Nitro compound

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The structure of the nitro group

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. They are one of the most common explosophores used globally.

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.

[edit] Occurrence in Nature

Natural products rarely contain nitro groups. An example of a naturally occurring aromatic nitro compound is 2-nitrophenol which is an aggregation pheromone in ticks. Examples of aliphatic nitro compounds include 3-nitropropionic acid found in fungi and plants (Indigofera, e.g.), and nitropentadecene, a defense compound found in termites. Many flavin dependent enzymes are capable of oxidizing aliphatic nitro compounds to less-toxic aldehydes and ketones. Nitroalkane oxidase and 3-nitropropionate oxidase oxidize aliphatic nitro compounds exclusively, while other enzymes such as glucose oxidase have other physiological substrates. ^[1]

[edit] Preparation

In organic synthesis various methods exists to prepare nitro compounds.

[edit] Aliphatic nitro compounds

• Nitromethane, nitroethane and nitropropanes are all produced industrially by treating propane with nitric acid.
• Nitromethane can be produced in the laboratory by treating sodium chloroacetate with sodium nitrite forming sodium bicarbonate and sodium chloride as byproducts.

[edit] Aromatic nitro compounds

• In a classic electrophilic substitution reaction, nitric acid and sulfuric acid produce nitronium ion which reacts with aromatic compounds in aromatic nitration.
• A classic method starting from halogenated phenols is the Zinke nitration.

[edit] Reactions

Nitro compounds participate in several organic reactions.

[edit] Aliphatic nitro compounds

• Aliphatic nitro compounds are reduced to amines with hydrochloric acid and an iron catalyst^{[citation needed]}
• Nitronates are a tautomeric form of aliphatic nitro compounds.
• Hydrolysis of the salts of nitro compounds yield aldehydes or ketones in the Nef reaction
• 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.^[2] 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 protonation to a nitronate 3 and finally nucleophilic displacement of chlorine based on an experimentally observed hydrogen kinetic isotope effect of 3.3 ^[3]. When the same reactant is reacted with potassium hydroxide the reaction product is the 1,2-dinitro dimer ^[4]

[edit] Aromatic nitro compounds

• Reduction of aromatic nitro compounds with hydrogen gas over a platinum catalyst gives anilines. A variation is formation of a dimethylaminoarene with palladium on carbon and formaldehyde:^[5]

• The Leimgruber-Batcho and Bartoli indole syntheses begin with aromatic nitro compounds.

• The presence of nitro groups facilitates nucleophilic aromatic substitution because they are very electron-withdrawing.

[edit] See also

• Functional group
• Reduction of nitro compounds
• Nitration
• Nitrite Also an NO₂ group, but bonds differently.

[edit] References

1. ^ Nagpal, Akanksha; Michael P. Valley, Paul F. Fitzpatrick, Allen M. Orville (1/5/2006). "Crystal Structures of Nitroalkane Oxidase: Insights into the Reaction Mechanism from a Covalent Complex of the Flavoenzyme Trapped during Turnover". Biochemistry. 
2. ^ Edmund ter Meer (1876). "Ueber Dinitroverbindungen der Fettreihe". Justus Liebigs Annalen der Chemie 181 (1): 1–22. doi:10.1002/jlac.18761810102. 
3. ^ 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
4. ^ 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)
5. ^ Organic Syntheses, Coll. Vol. 5, p.552 (1973); Vol. 47, p.69 (1967). http://orgsynth.org/orgsyn/pdfs/CV5P0552.pdf

[edit] External links

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