Microwave-assisted rapid dehydration of aldoximes to nitriles on a solid support

Article abstract of DOI:10.1081/SCC-100104327

p-toluenesulfonyl chloride has been proved out to be an efficient reagent for conversion of aldoximes to the corresponding nitriles under microwave irradiation. Extending the procedure to ketoximes, a 20-40% yield of Beckmann rearranged product was obtained.

Full text of DOI:10.1081/SCC-100104327

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MICROWAVE-ASSISTED RAPID DEHYDRATION OF
ALDOXIMES TO NITRILES ON A SOLID SUPPORT
a
a
M. Ghiaci & K. Bakhtiari
a
Department of Chemistry, Isfahan University of Technology, Isfahan, 84154, Iran
Published online: 16 Aug 2006.
To cite this article: M. Ghiaci & K. Bakhtiari (2001) MICROWAVE-ASSISTED RAPID DEHYDRATION OF ALDOXIMES TO NITRILES
ON A SOLID SUPPORT, Synthetic Communications: An International Journal for Rapid Communication of Synthetic Organic
Chemistry, 31:12, 1803-1807, DOI: 10.1081/SCC-100104327
To link to this article: http://dx.doi.org/10.1081/SCC-100104327
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SYNTHETIC COMMUNICATIONS, 31(12), 1803–1807 (2001)
MICROWAVE-ASSISTED RAPID
DEHYDRATION OF ALDOXIMES TO
NITRILES ON A SOLID SUPPORT
M. Ghiaci* and K. Bakhtiari
Department of Chemistry, Isfahan University of Technology,
Isfahan, Iran, 84154
ABSTRACT
p-toluenesulfonyl chloride has been proved out to be an effi-
cient reagent for conversion of aldoximes to the correspond-
ing nitriles under microwave irradiation. Extending the
procedure to ketoximes, a 20–40% yield of Beckmann rear-
ranged product was obtained.
Although traditionally other conditions have been used for the
1
dehydration of aldoximes, more recently clays such as Montmorillonites
2
KSF and K-10 have been used with advantage. For example, this trans-
formation has been described using KSF clay under reflux of toluene with
3
yield of 70% within 15 hours, or under microwave irradiation using
H SO –SiO in dry media with yield of 76% in a domestic oven within 4
2
4
2
4
minutes.
A reduction of reaction time and a mild condition was possible with
the use of p-toluenesulfonyl chloride and pyridine or Et N. We report here
3
the use of a reagent consisting p-toluenesulfonyl chloride adsorbed on
chromatographic grade alumina for rapid, high yield, selective dehydra-
*
Corresponding author.
1
803
Copyright & 2001 by Marcel Dekker, Inc.
www.dekker.com

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804
GHIACI AND BAKHTIARI
tion of aldoximes. When alumina (Fluka, basic alumina, type 507C) was
mixed with the oxime, p-toluenesulfonyl chloride and pyridine dissolved in a
ꢀ
polar volatile solvent such as CHCl , followed by evaporation at 40–50 C
3
under vacuum (20 mm Hg) for 30 min, a yellowish powder was obtained.
The mixture was introduced in a Pyrex flask and submitted to micro-
wave irradiation for 2–15 minutes with a domestic oven. The observed
yields of the different dehydration of aldoximes were given in Table 1.
In order to explore the scope of this condition, we were interested to
5
consider the possibility of the Beckmann rearrangement of ketoximes
using the p-toluenesulfonyl chloride adsorbed on chromatographic grade
alumina in the presence of pyridine. We have observed that this condi-
tion effectively convert ketoximes to the corresponding p-tosyl derivatives
when the migrating group is alkyl residue (entries 6, 7). But in other cases
that the migrating group is an aryl group we get a mixture of products.
The product of Beckmann rearrangement were less than 40% (entries 8, 9
and 12).
Certain ketoximes can be converted to nitriles by the action of proton
6
or Lewis acids. Among these are oximes of a-diketones, a-ketoacids,
a-dialkylamino ketones, a-hydroxy ketones and a-ketoethers. We checked
as above the behavior of p-toluenesulfonyl chloride toward the benzoin
oxime. In the best condition we separated benzaldehyde and benzonitrile
from the mixture of reaction as the main products.
In summary, it is worth noting that carrying out the organic reactions
on the solid support has a drawback. It is possible that they can be most
useful when their involvement is limited to their outer surface. By monitor-
ing the reaction mixture in all cases, there is only one spot for the product
without any trace of starting material, but the isolated yield in the best case
cannot exceed from 75%. We think that the remainder of the product
is adsorbed into the alumina, and we are hoping to find a means to improve
its recovery.

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DEHYDRATION OF ALDOXIMES TO NITRILES
1805
Table 1. Dehydration of Aldoximes to Nitriles

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806
GHIACI AND BAKHTIARI
EXPERIMENTAL
Typical procedure for the dehydration of aldoximes: A solution of
p-chlorobenzaldehyde oxime (1.16 g, 7.5 mmol), p-toluenesulfonyl chloride
2.86 g, 15 mmol) and pyridine (1.2 mL, 15 mmol) in CHCl (20 mL) was
(
3
mixed with 3 g alumina and concentrated under vacuum to give a yellowish
solid. The mixture was introduced in a Pyrex flask and submitted to micro-
wave irradiation. After completion of the reaction (TLC, 3–15 min) 50 mL
CH OH was added. The mixture was filtered and concentrated. To the
3
crude mixture, chloroform (25 mL) was added. The filtrate was washed
with brine (2 ꢁ 25 mL), and then with 2 ꢁ 25 mL of 5% sodium bicarbonate.
The collected organic phase was dried with MgSO , filtered and evaporated
4
to give the crude product with good chemical purity. Flash chromato-
graphy (cyclohexane–ethyl acetate) gave analytically pure sample in 64%
ꢀ
(
m.p. 89–90 C) isolated yield.
4
-Chlorobenzonitrile: IR (KBr): 2250 (m), 1630 (w), 1580 (m), 1480 (s),
ꢂ1
1
380 (s), 1080 (m), 820 (s), 780 (w), 750 (m), 700 (m), 680 (m), 550 (m) cm
.
1
H-NMR (CDCl , TMS): d, 7.56 (dd, 4H, J ¼ 6 Hz) ppm.
3
4
-Bromobenzonitrile: IR (KBr): 2250 (s), 1580 (s), 1480 (s), 1380 (m),
ꢂ1
1
1
060 (s), 820 (s), 770 (m), 700 (w), 550 (s) cm . H-NMR (CDCl , TMS): d,
3
7
.6 (dd, 4H, J¼3 Hz) ppm.
2,6-Dichlorobenzonitrile:IR(KBr):3020(m),2250(s),1680(w),1570(w),
550 (w), 1430 (s), 1220 (s), 1100 (m), 980 (w), 800 (m), 780 (s) cm . H-NMR
ꢂ1 1
1
(
CDCl , TMS): d, 7.45 (s, 3H) ppm.
3
3,4,5-Trimethoxybenzonitrile: IR (KBr): 2880 (m), 2250 (s), 1580 (s),
520 (s), 1460 (m), 1340 (s), 1240 (s), 1140 (s), 1000 (s), 960 (m), 860 (s), 820
1
(
ꢂ1
1
s), 780 (m), 745 (w), 700 (w), 630 (s) cm . H-NMR (CDCl , TMS): d, 6.9
3
(
s, 2H), 3.78 (s, 6H), 3.74 (s, 3H) ppm.
2-Hydroxybenzonitrile: IR (KBr): 3020 (m), 2250 (s), 2080 (w),
990 (m), 1950 (m), 1915 (m), 1660 (s), 1570 (w), 1480 (s), 1450 (s), 1370 (s),
1
1
ꢂ1 1
290 (s), 1080 (s), 1030 (m), 1015 (w), 960 (s), 910 (s), 590 (s) cm . H-NMR
(
CDCl , TMS): d, 8.93–7.18 (m, 4H), 2.48 (s, 1H) ppm.
3
ACKNOWLEDGMENT
This work is financially supported by IUT, Isfahan, Iran.
REFERENCES
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1807
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Received in Japan May 24, 2000

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