A facile reduction of nitroarenes to anilines using FeCl 3·6H2O/indium

Article abstract of DOI:10.1081/SCC-120022471

Reduction of a variety of nitroaromatic compounds to the corresponding anilines occurs chemoselectively in high yields upon treatment with a new reduction system consisting of FeCl₃·6H₂O/indium in aqueous methanol.

Full text of DOI:10.1081/SCC-120022471

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A Facile Reduction of Nitroarenes to Anilines Using
FeCl · 6H O/Indium
3
2
a
a
a
a
Professor Byung Woo Yoo , Jin Woo Choi , Sun Kyun Hwang , Dong Yoon Kim , Heung
a
b
b
Soo Baek , Kyung Il Choi & Joong Hyup Kim
a
Department of Chemistry , Korea University , Jochiwon, Chungnam, Korea
b
Biochemicals Research Center , Korea Institute of Science and Technology , Cheongryang,
Seoul, Korea
Published online: 21 Aug 2006.
To cite this article: Professor Byung Woo Yoo , Jin Woo Choi , Sun Kyun Hwang , Dong Yoon Kim , Heung Soo Baek , Kyung
Il Choi & Joong Hyup Kim (2003) A Facile Reduction of Nitroarenes to Anilines Using FeCl · 6H O/Indium, Synthetic
3
2
Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry, 33:17, 2985-2988, DOI:
0.1081/SCC-120022471
1
To link to this article: http://dx.doi.org/10.1081/SCC-120022471
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MARCEL DEKKER, INC. • 270 MADISON AVENUE • NEW YORK, NY 10016
©
2003 Marcel Dekker, Inc. All rights reserved. This material may not be used or reproduced in any form without the express written permission of Marcel Dekker, Inc.
Õ
SYNTHETIC COMMUNICATIONS
Vol. 33, No. 17, pp. 2985–2988, 2003
A Facile Reduction of Nitroarenes to Anilines
.
Using FeCl 6H O/Indium
3
2
1
,
1
1
Byung Woo Yoo, * Jin Woo Choi, Sun Kyun Hwang,
1
Dong Yoon Kim, Heung Soo Baek, Kyung Il Choi,
1
2
2
and Joong Hyup Kim
1
Department of Chemistry, Korea University,
Jochiwon, Chungnam, Korea
2
Biochemicals Research Center, Korea Institute of
Science and Technology, Cheongryang, Seoul, Korea
ABSTRACT
Reduction of a variety of nitroaromatic compounds to the corre-
sponding anilines occurs chemoselectively in high yields upon treat-
ment with a new reduction system consisting of FeCl ꢀ 6H O/indium
3
2
in aqueous methanol.
Key Words: Nitroarene; Aniline; Ferric chloride; Indium.
Aromatic amines are versatile synthetic intermediates in the prepa-
ration of important chemicals such as dyes, photographic, pharmaceuti-
*
Correspondence: Byung Woo Yoo, Professor, Department of Chemistry,
Korea University, Jochiwon, Chungnam, 339700, Korea; Fax: +82-041-867-
396; E-mail: bwyoo@korea.ac.kr.
5
2
985
DOI: 10.1081/SCC-120022471
Copyright & 2003 by Marcel Dekker, Inc.
0039-7911 (Print); 1532-2432 (Online)
www.dekker.com

MARCEL DEKKER, INC. • 270 MADISON AVENUE • NEW YORK, NY 10016
©
2003 Marcel Dekker, Inc. All rights reserved. This material may not be used or reproduced in any form without the express written permission of Marcel Dekker, Inc.
2
986
Yoo et al.
[
1]
cal and agricultural chemicals, and antioxidants. Many reducing agents
have been used to reduce aromatic nitro compounds to aromatic amines.
[
2]
[3]
[4]
Some of them include, selenol, H Te, NaTeH, N,N-dimethyl hydra-
2
[5]
[6]
[7]
[8]
zine/ferric chloride,
TiCl /Bu Te,
Sm/I2,
In/NH Cl,
and
B H /Pd/C. However, most methods still lack the desired chemoselec-
4
2
4
[9]
4
10
tivity when other reducible functional groups are present in the nitroar-
ene. In continuation of ourint ee rst on the applications of indium
[
10]
reagents for various transformations we wish to report here an efficient
and chemoselective method for the reduction of various aromatic nitro
compounds to the corresponding amines by treatment with
FeCl ꢀ 6H O/In (Eq. (1)). The high yields of the reduction products
3
2
demonstrate the efficiency of this new method. Table 1 illustrates the
generality of this reduction procedure. We have investigated the reactions
of FeCl ꢀ 6H O/In system with various nitroarenes and found that the
3
2
reductions generally proceeded with high yields and showed selectivity
over other labile substituents. The new reduction system was generated
by the addition of indium powder to a stirred solution of ferric chloride
hexahydrate in aqueous methanol under sonication. Some control experi-
a
Table 1. Reduction of nitroarenes to aromatic amines with FeCl
3
ꢀ 6H
2
O/In.
b
Reaction time
(h)
Yield
(%)
a
Entry
Substrate
Product
1
2
3
4
5
6
7
8
9
C H NO
6
C H NH
6
1.5
1.5
2.0
2.0
2.0
1.5
2.0
1.5
2.0
1.5
94
91
86
90
85
92
87
89
81
84
5
2
5
2
p-CH
p-HOC
p-BrC H NO
3
C
6
H
4
NO
2
p-CH
p-HOC
p-BrC H NH
3
C
6
H
4
NH
2
6
H
4
NO
2
6 4 2
H NH
6
4
2
6
4
2
m-BrC H NO
6
m-BrC H NH
6 4 2
4
2
p-ClC
o-CH
p-EtOOCC H NO
H
6 4
NO
2
p-ClC
o-CH
p-EtOOCC H NH
6
H
4
NH
6 4 2
COC H NH
2
3
OC
6
4
H NO
2
3
6
4
2
6
4
2
o-CH
3
OC
6
4
H NO
2
o-CH
3
OC
6
H
4
NH
2
1
1
1
0
p-HOOCC
6
H
4
NO
2
6 4 2
p-HOOCC H NH
Cl
Cl
Br
1
CH
3
NO
2
CH3
NH2
NH2
2:0
83
Br
2
3
CH3
NO2
CH3
2:0
1:5
84
91
1
NCCH
2
NO
2
NCCH2
NH2
a
All isolated amines were fully characterized by spectral analysis.
Isolated yield.
b

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2003 Marcel Dekker, Inc. All rights reserved. This material may not be used or reproduced in any form without the express written permission of Marcel Dekker, Inc.
.
FeCl3 6H O/Indium
2987
2
ments revealed that nitroarenes could not be reduced by ferric chloride
hexahydrate or indium alone under the reaction condition. It was worth
commenting that the sensitive carbonyl group remains intact without any
further reduction under the reaction condition (Entry 7). In addition,
4-nitrophenol proceeded successfully with this reduction system (Entry 3).
FeCl ·6 H O/In
3
2
ArNO2
ArNH2
ð1Þ
H O/MeOH
2
sonication
1
2
In comparison with other procedures, FeCl ꢀ 6H O/In system
3
2
reduces nitroarenes in higher yields (81–94%) and showed a good che-
moselectivity under mild condition. The functional group tolerance of
this method is evident from Entries 3–13 which show that halogen,
hydroxy, methoxy, ketone, carboxyl, ester, and cyano groups are unaf-
fected under the reaction conditions. Particularly haloaromatic nitro
compounds showed remarkable selectivity to give the anilines without
any further dehalogenation (Entries 4–6, 11 and 12). All the compounds
obtained showed IR, NMR and mass spectral data compatible with the
structure. In order to assess the generality of the process, the reaction was
studied with a variety of aromatic nitro compounds. Thus, we have been
able to demonstrate the utility of easily accessible FeCl ꢀ 6H O/In system
3
2
as a convenient reagent for effecting chemoselective reduction of nitroar-
enes. Although the role of ferric chloride hexahydrate is still not clarified,
it is assumed that reduction of ferric chloride with indium provides low-
[6]
valent iron complex, which might be reducing the nitroarenes 1 to
give the corresponding amines 2. The notable advantages of this
methodology are mild reaction condition, readily available and inexpen-
sive reagents, high yield, and tolerance of various functional groups on
the aromatic ring.
In conclusion, we believe that this procedure using FeCl ꢀ 6H O/In
3
2
system will present a useful and convenient alternative to the existing
methods for reduction of nitroarenes to the corresponding anilines.
Further investigations of FeCl ꢀ 6H O /In system as reducing agent in
3
2
organic synthesis are currently in progress.
General procedure for the reaction. Ferric chloride hexahydrate
130 mg, 0.5 mmol), indium powder(228 mg, 2.0 mmol) and
(
H2O/MeOH (1:1, 3 mL) were mixed and the resulting mixture was stirred
at room temperature under sonication for 30 min. A dark-yellow solution
of the complex was obtained. To this solution, nitrobenzene (60 mg,
0.5 mmol) was added. The reaction mixture was stirred for 2 h at room

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2
988
Yoo et al.
temperature. The solvent was evaporated under reduced pressure and the
residue was diluted with ether and filtered. The crude product was pur-
ified by silica gel column chromatography (hexane:ethyl acetate ¼ 6:1) to
afford aniline (44 mg, 94%).
ACKNOWLEDGMENT
This work was financially supported by Korea Institute of Science
and Technology (2E16800) and partially by Korea University.
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Received in the UK October4, 2002