Nitration

Source: Wikipedia, the free encyclopedia.
Not to be confused with Nitrification, Nitrosation, or Nitriding.

In

molecular structures of nitro compounds and nitrates (NO−3) is that the nitrogen atom in nitro compounds is directly bonded to a non-oxygen atom (typically carbon
or another nitrogen atom), whereas in nitrate esters (also called organic nitrates), the nitrogen is bonded to an oxygen atom that in turn usually is bonded to a carbon atom (nitrito group).

There are many major industrial applications of nitration in the strict sense; the most important by volume are for the production of nitroaromatic compounds such as nitrobenzene.

Nitration reactions are notably used for the production of explosives, for example the conversion of

trinitrotoluene (TNT). However, they are of wide importance as chemical intermediates and precursors. Millions of tons of nitroaromatics are produced annually.[1]

Aromatic nitration

Typical nitration syntheses apply so-called "mixed acid", a mixture of concentrated

catalyst as well as an absorbent for water. In the case of nitration of benzene, the reaction is conducted at a warm temperature, not exceeding 50 °C. [4] The process is one example of electrophilic aromatic substitution, which involves the attack by the electron-rich benzene
ring:

Aromatic nitration mechanism

Alternative mechanisms have also been proposed, including one involving

single electron transfer (SET).[5][6]
Acetyl nitrate had also been used as a nitration agent.[7][8]

Scope

Selectivity can be a challenge in nitrations because as a rule more than one compound may result but only one is desired, so alternative products act as contaminants or are simply wasted. Accordingly, it is desirable to design syntheses with suitable selectivity; for example, by controlling the reaction conditions, fluorenone can be selectively trinitrated[9] or tetranitrated.[10]

The substituents on aromatic rings affect the

methyl groups also amides and ethers
resulting in para and ortho isomers.

The direct nitration of aniline with nitric acid and sulfuric acid, according to one source,[11] results in a 50/50 mixture of para- and meta-nitroaniline isomers. In this reaction the fast-reacting and activating aniline (ArNH2) exists in equilibrium with the more abundant but less reactive (deactivated) anilinium ion (ArNH3+), which may explain this reaction product distribution. According to another source,[12] a more controlled nitration of aniline starts with the formation of acetanilide by reaction with acetic anhydride followed by the actual nitration. Because the amide is a regular activating group the products formed are the para and ortho isomers. Heating the reaction mixture is sufficient to hydrolyze the amide back to the nitrated aniline.

In the Wolffenstein–Böters reaction, benzene reacts with nitric acid and mercury(II) nitrate to give picric acid.

Ipso nitration

With aryl chlorides,

t-butanol in the presence of 0.5 mol% Pd2(dba)3, a biarylphosphine ligand and a phase-transfer catalyst to provide 4-nitro-n-butylbenzene.[15]

See also

References

  1. ISBN 978-3527306732
    .
  2. ^ John McMurry Organic Chemistry 2nd Ed.
  3. George A. Olah and Stephen J. Kuhn. "Benzonitrile, 2-methyl-3,5-dinitro-". Organic Syntheses
    ; Collected Volumes, vol. 5, p. 480.
  4. ^ "Nitration of benzene and methylbenzene".
  5. PMID 12696903
    .
  6. PMID 16872205
    .
  7. doi:10.1021/ja01499a029
    .
  8. doi:10.1002/047084289X.ra032
    .
  9. ^ E. O. Woolfolk and Milton Orchin. "2,4,7-Trinitrofluorenone". Organic Syntheses; Collected Volumes, vol. 3, p. 837.
  10. ^ Melvin S. Newman and H. Boden. "2,4,5,7-Tetranitrofluorenone". Organic Syntheses; Collected Volumes, vol. 5, p. 1029.
  11. ^ Web resource: warren-wilson.edu Archived 2012-03-20 at the Wayback Machine
  12. ^ Mechanism and synthesis Peter Taylor, Royal Society of Chemistry (Great Britain), Open University
  13. PMID 20146295
    .
  14. doi:10.1021/ja00743a015
    .
  15. PMID 19737014
    .
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