Wet alumina-supported chromium (VI) oxide: A mild, efficient, and inexpensive reagent for oxidative deoximation

Article abstract of DOI:10.1080/10426500490485264

A mild, efficient, and inexpensive method for the direct conversion of oximes to carbonyl compounds upon treatment with wet aluminasupported chromium (VI) oxide is described.

Full text of DOI:10.1080/10426500490485264

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WET ALUMINA-SUPPORTED
CHROMIUM (VI) OXIDE: A MILD,
EFFICIENT, AND INEXPENSIVE
REAGENT FOR OXIDATIVE
DEOXIMATION
Majid M. Heravi a , Darush Ajami b , Rahim Hekmat
Shoar a , Nooshin Sarmad a & Farnoush Faridbod
a Department of Chemistry, School of Sciences,
Alzahra University , Tehran, Iran
b Chemistry and Chemical Engineering Research
Center of Iran , Tehran, Iran
Published online: 16 Aug 2010.
To cite this article: Majid M. Heravi , Darush Ajami , Rahim Hekmat Shoar , Nooshin
Sarmad & Farnoush Faridbod (2004) WET ALUMINA-SUPPORTED CHROMIUM (VI)
OXIDE: A MILD, EFFICIENT, AND INEXPENSIVE REAGENT FOR OXIDATIVE DEOXIMATION,
Phosphorus, Sulfur, and Silicon and the Related Elements, 179:12, 2423-2427, DOI:
10.1080/10426500490485264
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Phosphorus, Sulfur, and Silicon, 179:2423–2427, 2004
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Copyright Taylor & Francis Inc.
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500490485264
WET ALUMINA-SUPPORTED CHROMIUM (VI)
OXIDE: A MILD, EFFICIENT, AND INEXPENSIVE
REAGENT FOR OXIDATIVE DEOXIMATION
Majid M. Heravi,a Darush Ajami,b Rahim Hekmat Shoar,a
Nooshin Sarmad,a and Farnoush Faridbod
Department of Chemistry, School of Sciences, Alzahra
University, Vanak, Tehran, Iran;a Chemistry and Chemical
Engineering Research Center of Iran, Tehran, Iranb
(Received February 20, 2004; accepted April 20, 2004)
A mild, efficient, and inexpensive method for the direct conversion
of oximes to carbonyl compounds upon treatment with wet alumina-
supported chromium (VI) oxide is described.
Keywords: Chromium (VI) oxide; oxidative deoximation; wet alumina
INTRODUCTION
Oximes are very useful protecting groups and are extensively used for
purification and isolation of carbonyl compounds. Since oximes can be
synthesized from noncarbonyl compounds,2 their synthesis provides an
alternative pathway to aldehydes and ketones. Oximes are also use-
ful in the preparation of amides via the Beckman rearrangment.3 Re-
generation of carbonyl compounds from their oximes was even more
important after the discovery of the Barton reaction, in which oximes
are produced at a nonactivated hydrocarbon site.4 Although literature
enumerates quite a number of methods for the conversion of oximes
into carbonyl compounds,5 the important role of oximes as protecting
groups owing to their hydrolytic stability has provided motivation for
the development of newer, milder, more efficient, and less expensive
reagents.
Financial support for this research from Azzahra University research council is grate-
fully appreciated.
Address correspondence to Majid M. Heravi, Department of Chemistry, School of Sci-
ences, Alzahra University, Vanak, Tehran, Iran. E-mail: mmheravi@alzahra.ac.ir
2423

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M. M. Heravi et al.
Chromium-based reagents have been used extensively in organic
synthesis.6 The concept of utilizing reagents7 adsorbed on inert inor-
ganic supports for organic synthesis has been reported and applied es-
pecially to chromium compounds.
In view of the current focus on using supported reagents on various
solid inorganic surfaces,8 there is merit in developing a truly hetero-
geneous reaction for the cleavage of oximes using mild, efficient, and
inexpensive reagents. In this communication we wish to report the use
of wet alumina-supported reagents chromium (VI) oxide as a mild, effi-
cient, and inexpensive reagent for oxidative deoximation in nonaqueous
condition. The reaction proceeds efficiently in high yields at refluxing
temperature within a few minutes (Scheme 1).
SCHEME 1
Chromium (VI) oxide was mixed with alumina and reacted with
oximes in CH2Cl2. In the absence of alumina the reaction did not occur
and, in the presence of alumina the reaction was sluggish, and consid-
erable amounts of starting material were recovered unchanged at room
temperature or even under refluxing for an extended period of time.
As an example, the reaction of benzaldoxime with dry alumina-CrO3
resulted in the formation of 35% benzaldehyde.
However, when alumina was premoistened and then mixed with
chromium oxide, benzaldoxime was converted to benzaldehyde almost
quantitatively in CH2Cl2 at room temperature.
To assess the generality of this oxidative deoximation method a vari-
ety of oximes were reacted under these conditions, and they yielded the
corresponding carbonyl compounds in good-to-excellent yields (Table I).
Aliphatic oximes gave low yields.
In conclusion, by comparison with presently existing methods, wet
alumina-supported chromium (VI) oxide has advantages. Mild condi-
tions, efficiency, selectivity, high yield, and being inexpensive are the
main advantages of this procedure. The only draw back for this method
is that in the case of none-benzylic oximes poor yields of deoximation
were obtained.

Deoximation
2425
TABLE I Oxidative Cleavage of Oximes with Wet Alumina-CrO3 in CH2Cl2
Carbonyl
Reaction
time (min)
Yieldc
(%)
Entry
1
Substratea
compoundb
40
90
2
40
85
3
4
5
40
40
40
83
82
85
6
7
40
40
84
82
aAll substrates were synthesized by known literature procedure.
bAll products were characterized by comparison of their m.p., IR, and 1HNMR spectra
with those of authentic samples.
cYields refer to isolated products.
EXPERIMENTAL
All oximes were prepared by standard methods.9 Products were
isolated, and their physical data were compared with those of known
samples. Yields given in Table I refer to isolated products. Wet
alumina was prepared by shaking neutral aluminum oxide (10 g,
Aldrich-Brockmann, 150 mesh) with distilled water (2 ml). The reagent

2426
M. M. Heravi et al.
was prepared by mixing CrO3 (0.8 g, 0.8 mmol) with wet alumina
(2.4 g) using pestle and mortar.
General Procedure
In a flask (50 ml) a solution of 1 mmol of oxime in 20 ml of CH2Cl2 was
prepared. Wet alumina-supported chromium oxide (0.06 g) was added,
and the mixture was stirred magnetically for 40 min. The progress of
reaction was monitored by thin layer chromatography (TLC) (eluent:
hexane, EtOAC, 8:2). The mixture was filtered, and the solid material
was washed with CH2Cl2. The filtrate was evaporated on a rotary evap-
orator, and the crude residue was directly subjected to column chro-
matography using the appropriate eluent. Pure carbonyl compounds
were obtained in good-to-excellent yields (Table I).
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