Solvent-free reduction of aromatic nitro compounds with alumina-supported hydrazine under microwave irradiation

Article abstract of DOI:10.1016/S0040-4039(01)01002-4

Aromatic nitro compounds are readily reduced to the corresponding amino compounds in good yield with hydrazine hydrate supported on alumina in the presence of FeCl₃·6H₂O, Fe(III) oxide hydroxide or Fe(III) oxides.

Full text of DOI:10.1016/S0040-4039(01)01002-4

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 42 (2001) 5347–5349
Solvent-free reduction of aromatic nitro compounds with
alumina-supported hydrazine under microwave irradiation
a
a
a
b,
Andr a´ s Vass, J o´ zsef Dud a´ s, Judit T o´ th and Rajender S. Varma *
a
Research Institute of Chemical and Process Engineering, University of Kaposvar, H-8200, Veszpr e´ m, Egyetem u.2, Hungary
b
Clean Processes Branch, National Risk Management Research Laboratory, U.S. Environmental Protection Agency, MS 443,
6 W. Martin Luther King Drive, Cincinnati, OH 45268, USA
2
Received 23 May 2001; revised 25 May 2001; accepted 11 June 2001
Abstract—Aromatic nitro compounds are readily reduced to the corresponding amino compounds in good yield with hydrazine
hydrate supported on alumina in the presence of FeCl ·6H O, Fe(III) oxide hydroxide or Fe(III) oxides. Published by Elsevier
3
2
Science Ltd.
Supported reagents on mineral oxide surfaces have
been widely employed in organic synthesis. Reagents
Herein, we report our results for a solvent-free
microwave reduction protocol that leads to a facile
preparation of aromatic amines from the corresponding
nitro compounds with hydrazine hydrate supported on
solid materials such as alumina, silica gel and clays.
Some non-traditional solid support materials, such as
NaCl, NaBr, NaI, KCl, KBr, KI, Na SO , K SO ,
1
immobilized on porous solid materials have several
advantages over the conventional solution phase reac-
tions because of the good dispersion of active sites
leading to improved reactivity and milder reaction con-
ditions. The solvent-free use of supported reagents in
combination with microwave irradiation provide ideal
reaction conditions with special attributes such as
reduced reaction time, easier work-up procedure and
2
4
2
4
CaCO3 etc., which couple poorly with microwaves,
have also been examined. Since only the supported
reactants absorb the microwave energy, a variety of
such chemically inactive supports can be utilized for the
2
enhanced selectivity and reactivity. The recyclability of
the inorganic solid support is often possible thus ren-
dering the procedure relatively environmentally
acceptable.
14
enhancement of organic reactions.
Two series of experiments were performed to identify
and optimize the ideal solid support material and the
appropriate catalyst to affect the reduction of aromatic
nitro compounds. First, the effect of supports on the
reduction of 4-nitroaniline to 1,4-phenylenediamine was
examined on various inorganic solid supports. The data
presented in Table 1 clearly show the efficiency of
alumina-supported hydrazine hydrate in the reduction
of 4-nitroaniline in good yield. The traditional solid
supports with soft acidic surface were found to be less
effective, whereas non-traditional solid supports with
soft basic or neutral surface are moderately effective.
Aromatic amines are widely used as intermediates for
dyes, photographic materials, pharmaceutical and agri-
cultural chemicals and as antioxidants. They are gener-
ally prepared by reduction of aromatic nitro
compounds using a vast array of reagents in solution
3
phase reactions. Hydrazine hydrate has been exten-
sively used for reduction purposes in the presence of
4
heterogeneous catalysts such as activated zinc–copper,
5
6
7a–c
7a,b
7b,8a–c
Raney Ni,
10a–c
Zn–C, Fe–C, Pd–C,
Pt–C,
9
a–d
FeCl ·6H O-activated carbon,
Fe(III) oxides,
3
2
1
1
12
13
Fe(III)–MgO, graphite and clays. The reduction is
usually conducted in refluxing alcoholic solvents or
dioxane, a process that requires several hours of reac-
tion time.
Some of them (K CO , NaI, KI) were chemically active
2
3
and participated in the reaction that led to the genera-
tion of several by-products.
In the second series of experiments, the catalytic activ-
ity of some well-known catalysts was examined under
solvent-free conditions using alumina as the solid sup-
port. Interestingly, Fe(III) chloride, Fe(III) oxide
Keywords: reduction; hydrazine hydrate; nitro compounds; aromatic
amines; microwave heating.
*
Corresponding author. Tel.: (513) 487-2701; fax: (513) 569-7677;
e-mail: varma.rajender@epa.gov
0
040-4039/01/$ - see front matter Published by Elsevier Science Ltd.
PII: S0040-4039(01)01002-4

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348
A. Vass et al. / Tetrahedron Letters 42 (2001) 5347–5349
Table 1. Reduction of 4-nitroaniline with hydrazine on various inorganic solid supports in the presence of catalytic
a
FeCl ·6H O under microwave irradiation
3
2
R1
R1
H NNH . H O / FeCl . 6H O
2
2
2
3
2
NO2
NH2
MW, 30-70 W
R2
R2
Supports surfaces
Final temperature (°C)
Conversion (%)
Yield (%)
Alumina
Silica gel
Florisil
K10
Talc
CaO
119–125
124–128
138–142
150–154
165–172
149–155
154–157
156–161
142–146
128–134
150–154
171–176
146–149
154–159
174–180
168–173
158–164
100
93
95
94
94
90
97
94
30
95
95
80
96
96
96
100
100
97
65
64
33
73
75
76
70
20
75
71
20
72
76
22
55
56
MgO
CaCO3
K CO3
2
NaCl
NaBr
NaI
KCl
KBr
KI
Na SO4
2
K SO4
2
a
Microwave heating was programmed as follows: 3/30, 5/45, 2/75 (min/W).
hydroxide and Fe O4 were found to be the most
effective catalysts (Table 2). In contrast to earlier
reports, it was found unnecessary to use acti-
vated carbon, since alumina ensured the high surface
area.
3
The following is the general procedure employed for
the reduction of nitro compounds. Aromatic nitro
compound (10 mmol) was mixed with inorganic solid
support or alumina (10 g) and the mixture was added
Table 2. Reduction of 4-nitroaniline with various catalysts
by alumina-supported hydrazine hydrate under microwave
a
irradiation
to hydrazine hydrate (30 mmol) and FeCl ·6H O (0.5
Catalyst
Yield (%)
Catalyst
Yield (%)
3
2
15
mmol). The solid homogenized mixture was placed
in a modified reaction tube which was connected to a
removable cold finger and sample collector to trap
excess hydrazine hydrate. The reaction tube was
placed in a Maxidigest MX 350 (Prolabo) microwave
reactor fitted with a rotational mixing system. After
irradiation for a specified period (see Table 3), the
contents were cooled to room temperature and the
Without catalyst
Fe(III) chloride
Fe(III) oxide
hydroxide
0
97
91
NiCl2
CoCl2
ꢀ5
10
0
SnCl2
Fe O4
78
K10 clay
0
3
a
Microwave heating was programmed as follows: 3/30, 5/45, 2/75
min/W).
(
Table 3. Microwave assisted reduction of aromatic nitro compounds with alumina-supported hydrazine hydrate and catalytic
FeCl ·6H O
3
2
R1
R2
Microwave irradiation
Reaction time (min)
Yield (%)
Power (W)
Temp. (°C)
H
H
H
H
H
H
H
H
H
30+45
30+45
30+45
30+45
30+45
30+45
30+45
30+45
30+45
45
5+2
5+3
5+2
4+2
4+4
2+4
6+2
6+3
3+5
6
108
108
108
112
108
103
110
115
119
111
116
89
96
89
96
91
92
81
92
97
96
83
4
4
4
4
3
2
2
4
2
2
-OCH3
-CH3
-Cl
-I
-OH
-OH
-NH2
-NH2
-NH2
-NH2
H
5-CH3
5-CF3
45
10

A. Vass et al. / Tetrahedron Letters 42 (2001) 5347–5349
5349
product extracted into ethyl acetate (2×20 mL). The
solid inorganic material was filtered and the solvent was
removed under reduced pressure to afford the product
that was further purified by crystallization.
Chapter 23, pp. 292–313; (f) Varma, R. S. Pure Appl.
Chem. 2001, 73, 193.
3. Larock, R. C. Comprehensive Organic Transformations;
VHC Publishers: New York, 1987.
4
. Han, B. H.; Shin, D. H.; Lee, Hyun R.; Ro, B. H. Bull.
Korean Chem. Soc. 1989, 10, 315; Chem. Abstr. 1990, 112,
55189e.
5. Lee, H. R.; Ryoo, E. S.; Shin, D. H. Taehan Hwhakhoe
Chi. 1988, 32, 607; Chem Abstr. 1988, 111, 194193u.
6. Han, B. H.; Shin, D. H. Bull. Korean Chem. Soc. 1985, 6,
320; Chem Abstr. 1986, 104, 129304x.
In conclusion, a facile solvent-free method for reduc-
tion of aromatic nitro compounds to aromatic amines
is developed. The reagent system described here may be
a good alternative to well known methods since the
reduction of aromatic nitro compounds proceeds expe-
ditiously and in high yields.
7
. (a) Entwistle, I. D.; Jackson, A. E.; Johnstone, R. A. W.;
Telford, R. P. J. Chem. Soc., Perkin Trans. 1 1977, 443;
(
6
b) Furst, A.; Berlo, R. C.; Hootom, S. Chem. Rev. 1965,
5, 51; (c) Bavin, P. M. G. Can. J. Chem. 1958, 36, 238.
Acknowledgements
8
. (a) Zhilina, O. D.; Vasilev, A. M.; Shagalov, L. B.;
Suvorov, N. N. Khim. Geterotsikl. Soedin 1986, 11, 1481;
Chem. Abstr. 1987, 107, 58779e; (b) Yuste, F. Tetra-
hedron Lett. 1982, 23, 147; (c) Balcom, D.; Furst, A.
J. Am. Chem. Soc. 1953, 75, 4334.
This work was financially supported, in part, by a
NATO grant (HTECH.LG 97.4558).
9. (a) Hung, Teljes HU 52,755, Chem. Abstr. 1991, 114,
References
142871f; (b) Hirashima, O.; Manabe, T. Chem. Lett.
1975, 259; (c) Clive, D. L. J.; Angoh, A. G.; Sharon, B.
1
. (a) Posner, G. H. Angew. Chem., Int. Ed. Engl. 1978, 17,
M. J. Org. Chem. 1987, 52, 1339; (d) Hine, J.; Hahn, S.;
Miles, D. E.; Ahn, K. J. Org. Chem. 1985, 50, 5092.
4
87; (b) McKillop, A.; Young, K. W. Synthesis 1979, 401
and 481; (c) Balogh, M.; Laszlo, P. Organic Chemistry
Using Clays; Springer-Verlag: Berlin, 1993; (d) Clark, J.
H. Catalysis of Organic Reactions by Supported Inorganic
Reagents; VCH Publisher: New York, 1994; (e) Clark, J.
H.; Macquarrie, D. J. Chem. Commun. 1998, 853; (f)
Kabalka, G. W.; Pagni, R. M. Tetrahedron 1997, 53,
10. (a) Miyata, T.; Ishino, Y.; Hirashima, T. Synthesis 1978,
834; (b) Lauwiner, M.; Rys, P.; Wissmann, J. Appl. Catal.
A 1998, 72, 141; (c) Benz, M.; van der Kraan, A. M.;
Prins, R. Appl. Catal. A 1998, 172, 149.
11. Kumar, P. S.; Sanchez-Valente, J.; Figueras, F. Tetra-
hedron Lett. 1998, 39, 2573.
7
999.
12. Han, B. H.; Shin, D. H.; Cho, S. Y. Tetrahedron Lett.
1985, 26, 6233.
13. Han, B. H.; Shin, D. H.; Cho, S. Y. Tetrahedron Lett.
2
. (a) Varma, R. S. Green Chem. 1999, 1, 43; (b) Varma, R.
S. Clean Products Processes 1999, 1, 132; (c) Varma, R. S.
In Green Chemistry: Challenging Perspectives; Tundo, P.;
Anastas, P., Eds. Environmentally benign organic trans-
formations using microwave irradiation under solvent-
free conditions. Oxford University Press: Oxford, 2000;
pp. 221–244; (d) Loupy, A.; Petit, A.; Hamelin, J.; Tex-
ier-Boullet, F.; Jacqualt, P.; Mathe, D. Synthesis 1998,
1990, 31, 1181.
14. (a) Vass, A.; Dudas, J.; Varma, R. S. Tetrahedron Lett.
1999, 40, 4951; (b) Patonay, T.; Varma, R. S.; Vass, A.;
Levai, A.; Dudas, J. Tetrahedron Lett. 2001, 42, 1403.
15. In control experiments with hydrazine hydrate without
any support, we explored the reactions with catalytic
1
213; (e) Varma, R. S. In ACS Symposium Series No.
FeCl and obtained very modest yields of amines. Among
3
7
67/Green Chemical Syntheses and Processes; Anastas, P.
the disadvantages are the formation of two phases which
could not be efficiently mixed. Further, while heating
beyond 70–80°C, intensive gas formation and bubbling
was observed that rendered the reaction uncontrollable.
T.; Heine, L.; Williamson, T., Eds. Expeditious solvent-
free organic syntheses using microwave irradiation.
American Chemical Society, Washington DC, 2000;
.