Hi
how do we prevent to produce by-products like niroso or N-hydroxy aromatic compounds and etc, in reduction of nitro aromatic compounds by hydrazinehydrate in presence of heterogeneous metallic catalyst?
You can simply choose some alternate method to reduce nitro to amines.
Please have a look at the available methods:
http://www.organic-chemistry.org/synthesis/N1H/reductionsnitrocompounds.shtm
For reduction of aromatic nitro compounds to aryl amines, hydrazine hydrate is a very efficient reagent. You can carry out the reduction by refluxing the nitro compound with NH2NH2.H2O (98%) containing 10% Pd-C (10% W/W) catalyst in MeOH. The reaction is complete within 3-6 hours and the yields are excellent. 1-(Phenylsulfonyl)indol-5-amine was prepared in ~89-90 % yield from 5-nitroindole, following this procedure [Ref. Chakrabarty M, Kundu T, Arima S, Harigaya Y. Tetrahedron Lett 2005, 46,2865] . Following the same procedure 5-amino- / 6-aminoindazole derivatives have also been prepared from respective nitroindole derivatives in 3 hours in excellent yields. The product quality in this reduction is normally very good and yields are also high. The procedure is also simple. After the reflux for the required time when the reduction is over (checked by TLC), the reaction mixture is filtered to separate the Pd-C charcoal cat. and the solvent (MeOH) is distilled out. The crude product obtained is purified by recrysallization from suitable solvent or by column chromatography.
You can try very simple reduction with N2H4*H2O using Ni-Re catalyst. In my hands the method worked excellently for such substrates like nitroheteroaryls (for example, pyrazoles) and even t-nitro aliphatics (like nitroadamantanes). For 3,5,7-trinitro-1-azaadamantane, all three NO2 groups were readily and very cleanly reduced to amines (without problems with mixtures of partially reduced products).
Commonly, NO2 compound is dissolved in alcohol, Ni-Re suspension in alcohol or water added, and then hydrazine added dropwise at 40-50 C for 5-10 h. Some more Ni-Re was added after half of the reaction. The isolable yields are commonly above 80-90% (filtration of Ni, evaporation and sublimation when appropriate) without by-products you mentioned. Reaction in EtOH or i-PrOH commonly is very clean, while such reductions in water are significantly faster but gives much more impurities.
Hi Mr Domasevitch. thank you so so much for your perfect answer.If it is possible to ask my another question. my reaction is reduction of 1-iodo-3-nitrobenzene by a bimetallic catalyst. the solvent of reaction is ethanol/water with ratio 4/1 (4 for ethanol) . I follow my reaction with TLC that show in addition product there are another spots on my tlc plate that not separate( even by column chromatography). in your opinion where is the problem? if it possible to be my problem at solvent? or my catalyst that can not help to reducruion of nitro compound? or problem is another things?
i will be greatfull if you answer my questions.
thank you again for your answer.
You can prepare aromatic amines by reduction of Nitrocompounds by H2/PtO2. The yield & the quality of the product is good. If H2 is not available then Fe/HCl is cheaper method.Sn/HCl as reducing agent works well but yield of amine is low.
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