ISSN 1070-3632, Russian Journal of General Chemistry, 2009, Vol. 79, No. 1, pp. 162–163. © Pleiades Publishing, Ltd., 2009.
Original Russian Text © D.P. Khrustalev, 2009, published in Zhurnal Obshchei Khimii, 2009, Vol. 79, No. 1, p. 165.
LETTERS
TO THE EDITOR
Synthesis of Pyridinecarboxylic Acid N-Oxides
and Their Amides under Microwave Irradiation Conditions
D. P. Khrustalev
Institute of Organic Synthesis and Coal Chemistry of the Kazakhstan Republic,
ul. Alikhanova 1, Karaganda, 100000 Kazakhstan
e-mail: khrustalev@mail.kz
Received May 4, 2008
DOI: 10.1134/S1070363209010344
The steadily growing scientific interest in N-oxides
is conditioned not only by their essential role in plant
and animal metabolism processes [1, 2], but also by
their valuable synthetic properties [3].
involves prolonged (4–6 h) refluxing of I–III with
hydrogen peroxide in glacial acetic acid [4]. Using
isonicotinic (I) and nicotinic (II) acids and
nicotinamide (III) as examples, we studied the
possibility of obtaining N-oxides IV–VI under
microwave irradiation, aimed at shortening reaction
time. The physicochemical characteristics of the
products are listed in the table.
A
standard procedure of synthesis of
pyridinecarboxylic acid N-oxides and their derivatives
R
R
H2O2, CH3COOH, MW
N
N
O
IV_VI
I_III
R = 4-COOH (I, IV); 3-COOH (II, V); 3-CONH2 (III, VI).
Physicochemical characteristics of compounds IV–VI prepared under usual and MW irradiation conditions
mp, °С
Yield, %
Calculated, %
Found, %
Comp.
no.
Formula
Usual
Usual
MW conditions
MW conditions
С
Н
С
Н
conditions [4]
conditions [4]
IV
V
260–262
258–259
265–267
291–292
89–92
85.5
70.3
70.5
C6H5NO3
C6H5NO3
C6H6N2O2
51.80
51.80
52.17
3.62
3.62
4.38
51.92
51.87
52.21
3.68
3.72
4.42
269–273
75–79
VI
289–293
73–82
Experiments with varied irradiation power and time
showed that the yields of compounds IV–VI are higher
under the following conditions. Compound I–III, 5 g,
was dissolved under heating in 30 ml of glacial acetic
acid in a conical flask of heat-resistant glass, and, after
addition of 15 ml of 30% hydrogen peroxide, the
mixture was subjected to a 70W microwave irradiation
for 20 min (4×5 min). The solution was diluted with
15 ml of water which was then distilled off under a
vacuum. After cooling to room temperature, the
product precipitated and was recrystallized from water.
The identity of compounds IV–VI were proved by
162