Transfer hydrogenation of aromatic nitro compounds using polymer-supported formate and Pd-C

Article abstract of DOI:10.1081/SCC-200048429

Transfer hydrogenation of aromatic nitro compounds using recyclable polymer-supported formate as hydrogen donor and Pd-C as a catalyst produces corresponding amines in excellent yields (90-98%).

Full text of DOI:10.1081/SCC-200048429

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Transfer Hydrogenation of
Aromatic Nitro Compounds
Using Polymer‐Supported
Formate and Pd‐C
K. Abiraj a , G. R. Srinivasa a & D. Channe Gowda a
a Department of Studies in Chemistry , University of
Mysore , Manasagangotri, Mysore, Karnataka, 570
006, India
Published online: 28 Jul 2007.
To cite this article: K. Abiraj , G. R. Srinivasa & D. Channe Gowda (2005) Transfer
Hydrogenation of Aromatic Nitro Compounds Using Polymer‐Supported Formate and
Pd‐C, Synthetic Communications: An International Journal for Rapid Communication
of Synthetic Organic Chemistry, 35:2, 223-230, DOI: 10.1081/SCC-200048429
To link to this article: http://dx.doi.org/10.1081/SCC-200048429
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Synthetic Communicationsw, 35: 223–230, 2005
Copyright # Taylor & Francis, Inc.
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1081/SCC-200048429
Transfer Hydrogenation of Aromatic Nitro
Compounds Using Polymer-Supported
Formate and Pd-C
K. Abiraj, G. R. Srinivasa, and D. Channe Gowda
Department of Studies in Chemistry, University of Mysore, Mysore,
Karnataka, India
Abstract: Transfer hydrogenation of aromatic nitro compounds using recyclable
polymer-supported formate as hydrogen donor and Pd-C as a catalyst produces corre-
sponding amines in excellent yields (90–98%).
Keywords: Nitro compounds, catalytic transfer hydrogenation, polymer-supported
formate, 10% Pd-C, amines
INTRODUCTION
Reduction of aromatic nitro compounds to the corresponding amines is an
important transformation. A number of reagents have been developed for
this purpose.[1,2] The heterogeneous catalytic transfer hydrogenation (CTH)
using hydrogen donors (e.g., ammonium formate) is safer, cost-effective,
highly selective, rapid, and environmental friendly.[3–9] Various hydrogen
donors such as cyclohexene,[10,11] 1,4-cyclohexadiene,[12,13] hydrazine,[14,15]
formic acid,[4,9] ammonium formate,[7,16,24] propan-2-ol,[7,17] triethyl-
ammonium formate,[18,19] and hydrazinium monoformate,[3,25] have been
developed for CTH. Ammonium formate sublimes and therefore has
limitation.
Received in India November 8, 2004
Address correspondence to D. Channe Gowda, Department of Studies in Chemistry,
University of Mysore, Manasagangotri, Mysore, Karnataka 570 006, India.
Fax: 091-0821-2421263/2518835; E-mail: dcgowda@yahoo.com

224
K. Abiraj, G. R. Srinivasa, and D. C. Gowda
Scheme 1.
Desai and Danks[20] and[21] performed the transfer hydrogenation of
alkenes using polymer-supported formate as hydrogen donor in the presence
of Wilkinson’s catalyst and Pd(OAc)2. However, it has been observed that
controlling the reduction rates is difficult with these active homogeneous
catalysts. The use of heterogeneous catalysts offers certain advantages, and
we report the 10% palladium on carbon catalyzed facile reduction of
aromatic nitro compounds to the corresponding amines using polymer-
supported formate as hydrogen donor at room temperature (Scheme 1).
A wide range of structurally varied nitroarenes underwent reduction, and
the results are summarized in Table 1. All the amine derivatives were charac-
terized by comparison of their TLC, melting points, IR spectra, and 1H-NMR
spectra with authentic samples. The reactions are reasonably fast and
high yielding (90–98%). The selectivity observed during the reduction of
nitro derivatives in the presence of sensitive functional groups such as
halogen[14,16] (entries 1–3 & 12), alkene[6,7] (entry 4), nitrile[3,17] (entry 5),
and carbonyl[9,17,26] (entries 6 and 7) group, was remarkable.
The separation of the amino derivatives from the reaction mixture
involved filtration to remove the catalyst and resin followed by evaporation of
the solvent. The crude product was of excellent purity in most of the cases.
The water-soluble aromatic amines are produced in high yields (entries 1,
12–16). Ten successive recycle runs were possible with polymer-supported
formate before there was an appreciable decrease in the reaction yield (Table 2).
In conclusion, we developed a novel CTH system for the clean and
efficient reduction of aromatic nitro compounds to the corresponding
amines using polymer-supported formate and 10% Pd-C.
EXPERIMENTAL
Materials
1H-NMR spectra were recorded on an AMX-400 MHz spectrometer using
CDCl3 as the solvent and TMS as internal standard. The IR spectra were

Transfer Hydrogenation of Aromatic Nitro Compounds
225

226
K. Abiraj, G. R. Srinivasa, and D. C. Gowda

Transfer Hydrogenation of Aromatic Nitro Compounds
227

228
K. Abiraj, G. R. Srinivasa, and D. C. Gowda
Table 2. Recycling of polymer-supported formate for the reduction of
p-chloronitrobenzene
Cycle
1
2
3
4
5
6
7
8
9
10
Time (hr)
Yield (%) 98
2.0
2.5
2.5
3.0
3.0
3.5
4.0
4.5
5.0
5.0
96
96
94
93
92
92
92
91
90
recorded on Shimadzu FTIR- 8300 spectrometer. The melting points were
determined by using Thomas–Hoover melting point apparatus and are
uncorrected. Thin-layer chromatography was carried out on silica gel plates
obtained from Whatman Inc. The substrates were either commercial
products and were used as purchased or were prepared according to literature
procedures. Aminomethyl polystyrene resin was purchased from Advanced
Chemtech (1% DVB cross-linked, 100–200 mesh, 2 mmol/g). 10% Pd-C
was purchased from E-Merck (India) Ltd. All of the solvents used were
analytical grade or were purified according to standard procedures.
Preparation of Polymer-Supported Formate
The polymer-supported formate was prepared by washing aminomethyl
polystyrene resin with 50% solution of formic acid in dichloromethane.
The resulting polymer was washed successively with dichloromethane and
ether, and dried. The resin was used as such for the reduction.
General Procedure for the Reduction of Aromatic Nitro
Compounds
To a solution of nitro compound (5 mmol) in methanol (15 mL) taken in a hori-
zontal solid phase vessel, polymer-supported formate (1.5 g) and 10% Pd-C
(100 mg) were added. The suspension was shaken well1 for the specified
time at room temperature (Table 1). After consumption of the starting
material, the reaction mixture was filtered and washed thoroughly with
methanol. The combined washings and filtrate were evaporated. The crude
product was found to be analytically pure in most cases. Wherever
necessary, the crude product was taken into organic layer and washed with
1The reaction mixture was subjected to shaking using a manual shaker as the
shaking of the polymer-supported formate instead of stirring increases its life for
recycling purpose.

Transfer Hydrogenation of Aromatic Nitro Compounds
229
saturated sodium chloride. For recycling purposes, the residue containing
polymer-supported formate and the catalyst was washed thoroughly and
successively with DMF, dichloromethane, 50% solution of formic acid in
dichloromethane, dichloromethane, and ether. Thus, activated resin along
with the catalyst was dried under vacuum and used as such for further
reduction reactions.
ACKNOWLEDGMENTS
We gratefully acknowledge financial support from the University Grants
Commission, New Delhi. We also acknowledge Council of Scientific and
Industrial Research, New Delhi, for a research fellowship (to KA).
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