Green Chemistry
Cite this: Green Chem., 2012, 14, 1086
PAPER
Chemoselective reduction of a nitro group through transfer hydrogenation
catalysed by Ru0-nanoparticles stabilized on modified Montmorillonite clay
Podma Pollov Sarmah and Dipak Kumar Dutta*
Received 11th November 2011, Accepted 30th January 2012
DOI: 10.1039/c2gc16441h
Ru0-nanoparticles of approximately 5 nm size were generated by incipient impregnation of RuCl3 into the
nanopores of the acid activated Montmorillonite clay followed by polyol reduction. Acid activation of the
clay increases the surface area by generating nanopores (0–10 nm), which act as a host and stabilize
nanoparticles in the pores. The generated Ru0-nanoparticles exhibit inter-planar lattice fringe spacing of
0.21 nm of the face centered cubic lattice of Ru0 crystals, and show efficient catalytic activity in the
chemoselective transfer hydrogenation reduction of substituted nitrobenzenes to corresponding anilines
with high yield of conversion (56–97%) and selectivity (91–100%) depending upon the nature of the
substituents. The reactions were carried out in the presence of isopropanol, which served as the solvent as
well as the reductant. The catalysts were found to be active for several catalytic runs.
The reduction of substituted nitrobenzenes to the correspond-
ing anilines is industrially important because anilines are impor-
1. Introduction
Supported metals are useful as heterogeneous catalysts in a wide
variety of organic transformation.1–4 Nanoparticles, in compari-
son to bulk solids, have a significantly high catalytic activity and
exhibit novel characteristics of quantum size effects.4,5 Hetero-
geneous catalysts are also in great demand for clean technology
and sustainable development. Among these, platinum group
metals have special importance in chemistry due to their wide
spread applications in catalysis, forming the backbones of
various important industries. Stabilized and dispersed Ru0-nano-
particles exhibit high catalytic activity in a wide range of organic
reactions, including hydrogenation, oxidation, C–C coupling and
related reactions.7–9 While nanoparticles are very active, they
tend to agglomerate to form large particles, leading to loss in
activity. To prevent the agglomeration, various stabilizers or sup-
ports are used6,10–12 and a good stabilizer is one that can prevent
the particle aggregation and control particle size but does not
passivate the nanoparticle surface. The stabilizer or support also
plays an important role in controlling the morphology, distri-
bution as well as the activity of the synthesized nanomaterials.
Controlled and precise growth of nanoparticles with the desired
shape and size can be tuned by altering the morphology of the
support. Recently, porous substances with a large internal
surface area like Montmorillonite clay (Mont) minerals, zeolites,
charcoals containing nanosize channels, etc. have been used for
the stabilization of metal nanoparticles.4,6,13–18
tant intermediates for the synthesis of organic fine chemicals,
dyes, biologically active compounds, pharmaceuticals, rubber,
photographic and agricultural chemicals.19–23 The traditional
synthesis routes for reduction of nitrobenzenes proceeds through
catalytic hydrogenation, electrolytic reduction, metal mediated
reductions etc.19 But these process mainly utilize potentially
explosive H2 gas, high pressure reactors, hazardous and harmful
materials like mineral acids etc. In general, the reduction of a
nitro group by hydrogen gas is carried out at a moderately high
pressure (10–50 bar)24–26,28 and temperature (100–150 °C),26,28
which lead to low selectivity (less than 70%) due to non-
selective hydrogenation of other functional groups.28 However,
transfer hydrogenation is advantageous over the traditional
hydrogenation reaction in respect of selectivity in which an
alcohol like isopropanol, considered as one of the green solvents,
acts as solvent as well as the source of hydrogen and the reaction
takes place at atmospheric pressure and relatively low
temperature.19,27–30 Moreover, the co-production of acetone in
the reaction is also a useful chemical and its production is ener-
getically more economical than the commercial ‘cumene per-
oxide’ process, which requires high pressure (30 bar) and
temperature (250 °C) and is also associated with distillation.31
The co-produced acetone can be easily isolated by distillation,
which makes the whole process ‘green’. Here we report the syn-
thesis of Ru0-nanoparticles of less than 5 nm size into the nano-
pores of acid activated Montmorillonite (AT-Mont) clay and their
application as a catalyst in the transfer hydrogenation of substi-
tuted nitrobenzenes to the corresponding anilines with high
activity and selectivity.
Materials Science Division, CSIR-North East Institute of Science and
Technology, Jorhat 785006, Assam, India. E-mail: dipakkrdutta@yahoo.
com; Tel: +91 376 2370081; Fax: +91 376 2370011
1086 | Green Chem., 2012, 14, 1086–1093
This journal is © The Royal Society of Chemistry 2012