Abstract:
The reduction of nitro group to amine is one of the most important transformations in
organic synthesis since the amino group is often used for further derivatization
towards valuable products such as dye stuffs, textile auxiliaries, pharmaceuticals,
agrochemicals, photographic materials, polymers, explosives, fibers, surfactants,
cosmetics etc. Mono, di and tri nitro aromatic compounds were reduced using
aluminium turnings and aluminium foil which are benign and cheap along with
ultrasound waves in moderate yield under mild conditions. 2,4,6-triaminophenol was
synthesized which was used as a standard in case of TLC analysis of picric acid. 1,3-
dinitrobenzene was first synthesized using traditional nitrating mixture of acids. Picric
acid was reduced for the first time using this milder approach. Picric acid was reduced
with yield of 61%. Optimization of reaction conditions was done with nitro benzene,
1,3-dinitrobenzene and picric acid using methanol, acetone, their combination with
water and pure water as reaction medium was also used. First of all optimization was
done with nitrobenzene then with 1,3-dinitrobenzene and in the end with picric acid.
For the solubility of organic substrates in pure water CTAB was used. Aluminium
turnings were more efficient as compared to aluminium foil because of purity.
Methanol showed shortest reaction time and greatest yield as compared to acetone and
pure water. Aromatic amines were characterized by IR, NMR, HPLC and TLC.
Presence of amino group in the products and absence of nitro groups was depicted by
IR analysis. HPLC was done in order to check the purity of aromatic amine formed as
a result of reduction. Single sharp peak confirmed the purity of product. NMR was
used to confirm the structure of aromatic amines. TLC was used in order to monitor
progress of reaction, completion and comparison with standards for product
confirmation. Facile, mild, greener and economical procedure has been optimized for
reduction of nitro aromatic compounds to obtain moderate yields. Shorter reaction
times, milder reagents, easy availability of reagents and cost effectiveness associated
with this method make this protocol industrially important.
