Facile Transfer Hydrogenation of Azo Compounds to Hydrazo Compounds and Anilines by Using Raney Nickel and Hydrazinium Monoformate

Article abstract of DOI:10.1081/SCC-120027231

Azo compounds are conveniently reduced to either partially reduced hydrazo compounds or completely reduced anilines by employing Raney nickel in presence of hydrazinium monoformate depending upon reaction conditions. The other reducible moieties like -COOH and halogens are tolerated. The reduction process is selective, rapid and high yielding.

Full text of DOI:10.1081/SCC-120027231

This article was downloaded by: [Tulane University]
On: 29 September 2014, At: 06:13
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer
House, 37-41 Mortimer Street, London W1T 3JH, UK
Synthetic Communications: An International Journal
for Rapid Communication of Synthetic Organic
Chemistry
Publication details, including instructions for authors and subscription information:
http://www.tandfonline.com/loi/lsyc20
Facile Transfer Hydrogenation of Azo Compounds
to Hydrazo Compounds and Anilines by Using Raney
Nickel and Hydrazinium Monoformate
H. S. Prasad a , Shankare Gowda a & D. Channe Gowda a
a Department of Studies in Chemistry , University of Mysore , Manasagangotri, Mysore,
Karnataka, India , 570 006
Published online: 16 Aug 2006.
To cite this article: H. S. Prasad , Shankare Gowda & D. Channe Gowda (2004) Facile Transfer Hydrogenation of Azo
Compounds to Hydrazo Compounds and Anilines by Using Raney Nickel and Hydrazinium Monoformate, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry, 34:1, 1-10, DOI:
10.1081/SCC-120027231
To link to this article: http://dx.doi.org/10.1081/SCC-120027231
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained
in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no
representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of
the Content. Any opinions and views expressed in this publication are the opinions and views of the authors,
and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied
upon and should be independently verified with primary sources of information. Taylor and Francis shall
not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other
liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or
arising out of the use of the Content.
This article may be used for research, teaching, and private study purposes. Any substantial or systematic
reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any
form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://
www.tandfonline.com/page/terms-and-conditions

SYNTHETIC COMMUNICATIONSw
Vol. 34, No. 1, pp. 1–10, 2004
Facile Transfer Hydrogenation of Azo
Compounds to Hydrazo Compounds
and Anilines by Using Raney Nickel
and Hydrazinium Monoformate
*
H. S. Prasad, Shankare Gowda, and D. Channe Gowda
Department of Studies in Chemistry, University of Mysore, Mysore,
Karnataka, India
ABSTRACT
Azo compounds are conveniently reduced to either partially reduced
hydrazo compounds or completely reduced anilines by employing Raney
nickel in presence of hydrazinium monoformate depending upon reaction
conditions. The other reducible moieties like –COOH and halogens are
tolerated. The reduction process is selective, rapid and high yielding.
Key Words: Azo compounds; Hydrazo compounds; Anilines; Raney
nickel; Hydrazinium monoformate; Catalytic transfer hydrogenation.
*
Correspondence: D. Channe Gowda, Department of Studies in Chemistry, University
of Mysore, Manasagangotri, Mysore, Karnataka, India 570 006; Fax: 091-0821-
2421263/2518835; E-mail: dcgowda@yahoo.com.
1
DOI: 10.1081/SCC-120027231
0039-7911 (Print); 1532-2432 (Online)
www.dekker.com
Copyright # 2004 by Marcel Dekker, Inc.

2
Prasad, Gowda, and Gowda
Reduction of aromatic azo and azoxy compounds has received a good
deal of attention, both preparatively and analytically. Reductive cleavage of
azo and azoxy benzenes has become a useful tool in structural determination
of azo dyes.[1] There are some methods available in the literature for the
conversion of azo compounds to hydrazo compounds[2–6] and amines.[1,2,7,8]
But the earlier mentioned methods require longer reaction time and expensive
catalysts such as Pd/C[2] and 5%Pd on asbestos.[9] If the azo compounds
contain reducible or hydrogenolysable groups like halogen or nitrile, then the
[10]
systems like 10% Pd-C/HCOONH4
and 10% Pd-C/triethylammonium
formate[11] reduce the nitriles to methyl groups and reductively remove the
halogen from the aromatic ring. Moreover, poor yields were reported during
the reduction of azo compounds to anilines.
Raney nickel is routinely used as a catalyst in the field of catalytic
[12]
hydrogenation
as well as in the field of heterogeneous catalytic transfer
hydrogenation.[13–18] It is used for the selective reduction of nitro com-
pounds,[15] dinitro substituted diphenylsulfones,[18] O- and N-benzyl contain-
ing nitro compounds,[13] for the conversion of nitro olefins into carbonyl
derivatives,[19] and for the synthesis of halo amines from halo nitro
compounds.[16] In all these cases, hydrogen donors like formic acid, cyclo-
hexene,[9] ammonium formate,[20] triethylammonium formate,[21] hydra-
zine[22] and hydrazine derivatives like methyl hydrazine,[22] unsymmetrical
dimethyl hydrazine[22] and phenyl hydrazine in presence of various metals are
commonly used. Recently, we reported that hydrazinium monoformate, a new
hydrogen donor with magnesium as catalyst for deblocking protecting groups
in peptide synthesis[23] and also successfully employed for the reduction of
nitro compounds and nitrile moieties to the corresponding amines and methyl
amines by using Raney nickel/hydrazinium monoformate.[24]
In this communication, we wish to report a rapid, selective and simple
transfer hydrogenation of symmetrically and unsymmetrically substituted azo
compounds to the corresponding hydrazo compounds and anilines by using
Raney nickel and hydrazinium monoformate when carried out at room
temperature (Sch. 1) and at reflux temperature (Sch. 2) respectively. The other
functional groups like –OH, –COOH and halogens are tolerated.
Scheme 1.

Azo Compounds
3
Scheme 2.
The reduction of azo compounds to hydrazo compounds in the presence
of Raney nickel and hydrazinium monoformate at room temperature was
completed within 5 to 15 min. The course of reaction was monitored by thin
layer chromatography (or colour disappearance of the starting material) and
concomitant formation of the product. All the reduced products of azo
compounds (few examples are listed in Table 1) by this system were
obtained in good yields. The products were characterized by comparison of
their melting points, TLC and IR spectra with authentic samples. The
disappearance of a strong absorption band between 1630–1575 cm21 due to
–N55N– stretching and the appearance of strong absorption band between
2290–2440 cm21 due to the –NH–NH– group, clearly showed that azo
compounds have been reduced to hydrazo compounds. When a control
experiment was carried out using azo compound with hydrazinium
monoformate, in absence of Raney nickel, the reaction did not proceed at
all.
The azo compounds were reductively cleaved to the corresponding
substituted anilines in the presence of Raney nickel and hydrazinium
monoformate at reflux temperature. The course of reaction was monitored by
thin layer chromatography and IR spectra. The work-up and isolation of the
products were easy. Thus, all the reduced products (few examples are listed in
Table 2) by this system were obtained in good yields. The products were
characterized by comparison of their melting points, TLC and IR spectra with
authentic samples. The disappearance of a strong absorption band between
1630–1575 cm21 due to the –N¼N– stretching and the appearance of a
strong absorption band between 3500–3300 cm21 due to the –NH2 group
clearly showed that the azo compounds had been cleaved into their substituted
anilines. Furthermore there was no absorption between 2290–2440 cm21
,
which clearly indicated the absence of the –NH–NH– group. A control
experiment was carried out using azo compounds with hydrazinium
monoformate in the absence of Raney nickel, but it did not yield the desired
product. The appearance of one spot in TLC in the case of symmetrical azo
compounds and two spots, in the case of unsymmetrical azo compounds
clearly indicated that no hydrazo compounds were formed during the
reductive cleavage of the azo compounds.

4
Prasad, Gowda, and Gowda

Azo Compounds
5
Furthermore, the hydrazinium monoformate/Raney nickel system is
more effective than either cyclohexene/5% Pd on asbestos,[9] hydrazine/10%
Pd-C[2] or HCOONH4/10% Pd-C,[1] Most of the reactions were completed in
less than 15 min. at reflux temperature. But the earlier mentioned methods
require longer reaction time e.g., 16 to 48 h and high temperature.
Thus the azo compounds were easily reduced to either hydrazo
compounds or anilines in a shorter duration, depending upon reaction
temperatures, with Raney nickel, instead of using expensive catalyst such as
palladium without affecting other reducible substituents. The yields were
virtually quantitative and the products were analytically pure. This procedure
will therefore be of general use, especially in cases where rapid, mild and
selective reduction is required.
EXPERIMENTAL
Materials
Some of the azo compounds were purchased from Aldrich Chemical
Company (USA). The rest of the azo compounds were prepared according to
standard procedures reported earlier.[5] Raney nickel, formic acid and
hydrazine were purchased from SISCO Research Laboratories Pvt. Ltd.,
Bombay (India). All of the solvents used were analytical grade or were
purified according to standard procedures. Thin layer chromatography was
carried out on silica gel plates obtained from Whatman Inc. The melting points
were determined by using a Thomas–Hoover melting point apparatus and are
uncorrected. IR spectra were recorded on a Shimadzu FTIR-8300
spectrometer. For preparative TLC plates were prepared from Kieselgel 60
GF254, Merck, Darmstadt and for column chromatography 60–120 mesh silica
gel was used (obtained from SISCO Research Laboratories) with a suitable
eluting system 50 : 50 chloroform : benzene, 60 : 40 chloroform : benzene,
80 : 20 chloroform : benzene, 90 : 10 chloroform : benzene, 80 : 20 chloro-
form : methanol, 85 : 15 chloroform : methanol, 9 : 10 chloroform : methanol,
95 : 5 chloroform : methanol.
Typical Procedure
(a) Procedure for the preparation of hydrazinium monoformate: Equal
moles of 85% formic acid and 99–100% hydrazine were neutralized slowly,
cooling in an ice bath with stirring to obtain hydrazinium monoformate. The
obtained hydrazinium monoformate is used as such for reactions.

6
Prasad, Gowda, and Gowda

Azo Compounds
7

8
Prasad, Gowda, and Gowda
(b) Procedure for the reduction of azo compounds to hydrazo com-
pounds: A suspension of an appropriate azo compound (10 mmole), Raney
nickel (30 mmole) in methanol or in any suitable solvent (15 mL or requisite
amount) and hydrazinium monoformate (20 mmole) was stirred under
nitrogen atmosphere at room temperature. After the completion of the reaction
(monitored by TLC or by colour disappearance of starting material), the
reaction mixture was filtered through celite pad and washed with solvent. The
combined filtrate and washings were evaporated under vacuum. The residue
was taken into 15 mL chloroform or ether, washed twice with 15 mL saturated
brine solution and finally with water. The organic layer was dried over
anhydrous magnesium sulfate and the solvent was removed using rotary
evaporator. Further, the products were purified either by preparative TLC or
column chromatography. After the purification, the products were character-
ized by IR spectra and the melting points were compared with authentic
samples.
(c) Procedure for the reduction of azo compounds to Amines: A
suspension of an appropriate azo compound (10 mmole), Raney nickel
(30 mmole) in methanol or in any suitable solvent (15 mL) and hydrazinium
monoformate (30 mmole) was stirred under nitrogen atmosphere at reflux
temperature. After the completion of the reaction (monitored by TLC), the
reaction mixture was filtered through celite pad and washed with solvent. The
combined filtrate and washings were evaporated under vacuum. The residue
was taken into 15 mL chloroform or ether, washed twice with 15 mL saturated
brine solution and finally with water. The organic layer was dried over
anhydrous magnesium sulfate and the solvent was removed using rotary
evaporator. Further, the products were separated and purified either by
preparative TLC or column chromatography. After the purification, the
products were characterized by IR spectra and the melting points were
compared with authentic samples.
ACKNOWLEDGMENT
The authors wish to thank the University Grants Commission, New Delhi,
India, for financial assistance.
REFERENCES
1. Jnaneshwara, G.K.; Sudalai, A.; Deshpande, V.H. Palladium catalyzed
transfer hydrogenation of azo compounds and oximes using ammonium
formate. J. Chem. Res. (S). 1998, (3), 160–161.

Azo Compounds
9
2. Bavin, P.M.G. The preparation of amines and hydrazo compounds using
hydrazine and palladium charcoal. Can. J. Chem. 1958, 36, 238–240.
3. Furst, A.; Moore, R.E. Reductions with hydrazine hydrate catalyzed by
Raney nickel. II. Aromatic nitro compounds to intermediate products.
J. Am. Chem. Soc. 1957, 79 (20), 5492–5493.
4. Hornsby, S.; Peacock, W.L. Reduction products obtained from nitrogen
compounds under the action of Raney nickel and hydrazine hydrate.
Chem. Ind. (London) 1958, (27), 858–859.
5. Vogel, A.I.; Wating, A.; Wating, J. The small-scale preparation of
azobenzene and of hydrazobenzene. J. Chem. Edu. 1958, 35, 40.
6. Gilchrist, T.L. Reduction of N55N, N–N, N–O and O–O bonds. In
Comprehensive Organic Synthesis; Fleming, I., Ed.; Pergamon Press:
Oxford, UK, 1991; Vol. 8, Ch. 2.2, 381–402.
7. Braude, E.; Linstead, R.P.; Mitchell, P.W.D.; Wooldridge, K.R.H.
Hydrogen transfer. Part VIII. Metal catalyzed transfer hydrogenation of
miscellaneous acceptors. J. Chem. Soc. 1954, 3595–3598.
8. Stafford, W.H.; Los, M.; Thomson, N. The reduction of azo-compounds
with hydrazine. Chem. Ind. (London) 1956, (43), 1277.
9. Ho, T.L.; Olah, G.A. Synthetic methods and reactions; 33. Palladium
catalyzed reductive cleavage of azoarenes and hydrazoarenes to amines
via hydrogen transfer from cyclohexene. Synthesis 1977, 169–170.
10. Brown, G.R.; Foubister, A.J. Direct transformation of cyano into methyl
groups under mild conditions. Synthesis 1982, 1036–1037.
11. Cortese, N.A.; Heck, R.F. Palladium-catalyzed reduction of halo- and
nitro aromatic compounds with triethylammonium formate. J. Org. Chem.
1977, 42 (22), 3491–3494.
12. House, H.O. Catalytic hydrogenation and dehydrogenation. In Modern
Synthetic Reactions; Breslow, R., Ed.; Benzamin, Inc.: Philippines, 1972;
1–44.
13. Yuste, F.; Saldana, M.; Walls, F. Selective reduction of aromatic nitro
compounds containing O- and N-benzyl groups with hydrazine and Raney
nickel. Tetrahedron Lett. 1982, 23 (2), 147–148.
14. Balcom, D.; Furst, A. Reductions with hydrazine hydrate catalyzed by
Raney nickel. I. Aromatic nitro compounds to amines. J. Am. Chem. Soc.
1953, 75, 4334.
15. Moore, R.E.; Furst, A. Reductions with hydrazine hydrate catalyzed by
Raney nickel. III. Effect of the catalyst on the reduction of 22-dinitro
phenyl. J. Org. Chem. 1958, 23, 1504–1506.
16. Leggeter, B.E.; Brown, R.K. Reduction of mono halogenated nitro
benzenes with hydrazine and Raney nickel. A convenient preparation of
halogenated anilines. Can. J. Chem. 1960, 38, 2363–2366.

10
Prasad, Gowda, and Gowda
17. Johnstone, R.A.W.; Wilby, A.H.; Entwistle, I.D. Heterogeneous catalytic
transfer hydrogenation and its relation to other methods for reduction of
organic compounds. Chem. Rev. 1985, 85, 129–170.
18. Ayyanger, N.R.; Lugade, A.G.; Nikrad, P.V.; Sharma, V.K. Catalytic
transfer hydrogenation of nitroarenes with hydrazine hydrate in suitable
solvents. Synthesis 1981, (8), 640–643.
19. Monti, D.; Gramatica, P.; Speranza, G.; Mannito, P. Reaction of nitro
olefins with Raney nickel and sodiumhypophosphite. A mild method for
converting nitro olefins into ketones. Tetrahedron Lett. 1983, 24,
417–418.
20. Ram, S.; Ehrenkaufer, R.E. Ammonium formate in organic synthesis: a
versatile agent in catalytic transfer hydrogenation. Synthesis 1988, (1),
91–95.
21. Terpko, M.O.; Heck, R.F. Palladium catalyzed triethylammonium
formate reductions. 3. Selective reductions of dinitro compounds. J. Org.
Chem. 1980, 45, 4992–4993.
22. Furst, A.; Berlo, R.C.; Hooton, S. Hydrazine as a reducing agent for
organic compounds (catalytic hydrazine reductions). Chem. Rev. 1965,
65, 51–63.
23. Gowda, D.C. Magnesium/hydrazinium monoformate: a new hydrogen-
ation method for the removal of some commonly used protecting groups
in peptide synthesis. Tetrahedron Lett. 2002, 43, 311–313.
24. Gowda, S.; Gowda, D.C. Application of hydrazinium monoformate as
new hydrogen donor with Raney nickel; a facile reduction of nitro and
nitrile moieties. Tetrahedron 2002, 58, 2211–2213.
25. Vogel, A.I. Text Book of Practical Organic Chemistry; Addison Wesley
Longman Limited: UK, 1997; 1394.
26. Vogel, A.I. Text Book of Practical Organic Chemistry; Addison Wesley
Longman Limited: UK, 1997; 1298–1398.
27. Budavari, S. The Merck Index, 11th Ed.; Budavari, S., Ed.; Merck & Co.,
Inc.: Rahway, NJ, USA, 1989; 3247.
28. Banik, B.K.; Suhendra, M.; Banik, I.; Becker, F.F. Indium/ammonium
chloride mediated selective reduction of aromatic nitro compounds:
practical synthesis of 6-aminocrysene. Synth. Commn. 2000, 30,
3745–3754.
Received in the USA July 24, 2003