Uncatalyzed reductive fission of azoarenes to aminoarene(s) by hydrazine hydrate

Article abstract of DOI:10.1081/SCC-200051672

Various azoarenes with hydrazine hydrate in refluxing ethanol undergo reductive fission to give easily isolable aminoarene(s) without use of any specialized catalyst. The reaction is fast and cost effective, and yields are excellent (85-95%). Substituents such as -OH, -OCH₃, -COOH, -Cl, and -Br are unaffected. The method affords an elegant route to the preparation of aminoarenes.

Full text of DOI:10.1081/SCC-200051672

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Uncatalyzed Reductive Fission of Azoarenes
to Aminoarene(s) by Hydrazine Hydrate
M. A. Pasha a & H. M. Nanjundaswamy b
a Department of Chemistry, Central College Campus, Bangalore University,
Bangalore, India
b Chemical Examination Section, Public Health Institute, Bangalore, India
Published online: 21 Aug 2006.
To cite this article: M. A. Pasha & H. M. Nanjundaswamy (2005) Uncatalyzed Reductive Fission of Azoarenes
to Aminoarene(s) by Hydrazine Hydrate, Synthetic Communications: An International Journal for Rapid
Communication of Synthetic Organic Chemistry, 35:7, 897-900, DOI: 10.1081/SCC-200051672
To link to this article: http://dx.doi.org/10.1081/SCC-200051672
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Synthetic Communicationsw, 35: 897–900, 2005
Copyright # Taylor & Francis, Inc.
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1081/SCC-200051672
Uncatalyzed Reductive Fission of Azoarenes
to Aminoarene(s) by Hydrazine Hydrate
M. A. Pasha
Department of Chemistry, Central College Campus,
Bangalore University, Bangalore, India
H. M. Nanjundaswamy
Chemical Examination Section, Public Health Institute, Bangalore, India
Abstract: Various azoarenes with hydrazine hydrate in refluxing ethanol undergo
reductive fission to give easily isolable aminoarene(s) without use of any specialized
catalyst. The reaction is fast and cost effective, and yields are excellent (85–95%).
Substituents such as 22OH, 22OCH3, 22COOH, 22Cl, and 22Br are unaffected. The
method affords an elegant route to the preparation of aminoarenes.
Keywords: Aminoarenes, azoarenes, hydrazine hydrate, reductive fission
Previous reports on the reductive cleavage of azoarenes to aminoarenes
have been reviewed.[1] The reduction of azoarenes is usually achieved with
HCOONH4/10% Pd-C,[2] cycohexene/5% Pd on asbestos,[3] Cp2TiBH4,[4]
Ni/HCO2NH4 or HCOOH,[5] and Zn/HCOOH.[6] More recently, Zn/
[7]
CH3CO2NH4 has been reported for the reduction of azoarenes to the
Received in India November 10, 2004
Address correspondence to M. A. Pasha, Department of Chemistry, Central College
Campus, Bangalore University, Bangalore 560 001, India. E-mail: m_af_pasha@
yahoo.co.in

898
M. A. Pasha and H. M. Nanjundaswamy
Scheme 1.
corresponding aminoarenes. Some of these procedures use expensive catalysts
such as, 5% Pd on asbestos, 10% Pd-C, and so forth. Dehalogenation was
observed with HCOONH4/10% Pd-C while benzidine rearrangement with
Raney Ni/HCOOH occurred as the reaction proceeded via hydrazobenzene
intermediate.
It is to be noted that systems such as NH2NH2/10% Pd-C[8] and
NH2NH2/Raney Ni[9] have been reported to convert azobenzene into hydra-
zobenzene. It is also worth noting that Yu Lu Wang[10] has recently
Table 1. Reduction of azoarenes into aminooarenes by hydrazine hydrate
Substrate
Producta
Yieldb (%)
Entry
R
R0
R
R0
1
2
1
2
H
H
H
H
95
94
95
94
90
92
92
92
85
87
93
—
—
—
—
—
—
—
94
92
95
94
2-CH3
3-CH3
3-OCH3
2-OH
20-CH3
30-CH3
30-OCH3
20-OH
20-Br
2-Cl
2-CH3
3-CH3
3-OCH3
2-OH
20-CH3
30-CH3
30-OCH3
20-OH
20-Br
20-Cl
3
4
5
6
2-Br
2-Cl
2-Br
2-Cl
7
8
2-OH
H
2-OH
H
9
2-COOH
4-COOH
4-NH2
40-N(CH3)2
2-COOH
4-COOH
4-NH2
40-N(CH3)2
10
11
H
H
H
H
aCharacterized by infrared spectral and on gas chromatographic analysis with
authentic samples.
bIsolated yields. (Boiling point/melting points were found to coincide with that of
authentic samples).

Reductive Fission of Azoarenes to Aminoarene(s)
899
reported the partial reduction of azoarenes using hydrazine hydrate as
reducant to get hydrazoarenes in refluxing ethanol after 20 min to 3 h
without a catalyst.
In this communication, we demonstrate that 99–100% hydrazine hydrate
in refluxing ethanol is a convenient, simple, and chemoselective system for the
reductive fission of azoarenes to aminoarenes as shown in Scheme 1.
In a typical experiment 10 mmol of azobenzene and 80 mmol of
.
99–100% NH2NH2 H2O in ethanol (20 mL) under reflux for 20–25 min
gave aniline (95%). Encouraged by this result, the potential of this reaction
was tested for the reductive fission of a variety of azoarenes. The results are
summarized in Table 1. The reaction was chemoselective as substituents
such as OH, OMe, COOH, Cl, and Br. present on azobenzene derivatives
were unaffected.
In conclusion, we have demonstrated for the first time the reductive
fission of easily accessible azoarenes by hydrazine hydrate in the absence of
any catalysts.
ACKNOWLEDGMENT
H. M. Nanjundaswamy thanks the Joint Director and the Chemical Examiner
of the Public Health Institute, Bangalore, India, for encouragement.
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M. A. Pasha and H. M. Nanjundaswamy
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