, 2006, 16(2), 109–111
Table 1 Deoximation with N-bromo-N-benzoyl-4-toluene sulfonamide at room temperature.
Entry
Substrate
Product
Time/h
Yield (%)a,b
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Cyclohexanone oxime
Acetophenone oxime
Benzaldehyde oxime
4-Chlorobenzaldehyde oxime
Benzophenone oxime
4-Methylacetophenone oxime
Isobutyraldehyde oxime
Cinnamaldehyde oxime
Isobutyl methyl ketone oxime
Diisopropyl ketone oxime
2-Chlorobenzaldehyde oxime
Ethyl methyl ketone oxime
Benzoin oxime
Cyclohexanone
Acetophenone
Benzaldehyde
4-Chlorobenzaldehyde
Benzophenone
4-Methylacetophenone
Isobutyraldehyde
Cinnamaldehyde
Isobutyl methyl ketone
Diisopropyl ketone
2-Chlorobenzaldehyde
Ethyl methyl ketone
Benzoin
1.5
1.5
1.5
1.5
1.5
1.5
2
93
93
93
93
92
92
90d
80
88
87
84c
84d
83c
83c
81
2.25
2
2.3
2.5
2.5
2.5
3.3
3
Camphor oxime
Cyclopentanone oxime
Camphor
Cyclopentanone
aProducts were characterised by their physical constants, comparison with authentic samples and melting points of 2,4-dinitrophenyl hydrazone derivatives
and by their IR and NMR spectra. bIsolated yields. cUnder reflux conditions. dCH2Cl2/H2O was used as a solvent.
equimolar mixtures of camphor oxime and benzyl alcohol in
acetone and water were allowed to react with N-bromo-N-ben-
zoyl-4-toluenesulfonamide at room temperature, the ketone oxime
underwent chemoselectively oxidative deoximation giving (82%)
camphor, whereas benzyl alcohol was not oxidised to benzal-
dehyde (Scheme 3).
NOH
HC
CHO
COOH
2, acetone, H2O
room temperature
93%
0%
R1
R2
O
Scheme 2
N
Me
SO2NC
An unsaturated oxime (entry 8) was cleaved to the corre-
sponding unsaturated aldehyde without affecting the double
bond. Thus, we observed the competitive oxidation of oximes
in the presence of alkenes (Scheme 4).
OH
Br
2
After the reaction was completed, according to Scheme 1,
compound 2, was converted into N-benzoyl-4-toluenesulfon-
amide 1, which can be isolated, brominated and reused many
times as a deoximating reagent.
R1
R2
O
acetone, H2O
room temperature
or reflux
O
Me
SO2NC
H
1
Scheme 1
2, acetone, H2O
NOH
CH2OH
reflux
†
1
IR and H NMR spectra were recorded using a Shimadzu 435-U-04
spectrophotometer (paraffin) and a 90 MHz Jeol FT-NMR spectrometer,
respectively. 1H NMR chemical shifts were measured relative to TMS.
Solvent-free preparation of N-benzoyl-4-toluene sulfonamide 1.
A mixture of 10.0 g (58.4 mmol) of 4-toluene sulfonamide and 10.2 ml
(87.6 mmol) of benzoyl chloride was placed in a beaker. The beaker was
heated in an oil bath (140 °C). The mixture was stirred with a mechanical
stirrer for 1 h. Then, it was cooled to room temperature, and the product
was recrystallised from ethanol. The yield of pure compound 1 was
15.1 g (94%), mp 147–149 °C. 1H NMR ([2H6]acetone) d: 2.34 (s, 3H),
7.31–7.95 (m, 9H), 10.9 (s, 1H). 13C NMR ([2H6]acetone) d: 21.88,
129.22, 129.50, 129.79, 130.54, 133.02, 134.31, 137.94, 145.84, 166.14.
IR (paraffin, n/cm–1): 3309, 1709, 1597, 1493, 1335, 1235, 1165, 1059,
888, 841, 791, 678. Found (%): C, 61.32; H, 4.62; N, 5.22. Calc. for
C14H13NO3S (%): C, 61.07; H, 4.76; N, 5.09.
O
CHO
82%
oxidised alcohol
0%
Scheme 3
In conclusion, the test reaction occurs at room temperature
without the formation of overoxidation products due to high
chemoselectivity of reagent 2. The OH and C=C functional
groups in the oxime structure were not oxidised to other
functional groups. Finally, the oxidative reagent can be recovered
and reused many times.
Preparation of N-bromo-N-benzoyl-4-toluene sulfonamide 2. 5.0 g
(18.2 mmol) of N-benzoyl-4-toluene sulfonamide 1 was dissolved in a
chilled aqueous sodium hydroxide solution (~2 M) at room temperature,
and the solution was transferred to a beaker. 0.93 ml (18.2 mmol) of
bromine dissolved in 2 ml of tetrachloromethane was added to the solu-
tion with vigorous stirring, and a yellow precipitate was immediately
formed. The yellow product was separated from the aqueous layer and
recrystallised from acetone. The yield of pure 2 was 5.2 g (80%),
mp 204–207 °C. 1H NMR ([2H6]acetone) d: 2.28 (s, 3H), 7.13–8.00
(m, 9H). 13C NMR ([2H6]acetone) d: 21.81, 127,44, 128.45, 129.09,
130.00, 130.64, 132.49, 138.22, 143.21, 165.28. IR (paraffin, n/cm–1):
1697, 1596, 1456, 1333, 1231, 1128, 895, 860, 719, 663. Found (%):
C, 47.78; H, 3.25; N, 4.10. Calc. for C14H12BrNO3S (%): C, 47.47;
H, 3.41; N, 3.95.
Reagent 2 is a competitor to the known reagents NBS and
N-bromophthalimide with the advantage of easier preparation.
This work was supported by the Bu-Ali Sina University
Research Council.
CH2
HC
NOH
2, acetone
Me
H2O, room temperature
‡
General procedure for deoximation. A mixture of an oxime (3 mmol)
CHO
O
and reagent 2 (4.5 mmol) in acetone (10 ml) and water (0.1 ml) was
stirred at a temperature specified in Table 1. After the reaction was
completed (TLC), the solvent was removed under reduced pressure, and
diethyl ether (20 ml) was added to the mixture, which was stirred for
10 min; then, sulfonamide 1 was removed by filtration, and the product
was purified by column chromatography (hexane–diethyl ether, 4:1,
CH2Cl2 was used for isobutyraldehyde and ethyl methyl ketone).
Me
91%
oxidised alkene
0%
Scheme 4
110 Mendeleev Commun. 2006