Oxidative deoximation with catalytic sodium tungstate

Article abstract of DOI:10.1081/SCC-120024008

A simple and mild method of oxidative deoximation based on catalytic amount of sodium tungstate is described. This method is effective for deprotection of ketones and aldehydes.

Full text of DOI:10.1081/SCC-120024008

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Oxidative Deoximation with Catalytic Sodium Tungstate
A. Manjula a , G. Narsimha Reddy a & B. Vittal Rao a
a Organic Division II , Indian Institute of Chemical Technology , Hyderabad, India
Published online: 15 Aug 2006.
To cite this article: A. Manjula , G. Narsimha Reddy & B. Vittal Rao (2003) Oxidative Deoximation with Catalytic Sodium
Tungstate, Synthetic Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry,
33:19, 3455-3459
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SYNTHETIC COMMUNICATIONSÕ
Vol. 33, No. 19, pp. 3455–3459, 2003
Oxidative Deoximation with Catalytic
Sodium Tungstate#
*
A. Manjula, G. Narsimha Reddy, and B. Vittal Rao
Organic Division II, Indian Institute of Chemical
Technology, Hyderabad, India
ABSTRACT
A simple and mild method of oxidative deoximation based on
catalytic amount of sodium tungstate is described. This method is
effective for deprotection of ketones and aldehydes.
A number of carbonyl functional group equivalents are routinely
employed in organic synthesis. Oximes are readily available and
highly stable derivatives of carbonyl compounds that have been regarded
both as protective[1] as well as activating groups. Oximes have been used
extensively for purification and characterization of carbonyl com-
pounds.[2] They also provide a viable route to amides from carbonyl
#IICT Communication No. 021201.
*Correspondence: B. Vittal Rao, Organic Division II, Indian Institute of Chemical
Technology, Hyderabad 500 007, India; E-mail: vittalrao@iict.ap.nic.in.
3455
DOI: 10.1081/SCC-120024008
Copyright & 2003 by Marcel Dekker, Inc.
0039-7911 (Print); 1532-2432 (Online)
www.dekker.com

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3456
Manjula, Reddy, and Rao
equivalents via Beckmann rearrangement.[3] However, the utility of
oximes as carbonyl equivalents is limited by the methods employed for
their regeneration. Classically they are regenerated by acid hydrolysis
under suitable conditions.[4] This process removes hydroxylamine from
the equilibrium. There are limits to the scope of this reaction since
compounds containing acid sensitive groups cannot be subjected to this
hydrolysis. Recently there has been a lot of stress on the oxidative,[5]
reductive[6] and microwave irradiation[7] methods for cleavage of deox-
imation. It has been found that most of the oxidative methods use non
catalytic amount of corrosive and carcinogenic metals such as chromium
or expensive catalysts or mostly involve microwave techniques. In view of
the recent stress on the catalytic processes towards the development of
clean and green chemical processes, investigation of new, less hazardous
chemical oxidants has become a priority for the synthetic organic che-
mists. Herein, we report the use of a combination of catalytic amount
sodium tungstate and hydrogen peroxide as a novel reagent system for
the oxidative deoximation.
Treatment of oxime (both ketoximes and aldoximes) with 30%
hydrogen peroxide in acetone, in the presence of catalytic amount
(10 mol%) of sodium tungstate at ambient temperature afforded the
corresponding carbonyl compound.[8] In order to test the generality of
the deoximation various types of oximes were subjected to the oxidation
in the presence of catalytic amount of sodium tungstate and 30%
hydrogen peroxide to yield the corresponding carbonyl compounds in
moderate to good yields. The reaction conditions are mild. Moreover
the method is a general one applicable to all classes of aldehydes and
ketones. The reaction times and the yield of deoximation are presented
in Table 1.
The deoximation was applicable for enolisable carbonyl compounds
also. The yields for the deprotection of ketoximes were of the higher
order compared to those of the aldoximes. It is noteworthy that when
the oxidation was done with a mixture of the oxime and an alcohol, the
alcohol remained unaffected while the oxime was completely converted to
the corresponding ketone (as represented in the Sch. 1). The deprotec-
tions with the aldoximes gave lesser yields of the product because of the
oxidation to the corresponding acid. It was found that with the aldoximes
when the oxidation times were shorter the deoximation was incomplete
and small amount of acid was formed at the end of deoximation.
In conclusion, an efficient and inexpensive protocol for regeneration
of carbonyl compounds has been realized using catalytic amount of
sodium tungstate. The significant features being (a) operational simpli-
city; (b) use of inexpensive reagent for performing the reaction; (c) does

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Catalytic Sodium Tungstate
3457
Table 1.a
OH
30% H2O2, acetone
O
N
10 mole% sodium tungstate
R1
R2
R1
R2
Entry
1
Substrate
Time (h)
4
Yield (%)
CHNOH
78
98
H3CO
Cl
CNOH
2
5
CHNOH
3
4
4
12
70
85
Cl
CHNOH
Cl
Cl
Cl
Cl
O
5
6
7
8
CHNOH
4
5
60
96
92
70
N
C(CH3)NOH
O2N
C(CH3)NOH
OMe
10
5
NOH
C(CH3)NOH
9
5
6
95
95
Me
NOH
10
HON
11
12
6
6
90
80
NOH
H
NOH
13
6
60
Cl
Cl
Cl
O
N
aUnoptimized yields of pure products exhibited physical and spectral prop-
erties in accordance with the assigned structures.

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3458
Manjula, Reddy, and Rao
OH
R2
30% H2O2, acetone
O
N
10 mole% sodium tungstate
R1
R2
R1
R1 = A r
R2 = H , C H 3
OH
HO
N
30% H2O2, acetone
O
HO
+
+
10 mole% sodium tungstate
R1
R2
R1
R2
R2
R1
R2
R1
NO OXIDATION
OF ALCOHOL
R1 = A r
R2 = H , C H 3
Scheme 1.
not involve any additives for promoting the reaction; (d) a variety of
functional groups remain unaffected during the transformation.
REFERENCES
1. Greene, T.G.; Wuts, P.G.M. Protective Groups in Organic Synthesis,
2nd Ed.; John Wiley & Sons: New York, 1991.
2. Shriner, R.L.; Fuson, R.C.; Curtin, D.Y.; Morrill, T.C. The
Systematic Identification of Organic Compounds, 6th Ed.; Wiley:
New York, 1980.
3. Donaruma, L.G.; Heldt, W.Z. Org. React. 1960, 11, 1.
4. (a) Hershberg, E.B. J. Org. Chem. 1948, 13, 542; (b) Bandgar, B.P.;
Shaikh, S.I.; Iyer, S. Synth. Commun. 1996, 26, 1163.
5. Ganguly, N.C.; De, P.; Sukai, A.K.; De, S. Synth. Commun. 2002,
32, 1, and references cited therein.
6. Firouzabadi, H.; Jamalian, A.; Babak, K. Bull. Chem. Soc. Jpn.
2002, 75, 1761, and references cited therein.
7. Heravi, M.M.; Ajami, D.; Mohajerani, B.; Tabar-Hydar, K.;
Ghassemzadeh, M. Synth. Commun. 2002, 32, 3325 and references
cited therein.
8. In a typical experiment, the oxime (3 mmols) was dissolved in acetone
5 mL and sodium tungstate (10-mol%) was added to it. The reaction
mixture was cooled to ꢀ5ꢁC in ice-salt mixture. To a stirred mixture
of the above 1.5 mL of H2O2 was added dropwise. The reaction
was monitored by TLC and the solvent was removed and water
added to the residue. The mixture was extracted with ether,

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Catalytic Sodium Tungstate
3459
combined ether extracts were washed with 5% Na2S2O3, water and
dried over anhydrous sodium sulfate. Evaporation of the solvent
gives crude carbonyl compound, which is further purified by crystal-
lization/distillation.
Analytical data for new compounds is given below:
5. Oxime: M.p. 234–236ꢁC. H NMR (200 MHz, CDCl3): ꢀ 7.15 (d,
1
J ¼ 6 Hz, 2H, ArH); 7.65 (d, J ¼ 6 Hz, 2H, ArH), 7.85 (s, 1H, ArH);
8.10 (s, 1H, CH¼NH). EIMS m/z: 318 (Mþ).
Aldehyde: M.p. 123–124ꢁC. H NMR (200 MHz, CDCl3): ꢀ 7.3 (d,
1
J ¼ 6 Hz, 2H, ArH), 7.8 (s, 1H, ArH), 7.9 (d, J ¼ 6 Hz, 2H, ArH), 10.0
(s, 1H, CHO). IR (KBr) ꢁ ¼ 1413, 1698 cmꢀ1. EIMS: 303 (Mþ).
1
13. Oxime H NMR (200 MHz, CDCl3): ꢀ 2.0 (s, 3H, CH3), 6.75 (s,
1H, CH¼CH), 7.1 (d, J ¼ 6 Hz, 2H, ArH), 7.5 (m, 3H, ArH &
CH¼CH), 7.8 (s, 1H, ArH). IR (KBr) ꢁ ¼ 3286, 3124, 2897, 1536,
1406, 1167 cmꢀ1
.
1
Ketone. H NMR (200 MHz, CDCl3): ꢀ 2.4 (s, 3H, CH3), 6.70 (d,
J ¼ 10 Hz, 1H, CH¼CH), 7.2 (d, J ¼ 6 Hz, 2H, ArH), 7.5 (d, 1H,
J ¼ 10 Hz, CH¼CH), 7.6 (d, J ¼ 6 Hz, 2H, ArH), 7.85 (s, 1H, ArH).
IR (KBr) ꢁ ¼ 3102, 1654, 1502, 1403, 1178 cmꢀ1. EIMS: 343 (Mþ).

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