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Nitration is a general chemical process for the introduction of a nitro group in a chemical compound by means of a chemical reaction.
Examples of simple nitrations are the conversion of glycerin to nitroglycerin with nitric acid and sulfuric acid, the nitration of acetone cyanohydrin with nitric acid in acetic anhydride to Acetone cyanohydrin nitrate 4-Nitro-morpholine Jeremiah P. Freeman and Inella G. Shepard Organic Syntheses, Coll. Vol. 5, p.839 (1973); Vol. 43, p.83 (1963) Article. and the conversion of Ethyl α-bromobutyrate to ethyl α-nitrobutyrate with sodium nitrite ethyl α-nitrobutyrate Nathan Kornblum and Robert K. Blackwood Organic Syntheses, Coll. Vol. 4, p.454 (1963); Vol. 37, p.44 (1957). Article.
Aromatic nitration
Aromatic 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 → 2HSO41- + NO2+ + H3O+
(2) C6H6 + NO2+ → C6H5NO2 + H+
(3) H+ + H3O+ + 2HSO41- → H2O + 2H2SO4
The sulfuric acid is regenerated and hence acts as a catalyst.
The formation of a nitronium ion (the electrophile) from nitric acid and sulfuric acid is shown below:
Selectivity is always a challenge in nitrations, Fluorenone nitration is selective and yields a tri-nitro compound 2,4,7-Trinitrofluorenone E. O. Woolfolk and Milton Orchin Organic Syntheses, Coll. Vol. 3, p.837; Vol. 28, p.91 Article or tetra-nitro compound 2,4,5,7-tetranitrofluorenone Melvin S. Newman and H. Boden Organic Syntheses, Coll. Vol. 5, p.1029; Vol. 42, p.95 Article 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 Benzonitrile, 2-methyl-3,5-dinitro- George A. Olah and Stephen J. Kuhn Organic Syntheses Annual Volume 47, page 56 , Article. Aromatic nitro compounds are important intermediates to anilines by action of a reducing agent.
References
Nitrace | Nitrierung | ניטרציה | nitratie | Nitrowanie | Nitração | 硝化反应
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