Ultrasound-promoted rapid oxidative cleavage of oximes with NaBrO3/ion exchange resin

Article abstract of DOI:10.1080/00397910701575459

The oxidative cleavage of oximes has been studied under solvent-free ion exchange resin (IER) catalysis by sodium bromate using ultrasonic irradiation. Both aldoximes and keto-oximes selectively converted to the corresponding carbonyl compounds in high yields within short times at room temperature. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397910701575459

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Ultrasound‐Promoted Rapid Oxidative
Cleavage of Oximes with NaBrO /Ion
3
Exchange Resin
a
a
a
Ahmad Shaabani , Abbas Rahmati & Soheila Naderi
a
Department of Chemistry , Shahid Beheshti University , Tehran, Iran
Published online: 19 Nov 2007.
To cite this article: Ahmad Shaabani , Abbas Rahmati & Soheila Naderi (2007) Ultrasound‐Promoted
Rapid Oxidative Cleavage of Oximes with NaBrO /Ion Exchange Resin, Synthetic Communications: An
3
International Journal for Rapid Communication of Synthetic Organic Chemistry, 37:22, 4035-4042, DOI:
10.1080/00397910701575459
To link to this article: http://dx.doi.org/10.1080/00397910701575459
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Synthetic Communications , 37: 4035–4042, 2007
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910701575459
Ultrasound-Promoted Rapid Oxidative
Cleavage of Oximes with NaBrO /Ion
Exchange Resin
3
Ahmad Shaabani, Abbas Rahmati, and Soheila Naderi
Department of Chemistry, Shahid Beheshti University, Tehran, Iran
Abstract: The oxidative cleavage of oximes has been studied under solvent-free ion
exchange resin (IER) catalysis by sodium bromate using ultrasonic irradiation. Both
aldoximes and keto-oximes selectively converted to the corresponding carbonyl
compounds in high yields within short times at room temperature.
3
Keywords: NaBrO /ion exchange resin, oxidation, oxime, ultrasound
INTRODUCTION
Because of their hydrolytic stability, oximes are used as carbonyl protec-
tors
[1,2]
from which the parent carbonyl compounds must be regenerated at
the completion of a synthetic procedure. Regeneration of the carbonyl
compound requires the use of mild reagents and reaction conditions that
will cleave the C 55 N bond without modification to the rest of the molecule.
Furthermore, because oximes can also be prepared from noncarbonyl
compounds, the generation of carbonyl compounds from them provides an
[3–6]
alternative method for the preparation of aldehydes and ketones.
Because of their low price and versatility, halogens and halogenated
compounds (bromine, iodine, hypoclorite, N-bromoamides, percholoric acid,
percholorates, periodic acid) have been used in reactions of deoximation
[
2]
and have delivered good results.
Received in the U.K. October 4, 2006
Address correspondence to Ahmad Shaabani, Department of Chemistry, Shahid
Beheshti University, P. O. Box 19839-4716, Tehran, Iran. E-mail: a-shaabani@cc.
sbu.ac.ir
4
035

4
036
A. Shaabani, A. Rahmati, and S. Naderi
Sodium bromate is commercially available as a stable solid, which
potentially is an interesting candidate for the oxidation of organic
compounds because of its capability in multi-electron transfer. Thermodyna-
mically sodium bromate is a strong oxidant, but according to the literature,
bromate itself is not able to oxidize organic compounds. It is usually used
[7]
[8]
in aqueous media in the presence of coreactants such as NaHSO , HBr,
3
[
9]
Br2, NH Cl,
[10–12]
[13]
[14]
FeCl3,
[16]
[CH (CH ) ] NHSO ,
cerium(IV) ammonium nitrate (CAN),
4
[
15]
[17]
[18]
H SO ,
2
KHSO4,
and HClO4.
In most of
4
3
2 3 4
4
these oxidation systems, not only the reaction conditions are hard, but the
removal of excess sodium bromate from the coreactant is difficult.
In continuation of our studies on the oxidation of organic compounds with
[
10–13,17]
[19]
sodium bromate
and deoximation of keto-oximes with KMnO4,
we have used a combination of a solvent-free reaction strategy and solid
ion-exchange resin (IER) catalysis using ultrasound irradiation in the
oxidative cleavage of oximes for the first time by sodium bromate, which
not only overcomes the previously mentioned disadvantages but also has
other advantages: easy and quick separation of the products from the
þ
oxidant and catalyst, better selectivity because of lower activity of H in
the solid state, high yields, and faster reaction.
In addition, because of the higher concentration of oxidant and lower
reaction temperature, less toxic effluent can be used, and other waste
problems can be minimized. The catalyst is regenerable and does not have
the problem of the limited use of bromate resluting from its insolubility in
almost all organic solvents.
As shown in Table 1, a wide variety of aryl aldoximes and aryl and alkyl
keto-oximes could be easily oxidized to corresponding carbonyl compounds
using ultrasound irradiation in high yields at room temperature (Scheme 1).
Comparisons of the time and yield of this method with our previous
method using KMnO supported on MnSO or MnO under solvent-free con-
4
4
2
ditions are indicated in Table 1. The current procedure is usually much faster
in a similar range of yields. In addition, most standard oxidants of aldoximes
[19,20]
result in the formation of acids;
however, by controlling the times,
aldehydes librated via deprotective reaction are not further oxidized to the cor-
responding acids (entries 15–22).
In conclusion, both sodium bromate and IER are cheap and commercially
available reagents, and not only is ion-exchange resin is regenerable but also
excess bromate ions are easily separated from the reaction mixture and
recycled.
EXPERIMENTAL
Melting points were measured on an Electrothermal 9100 apparatus.
Elemental analyses were performed using a Heraeus CHN–O–Rapid
analyzer. The results were in agreement with the calculated values. Mass

Table 1. Oxidation of oximes by NaBrO
3
/ion exchange resin under ultrasonic irradiation at room temperature
Isolated Yield Ref. [19] Yield
Time (min) Time (min)
GC Yield
Time (min)
Entry
1
Reactant
Product
%
%
%
79
10
75
90
78
45
2
78
15
73
100
85
55
3
4
5
83
84
81
25
35
60
70
83
81
120
110
150
75
85
84
75
90
75
(
continued)

Table 1. Continued
Isolated Yield
Time (min)
Ref. [19] Yield
Time (min)
GC Yield
Time (min)
Entry
6
Reactant
Product
%
%
%
80
15
71
85
79
45
7
8
9
76
30
20
—
—
—
—
—
—
—
—
71
a
97
15
20
20
5
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
a
1
1
1
0
1
2
84
72
a
63
a
54
13
20
—
—
—
—

a
1
4
5
54
20
15
—
72
—
75
—
73
—
50
1
81
84
1
1
6
7
10
20
71
—
70
—
80
—
35
—
79
1
1
8
9
68
79
45
10
—
—
—
—
—
—
—
—
(
continued)

Table 1. Continued
Isolated Yield
Time (min)
Ref. [19] Yield
Time (min)
GC Yield
Time (min)
Entry
Reactant
Product
%
%
%
20
21
22
68
45
25
10
—
—
—
—
—
—
—
—
71
74
—
—
—
—
a
GC yield.

Oxidative Cleavage of Oximes
4041
1
2
1
2
Scheme 1. R and R ¼ aryl and alkyl; R ¼ aryl and R ¼ H.
spectra were recorded on a Finnigan-MAT 8430 mass spectrometer operating
at an ionization potential of 70 eV. IR spectra were recorded on a Shimadzu
1
13
IR-470 spectrometer. H and C NMR spectra were recorded on a Bruker
DRX-300 Avance spectrometer at 300.13 and 75.47 MHz. NMR spectra
were obtained on solutions in CDCl . All products are known compounds,
3
1
which were identified by IR and H NMR spectral data, and their melting
points were compared with literature reports.
General Procedure for Oxidation of Oximes
A mixture of oxime (1 mmol), IER (0.2 g), and sodium borate (0.5 g,
3
.3 mmol) was ground and then successively charged into a screw-capped
vial. The mixture was irradiated in a water bath of the ultrasonic cleaner
Eyela-92303, Tokyo Rikakikai Co.) at 25–308C for 15–30 min. Then, the
(
3
reaction mixture was washed with 25 cm of chloroform. The crude product
was purified by column chromatography on silica gel using n-heptane–ethyl
acetate (9:1) as eluent to afford the pure product.
ACKNOWLEDGMENTS
Financial assistance from the Research Council of Shahid Beheshti University
of Iran is gratefully acknowledged.
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2