Microwave-induced synthesis of nitrostilbenes under neat condition

Article abstract of DOI:10.1081/SCC-100103315

Nitrostilbenes 3a-e were synthesized in good yield using microwave under neat conditions, whereas heating at 90°C resulted in poorer yields of products.

Full text of DOI:10.1081/SCC-100103315

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MICROWAVE-INDUCED
SYNTHESIS OF
NITROSTILBENES UNDER NEAT
CONDITION
S. Saravanan a & P. C. Srinivasan b
a Department of Organic Chemistry, University of
Madras, Guindy Campus, Chennai, 600 025, India
b Department of Organic Chemistry, University of
Madras, Guindy Campus, Chennai, 600 025, India
Published online: 09 Nov 2006.
To cite this article: S. Saravanan & P. C. Srinivasan (2001) MICROWAVE-INDUCED
SYNTHESIS OF NITROSTILBENES UNDER NEAT CONDITION, Synthetic Communications:
An International Journal for Rapid Communication of Synthetic Organic Chemistry,
31:6, 823-826, DOI: 10.1081/SCC-100103315
To link to this article: http://dx.doi.org/10.1081/SCC-100103315
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SYNTHETIC COMMUNICATIONS, 31(6), 823–826 (2001)
MICROWAVE-INDUCED SYNTHESIS OF
NITROSTILBENES UNDER NEAT
CONDITION
S. Saravanan and P. C. Srinivasan*
Department of Organic Chemistry, University of Madras,
Guindy Campus, Chennai-600 025, India
ABSTRACT
Nitrostilbenes 3a–e were synthesized in good yield using
microwave under neat conditions, whereas heating at 90ꢀC
resulted in poorer yields of products.
During the last decade, microwave methodology1–5 and solventless6,7
experiments have been carried out in organic synthesis. They offer shorter
reaction times, increased yields, clean, efficient, economical procedures, and
safer work-up and are environmentally friendly. In the present investigation,
solvent-free microwave technique was employed to synthesize nitrostilbenes.
These compounds 3a–d were synthesized8 in boiling benzene with piperidine
as catalyst. It is our interest to synthesize these nitrostilbenes as precursors
for polynitroaromatic compounds as potential high-temperature explosives9
and for electrochemical studies.10 Neat condensation of 2,4-dinitrotoluene11
1 with various aromatic aldehydes 2a–e in the presence of pyrrolidine under
microwave irradiation of 800 W power gave nitrostilbenes 3a–e in good yield
(60–85%, Scheme 1). Simple heating on a water bath upto 15 min gave the
same in comparatively poorer yield (18–68%). A comparison of yields
obtained by both methods is shown in the Table.
* Corresponding author.
823
Copyright & 2001 by Marcel Dekker, Inc.
www.dekker.com

824
SARAVANAN AND SRINIVASAN
Scheme 1.
Table.
Stilbene
Activation Mode
Time (min)
Yield %
m.p.ꢀC
139
3a
Microwave
Thermal
0.5
15
0.5
15
0.5
15
0.5
15
0.5
15
85
68
3b
3c
3d
3e
Microwave
Thermal
70
28
142
162
187
180
Microwave
Thermal
82
52
Microwave
Thermal
60
18
Microwave
Thermal
80
35

NITROSTILBENES
825
In summary, a rapid synthesis of nitrostilbenes in good yields under
microwave irradiation was developed.
EXPERIMENTAL
General
The nitrostilbenes 3a–d had the correct melting point as reported in
the literature.8 The structure of 3e was consistent with its spectral data.
Preparation of 2,4-Dinitrotoluene 1
4-Nitrotoluene (13.7 g, 100 mmol) was dissolved in con. sulphuric acid
(30.6 g, 312 mmol). Fuming nitric acid (15 g, 230 mmol) was added slowly
with stirring. The temperature was maintained below 50ꢀC by occasional
cooling in water. Then the mixture was heated at 90ꢀC for 30 min, cooled to
25ꢀC, and poured over crushed ice. The crude product was filtered, dried,
and recrystallized from methanol. Yield: 95%; m.p. 71ꢀC.
General Procedure for the Synthesis of Stilbenes Under Microwave
Irradiation and Conventional Heating
Synthesis of stilbene 3e is representative for the general procedure
followed. A mixture of 2,4-dinitrotoluene 1 (0.93 g, 5 mmol) and aldehyde
2e (0.63 g, 5 mmol) was irradiated under microwave of 800 W in a domestic-
type microwave oven in the presence of pyrrolidine (0.106 g, 1.5 mmol) for
30 sec. The resultant mixture was washed with ethanol. The solid product
was filtered and dried. Yield: 80%; m.p. 180ꢀC; IR(KBr) 1600, 1570,
1
1380 cmꢁ1; H NMR (400 MHz, CDCl3) ꢀ 8.9 (d, J ¼ 2.4 Hz, 1H), 8.51 (d,
J ¼ 7.8 Hz, 1H), 8.4 (d, J ¼ 2.2 Hz, 1H), 8.25 (d, J ¼ 9.2 Hz, 1H), 7.98 (d,
J ¼ 8.1 Hz, 1H), 7.93 (d, J ¼ 7.84 Hz, 1H), 7.78 (d, J ¼ 16.1 Hz, 1H), 7.65 (m,
1H), 7.3 (d, J ¼ 15.6 Hz, 1H) MS: m/z 315 (2% Mþ), 182 (28%), 165 (100%),
151 (95%).
The above procedure was repeated using heating at 90ꢀC for 15 min in
a water bath. Yield 3e: 35%.
ACKNOWLEDGMENTS
The authors thank CSIR, New Delhi, for financial support; UGC-SAP
for equipment grants to their department; and Ms. Baby, RSIC, IIT
Chennai, for recording pmr spectrum of compound 3e.

826
SARAVANAN AND SRINIVASAN
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Received in Japan March 27, 2000