Nitration

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Nitration occurs with aromatic organic compounds via an electrophilic substitution mechanism involving the attack of the electron-rich benzene ring by the (nitryl) nitronium ion.

Benzene is nitrated by refluxing with concentrated sulfuric acid and concentrated nitric acid at 50°C.

(1) 2H₂SO₄ + HNO₃ → 2HSO₄^1- + NO₂⁺ + H₃O⁺

(2) C₆H₆ + NO₂⁺ → C₆H₅NO₂ + H⁺

(3) H⁺ + H₃O⁺ + 2HSO₄^1- → H₂O + 2H₂SO₄

The sulfuric acid is regenerated and hence acts as a catalyst.

Image:OChem-Reaction-NitrationBenzene.png

The formation of a nitronium ion (the electrophile) from nitric acid and sulfuric acid is shown below:

Image:Chem-Mech-NitroniumFormationWH2SO4.png

Selectivity is always a challenge in nitrations, Fluorenone nitration is selective and yields a tri-nitro compound ^[1] or tetra-nitro compound ^[2] by tweaking reaction conditions just slightly. Another example of trinitration can be found in the synthesis of phloroglucinol.

Other nitration reagents include nitronium tetrafluoroborate which is a true nitronium salt. This compound can be prepared from hydrogen fluoride, nitric acid and boron trifluoride ^[3]. Aromatic nitro compounds are important intermediates to anilines by action of a reducing agent.

References

• ^[1] 2,4,7-Trinitrofluorenone E. O. Woolfolk and Milton Orchin Organic Syntheses, Coll. Vol. 3, p.837; Vol. 28, p.91 Article
• ^[2] 2,4,5,7-tetranitrofluorenone Melvin S. Newman and H. Boden Organic Syntheses, Coll. Vol. 5, p.1029; Vol. 42, p.95 Article
• ^[3] Benzonitrile, 2-methyl-3,5-dinitro- George A. Olah and Stephen J. Kuhn Organic Syntheses Annual Volume 47, page 56 , Articlede:Nitrierung

he:ניטרציה nl:nitratie pl:Nitrowanie pt:Nitração zh:硝化反应 de:Nitrierung