Efficient reduction of nitroarenes to the corresponding anilines with sulfur in basic media under solvent-free conditions

Article abstract of DOI:10.1080/10426500307905

Aromatic nitro compounds can be conveniently reduced to the corresponding primary amines in the presence of S₈ under solvent-free conditions in excellent yields. Alumina supported NaOH catalyses this transformation. Chemoselectivity was observed in the reduction of the nitro group in the presence of phenol, carboxylic acid, aldehyde, and benzyl halide groups.

Full text of DOI:10.1080/10426500307905

This article was downloaded by: [University of Western Cape]
On: 21 November 2012, At: 03:48
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
Phosphorus, Sulfur, and Silicon and the Related
Elements
Publication details, including instructions for authors and subscription information:
http://www.tandfonline.com/loi/gpss20
Efficient Reduction of Nitroarenes to the
Corresponding Anilines with Sulfur in Basic Media
under Solvent-Free Conditions
Khodabakhsh Niknam a , Ali Reza Kiasat a , Foad Kazemi b & Abolghasem Hossieni a
a Persian Gulf University, Bushehr, Iran
b Shahid Chamran University, Ahvaz, Iran
Version of record first published: 27 Oct 2010.
To cite this article: Khodabakhsh Niknam, Ali Reza Kiasat, Foad Kazemi & Abolghasem Hossieni (2003): Efficient Reduction of
Nitroarenes to the Corresponding Anilines with Sulfur in Basic Media under Solvent-Free Conditions, Phosphorus, Sulfur, and
Silicon and the Related Elements, 178:6, 1385-1389
To link to this article: http://dx.doi.org/10.1080/10426500307905
PLEASE SCROLL DOWN FOR ARTICLE
Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditions
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.
The publisher does not give any warranty express or implied or make any representation that the contents
will be complete or accurate or up to date. The accuracy of any instructions, formulae, and drug doses should
be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims,
proceedings, demand, or costs or damages whatsoever or howsoever caused arising directly or indirectly in
connection with or arising out of the use of this material.

Phosphorus, Sulfur, and Silicon, 178:1385–1389, 2003
C
Copyright Taylor & Francis Inc.
ISSN: 1042-6507 print
DOI: 10.1080/10426500390200701
EFFICIENT REDUCTION OF NITROARENES TO
THE CORRESPONDING ANILINES WITH SULFUR
IN BASIC MEDIA UNDER SOLVENT-FREE
CONDITIONS
Khodabakhsh Niknam,a Ali Reza Kiasat,a Foad Kazemi,b
and Abolghasem Hossienia
Persian Gulf University, Bushehr, Irana and Shahid Chamran
University, Ahvaz, Iranb
(Received October 24, 2002; accepted December 3, 2002)
Aromatic nitro compounds can be conveniently reduced to the corre-
sponding primary amines in the presence of S8 under solvent-free condi-
tions in excellent yields. Alumina supported NaOH catalyses this trans-
formation. Chemoselectivity was observed in the reduction of the nitro
group in the presence of phenol, carboxylic acid, aldehyde, and benzyl
halide groups.
Keywords: Alumina supported NaOH; chemoselectivity; nitroarens;
reduction; sulfur
Aromatic amines are used widely as intermediates for dyes, photo-
graphic materials, pharmaceutical chemicals, agricultural chemicals,
and antioxidants. Further, the primary aromatic amines are converted
readily into diazonium salts, which can be substituted for many other
functional groups. In spite of numerous methods available, the reduc-
tion of nitroarenes to primary amines is of practical importance and the
development of efficient and reliable reagents for this propose has been
an objective of synthetic chemists.1 It is usually accomplished by means
of catalytic hydrogenation,2 metal, and acids,3 hydride reagents,4
NaBH4 transition metal salts,5 and BER- Ni(OAc)2.6 However, most of
them have some disadvantages in relation to their general applicabil-
ity, selectivity, ready availability, and operational convenience. Thus,
a simple and efficient reducing agent of general applicability for the
reduction of aryl nitro compounds will be well appreciated.
Address correspondence to A. R. Kiasat, Chemistry Department, College of Sciences,
Sahid Chamran University, Ahvaz, Iran.
1385

1386
K. Niknam et al.
Over the years, reducing agents and catalysts based on sulfur have
had wide applications in organic chemistry because of their availability,
easy handling, and low cost. Onopchenko et al.7 have prepared cobalt
polysulfide by treatment of cobaltous chloride with sulfur and have
used it as a catalyst for the hydrogenation of aromatic nitro groups.
In 1972, a report by Lalancete8 outlined the preparation of sodium
sulfurated borohydride, NaBH2S3 by treatment of NaBH4 with a con-
trolled amount of sulfur in anhydrous THF. The reduction of aromatic
nitro compounds has been achieved with this reducing agent. Recently,
Firouzabadi et al.9 have prepared Ca(BH2S3)2 as a modified and sta-
ble form of NaBH2S3 by metathetical reaction between NaBH2S3 and
CaCl2 in THF. They have reported the reduction of aryl nitro compounds
with this modified reducing agent in dry THF.
Direct application of sulfur in the reduction of a nitro group was
reported in 1950 by Hirao10 who outlined the application of sul-
fur in dilute NaOH for the reduction of PhNO2 according to the
equation:
2 PhNO2 + 6 S + 6 NaOH H→2O 2 PhNH2 + 3 Na2S2O3 + H2O
The facile reduction of NO2 by this method was however disturbed by
further substitution in the aromatic ring.
Many interesting reactions under dry conditions in the pres-
ence of inorganic solids such as alumina,11 clay,12 and silica gel13
have been reported in recent years. The notable advantages for
most of these reactions are operational simplicity, generality, ex-
cellent regioselectivity, absence of side reactions, and quantitative
yields.
Having the above facts in mind, we now report that a system com-
prising Alumina/S8/NaOH is able to perform reduction of aryl nitro
compounds conveniently under nonsolvent conditions.
RESULTS AND DISCUSSION
Several reduction reactions of nitrobenzene were performed at various
temperatures and with different amounts of sulfur, inorganic solid, and
sodium hydroxide in order to find the most adequate condition for this
reaction under solvent-free conditions. In a preliminary study, the effect
of some inorganic solids on the yield of reduction was investigated with
the reaction of nitrobenzene as a model reaction. As shown in Table I,
alumina is the best solid support for this reaction. The required mole

Sulfur in Basic Media under Solvent-Free Conditions
1387
TABLE I Reduction of Nitrobenzene with Sulfur
and NaOH on Various Solid Supports at 80 C
Support surfaces
Time (h)
Conversion
Alumia
Silica gel
K2CO3
Na2SO4
Clay
Molecular sive
0.5
15
24
2
24
24
100
30
5
50
20
10
ratio, 3:3:1, of sulfur, NaOH, and substrate, respectively, alumina 2g,
and the maximum oil bath temperature of 80 C were found to be optimal
conditions.
Ar-NO2 Alumina/S /KO→H Ar-NH2
8
Solvent free condition
SCHEME 1
A variety of nitroarenes carrying electron-withdrawing or electron-
donating groups are reduced in the presence of alumina/S8/NaOH
system to the corresponding primary amines as exclusive and vir-
1
tually pure products according to TLC and H NMR under solvent-
free conditions in good isolated yields. Several examples illustrating
this facile procedure for the reduction of nitroarenes are listed in
Table II.
It is noteworthy that under similar reaction conditions, when ni-
tro benzene was reacted with sulfur and NaOH in the absence of
alumina, GC and TLC analysis of the reaction mixture did not show
formation of any product after 24 h. By this method, absolute selec-
tivity is observed for the reduction of nitro functionality in the pres-
ence of phenol, carboxylic acid, aldehyde, and benzyl halide groups
(Table I).
CONCLUSION
We believe that the present methodology offers a simple and efficient
method for the reduction of aromatic nitro compounds. In addition,
availability of the reagent, easy work-up, high yields, and absolute
selectivity compares favorably with known methods and makes this
method a useful addition to the present methodologies.

1388
K. Niknam et al.
TABLE II Reduction of Aromatic Nitro Compounds with
Alumina Supported Sulfur and NaOH
Entry
Substrate
Product
Time
0.5
Yield (%)a,b
86
1
2
3
4
0.5
5
67
81
80
2
5
6
2
77
83
2.5
7
8
4
3
68
69
9
1
7
85
65
10
11
4
73
12
13
0.7
1
64
68
aYields referred to isolated yields.
bProducts were characterized by comparison of their physical
data, IR, NMR spectra with known samples.
EXPERIMENTAL
General
Products were characterized by comparison of their physical data with
those of authentic samples. All yields refer to isolated products. IR

Sulfur in Basic Media under Solvent-Free Conditions
1389
spectra were recorded on a Shimadzo 450 spectrophotometer. 1H NMR
spectra were recorded on a Bruker Avance DPX instrument (250 MHZ).
Melting points were determined in open capillaries with a Galen-Kamp
melting point apparatus. TLC accomplished the purity determination of
the substrates and reaction monitoring on silica gel polygram SILG/UV
254 plates.
General Procedure for the Reduction
of Nitro Compounds
A mixture of nitroarene, sulfur, alumina, and sodium hydroxide was
ground in a mortar and then placed in a round-bottomed flask and
magnetically stirred and heated in an oil bath at 80 C for the appro-
priate time (see Table II). The reaction mixture was then allowed to
reach room temperature and acidified with HCl solution (10%) until
the pH of the reaction mixture reached 1. The reaction mixture was
filtered and the solid material was washed with dichloromethane sev-
eral times. The combined filtrate was extracted with dichlomethane
(2 15 ml). The aqueous layer was separated and the pH of the mix-
ture adjusted to about 11 with a solution of NaOH (10%). The aqueous
layer was extracted again with Et2O (15 ml) and the combined extracts
were dried over anhydrous Na2SO4 and evaporated to give the product
in 64–86% isolated yields.
REFERENCES
[1] D. G. Desai, S. S. Swami, and S. B. Hapase, Synth. Commun., 29, 1033 (1999).
[2] P. Rylander, Hydrogenation in Organic Synthesis (Academic Press, New York,
(1979), p. 114.
[3] C. A. Buehler and D. A. Pearson, Survey of Organic Synthesis (John Wiley & Sons,
New York, 1970), p. 413.
[4] J. Malek and M. Gerny, Synthesis, 217 (1972).
[5] S. Yoo and S. Lee, Synlett, 419 (1990).
[6] J. Ulman, The Alembic, 1 (1995).
[7] A. Onopchenko, E. T. Sabourin, and C. M. Selwitz, J. Org. Chem., 44, 3671 (1979).
[8] J. M. Lalancette, A. Freche, J. R. Brindle, and M. Laliberte, Synthesis, 526 (1972).
[9] H. Firouzabadi, B. Tamami, and A. R. Kiasat, Synth. Commun., 30, 587 (2000).
[10] N. Hirao., J. Osaka, Inst. Sci. Technol., 1(2), 57 (1950); Chem. Abstr., 48, 2622h
(1954).
[11] T. Sakamoto and H. C. Yonehara, J. Org. Chem., 62, 3194 (1997).
[12] P. Laszlo, Science, 235, 1473 (1987).
[13] H. M. Sampath Kumar, K. M. Pradyumna, M. Suresh Kumar, and J. S. Yadav, Synth.
Commun., 1327 (1997).