Reduction of aromatic nitro compounds using samarium metal in the presence of a catalytic amount of iodine under aqueous media

Article abstract of DOI:10.1055/s-1999-2788

In the presence of a catalytic amount of iodine, aromatic nitro compounds can be reduced to the corresponding primary amines and hydrazines in good yields with Sm/THF-NH₄Cl (aq.) system at room temperature. The primary amine is in the majority and the halogen, amido substituents on aromatic ring are unaffected during the reaction.

Full text of DOI:10.1055/s-1999-2788

LETTER
1065
Reduction of Aromatic Nitro Compounds Using Samarium Metal in the
Presence of a Catalytic Amount of Iodine under Aqueous Media
Lei Wang, Longhu Zhou, Yongmin Zhang*
Department of Chemistry, Zhejiang University at Xixi Campus, Hangzhou, 210028, P. R. China
Fax +86 517 8273802
Received 14 April 1999
The results of reduction of aromatic nitro compounds us-
ing samarium are summarized in Table. We found that the
reduction of aromatic nitro compounds proceeded
smoothly in the presence of a catalytic amount of iodine
with metallic samarium under aqueous NH4Cl-THF con-
dition at room temperature. The reactions are completed
within 6 hours, and give the corresponding primary amine
and hydrazine in moderate to good yields. The amine is in
the majority. In the course of this process, substituents
such as chloro, bromo, iodo, methyl, methoxy, or amide
groups are not affected. The experimental results indicat-
ed no dehalogenation, demethylation or hydrolysis was
observed during the reaction.
Abstract: In the presence of a catalytic amount of iodine, aromatic
nitro compounds can be reduced to the corresponding primary
amines and hydrazines in good yields with Sm/THF-NH4Cl (aq.)
system at room temperature. The primary amine is in the majority
and the halogen, amido substituents on aromatic ring are unaffected
during the reaction.
Key words: reduction, aromatic nitro compounds, samarium metal,
aqueous media, aromatic amines
Samarium diiodide and organosamarium compounds
have been widely employed as useful reagents in organic
synthesis1. However, relatively few reports on the direct
use of samarium metal in organic synthesis have been
reported2, because the surface of samarium metal is
unactive3. In order to improve the reactivity of samarium,
Interestingly, addition of trace amount of iodine not only
accelerates the reduction of aromatic nitro compounds,
but also increases the yields of products. However, aro-
matic amine as a major product in this reaction is different
from aromatic azoxy compounds as a major product in
Hou’s results7. This difference is not full clearly till now
and the study concerning about this is in progress in our
laboratory.
4
some additives, such as HgCl2 , TMSCl5 or NH4Cl (aq.)6
were added for this purpose. Hou et al have reported the
use of samarium metal in the presence of a catalytic
amount of allyl iodide for the selective synthesis of aro-
matic azoxy compounds from reduction of nitroarenes7.
Aromatic amines, widely used as intermediate for dyes,
photographic, pharmaceutical and agricultural chemicals
and antioxidants, can be easily prepared by reduction of
aromatic nitro compounds using a variety of reductant,
such as catalytic hydrogenation8, carbon monoxide and
ruthenium carbonyl9, titanium (IV) chloride and dialkyl
telluride10, etc. The drawback of the former method is lack
of chemoselectivity, while the later method require rather
long reaction time, high cost and toxicity of the reagents
and usually results only in poor yields. Recently, there are
some reagents, such as diethyl chlorophosphite11, N, N-
dimethyl hydrazine/ferric chloride (cat.)12, nickel-stabi-
lized zirconia13, hydrazine hydrate/iron(III) oxide-
MgO(cat.)14 and indium metal15, reported for the modifi-
cation of this transformation. We report herein the reduc-
tion of aromatic nitro compounds using samarium metal
in the presence of a catalytic amount of iodine under aque-
ous media at room temperature.
Table Reduction of aromatic nitro compounds using samarium
metal in the presence of a catalytic amount of iodine under aqueous
media
Scheme
Synlett 1999, No. 07, 1065–1066 ISSN 0936-5214 © Thieme Stuttgart · New York

1066
L. Wang et al.
LETTER
(5) Wang, L.; Zhang, Y. Tetrahedron 1998, 54, 11129; Lautens,
M.; Ren, Y. J. Org. Chem. 1996, 61, 2210.
(6) Wang, L.; Zhang, Y. Tetraheddron, Lett. 1998, 39, 5257.
(7) Hou, Z.; Fujiwara. Y.; Taniguchi, H. J. Org. Chem. 1988, 53,
3118.
(8) Tafesh, A. M.; Weiguny, J. Chem. Rev. 1996, 96, 2035.
(9) Alper, H.; Amaratunga, S. Tetrahedron Lett. 1980, 21, 2603.
(10) Suzuki, H.; Hanazaki, Y. Chem. Lett. 1986, 549.
(11) Fischer, B.; Sheihet, L. J. Org. Chem. 1998, 63, 393.
(12) Boothroyd, S. R.; Kerr, M. A. Tetrahedron Lett. 1995, 36,
2411.
In conclusion, we have demonstrated that Sm-I2 (trace)/
THF-NH4Cl (aq.) system can be used for the selective re-
duction of aromatic nitro compounds to the corresponding
aromatic amines. The notable advantages of this reaction
are its simplicity, mild reaction conditions and good
yields. It provides a new way for using metallic samarium
in organic synthesis.
Acknowledgement
(13) Upadhya, T. T.; Katdare, S. P.; Sabde, D. P.; Ramaswamy, V.;
Sudalai, A. J. Chem. Soc., Chem. Commun. 1997, 1119.
(14) Kumbhar, P. S.; Sanchez-Valente, J.; Figueras, F.
Tetrahedron Lett. 1998, 39, 2573.
We thank the National Natural Science Foundation of China (Pro-
ject No. 29872010), the NSF of Zhejiang Province, China and the
Laboratory of Organometallic Chemistry, Shanghai Institute of Or-
ganic Chemistry, Chinese Academy of Sciences for financial sup-
ports.
(15) Moody, C. J.; Pitts, M. R. Synlett 1998, 1028.
(16) Typical procedure: Under an inert atmosphere of nitrogen,
metallic samarium powder (0.6 g, 4.0 mmol) and aromatic
nitro compound (1.0 mmol) were placed in a round-bottomed
flask. Then THF (5 mL), a small grain of iodine and NH4Cl
(aq., 0.5 mL) were added successively to it. The reaction
mixture was stirred for the time indicated in Table at room
temperature. The reaction was then quenched by the addition
of HCl (1 mol/L, 2 mL). The mixture was extracted with ether
(25 mL x 2). The combined organic layer was washed with
brine, dried over magnesium sulfate, and concentrated. The
product was isolated by preparative TLC on silica gel eluting
with cyclohexane-ethyl acetate (3:1).
References and Notes
(1) Kagan, H. B.; Namy, J. L. Tetrahedron 1986, 42, 6573;
Molander, G. A. Chem. Rev. 1992, 92, 29; Molander, G. A.
Organic Reaction 1994, 46, 211; Molander, G. A.; Harris, C.
R. Chem. Rev. 1996, 96, 307.
(2) Yanada, R.; Negoro, N.; Yanada, K.; Fujita, T. Tetrahedron
Lett. 1997, 38, 3271; Yanada, R.; Negoro, N.; Yanada, K.;
Fujita, T. Tetrahedron Lett. 1996, 37, 9313; Lautens, M.;
Delanghe, P. H. J. Org. Chem. 1995, 60, 2474.
(3) Hou, Z.; Takamine, K.; Fujiwara, Y. Chem. Lett. 1987, 305.
(4) Molander, G. A.; Harring, L. S. J. Org. Chem. 1989, 54, 3525;
Clive, D, L. J.; Daigneault, S. J. Org. Chem. 1991, 56, 3801.
Article Identifier:
1437-2096,E;1999,0,07,1065,1066,ftx,en;Y09499ST.pdf
Synlett 1999, No. 07, 1065–1066 ISSN 0936-5214 © Thieme Stuttgart · New York