Synthesis of nitriles from aldoximes using silica gel as catalyst under microwave irradiation

Article abstract of DOI:10.1081/SCC-120022486

A rapid and efficient synthesis of nitriles via dehydration from the corresponding aldoximes has been carried out in the presence of Silica gel as catalyst under microwave irradiation in 83-95% yield.

Full text of DOI:10.1081/SCC-120022486

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Õ
SYNTHETIC COMMUNICATIONS
Vol. 33, No. 17, pp. 3085–3088, 2003
Synthesis of Nitriles from Aldoximes Using Silica
Gel as Catalyst Under Microwave Irradiation
Sharwan K. Dewan* and Ravinder Singh
Laboratory of Synthetic Methodologies, Department of
Chemistry, M.D. University, Rohtak, Haryana, India
ABSTRACT
A rapid and efficient synthesis of nitriles via dehydration from the
corresponding aldoximes has been carried outin ht e presence of
Silica gel as catalyst under microwave irradiation in 83–95% yield.
Key Words: Aldoximes; Dehydration; Nitriles; MW.
Nitriles can be prepared from the corresponding oximes via dehydra-
tion (Sch. 1) by a variety of methods employing reagents like trimethyl-
[
1]
[2]
[3]
amine/sulphur dioxide, zeolites, sulphuryl chloride fluoride, etc. But
most of them suffer from some limitations such as longer reaction times,
*Correspondence: Sharwan K. Dewan, 1167, Sector-1, Rohtak-124001, India;
E-mail: sharwandewan@rediffmail.com.
3
085
DOI: 10.1081/SCC-120022486
Copyright & 2003 by Marcel Dekker, Inc.
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2003 Marcel Dekker, Inc. All rights reserved. This material may not be used or reproduced in any form without the express written permission of Marcel Dekker, Inc.
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086
Dewan and Singh
Scheme 1.
expensive reagents, low yields, drastic reaction conditions and tedious
work-up. So, we became interested in developing a new, rapid and effi-
cientme ht od.
We thought of using Silica gel as the inexpensive acidic catalyst in
combination with microwave irradiation in dry media. Microwave acti-
vation as a non-conventional energy source has become a very popular
and useful technology in organic chemistry and reactions under solvent-
free conditions do away with the safety hazards associated with low
[4]
boiling solvents.
A variety of aldoximes (syn as well as anti) such as benzaldoximes,
p-methoxy benzaldoximes, o-hydroxy benzaldoximes, p-hydroxy-3-meth-
oxy benzaldoximes were dehydrated to the corresponding nitrile in
83–95% yield in 1–3 min. The results obtained are recorded in Table 1.
The products were identified on the basis of NMR, IR, and mass spectra
and by comparison of their m.p./b.p. and Rf values with those of the
authentic samples prepared by standard routes reported in the litera-
[5]
ture. Both the syn and anti forms gave comparable yields.
CONCLUSION
We have developed a new, simple, and efficient method for the
dehydration of aldoximes into nitriles under microwave irradiation
using silica gel as an inexpensive, easy to handle, and environmentally
friendly catalyst.
TYPICAL EXPERIMENTAL PROCEDURE
Benzaldoxime (prepared by standard method reported in the litera-
[5]
ture), (0.121 g, 1 mmol) was mixed with Silica gel (3 in an Erlenmeyer
flask (100 mL) and irradiated at 560 W for 1–3 min in an unmodified
domestic Microwave oven (Kenster OM–9925E, 800 W, operating at
2450 MHz). The flask was taken out, cooled and ether (50 mL) was
added. The catalyst was filtered off and the resultant solution evaporated
to afford the desired nitrile. Silica gel G used in these studies was from

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Synthesis of Nitriles from Aldoximes
3087
Table 1. Dehydration of aldoximes into nitriles in the presence of silica gel
under microwave irradiation.
M.p./b.p. (760 mm)
ꢁ
in C
Entry
no.
Irradiation Time
condition (min) % yield Observed
Product
Benzonitrile
4-Methoxy
Lit.
[
[
5]
1
2
560 W
560 W
2
1
84
91
190
58.5
191
59
6]
5]
6]
6]
6]
benzonitrile
Cinnamonitrile
[
[
[
[
3
4
5
6
560 W
560 W
560 W
560 W
2
3
1
1
85
83
91
96
254
94.5
110
62.5
255
95
(trans)
2-Hydroxy
benzonitrile
4-Hydroxy
110
63
benzonitrile
3,4-Dimethoxy
benzonitrile
2-Nitro Benzonitrile
4-Hydroxy-3-
methoxy
[
[
5]
6]
7
8
560 W
560 W
2
1
83
95
110
87
111
88
benzonitrile
Merck. TLC was done on Silica Gel G plates with benzene–ethyl acetate
(
2:1) system. The physical analysis of the products is as follows:
1
Benzonitrile (1). H-NMR (CCl ), 7.5 (m, 5H, Ar-H); IR (neat) 3030
4
ꢁ
(
bulb distillation) Rf: 0.33.
C-H str.), 2240 (CꢀN str.), 1500 & 1450 (C-C str.); b.p. 190 C (bulb to
1
-Methoxy benzonitrile (2). H-NMR (CCl ), 3.8 (s, 3H, -CH ), 7.0
4
4 3
(
str.), 1610 & 1540 (C-C str.); m.p. 58.5 C, Rf: 0.39.
m, 2H, Ar-H), 7.6 (m, 2H, Ar-H); IR (neat) 2940 (C-H str.), 2170 (CꢀN
ꢁ
1
Cinnamonitrile (trans) (3). H-NMR (CCl ), 5.8 (d, 1H, ¼CH-CN,
4
J ¼ 17 Hz), 7.35 (d, 1H, ¼CH-Ph, J ¼ 17 Hz), 7.4 (m, 5H, Ar-H), IR
(
b.p. 254 C (bulb to bulb distillation), Rf: 0.37.
neat) 3030 (¼CH str.) 2220 (CꢀN str.). 1610, 1560 & 1450 (C-C str.):
ꢁ
1
-Hydroxy benzonitrile (4). H-NMR (CDC1 ), 6.16 (br, 1H, -OH),
2
.95–7.04 (m, 2H, Ar-H), 7.4–7.51 (m, 2H, Ar-H); IR (neat) 3264 (OH
3
6
ꢁ
str.), 2232 (CꢀN str.), 1560, 1503 & 1454 (C-C str.); m.p. 94.5 C, Rf: 0.36.
1
-Hydroxy benzonitrile (5). H-NMR (DMSO), 7.0 (m, 2H, ArH). 7.6
4
(
str.). 1587, 1493 & 1449 (C-C str.); m.p. 110 C, Rf: 0.35.
m, 2H, ArH) 10.4 (s, 1H, -OH); IR (neat) 3333 (OH str.), 2222 (CꢀN
ꢁ

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088
Dewan and Singh
,4-Dimethoxy benzonitrile (6). H-NMR (CDCl ), 3.8 (s, 3H,
1
3
3
-
OCH ), 3.9 (s, 3H, -OCH ) 6.9 (m, IH, ArH), 7.0 (m, 2H, ArH);
3 3
IR (neat) 2940 (C-H str.), 2220 (CꢀN str.), 1610, 1540 & 1450 (C-C
ꢁ
str.); m.p. 62.5 C, Rf 0.41.
2
.91-7.96 (m, 1H, ArH), 8.33–8.39 (m, 1H, ArH), IR (neat) 3050 (C-H
1
-Nitro benzonitrile (7). H-NMR (CDCl ), 7.81–7.87 (m, 1H, ArH)
3
7
ꢁ
str.), 2225 (CꢀN str.), 1540 & 1340 (-NO str., Arom); m.p. 110 C,
2
Rf: 0.34.
4
1
-Hydroxy-3-methoxy benzonitrile (8). H-NMR (CDCl ), 3.93
3
(
s, 3H, -CH ), 6.98 (d, J ¼ 8.0 Hz, 1H, ArH), 7.09 (s, 1H, ArH) 7.23 (d,
3
J ¼ 8.0 Hz, 1H, ArH); IR (neat) 3364 (OH str.), 2955 (C-H str.), 2225
ꢁ
(
CꢀN str.), 1590, 1515 & 1458 (C-C str.); m.p. 87 C, Rf: 0.38.
ACKNOWLEDGMENT
We thank Professor A. J. Bellamy for inspiration and Mr. Yashwant
for a gift of the microwave oven used in this investigation.
REFERENCES
1. Olah, G.A.; Vankar, Y.D. Synthesis 1978, 702.
2. Narayana, Rao, M.; Kumar, P.; Garyali, K. Org. prep. Proced. Int.
1989, 21, 230.
3
4
. Olah, G.A.; Narang, S.C.; Garcia-Luma, A. Synthesis 1980, 659.
. Loupy, A.; Petit, A.; Hamelin, J.; Texier-Boullet, F.; Jackqualt, P.;
Mathe, D. Synthesis 1998, 1, 213.
5. Vogel, A.I. A Text Book of Practical Organic Chemistry, 4th Ed.;
ELBS and Longmann, 1978.
6. Sakamoto, T.; Ohsawa, K. J. Chem. Soc., Perkin Trans. 1999, 1,
2323.
Received in the USA December 12, 2002

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