Nitro compound

  Nitro compounds are organic compounds that contain one or more nitro functional groups (-NO₂). They are often highly explosive, especially when the compound contains more than one nitro group. The presence of impurities or improper handling can trigger a violent exothermic decomposition.

Aromatic nitro compounds are typically synthesized by the action of a mixture of nitric and sulfuric acids on a suitable organic molecule. Some examples of such compounds are trinitrophenol (picric acid), trinitrotoluene (TNT), and trinitroresorcinol (styphnic acid). Chloramphenicol is a rare example of a naturally occurring nitro compound.

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Preparation

In organic synthesis various methods exists to prepare nitro compounds.

Aliphatic nitro compounds

• Nitromethane adds to aldehydes in 1,2-addition in the nitroaldol reaction
• Nitromethane adds to alpha-beta unsaturated carbonyl compounds as a 1,4-addition in the Michael reaction as a Michael donor
• Nitroethylene is a Michael acceptor in a Michael reaction with enolate compounds
• In nucleophilic aliphatic substitution sodium nitrite (NaNO₂) replaces an alkyl halide. In the so-called ter Meer reaction (1876)

^[1] the reactant is a 1,1-halonitroalkane:

In one study, a reaction mechanism is proposed in which in the first slow step a proton is abstracted from nitroalkane 1 to a carbanion 2 followed by isomerization to a sodium nitronate 3 and finally nucleophilic displacement of chlorine based on an experimentally observed kinetic isotope effect of 3.3 ^[2]. When the same reactant is reacted with potassium hydroxide the reaction product is the 1,2-dinitro dimer ^[3]

Aromatic nitro compounds

• In electrophilic substitution nitric acid reacts with aromatic compounds in nitration
• A classic method starting from halogenated phenols is the Zinke nitration

Reactions

Nitro compounds participate in several organic reactions.

Aliphatic nitro compounds

• Aliphatic nitro compounds are reduced to amines with hydrochloric acid and an iron catalyst
• Nitronates form by adding acids to nitro salts.
• Hydrolysis of the salts of nitro compounds yield aldehydes or ketones in the Nef reaction

Aromatic nitro compounds

• Reduction of aromatic nitro compounds with hydrogen gas over a platinum catalyst gives anilines.
• The presence of nitro groups facilitates nucleophilic aromatic substitution.

See also

• Functional group
• Reduction of nitro compounds
• Nitration

References

1. ^ Edm. ter Meer (1876). "Ueber Dinitroverbindungen der Fettreihe". Justus Liebigs Annalen der Chemie 181 (1): 1 - 22. doi:10.1002/jlac.18761810102.
2. ^ aci-Nitroalkanes. I. The Mechanism of the ter Meer Reaction M. Frederick Hawthorne J. Am. Chem. Soc.; 1956; 78(19) pp 4980 - 4984; doi:10.1021/ja01600a048
3. ^ 3-Hexene, 3,4-dinitro- D. E. Bisgrove, J. F. Brown, Jr., and L. B. Clapp. Organic Syntheses, Coll. Vol. 4, p.372 (1963); Vol. 37, p.23 (1957). (Article)