Oxidative bromination of aniline and its derivatives

Article abstract of DOI:10.1134/S1070427208080314

Oxidative bromination of aniline and its derivatives containing various substituents (CH₃, Cl, NO₂, COOH) in ortho, meta, and para positions with a brominating mixture of NaBr (KBr) and 20-22% hydrogen peroxide in 6-8% hydrochloric acid at the molar ratio aniline: NaBr (KBr): H ₂O₂: HCl = 1: 3.5: 3.2: 4.5 is described.

Full text of DOI:10.1134/S1070427208080314

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2008, Vol. 81, No. 8, pp. 1479–1481. © Pleiades Publishing, Ltd., 2008.
Original Russian Text © M.S. Salakhov, B.T. Bagmanov, V.S. Umaeva, M.I. Bagmanova, 2008, published in Zhurnal Prikladnoi Khimii, 2008, Vol. 81,
No. 8, pp. 1404–1406.
BRIEF
COMMUNICATION
Oxidative Bromination of Aniline and Its Derivatives
M. S. Salakhov, B. T. Bagmanov, V. S. Umaeva, and M. I. Bagmanova
Institute of Polymeric Materials, National Academy of Sciences of Azerbaijan, Sumgait, Azerbaijan
Received December 12, 2007
Abstract—Oxidative bromination of aniline and its derivatives containing various substituents (CH
COOH) in ortho, meta, and para positions with a brominating mixture of NaBr (KBr) and 20–22% hydrogen
peroxide in 6–8% hydrochloric acid at the molar ratio aniline : NaBr (KBr) : H : HCl = 1 : 3.5 : 3.2 : 4.5 is de-
3 2
, Cl, NO ,
2 2
O
scribed.
DOI: 10.1134/S1070427208080314
Compounds containing nitrogen and bromine are
effective antipyrenes used to prepare noncombustible
polymeric materials [1, 2]. To compounds of this class
belongs 2,4,6-tribromoaniline (TBA), which also finds
use as a constituent of biologically active preparations,
pharmaceuticals [3], and herbicides [4]. A variety of meth-
ods for preparing TBA have been described [4–8].
However, all these methods [2, 5] provide only a 15–50%
yield of a product that requires additional purification.
stituents (CH , Cl, NO , COOH). To determine the op-
3 2
timal conditions of oxidative bromination, we studied
how the concentrations of hydrogen peroxide and hy-
drochloric acid and the molar ratio of the reagents af-
fect the yield of tribromoaniline (TBA) for the exam-
ple of aniline and its m-substituted derivatives.
The reaction was performed in hydrochloric acid
at 15 ± 5°C in the course of 2 h.
In studying the influence exerted by the hydrogen
peroxide concentration, a 20–22% aqueous solution at
the molar ratio NaBr (KBr) : H O : HCl = 1 : 3.5 : 3.2 :
This study is concerned with the development of
a wasteless method for preparation of TBA and its de-
rivatives by oxidative bromination of aniline with a mix-
ture containing a brominating agent (potassium or so-
dium bromide) and 20–22% hydrogen peroxide in 6–8%
hydrochloric acid at 15 ± 5°C for 2 h [8] by the scheme:
2
2
4
.5 was found to be the optimal.
Under these conditions, the yield of TBA reaches
99.9%. With concentration of the H aqueous solu-
O
2 2
tion raised to 25% or lowered to 16–18%, the TBA
yield decreases to 86 and 90.2%, respectively.
The yield of TBA is the highest (99.9%0) at a hy-
drochloric acid concentration of 6–8%. Lowering the
HCl concentration to 4% or raising it to 10% leads to a
decrease in the TBA yield to 86 and 90.9%, respec-
tively.
I–V, XI–XIV
Z = Z' = X = Y = H (I), Z = Z' = X = Br, Y = H (VI); Z = Z' =
X = H, Y = CH (II), Z = Z' = X = Br, Y = CH (VII); Z =
II–X, XV–XVIII
3
3
The influence exerted by the molar ratio of the re-
agents on the TBA yield in oxidative bromination of
aniline was studied at NaBr(KBr) : 20–22% H O : 6–8%
Z' = X = H, Y = Cl (III), Z = Z' = X = Br, Y = Cl (VIII);
Z = Z' = X = H, Y = NO (IV), Z = Z' = X = Br, Y = NO
IX); Z = Z' = X = H, Y = COOH (V), Z = Z' = X = Br, Y =
COOH (X); Z = Z' = Y = H, X = NO (XI), Z = Z' = X = Br,
X = NO (XV); Z = Z' = Y = H, X = COOH (XII), Z = Z' =
X = Br, X = COOH (XVI); Z = Y = X = H, Z' = NO (XIII),
Z = Z' = X = Br, Z' = NO (XVII); Z = Y = X = H, Z' =
2
2
2
2
(
HCl = 1 : 3 : 3 : 3, temperature of 15 ± 5°C, and reaction
time of 2 h.
2
2
2
It was shown that, under the above conditions,
the yield of TBA is 98%, whereas at a NaBr(KBr) : H O :
2
2
2
COOH (XIV), Z = Z' = X = Br, Z' = COOH (XVIII).
HCl molar ratio equal to 1 : 4.5 : 6.5 : 8.0, the TBA yield
reaches 99.9%. At the same time, to use the latter ratio
is unreasonable, because the same yield of TBA is
The reaction involved aniline and its ortho-, meta-,
and para-substituted analogues containing various sub-
1479

1
480
SALAKHOV et al.
Characteristics of the compounds synthesized
Found
–
—–––––––
Calculation
Yield, mp, °
Compound
R
f
%
C
Empirical
formula
C
H
Hal
N
2
1.80
1.75
1.35
1.30
72.60
72.72
4.28
4.28
2
3
3
3
3
4
4
2
2
,4,6-Tribromoaniline (VI)
99.9
99.6
99.8
122
101
124
102
170
195
330
128
76
0.56
0.62
0.78
0.69
0.71
0.70
0.72
0.68
0.76
C
6
C
7
C
6
C
6
C
7
C
6
C
7
C
6
C
7
H
H
H
H
H
H
H
H
H
4
6
3
3
4
4
5
4
5
Br
Br
Br
Br
Br
Br
Br
Br
Br
3
3
3
3
3
2
2
2
2
N
2
2
2
4.31
4.42
1.72
1.74
69.80
70.00
4.01
4.07
-Methyl-2,4,6-tribromoaniline (VII)
-Chloro-2,4,6-tribromoaniline (VIII)
-Nitro-2,4,6-tribromoaniline (IX)
-Carboxy-2,4,6-tribromoaniline (X)
-Nitro-2,6-dibromoaniline (XV)
-Carboxy-2,6-dibromoaniline (XVI)
-Nitro-4,6-dibromoaniline (XVII)
N
1
1
9.60
9.75
0.81
0.82
75.74
75.75
3.79
3.84
ClN
1
8.98
0.61
0.80
63.88
64.00
7.12
7.47
N
2
О
2
2
2
9
5.0
19.20
2
2
2.30
2.46
1.00
1.07
64.07
64.17
3.67
3.74
98.0
NO
2
2
2
4.00
4.32
1.11
1.35
53.78
54.05
9.05
9.45
93.0
95.0
94.0
2
N O
2
2
8.12
8.47
1.51
1.69
54.00
54.24
4.48
4.74
NO
2
2
2
4.19
4.32
1.27
1.35
53.79
54.05
9.16
9.46
2
N O
2
2
8.10
8.48
1.53
1.70
53.87
54.10
4.51
4.74
-Carboxy-4,6-dibromoaniline (XVIII) 95.0
NO
2
reached at a ratio NaBr(KBr) : H O : HCl = 1 : 3.3 : 3.2 :
stituents in the stabilization of the aromatic nucleus in
the course of oxidative bromination.
2
2
4
.5.
m-Substituted TBAs containing electron-donating
The structure of compounds VI–X and XV–XVIII
was found from IR spectra, in which bands associated
and electron-accepting substituents in the aromatic ring
were obtained similarly. In all cases, m-substituted
TBAs were isolated in quantitative yield and no addi-
tional purification was required. The characteristics of
compounds VI–X are listed in the table.
with stretching vibrations of the C–Br bond at 540–
–1
6
80 cm were observed, and from a comparison of
their physical parameters (melting point, elemental
composition) with the known data [2, 3, 6, 8].
The oxidative bromination of o- and p-substituted
anilines differs from the bromination of m-substituted
derivatives and depends on the electronic nature of
substituents in the phenyl ring. It was found that, in o-
and p-substituted anilines, substituents of the first kind
EXPERIMENTAL
The IR spectra of the compounds (suspensions in
Vaseline oil) were recorded on an UR-20 spectropho-
tometer.
(
CH , –Cl) lead to black solid products. This shows
3
that, in the course of oxidative bromination, molecules
of o- and p-substituted anilines can take on a quinoid
structure, which is facilitated by electron-donating sub-
stituents. The target products were not isolated.
The purity R of the compounds was monitored by
f
TLC on Silufol plates with spot development by UV
light [9]. A mixture of benzene, dichloroethane, and
acetic acid [benzene : dichloroethane : acetic acid = 4 :
1
.5 : 1 (by volume)] served as eluent.
With substituents of the second kind (COOH,
NO ), o- and p-substituted anilines undergo oxidative
2,4,6-Tribromaniline VI. A flask was charged
2
bromination under the optimal conditions without
blackening of the reaction mass, with 2,4- and 2,6-di-
bromoanilines isolated as a target product. This confirms
the decisive role of the electronic nature of the sub-
with 0.1 M of aniline and 0.45 M of 6% hydrochloric
acid. To the reaction mixture was added dropwise un-
der agitation 0.35 M of NaBr or KBr dissolved in 0.32 M
of 20% hydrogen peroxide. The temperature was main-
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 81 No. 8 2008

OXIDATIVE BROMINATION OF ANILINE AND ITS DERIVATIVES
1481
tained within 15±5°C. Molar ratio aniline : NaBr(KBr) :
H O : HCl = 1 : 3.5 : 3.2 : 4.5. After addition of
the brominating mixture was terminated, the flask was
charged with 100 ml of water and the agitation was
continued for another 1 h. The precipitated crystals
were filtered off, washed with water to neutral reac-
tion, and dried. The yield of TBA VI was 99.9%.
(
2) Use of o- and p-substituted anilines with sub-
2
2
stituents of the second kind results in the formation of
,4- or 2,6-dibromoanilines.
2
REFERENCES
1
. Aseeva, R.M. and Zaikov, G.E., Snizhenie goryuchesti
polimernykh materialov (Reducing the Combustibility of
Polymeric Materials), Moscow: Znanie, 1981.
The oxidative bromination of m-substituted ani-
lines II–V was performed similarly. m-Substituted tri-
bromoanilines VII–X were isolated. Their characteris-
tics are listed in the table.
2. Gaevskii, B.D., Dorofeev, V.T., Matveeva, A.P., and
Rilo, R.P., Chemistry of 2,4,6-tribromoaniline, VNIIio-
dobrom, Available from VINITI, Saki, no. 962.
3
. Bаdische Anilin und Soda Fabrik, Chem. Industrie J.,
954, vol. 72, no. 5, pp. 965–968.
1
Dibromo-substituted anilines XV–XVIII. The re-
action was similar to that employed to obtain tribro-
moaniline, but with p-substituted anilines XI, XII and m-
sub-stituted anilines XII, XIV used. The characteris-
tics of dibromo derivatives XV–XVIII are listed in
the table.
4. JPN patent 7521.
5. Golodnikov, G.V., and Mandel’shtam, T.V., Praktikum
po organicheskomu sintezu (Practical Course of Organic
Synthesis), Ogloblin, K.A., Ed., Leningrad: Len. Gos.
Univ., 1976.
6
7
. FRG Patent Appl. 2 723 137.
. Snyder, H.R. and Geller, H.C., J. Amer. Chem. Soc.,
1
952, vol. 74, p. 2006.
CONCLUSIONS
8
9
. USSR Inventor’s Certificate, no. 1 398 346.
(
1) Irrespective of the nature of a substituent in
. Akhrem, R.M. and Kuznetsova, A.I., Tonkosloinaya
khromatographiya (Thin-Film Chromatography), Mos-
cow: Nauka, 1964.
the phenyl ring, m-substituted anilines result in the for-
mation of 2,4,6-tribromoanilines in high yield.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 81 No. 8 2008