Reduction of nitro compounds

The reduction of nitro compounds are chemical reactions of wide interest in organic chemistry. The conversion can be effected by many reagents. The nitro group was one of the first functional groups to be reduced. Alkyl and aryl nitro compounds behave differently. Most useful is the reduction of aryl nitro compounds.

Aromatic nitro compounds

Reduction to anilines

Generalization of the reduction of a nitroarene to aniline

The reduction of nitroaromatics is conducted on an industrial scale.[1] Many methods exist, such as:

Metal hydrides are typically not used to reduce aryl nitro compounds to anilines because they tend to produce azo compounds. (See below)

Reduction to hydroxylamines

Several methods have been described for the production of aryl hydroxylamines from aryl nitro compounds:

Reduction to hydrazine compounds

Treatment of nitroarenes with excess zinc metal results in the formation of N,N'-diarylhydrazine.[19]

Reduction to azo compounds

Generalization of the reduction of a nitroarene to an azo compound

Treatment of aromatic nitro compounds with metal hydrides gives good yields of azo compounds. For example, one could use:

Aliphatic nitro compounds

Reduction to hydrocarbons

Generalization of the reduction of a nitroalkane to an alkane

Hydrodenitration (replacement of a nitro group with hydrogen) is difficult to achieve but can be effected by catalytic hydrogenation over platinum on silica gel at high temperatures.[21] The reaction can also be effected through radical reaction with tributyltin hydride and a radical initiator, AIBN as an example.[22]

Reduction to amines

Generalization of the reduction of a nitroalkane to an amine

Aliphatic nitro compounds can be reduced to aliphatic amines by several reagents:

α,β-Unsaturated nitro compounds can be reduced to saturated amines by:

Reduction to hydroxylamines

Aliphatic nitro compounds can be reduced to aliphatic hydroxylamines using diborane.[30]

Generalization of the reduction of a nitroalkane to a hydroxylamine

The reaction can also be carried out with zinc dust and ammonium chloride:[31][32][33]

R-NO2 + 4 NH4Cl + 2 Zn → R-NH-OH + 2 ZnCl2 + 4 NH3 + H2O

Reduction to oximes

Generalization of the reduction of a nitroalkane to an oxime

Nitro compounds are typically reduced to oximes using metal salts, such as tin(II) chloride[34] or chromium(II) chloride.[35] Additionally, catalytic hydrogenation using a controlled amount of hydrogen can generate oximes.[36]

References

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