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Reduction of nitro compounds

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Reduction of nitro compounds

The chemical reactions described as reduction of nitro compounds can be facilitated by many different reagents and reaction conditions. Historically, the nitro group was one of the first functional groups to be reduced, due to the ease of nitro-group reduction.

Nitro-groups behave differently whether a neighboring hydrogen is present or not. Thus, reduction conditions can be initially classified by starting materials: aliphatic nitro compounds or aromatic nitro compounds. Secondary classifications are based upon reaction products.

Aliphatic nitro compounds

Reduction to hydrocarbons

Hydrodenitration (replacement of a nitro group with hydrogen) is difficult to achieve, but can be completed by catalytic hydrogenation over platinum on silica gel at high temperatures.[1]

Reduction to amines

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

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

Reduction to hydroxylamines

Aliphatic nitro compounds can be reduced to aliphatic hydroxylamines using diborane.[7]

Reduction to oximes

Nitro compounds are typically reduced to oximes using metal salts, such as stannous chloride[8] or chromium(II) chloride.[9] Additionally, catalytic hydrogenation using a controlled amount of hydrogen can generate oximes.[10]

Aromatic nitro compounds

The reduction of aryl nitro compounds can be finely tuned to obtain a different products typically in high yields.

Reduction to anilines

Many methods for the production of anilines from aryl nitro compounds exist, such as:

It is also possible to form a nitroanilineTemplate:Dn by reduction of a dinitroarene using sodium sulfide.[17]

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 for the production of aryl hydroxylamines from aryl nitro compounds exist:

Reduction to hydrazino compounds

Treatment of nitroarenes with excess zinc metal results in the formation of N,N'-diarylhydrazine.[21]

Reduction to azo compounds

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

Reduction to azoxy compounds

References

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