Reduction Of Nitro Compounds

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

Samarium diiodide

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

Catalytic hydrogenation over palladium-on-carbon

Iron metal

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 hydrosulfite

Sodium sulfide (or hydrogen sulfide and base)

Tin(II) chloride

Titanium(III) chloride

Zinc

Samarium

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

Electrolytic reduction

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.

References

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^ A. Burger, M. L. Stein and J. B. Clements (1957). “Some Pyridylnitroalkenes, Nitroalkanols, and Alkylamines”. J. Org. Chem. 22 (2): 143144. doi:10.1021/jo01353a010. 

^ H. Feuer, R. S. Bartlett, B. F. Vincent and R. S. Anderson (1965). “Diborane Reduction of Nitro Salts. A New Synthesis of N-Monosubstituted Hydroxylamines”. J. Org. Chem. 30 (9): 28802882. doi:10.1021/jo01020a002. 

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^ C. Grundmann (1950). “ber die partielle Reduktion von Nitro-cyclohexan”. Angewandte Chemie 62 (23-24): 558560. doi:10.1002/ange.19500622304. 

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^ Template:Tet. Let.

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^ Ayyangar, N. R.; Brahme, K. C.; Kalkote, U. R.; Srinivasan, K. V. (1984). “Facile Transfer-Reduction of Nitroarenes to N Arylhydroxylamines with Hydrazine in the Presence of Raney Nickel”. Synthesis 1984 (11): 938. doi:10.1055/s-1984-31027. 

^ Harman, R. E. (1963), “Chloro-p-benzoquinone”, Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv4p0148 ; Coll. Vol. 4: 148 

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^ a b Bigelow, H. E.; Robinson, D. B. (1955), “Azobenzene”, Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv3p0103 ; Coll. Vol. 3: 103 

^ R. F. Nystrom and W. G. Brown (1948). “Reduction of Organic Compounds by Lithium Aluminum Hydride. III. Halides, Quinones, Miscellaneous Nitrogen Compounds”. J. Am. Chem. Soc. 70 (11): 37383740. doi:10.1021/ja01191a057. 

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