Synthesis of 2-cyano-1-(4-nitrophenyl)pyrrole and its 5-bromo- and 4,5-dibromo derivatives

Article abstract of DOI:10.1023/A:1013139823201

1-(4-Nitrophenyl)pyrrole-2-carbaldehyde and its 5-b + romo- and 4,5-dibromo derivatives react with hydrazoic acid in chloroform in the presence of Mg(CIO₄)₂·2.5H₂O (Schmidt reaction) to form the corresponding pyrrole-2-car

Full text of DOI:10.1023/A:1013139823201

Russian Journal of Organic Chemistry, Vol. 37, No. 9, 2001, pp. 1310 1312. Translated from Zhurnal Organicheskoi Khimii, Vol. 37, No. 9, 2001,
pp. 1376 1378.
Original Russian Text Copyright
2001 by Pavlov.
Synthesis of 2-Cyano-1-(4-nitrophenyl)pyrrole
and Its 5-Bromo- and 4,5-Dibromo Derivatives
P. A. Pavlov
Kuban’ State University, ul. Stavropol’skaya 149, Krasnodar, 350040 Russia
Received July 4, 2000
Abstract 1-(4-Nitrophenyl)pyrrole-2-carbaldehyde and its 5-bromo- and 4,5-dibromo derivatives react with
hydrazoic acid in chloroform in the presence of Mg(ClO4)2 2.5H2O (Schmidt reaction) to form the corre-
sponding pyrrole-2-carbonitriles.
1
The Schmidt reaction [1] is superior to the other
methods of preparation of nitriles, for it includes only
one step and utilizes readily accessible initial com-
pounds (aldehydes). Moreover, this procedure ensures
simple isolation of the target products (nitriles) and
regeneration of the reaction medium.
UV, and H NMR spectroscopy (Table 2). Cyanopyr-
roles I III are colorless (I) or slightly yellowish
(II, III) crystalline substances with sharp melting
points. They are readily soluble in most organic
solvents at room temperature, sparingly soluble in
alcohol and benzene, and insoluble in water and ali-
phatic hydrocarbons.
The results of our previous studies on the trans-
formation of aldehydes into nitriles via the Schmidt
In the IR spectra of I III stretching vibrations of
reaction involving perchloric acid and its derivatives the cyano group give a strong absorption band in the
1
as catalyst [2 6] allowed us to synthesize some
nitriles of the pyrrole series from the corresponding
aldehydes. As starting compounds we used 1-(4-nitro-
phenyl)pyrrole-2-carbaldehyde and its 5-bromo- and
4,5-dibromo derivatives which were prepared by the
procedure reported in [7]. The most appropriate
solvent was found to be chloroform which is usually
used in the classical Schmidt reaction. Chloroform is
inert toward HN3 and well dissolve the pyrroles under
study. As catalyst we used hydrated magnesium per-
chlorate Mg(ClO4)2 2.5H2O.
region 2220 2225 cm . Three bands at 1550 1520,
1
1350 1320, and 860 5 cm belong to the nitro
group vibrations [8]. Out-of-plane bending vibrations
of the pyrrolic C H bonds appear at 735 15 cm .
Aromatic C C bonds give rise to absorption at
1605 5 cm , and the band at 765 10 cm corre-
sponds to out-of-plane bending vibrations of C H
bonds in the para-substituted benzene ring [9].
The UV spectra of compounds I and II are charac-
terized by the presence of two absorption maxima
(Table 2). Introduction of the second bromine atom
into the pyrrole ring (compound III) leads to disap-
pearance of the short-wave maximum. These data are
1
1
1
The structure of products I III (Scheme 1) was
confirmed by elemental analysis (Table 1) and IR,
Scheme 1.
I, R = R = H; II, R = Br, R = H; III, R = R = Br.
1070-4280/01/3709-1310$25.00 2001 MAIK Nauka/Interperiodica

SYNTHESIS OF 2-CYANO-1-(4-NITROPHENYL)PYRROLE
1311
Table 1. Yields, melting points, and elemental analyses of 2-cyano-1-(nitrophenyl)pyrroles I III
Found, %
Calculated, %
Comp. Yield,
mp,
C
Formula
no.
%
C
H
Br
N
C
H
Br
N
I
97
98
98
95
61.64
45.16
35.49
3.20
1.98
1.22
19.68
C11H7N3O2
61.91
45.20
35.57
3.28
2.05
1.34
19.71
II
III
128
214
27.28 14.30
43.05 11.30
C11H6BrN3O2
C11H5Br2N3O2
27.39 14.38
43.12 11.32
Table 2. IR, UV, and 1H NMR spectra of compounds I III
1
IR spectrum, , cm
CN NO2
UV spectrum,
max, nm
Comp.
no.
1H NMR spectrum, , ppm
(log )
3
3
I
2225 1550, 1350, 1320 222 (3.51), 6.43 d.d (1H, 4-H, J4, 5 = 3.0, J4, 3 = 4.0 Hz), 7.15 d.d (1H, 3-H,
3
3
281 (4.23)
4J3, 5 = 1.75, J3, 4 = 4.0 Hz), 7.48 d.d (1H, 5-H, J5, 4 = 3.0,
4J5, 3 = 1.75 Hz), 7.85 d (2H, Hb, J = 10.0 Hz), 8.32 d (2H, Ha,
3
3J = 10.0 Hz)
3
II
2210 1545, 1350, 1320 218 (3.43), 6.53 d (1H, 4-H, J = 3.5 Hz), 7.13 d (1H, 3-H, 3J = 3.5 Hz), 7.78 d
255 (4.21)
(2H, Hb, J = 9 Hz), 8.47 d (2H, Ha, J = 9 Hz)
III
2200 1520, 1350, 1320 257 (4.09) 7.16 s (1H, 3-H), 7.73 d (2H, Hb, J = 10 Hz), 8.43 d (2H, Ha, J =
10 Hz)
1
typical of such pyrrole derivatives [10, 11]. The H
NMR spectra of compounds I III contain signals
from aromatic protons as two doublets at 7.7 7.9
and 8.3 8.5 ppm with a coupling constant of 9 10 Hz.
The signals from the ortho-protons (with respect to
the nitro group) are located in a weaker field than
those from the meta-protons [8]. Signals from the
pyrrole ring protons are observed in the region 6.4
7.5 ppm (Table 2).
visualized by treatment with iodine vapor. Solutions
of hydrazoic acid in chloroform were prepared by the
procedure reported in [1].
1-(4-Nitrophenyl)-2-pyrrolecarbonitrile (I).
A three-necked flask equipped with a mechanical
stirrer and reflux condenser was charged with 21.6 g
(0.1 mol) of 1-(4-nitrophenyl)pyrrole-2-carbaldehyde,
a solution of 0.11 mol of hydrazoic acid in chloro-
form, and 25 g (0.1 mol) of Mg(ClO4)2 2.5H2O.
After 5 min, nitrogen began to evolve, and the mix-
ture warmed up to 30 35 C. It was kept for 2 h at
that temperature (until nitrogen no longer evolved)
and was refluxed for 1 h. The mixture was then cooled
to room temperature, treated with water, and filtered.
The organic layer was washed with two portions of
water, treated with charcoal (to decolorize), and fil-
tered. The solvent was evaporated under reduced
pressure to obtain 20.5 g (97%) of compound I with
mp 95 C. Compounds II and III were synthesized in
a similar way.
EXPERIMENTAL
The IR spectra were recorded on a UR-20 spec-
1
trometer in mineral oil. The H NMR spectra were
obtained on a Tesla BS-487 instrument (80 MHz) in
DMSO-d6 using t-BuOH as internal reference. The
UV spectra were measured on a Specord UV-Vis
spectrophotometer in ethanol. The purity of the prod-
ucts was checked by TLC on Silufol UV-254 plates
using ethanol toluene (3:20) as eluent; spots were
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 37 No. 9 2001

1312
PAVLOV
6. Pavlov, P.A. and Kul’nevich, V.G., Khim. Getero-
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RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 37 No. 9 2001