Bromination of pyrazole-3(5)-carboxylic acid

Full text of DOI:10.1134/S1070363207090289

ISSN 1070-3632, Russian Journal of General Chemistry, 2007, Vol. 77, No. 9, pp. 1652 1653.
Pleiades Publishing, Ltd., 2007.
Original Russian Text
G.A. Akopyan, 2007, published in Zhurnal Obshchei Khimii, 2007, Vol. 77, No. 9, pp. 1581 1582.
LETTERS
TO THE EDITOR
Bromination of Pyrazole-3(5)-carboxylic Acid
G. A. Akopyan
ARIAK Institute of Applied Chemistry, Republic of Armenia,
Artashatskoe sh. 5/2, Yerevan, 375053 Armenia
Received May 31, 2007
DOI: 10.1134/S1070363207090289
Earlier we showed [1] that the bromination of 1,3-
dimethyl- and 1,5-dimethylpyrazole-4-carboxylic
acids in the presence of sodium hydroxide involves
substitution of the carboxy group by bromine.
The structure of compounds II, III was proved by
1H NMR spectroscopy, mass spectrometry, and ele-
mental analysis. The positions and integral intensities
1
of the NH and COOH signals in the H NMR spectra
of compounds II, III are fully consistent with the
1
proposed structures. The H NMR spectra were ob-
These data gave us grounds to suggest that by bro-
minating pyraxole-3(5)-carboxylic acid (I) under
analogous conditions we could prepare hardly ac-
cessible 3(5)-bromopyrazole.
tained on a Varian Mercury 300 instrument in
(CD3)2SO. The mass spectrum was taken on an MX-
1321A instrument (direct inlet, ionizing energy 60 eV).
Br
N
Br
3,4,5-Tribromopyrazole (II). Bromine, 16 g, was
added dropwise at room temperature over the course
of 1 h to a solution of 11.2 g of pyrazole-3(5)-car-
boxylic acid in 100 ml of water and 12 g of NaOH.
Crystals formed and were filtered off and recrystal-
lized to obtain 9 g (90% by volume) of compound II,
1:3:1
Br
N
H
COOH
I:NaOH:Br
N
II
N
1
mp 184 C (water + ethanol, 1:1). H NMR spectrum
COOH
Br
H
(DMSO-d6, 300 MHz), , ppm: 13 14 br (1H, NH).
Mass spectrum, M+: found: 305; calculated: 305.
Found, %: C 12.25; H 0.52; N 9.53; Br 79.21.
C3HN2Br3. Calculated, %: C 11.80; H 0.33; N 9.18;
Br 78.69.
1:1:1
+ II
N
I
N
H
III
4-Bromopyrazole-3(5)-carboxylic acid (III).
Bromine, 16 g, was added dropwise at room tem-
perature over the course of 1 h to a solution of 11.2 g
of pyrazole-3(5)-carboxylic acid in 100 ml of water
and 4 g of NaOH. The reaction mixture was stirred
for 3 h at the same temperature. Crystals formed and
were filtered off and dissolved in ethanol, after which
ethanolic KOH (1:1) was added. The precipitate was
filtered off and dissolved in water. The solution was
acidified to obtain 17.2 g (90%) of compound III, mp
260 C (decomp.). 1H NMR spectrum (DMSO-d6,
300 MHz), , ppm: 7.91 s (1H, 5-H), 13 14 br (2H,
However, bromination of acid I, gave, instead of
the expected product, 3,4,5-tribromopyrazole (II),
yield 90%, mp 184 C [2].
With a 1:1:1 molar ratio of I, NaOH, and Br2, the
yield of compound II sharply falls (8.8%), and the
major reaction product (90%) in this case is 4-bro-
mopyrazole-3(5)-carboxylic acid (III). 4-Bromo-
pyrazole, mp 92 C, prepared by decarboxylation of
compound II, is identical to the product prepared by
direct bromination of pyrazole [2].
1652

BROMINATION OF PYRAZOLE-3(5)-CARBOXYLIC ACID
NH, COOH). Mass spectrum, M+: found: 191; cal-
1653
REFERENCES
culated: 191. Found, %: C 26.71; H 1.84; N 15.23;
Br 42.15. C4H3N2O2Br. Calculated, %: C 25.13; H
1.57; N 14.66; Br 41.88. Hot water was added to the
filtrate, and the precipitate that formed was filtered
off to obtain 0.9 g (8.8%) of compound II, mp 184 C
(water + ethanol, 1:1).
1. Attaryan, O.S., Akopyan, G.A., Badalyan, K.S., and
Asratyan, G.V., Zh. Obshch. Khim., 2007, vol. 77,
no. 2, p. 335.
2. Huttel, R., Wagner, H., and Jochum, P., Justus
Liebigs Ann. Chem., 1955, vol. 593, p. 179.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 77 No. 9 2007