A Simple and Efficient Method for the Reduction of Azo Compounds

Article abstract of DOI:10.1081/SCC-120026848

Reduction of azo compounds using hydrazine hydrate as reducant without catalyst is described, which proceeded smoothly in mild condition and did not pollute the environment.

Full text of DOI:10.1081/SCC-120026848

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A Simple and Efficient Method for the Reduction of Azo
Compounds
Chang-Rui Zhang a & Yu-Lu Wang b
a College of Chemistry and Environmental Science of Henan Normal University, Henan
Xinxiang, P.R. China
b The Key Laboratory of Environmental Science and Technology of High Education of Henan
Province, P.R. China
Version of record first published: 21 Aug 2006.
To cite this article: Chang-Rui Zhang & Yu-Lu Wang (2003): A Simple and Efficient Method for the Reduction of Azo
Compounds, Synthetic Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry,
33:24, 4205-4208
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SYNTHETIC COMMUNICATIONSÕ
Vol. 33, No. 24, pp. 4205–4208, 2003
A Simple and Efficient Method for the
Reduction of Azo Compounds
Chang-Rui Zhang1 and Yu-Lu Wang2,
*
1College of Chemistry and Environmental
Science of Henan Normal University,
Henan Xinxiang, P.R. China
2The Key Laboratory of Environmental
Science and Technology of High Education of Henan
Province, P.R. China
ABSTRACT
Reduction of azo compounds using hydrazine hydrate as reducant
without catalyst is described, which proceeded smoothly in mild
condition and did not pollute the environment.
There are many methods of reduction of azo compounds reported
in the literature. Of many reductive systems, traditional metals such
as Li,[1,2] Cu,[3] Na,[4] and their complexes are usually used as
reductants. Organic compounds such as sulfonyl hydrazide,[5] anilines,[6]
*Correspondence: Yu-Lu Wang, The Key Laboratory of Environmental Science
and Technology of High Education of Henan Province, P.R. China; E-mail:
zhangcr2001@163.com.
4205
DOI: 10.1081/SCC-120026848
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4206
Zhang and Wang
substituted aliphatic amines,[6] saturated acyclic hydrocarbon[7] have
good effect as reductants. It was reported that azobenzene had also
been successfully reduced by catalytic hydrogenation,[8] sodium amal-
gam,[9] aluminum amalgam,[10] zinc in alcoholic ammonia,[11] and stan-
nous chloride[12] in ethanolic sodium hydroxide. Although these systems
have their own merits, they also have drawbacks, for example: reaction
conditions are not mild, catalysts and reductants are expensive, operation
are tedious, the functionality such as the nitro and carbonyl groups
contained azo compounds are also reduced, and in some cases, azo
compounds are easily over reduced to arylamines, not the desired
product.
Hydrazine hydrate is well known as reductant. It has been used in a
variety of reactions. In previous study, it was reported that with hydra-
NH2NH2 H2O
2
1
1
2
Ar N=NAr
Ar NHNHAr
CH3CH2OH
2
1
NH2 NH2 H2O
CH3 CH2 OH
1
2
1
2
Ar NHCON=NAr
Ar NHCONHNHAr
4
3
NH2NH2 H2O
CH3CH2OH
1
2
1
2
Ar CON=NAr
Ar CONHNHAr
5
6
Scheme 1.
Table 1. Results of reduction of azo compounds.
Reaction
time (min)
M.p.
(ꢀC)
Lit. m.p. Yield
(ꢀC)
Entry
Ar1
C6H5
Ar2
C6H5
(%)
2a
2b
2c
2d
2e
2f
30
20
30
40
35
20
20
30
30
180
20
45
121–123 125–127[15]
131–132 133–134[15]
92
88
91
88
94
91
69
90
79
86
70
77
p-CH3C6H4
p-ClC6H4
p-CH3OC6H4 C6H5
p-CH3C6H4
p-ClC6H4
121–122
69–71
122[15]
71–72[15]
130[15]
p-BrC6H4 p-BrC6H4
3,4-Me2C6H3 3,4-Me2C6H3
128–130
104–106 106–107[15]
144–146 147–148[16]
182–184 184–186[16]
200–202 204–205[16]
204–205 207–209[16]
156–158 159–160[16]
4a
4b
4c
4d
4e
6a
p-FC6H4
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
p-ClC6H4
p-BrC6H4
p-CH3C6H4
m-ClC6H4
p-O2NC6H4
193
193–195[17]

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Reduction of Azo Compounds
4207
zine hydrate with catalyst (such as Cuþþ),[13] reduction of symmetrical
multiple bonds proceeded readily, whereas reactions of more polar func-
tions were more difficult. Cinnamic acid has been selectively reduced with
hydrazine hydrate catalyzed by Raney Ni to produce 3-phenylpropanoic
acid.[14] We tried to reduce azo compounds with hydrazine hydrate
without catalyst. It was demonstrated that this is an effective reagent to
reduce azo compounds. All actions proceeded smoothly with good yields.
The results are summarized in Table 1. Compared to the above systems,
merits of this system lie in convenient operation, mild reaction condition,
easily accessible reagents, high selectivity, and without pollution.
EXPERIMENTAL
Typical Procedure
Hydrazine hydrate (1 mL) was added to a solution of azo compounds
(0.2 mmol) in ethanol (5 mL). The reaction mixture was heated at 60ꢀC.
After being stirred for 20 min–3 h (the reaction was detected by the color,
which changed from deep red to colorless). The solution was poured into
ice. Then, the crystals obtained were filtrated and dried. The crude
product was recrystallized from 95% ethanol.
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