
3 4
O -L1/C) was successfully recycled without any
(
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
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3
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3
3
3
3
3
4
4
4
4
4
4
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6
1
10
00
1
9
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0
0
0
0
0
1
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0
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0
1
2
3
4
5
6
7
8
9
0
50
0
1
2
3
4
5
6
Recycle time
Figure 1. Methyl esterification of benzyl alcohol:
Recycling of the Co -N@C-catalyst. Reaction
conditions: 2 mmol benzyl alcohol, 6 mL MeOH, 0.4
3
O
4
0
mmol K
2 3
CO , 100 mg catalyst (2.5 mol% Co), 60 C, 24 h.
Yields were determined by GC.
3 4
Scheme 2. Preparation of Co O -N/C materials with
different ligands (Co-L1/C pyrolyzed at 800 °C for 2h
under Ar (Co = 3 wt%, Co:1 = 1:2)
3 4
Table 1: Co O -N@C-catalyzed cross esterification of
a-d
benzyl alcohol and methanol
Interestingly, pyrolyzed carbon-supported Co(OAc)
2
showed little activity and produced methyl benzoate in 12%
yield (Table 1, entry 6). Unfortunately, no further
improvements could be achieved with this catalyst. To our
delight, pyrolysis of the in situ-generated complex of
f
f
Entry Carbon Cobalt
L
Pyrolysis
C
Y
2
Co(OAc) and L1 supported on carbon led to a highly active
catalyst material for the direct oxidative esterification and
produced methyl benzoate in 97% yield (Table 1, entry 7)!
Notably, the pyrolyzed catalyst system is highly stable and
can be re-used several times (see below).
Support Salt
[°C,h, gas] [%] [%]
a
1
-
-
-
-
-
-
-
-
-
<2
5
<1
<1
<1
2
a
.
.
.
2
Co(OAc)
Co(OAc)
Co(OAc)
2
2
2
4H
2
4H
2
4H
2
O
O
O
-
a
3
4
L1
-
12
7
Characterization of the metal species in the active catalyst
b
Vulcan
XC72R
(
3 4
Co O -L1/C) by XRD, TEM, XPS and EPR revealed the
preferential formation of small (2-10 nm) Co O particles on
3
4
b
b
b
.
.
.
5
6
7
Vulcan
XC72R
Co(OAc)
Co(OAc)
Co(OAc)
2
2
2
4H
2
4H
2
4H
2
O
O
O
L1
-
-
12
2
a carbon-nitrogen based support surface (see supporting
information). Besides, a few larger particles of 20-80 nm and
occasionally of up to 800 nm size are also present, which
Vulcan
XC72R
800, 2, Ar 20
12
consist of a Co and/or CoO core and a Co
Interestingly, XPS analysis showed three distinct peaks in the
N1s spectra of Co -L1/C with an electron binding energy
3 4
O shell.
Vulcan
L1
800, 2, Ar >99 97
XC 72R
3
O
4
b
b
.
.
of 399.0 eV, 400.8 eV, and 402.3 eV. The lowest binding
energy peak is attributed to pyridine-type nitrogen, which is
8
9
Vulcan
XC72R
Co(OAc)
2
4H
2
2
O
O
L2
L3
-
800, 2, Ar 80
800, 2, Ar 68
800, 2, Ar <3
800, 2, Ar <4
74
60
<1
<1
[
20a]
bound to a metal ion.
The electron binding energy of
Vulcan
XC72R
Co(OAc)
2
4H
400.8 eV is characteristic for pyrrole-type nitrogen
contributing two electrons to the carbon matrix. Some of the
nitrogen atoms are also bound to a hydrogen atom. Such
types of nitrogen are often found after the carbonization of
b
b
10
Vulcan
XC72R
-
-
1
1
Vulcan
XC72R
L1
[
20b]
nitrogen-containing organic materials.
Finally, the small
peak at 402.3 eV is typical for quaternary amine species
b
b
c
.
.
.
1
1
1
2
3
4
Al
2
O
3
Co(OAc)
Co(OAc)
Co(OAc)
2
2
2
4H
2
4H
2
4H
2
O
O
O
L1
L1
L1
800, 2, Ar 83
800, 2, Ar 52
79
45
4
+
[20c]
(
NR
4
).
The ratio between all Co atoms and all N atoms
TiO
2
in the near surface region is 1:4.7. Deconvolution suggests
that around 64% of all N atoms are bound to the metal ions.
Vulcan
XC72R
800, 2, Ar
6
While to the best of our knowledge Co
3
O
4
on carbon-
d
e
.
.
1
1
5
6
Vulcan
XC72R
Co(OAc)
2
2
4H
2
2
O
O
L1
L1
800, 2, Ar 40
15
7
nitrogen based materials has not been described as efficient
oxidation catalyst under mild conditions, some oxidations of
the parent metal oxide are known. In this respect, the recent
work of Schüth and co-workers is noteworthy, who studied in
Vulcan
XC72R
Co(OAc)
4H
800, 2, Ar 16
a
C=Conversion, Y= Yield.
catalysis conditions: 0.5 mmol benzyl alcohol, 4 mL CH OH,
0.0125 mmol Co(OAc) . 4H O, 0.025 mmol ligand, 0.1
mmol K2CO3. Heterogeneous catalysis conditions: (3 wt%
L
=
ligand. Homogeneous
detail the preparation of Co
CO with these particles. Furthermore, Co O has been used
3
O
4
and the catalytic oxidation of
[18]
3
3
4
[19a]
[19b]
2
2
for the oxidation of cyclohexane
more drastic conditions.
and alcohols
under
b
Co): 0.5 mmol benzyl alcohol, 4 mL CH OH, 0.1 mmol
3
In order to demonstrate the stability and reusability of the
catalyst material, six consecutive oxidation experiments of
the model system were performed. In fact, the Co O -N@C-
3 4
c
K CO , 25 mg catalyst (2.5 mol% Co). Same as ‘b’ without
2
3
d
e
2
base and O . Same as ‘b’ without base. Same as ‘b’ in the
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f
absence of O
2
.
Determined by GC. In
case of lower yields, benzaldehyde was detected as a minor
product.
d
1
2
3
4
5
6
7
8
9
6
7
92
Other pyrolyzed carbon-supported Co-catalysts using
related nitrogen ligands such as terpyridine, and
pyridinebisimidazolines showed also activity, producing
methyl benzoate in 60-74% yield (Table 1, entries 8-9).
Next, pyrolysis of Co-L1 on Al O and TiO supports gave
89
2
3
2
8
89
also active catalyst materials, which produced methyl
benzoate in 45-79% (Table 1, entries 12-13). From all the
results, the Co-L1 supported on carbon found to be the most
active catalyst. Using the latter catalyst we performed the
direct oxidative esterification of different alcohols. It is
evident from the Table 1 (Table 1, entries 14-16) that both the
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59
60
d
9
88
87
92
92
94
94
2
oxidant (O ) and base are crucial for the oxidative
esterification process.
10
2. Synthesis of methyl esters. After having demonstrated
the excellent activity of the Co O -N@C-catalyst (Co O -
3
4
3
4
1
1
1
2
L1@C) in the model reaction, we investigated the oxidative
methyl esterification of a series of structurally diverse
benzylic alcohols. As shown in Table 2, good to excellent
yields of the corresponding methyl esters are obtained. Apart
from simple and alkyl-substituted benzyl alcohols (Table 2,
entries 1-9), also halide, trifluoromethyl-, nitro-, ether-, and
even thioether-substituted benzylic alcohols were selectively
esterified (Table 2, entries 10-22). Especially the latter
reaction is remarkable from the viewpoint of
chemoselectivity. Furthermore, di- and tri-esters can be
obtained in a straightforward manner in up to 91% yield
13
O
O
1
4
(
Table 2, entries 23-26). Notably, also more sensitive allylic
alcohols undergo this cross esterification in high yields
(Table 2, entries 27-30).
I
15
16
95
3 4
Table 2: Co O -N@C-catalyzed synthesis of methyl esters
a
from benzylic alcohols
d
91
Entry Benzylic alcohol Methyl ester
Yield [%]
17
18
87
85
88
1
97
c
9
3
1
9
2
3
95
92
20
21
95
92
94
4
5
97
90
2
2
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benzylic alcohols we were interested to demonstrate similar
selective oxidative couplings for different alkyl esters. Not
surprisingly, such cross esterifications have been scarcely
studied in the past due to the potential problem oxidizing one
alcohol in the presence of another.
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
23
24
91
e
Nevertheless, ethyl esters of both benzylic and
heterocyclic alcohols are conveniently obtained in up to 92%
yield (Table 3, entries 1-9). The procedure also works well
for the synthesis of propyl, butyl, pentyl, and hexyl benzoates
89
85
O
0
in 81-87% yield at slightly higher temperatures (90-110 C)
O
e
2
5
(Table 3, entries 10-13).
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
O
O
3 4
Table 3: Co O -N@C-catalyzed synthesis of alkyl esters of
a
benzylic alcohols
f
26
27
84
88
89
0
b
Entry Ester
1
T [ C]
Yield [%]
2
2
8
70
70
70
91
c
8
8
9
0
84
80
2
3
92
87
3
a
Reaction conditions: 0.5 mmol benzylic alcohol, 4 mL
OH, 0.1 mmol K CO , 25 mg catalyst (2.5 mol% Co).
Determined by GC. Scaled up by factor 4 and isolated
CH
3
2
3
b
c
4
5
6
7
70
70
70
70
85
82
91
88
d
0
e
yields. Same as ‘a’ at 80 C. Same as ‘a’ with 0.2 mmol
K CO . Same as ‘a’ with 0.3 mmol K CO .
2 3 2 3
f
Next, the oxidative esterification of heterocyclic alcohols
was investigated. Gratifyingly, heterocyclic carboxylic acid
esters, which constitute important intermediates especially for
agrochemicals, were obtained in up to 94% yields (Scheme
3).
O
O
N
90%
8
70
70
90
81
77
87
9
10
11
110
110
110
86
82
81
Scheme 3. Co O -N@C-catalyzed synthesis of methyl
esters of heterocyclic alcohols. Reaction conditions: 0.5
mmol heterocyclic alcohol, 4 mL CH OH, 0.1 mmol
3
4
1
1
2
3
3
K
2
CO
3
, 25 mg catalyst (2.5 mol% Co), yields were
0
determined by GC. *Similar reaction conditions at 80 C.
3
. Synthesis of different alkyl esters. After the
successful cross esterification of methanol and various
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Journal of the American Chemical Society
a
Reaction conditions: 0.5 mmol benzylic alcohol, 1 mL
aliphatic alcohol, 0.25 mmol K CO , 25 mg catalyst (2.5
mol% Co), 4 mL n-heptane. Determined by GC. Scaled
up by factor 4 and isolated yields.
1
2
3
4
5
6
7
8
9
2
3
b
c
Scheme 4. Co
esterification of benzylic alcohols. Reaction Conditions:
.5 mmol benzylic alcohol, 0.5 mmol K PO , 25 mg
catalyst (2.5 mol% Co), 5 mL n-heptane. Yields were
determined by GC
3 4
O -N@C-catalyzed oxidative self-
4. Self esterification of aliphatic and benzylic
0
3
4
alcohols. So far, only few examples are known for the direct
6
a, 8, 10
self-esterification of aliphatic alcohols.
In this respect,
.
recently, we described homogeneous palladium and
ruthenium complexes for the self-esterification of 1-octanol
and ethanol to produce octyl octanoate and ethyl acetate.
Because most of the catalytic experiments were run on
.5-2 mmol scale, we wanted to demonstrate the synthetic
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
[6a,8c]
.
0
Furthermore, Milstein and co-workers performed the self-
esterification of 1-butanol, 1-pentanol and 1-hexanol using
utility of our catalyst system more clearly. Thus, we
performed 5 gram-scale reactions for selected substrates. As
shown in Scheme 5 in all these cases the previous yields were
verified and we obtained the corresponding products in up to
94% (Scheme 5).
[
8a-b]
homogeneous ruthenium pincer catalysts.
In addition, the
oxidative dimerization of some aliphatic alcohols to esters
[
10]
has also been reported using organocatalysts.
As seen from Table 4, different aliphatic alcohols
undergo oxidative self-esterification in presence of our
Co O -N@C-catalyst using only 1 bar of molecular oxygen.
O
O
3
4
It should be noted that the bulk chemical ethyl acetate can be
obtained from ethanol in good yield under such mild
conditions (Table 4, entry 1). No further optimization has
been done on this industrially important intermediate.
Similarly, the oxidative self-esterification of other aliphatic
alcohols was also achieved in a straightforward manner and
we obtained the corresponding esters in 71-75% yield (Table
92%
4, entries 2-6).
Scheme 5. Gram scale reactions: 5 g benzylic alcohol, 0.2
equiv. K CO , weight of Co O -N@C corresponds to 2.5
2 3 3 4
0
mol% Co, 150-200 mL MeOH, 60 C, 24-30 h, isolated
yields.
Table 4: Co
aliphatic alcohols.
3 4
O -N@C-catalyzed oxidative esterification of
a-b
SUMMARY
Co3O4-N@C
(3 mol% Co)
O
R
OH
R
O
R
In summary, a stable, inexpensive and reusable Co3O4
1 bar O2, 1 Equiv. K3PO4
n-Heptane, 90-120 C, 24 h
R = aliphatic
0
catalyst is shown to be active and selective for the direct
oxidative esterification of alcohols using 1 bar of molecular
oxygen as benign oxidant. The novel supported catalyst is
prepared by pyrolysis of amino-ligated cobalt(II) acetate on
commercial Vulcan XC72R. It allows for the synthesis of a
series of structurally divers methyl esters and as well as other
alkyl esters in good to excellent yields. The oxidative self-
esterification of both aliphatic and aromatic alcohols has been
well demonstrated. In general, the process is simple, cost-
effective and environmentally benign.
0
c
Entry Ester
T [ C]
Yield [%]
a
1
90
65
71
72
73
75
b
2
90
b
3
110
110
120
b
4
b
5
[d]
EXPERIMENTAL SECTION
7
1
b
6
120
75
3 4
Methyl esterification: 25 mg Co O -N /C (Co-L1/C)
catalyst (2.5 mol% Co) and K CO (0.1 mmol) were added to
2
3
a
oven dried Schlenk tube. Then, methanol (4 mL) and
corresponding benzylic alcohol (0.5 mmol) were added
sequentially. The Schlenk tube was evacuated, refilled with 1
Reaction conditions: 2 mmol ethanol, 2 mmol K
3
PO
4
,
b
120 mg catalyst (3 mol% Co), 8 mL n-heptane. 0.5 mmol
alkyl alcohol, 0.5 mmol K PO , 30 mg cataylst (3 mol%
3
4
c
d
bar O and closed with septum. The reaction was stirred at 60
Co), 5 mL n-heptane. Determined by GC. Scaled up by
factor 4 and isolated yield.
2
0
C (refluxed condenser was fixed in case of the reactions
0
carried out at 80 C) for 24 h by passing 1 bar O
2
. After
cooling the reaction mixture to the room temperature, 100 µL
n-hexadecane as internal standard was added and diluted with
ethyl acetate. Then, catalyst was filtered off, and the sample
of the mixture was directly subjected to GC analysis.
Conversion and yields were determined by GC-FID (HP6890
with FID detector, column HP530 m x 250 mm x 0.25 µm)
and compared with authentic samples. Quantitative and
Finally, we also performed the self-esterification of
benzylic alcohols. Here, again the catalyst is highly selective
and we obtained the corresponding substituted benzyl
benzoates in up to 85% yield (Scheme 4).
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qualitative analysis of all esters were made by GC, GC–MS
and identified by comparison with authentic samples.
15096–15098. (c) Owston, N. A.; Parker, A. J.; Williams, J. M. J.
Chem. Commun. 2008, 624–625.
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For methyl esterification of benzyl alcohol, the reaction
was scaled up by factor 4 and the corresponding methyl
benzoate was isolated. After completion of the reaction, the
solid catalyst was filtered off and washed thoroughly with
ethyl acetate. The solvent was evaporated and the reaction
product was treated with water. The mixture was then
extracted with ethyl acetate, the combined organic layers
were dried over MgSO , and the solvent was removed in
4
vacuo. Finally, the methyl benzoate was purified by column
chromatography (silica; n-hexane-ethyl acetate mixture).
VCH, Weinheim, 2008. (b) Plietker, B. in Iron Catalysis:
Fundamentals and Applications, Springer, Berlin, 2010. (c) Boddien,
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ASSOCIATED CONTENT
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Supporting Information. Catalyst preparation. Detailed
procedure for oxidative esterification. EPR TEM and XPS
analysis. This material is available free of charge via the
Internet at http://pubs.acs.org
11128. (d) Gao, K.; Yoshikai, N. Angew. Chem. Int. Ed. 2011, 50,
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AUTHOR INFORMATION
Corresponding Author
1
(
*
Matthias.Beller@catalysis.de
Applications, Marcel Dekker, New York, 1997. (b) Phipps, R. J.;
Gaunt, M. J. Science, 2009, 323, 1593-1597. (c) Gamez, P.; Aubel,
P. G.; Driessen, W. L.; Reedijk, J. Chem. Soc. Rev. 2001, 30, 376-
Funding Sources
This work has been supported by the State of Mecklenburg-
Vorpommern, and the BMBF (Bundesministerium für
Bildung und Forschung).
385. (d) Hein, J. E.; Fokin, V. V. Chem. Soc. Rev. 2010, 39, 1302-
1315.
(16) For catalytic reductions of nitroarenes using this type of
heterogeneous catalysts see: (a) Jagadeesh, R. V. ; Wienhöfer, G.;
Westerhaus, F. A.; Surkus, A.-E.; Pohl, M.-M.; Junge, H. ; Junge,
K.; Beller, M. Chem. Commun. 2011, 47, 10972-10974. (b)
Westerhaus, F. A. ; Jagadeesh, R. V.; Wienhöfer, G.; Pohl, M.-M.;
Radnik, J.; Surkus, A.-E.; Rabeah, J.; Junge, K.; Junge, H.; Nielsen,
M.; Brückner, A.; Beller, M. Nature Chem. 2013, in press.
ABBREVIATIONS
K CO -Potassium carbonate, K PO -Potassium phosphate,
2
3
3
4
MeOH-Methanol, T-Temperature.
(17) (a) Bäckvall, J. E. Modern Oxidation Methods, Wiley-VCH,
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Table of Contents (TOC) graphic
Selective Oxidation of Alcohols to Esters Using Heterogeneous Co O -N@C Catalysts under mild Conditions
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Rajenahally V. Jagadeesh, Henrik Junge, Marga-Martina Pohl, Jörg Radnik, Angelika Brückner, and Matthias Beller*
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