Nitro compound


Nitro compound
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 and is impure. The nitro group is one of the most common explosophores (functional group that makes a compound explosive) used globally. This property of both nitro and nitrate groups is because their thermal decomposition yields molecular nitrogen N2 gas plus considerable energy, due to the high strength of the bond in molecular nitrogen.

Aromatic nitro compounds are typically synthesized by the action of a mixture of nitric and sulfuric acids on an organic molecule. The one produced on the largest scale, by far, is nitrobenzene. Many explosives are produced by nitration including trinitrophenol (picric acid), trinitrotoluene (TNT), and trinitroresorcinol (styphnic acid).[1]

Contents

Occurrence in nature

Chloramphenicol is a rare example of a naturally occurring nitro compound. At least some naturally occurring nitro groups arise by the oxidation of amino groups.[2] 2-Nitrophenol is an aggregation pheromone of ticks.

Only two examples of aliphatic nitro compounds are known in nature. 3-Nitropropionic acid found in fungi and plants (Indigofera). Nitropentadecene is 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, whereas other enzymes such as glucose oxidase have other physiological substrates.[3]

Preparation

In organic synthesis various methods exists to prepare nitro compounds.

Aliphatic nitro compounds

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

Aromatic nitro compounds

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

Reactions

Nitro compounds participate in several organic reactions, the most important being their reduction to the corresponding amines:

RNO2 + 3 H2 → RNH2 + 2 H2O

Virtually all aromatic amines (anilines) are derived from nitroaromatics.

Aliphatic nitro compounds

The ter Meer reaction
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.[5] When the same reactant is reacted with potassium hydroxide the reaction product is the 1,2-dinitro dimer [6]

Aromatic nitro compounds

Nitro compound hydrogenation

See also

References

  1. ^ Gerald Booth "Nitro Compounds, Aromatic" Ullmann's Encyclopedia of Industrial Chemistry, 2005, Wiley-VCH, Weinheim. doi:10.1002/14356007.a17_411
  2. ^ Georg Zocher, Robert Winkler, Christian Hertweck, Georg E. Schulz "Structure and Action of the N-oxygenase AurF from Streptomyces thioluteus" J. Molecular Biology (2007) 373, 65–74. doi:10.1016/j.jmb.2007.06.014
  3. ^ 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. doi:10.1021/bi051966w. PMID 16430210. 
  4. ^ Edmund ter Meer (1876). "Ueber Dinitroverbindungen der Fettreihe". Justus Liebigs Annalen der Chemie 181 (1): 1–22. doi:10.1002/jlac.18761810102. 
  5. ^ 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
  6. ^ 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)
  7. ^ Organic Syntheses, Coll. Vol. 5, p.552 (1973); Vol. 47, p.69 (1967). http://orgsynth.org/orgsyn/pdfs/CV5P0552.pdf

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