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.
Reduction to amines
Aliphatic nitro compounds can be reduced to aliphatic amines using several different reagents:
Catalytic hydrogenation using platinum(IV) oxide (PtO2) or Raney nickel
Iron metal in refluxing acetic acid
,-Unsaturated nitro compounds can be reduced to saturated amines using:
Catalytic hydrogenation over palladium-on-carbon
Lithium aluminium hydride (Note: Hydroxylamine and oxime impurities are typically found.)
Reduction to hydroxylamines
Aliphatic nitro compounds can be reduced to aliphatic hydroxylamines using diborane.
Reduction to oximes
Nitro compounds are typically reduced to oximes using metal salts, such as stannous chloride or chromium(II) chloride. Additionally, catalytic hydrogenation using a controlled amount of hydrogen can generate oximes.
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:
Catalytic hydrogenation using palladium-on-carbon, platinum(IV) oxide, or Raney nickel
Iron in acidic media (Note: Iron is particularly well suited for this reduction as the reaction conditions are typically gentle and also because iron has a high functional group tolerance.) (See Bechamp reduction)
Sodium sulfide (or hydrogen sulfide and base)
It is also possible to form a nitroaniline by reduction of a dinitroarene using sodium sulfide.
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:
Raney nickel and hydrazine at 0-10 C
Zinc metal in aqueous ammonium chloride
Reduction to hydrazo compounds
Treatment of nitroarenes with excess zinc metal results in the formation of N,N’-diarylhydrazine.
Reduction to azo compounds
Treatment of aromatic nitro compounds with metal hydrides gives good yields of azo compounds. For example, one could use:
Lithium aluminium hydride
Zinc metal with sodium hydroxide. (Excess zinc will reduce the azo group to a hydrazino compound.)
Reduction to azoxy compounds
This section requires expansion.
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