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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) named after Edmund ter Meer.
[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
References
- ^ Edmund ter Meer (1876). "Ueber Dinitroverbindungen der Fettreihe". Justus Liebigs Annalen der Chemie 181 (1): 1–22. doi:.
- ^ 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-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)
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