Novel Vanadium-Catalyzed Oxidation of Alcohols to Aldehydes and Ketones under Atmospheric Oxygen

Article abstract of DOI:10.1021/ol036166x

(Matrix presented) Oxidation of alcohols to aldehydes and ketones has been studied in high yields using atmospheric oxygen and a catalytic amount of V ₂O₅ in toluene under heating (ca. 100°C). Secondary alcohols can be chemoselectively converted into ketones in the presence of primary hydroxy groups.

Full text of DOI:10.1021/ol036166x

ORGANIC
LETTERS
2004
Vol. 6, No. 2
217-219
Novel Vanadium-Catalyzed Oxidation of
Alcohols to Aldehydes and Ketones
under Atmospheric Oxygen
Subbarayan Velusamy and T. Punniyamurthy*
Department of Chemistry, Indian Institute of Technology Guwahati,
Guwahati 781039, India
tpunni@iitg.ernet.in
Received November 5, 2003
ABSTRACT
Oxidation of alcohols to aldehydes and ketones has been studied in high yields using atmospheric oxygen and a catalytic amount of V O in
2
5
toluene under heating (ca. 100 °C). Secondary alcohols can be chemoselectively converted into ketones in the presence of primary hydroxy
groups.
The oxidation of alcohols to aldehydes and ketones plays a
central role in organic chemistry both at the laboratory and
Scheme 1
industry level.1,2 Several methods are available to effect this
conversion, and continuous attention is drawn to newer and
more selective methods of oxidation. Catalytic oxidation with
molecular oxygen is particularly attractive from an economic
and environmental point of view. Recently, CuCl-Phen,3
polyoxometalates,4 Mo-Cu,5 Os-Cu,6 CoLn,7 RuLn,8,9 Ni-
hydrotalcite,10 manganese oxide octahedral molecular sieves,11
(1) Sheldon, R. A.; Kochi, J. K. Metal-Catalyzed Oxidations of Organic
Compounds; Academic Press: New York, 1981.
(2) Cainelli, G.; Cardillo, G. Chromium Oxidations in Organic Chemistry;
Springer: Berlin, 1984.
and VOLn12 have been designed and developed for the
aerobic oxidation of alcohols and await the further discovery
(3) Marko, I. E.; Giles, P. R.; Tsukazaki, M.; Chelle-Regnaut, I.; Gautier,
A.; Brown, S. M.; Urch, C. J. J. Org. Chem. 1999, 64, 2433.
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655.
of suitable catalytic systems, especially without sacrificial
Scheme 2
(6) Muldoon, J.; Brown, S. N. Org. Lett. 2002, 4, 1043.
(7) (a) Yamada, T.; Mukaiyama, T. Chem. Lett. 1989, 519. (b) Punniya-
murthy, T.; Iqbal, J. Tetrahedron Lett. 1994, 35, 4007. (c) Kalra, S. J. S.;
Punniyamurthy, T.; Iqbal, J. Tetrahedron Lett. 1994, 35, 4847. (d) Iwahama,
T.; Yoshino, Y.; Keitoku, T.; Sakaguchi, S.; Ishii, Y. J. Org. Chem. 2000,
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D. S.; Thomas, A. W. Chem. Commun. 1999, 1907. (b) Masutani, K.;
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2002, 67, 1657.
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Am. Chem. Soc. 2000, 122, 7144.
10.1021/ol036166x CCC: $27.50 © 2004 American Chemical Society
Published on Web 12/18/2003

The oxidation of benzoin was first investigated as a
standard substrate using V2O5 under atmospheric oxygen
(Table 1). Dichloromethane, acetonitrile, water, and toluene
were employed as the solvents. We were pleased to find that
the alcohol was oxidized to benzil in 6-95% yields. Among
the solvents examined, toluene was found to be the best for
this protocol.
Table 1. Aerobic Oxidation of Benzoin with V2O5
entry
solvent
temp (°C)
yield (%)a,b
To evaluate the scope of this protocol, the oxidation of
other alcohols was further studied (Table 2, entries 1-14).12
As above, secondary alcohols, cyclohexanol, (()-menthol,
phenylethanol, and diphenylmethanol oxidized to the cor-
responding ketones in high yields. The oxidation of primary
alcohols to aldehydes required 0.5 equiv of K2CO3, and in
its absence, the corresponding esters were obtained (Scheme
2). Aromatic alcohols having electron-donating and -with-
drawing groups in the aromatic ring, 4-methoxy-, 3,4,5-
trimethoxy-, and 4-nitrobenzyl alcohol, were converted to
1
2
3
4
CH2Cl2
CH3CN
H2O
20
80
100
100
6
31
30
95
toluene
reducing agents. In continuation of our studies on the
oxidation of organic compounds,13 we report here a novel
method for the oxidation of alcohols to aldehydes and ketones
using a catalytic amount of V2O5 under atmospheric oxygen
(Schemes 1 and 2).
Table 2. Aerobic Oxidation Results of Alcohols Using V2O5
a Mixture of V2O5 (5 mol %), alcohol (2 mmol), K2CO3 (1 mmol), and toluene (3 mL) was stirred at ca. 100 °C for the appropriate time under atmospheric
oxygen. b Isolated yield. c GC yield. d Reactions carried out in the absence of K2CO3.
218
Org. Lett., Vol. 6, No. 2, 2004

Scheme 3
the corresponding aldehydes in 83-93% yields (entries 2-4).
formation of a hemiacetal and its subsequent oxidation to
ester as shown in Scheme 5.14b This is due to the weakly
Similarly, allylic alcohols, geraniol and cinnamyl alcohol,
oxidized to aldehydes without cleavage of the carbon-carbon
double bonds. Furthermore, pyridine-2-methanol and furfurol
were oxidized to the corresponding aldehydes in high yields.
Saturated alcohols, heptyl and decyl alcohol, were moderately
reactive, and the aldehydes were obtained in 38-43% yields.
To study the chemoselectivity, a mixture of primary and
secondary alcohols was next subjected to oxidation in the
presence of 0.5 equiv of K2CO3 (Scheme 3). When cyclo-
hexanol and heptyl alcohol were allowed to react, the former
oxidized to cyclohexanone in 87% yield and the latter gave
heptanal in <5% yield. A similar result was obtained in the
oxidation of cyclododecanol and n-dodecanol, affording
cyclododecanone and dodecanal in 81 and <3% yields,
respectively. These studies clearly reveal that this method
can be applied for the chemoselective oxidation of secondary
alcohols in the presence of primary hydroxy groups.
Scheme 5
acidic nature of the reaction medium (pH ) 6). The addition
of K2CO3 in the oxidation of primary alcohols increases the
pH to 9, inhibiting the hemiacetal formation.
In conclusion, a novel and efficient protocol is presented
for the aerobic oxidation of alcohols to aldehydes and
ketones. Secondary alcohols can be chemoselectively con-
verted into ketones in high yields in the presence of primary
hydroxy groups. It is noteworthy that the aldehydes do not
undergo further oxidation to carboxylic acids.
Regarding the mechanism, a catalytic cycle is proposed
for the oxidation of alcohols to aldehydes and ketones in
Scheme 4.14a The formation of ester from the oxidation of
primary alcohol in the absence of K2CO3 may be due to the
Acknowledgment. This work was supported by the
Department of Science and Technology (Sanction No. SR/
S1/OC-092002), New Delhi, and by the Council of Scientific
and Industrial Research (Sanction No. 01(1804)/02/EMR-
II), New Delhi.
Scheme 4
Supporting Information Available: General experimen-
tal procedure and data. This material is available free of
charge via the Internet at http://pubs.acs.org.
OL036166X
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Org. Lett., Vol. 6, No. 2, 2004
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