Nitration
692867
222600515
2008-06-30T05:23:21Z
Persian Poet Gal
538346
Reverted edits by [[Special:Contributions/Moosie beans|Moosie beans]] ([[User talk:Moosie beans|talk]]) to last version by BalazsH
'''Nitration''' is a a general [[chemical process]] for the introduction of a [[nitro compound|nitro group]] into a [[chemical compound]]. Examples of nitrations are the conversion of [[glycerin]] to [[nitroglycerin]] and the conversion of [[toluene]] to [[trinitrotoluene]]. Both of these conversions use [[nitric acid]] and [[sulfuric acid]].
==Aromatic nitration==
In "aromatic nitration," [[aromatic compound|aromatic organic compounds]] are nitrated via an [[electrophilic aromatic substitution]] mechanism involving the attack of the electron-rich [[benzene]] ring by the [[nitronium ion]]. Alternative mechanisms have also been proposed, as the one involving single electron transfer (SET)<ref>[Unified Mechanism Concept of Electrophilic Aromatic Nitration Revisited: Convergence of Computational Results and Experimental Data, Esteves, P. M.; Carneiro, J. W. M.; Cardoso, S. P.; Barbosa, A. G. H.; Laali, K. K.; Rasul, G.; Prakash, G. K. S.; e Olah, G. A. ''J. Am. Chem. Soc.'' '''2003''', 125(16),4836-4849.(http://dx.doi.org/10.1021/ja021307w)</ref><ref>[Electrophilic Aromatic Nitration: Understanding Its Mechanism and Substituent Effects, Queiroz, J. F.; Carneiro, J. W. M.; Sabino A. A.; Sparapan, R.; Eberlin, M. N.; Esteves, P. M. J. Org. Chem. 2006, 71(16), 6192-6203.(http://dx.doi.org/10.1021/jo0609475)]</ref>. Aromatic nitro compounds are important intermediates to [[aniline]]s by action of a [[reducing agent]]. Benzene is nitrated by refluxing with concentrated sulfuric acid and concentrated nitric acid at 50 °C.
:2 H<sub>2</sub>SO<sub>4</sub> + HNO<sub>3</sub> → 2 HSO<sub>4</sub><sup>-</sup> + NO<sub>2</sub><sup>+</sup> + H<sub>3</sub>O<sup>+</sup>
:C<sub>6</sub>H<sub>6</sub> + NO<sub>2</sub><sup>+</sup> → C<sub>6</sub>H<sub>5</sub>NO<sub>2</sub> + H<sup>+</sup>
:H<sup>+</sup> + H<sub>3</sub>O<sup>+</sup> + 2 HSO<sub>4</sub><sup>-</sup> → H<sub>2</sub>O + 2H<sub>2</sub>SO<sub>4</sub>
The sulfuric acid is regenerated and hence acts as a [[catalyst]]. It also absorbs water.
:[[Image:OChem-Reaction-NitrationBenzene.png|610px|thumb|none|Nitration of benzene]]
The formation of a nitronium ion (the electrophile) from nitric acid and sulfuric acid is shown below:
:[[Image:Chem-Mech-NitroniumFormationWH2SO4.png|frame|none|Reaction of nitric acid and sulfuric acid]]
===Scope===
Selectivity is always a challenge in nitrations, The nitration of [[fluorenone]] is selective and yields a tri-nitro compound<ref> ''2,4,7-Trinitrofluorenone'' E. O. Woolfolk and Milton Orchin [[Organic Syntheses]], Coll. Vol. 3, p.837; Vol. 28, p.91 [http://www.orgsyn.org/orgsyn/prep.asp?prep=cv3p0837 Article]</ref> or tetra-nitro compound <ref>''2,4,5,7-tetranitrofluorenone '' Melvin S. Newman and H. Boden [[Organic Syntheses]], Coll. Vol. 5, p.1029; Vol. 42, p.95 [http://www.orgsyn.org/orgsyn/prep.asp?prep=cv5p1029 Article]</ref> by modifying reaction conditions. Another example of trinitration can be found in the synthesis of [[phloroglucinol]].
Other nitration reagents include [[nitronium tetrafluoroborate]], a nitronium salt. This compound can be prepared from [[hydrogen fluoride]], [[nitric acid]], and [[boron trifluoride]].<ref>''Benzonitrile, 2-methyl-3,5-dinitro-'' [[George A. Olah]] and Stephen J. Kuhn [[Organic Syntheses]] Annual Volume 47, page 56 , [http://www.orgsyn.org/orgsyn/prep.asp?prep=cv5p0480 Article]</ref>
The substituents on aromatic rings affect the [[reaction rate|rate]] of this [[electrophilic aromatic substitution]]. [[Deactivating group]]s such as other [[nitro]] groups have an electron-withdrawing effect. Such groups deactivate (slow) the reaction and directs the electrophilic nitronium ion to attack the [[aromatic meta position]]. Deactivating meta-directoring substituents include [[sulfonyl]], [[cyano]] groups, [[Ketone|keto]], [[ester]]s, and [[carboxylate]]s. Nitration can be accelerated by [[activating group]]s such as [[amino]], [[hydroxy]] and [[methyl]] groups also [[amide]]s and [[ether]]s resulting in para and ortho isomers.
The direct nitration of [[aniline]] with nitric acid and sulfuric acid, according to one source <ref>Web resource: [http://www.warren-wilson.edu/~research/Undergrad_Res/nss97-98/abstrspr98.htm Link]</ref> results in a 50/50 mixture of para and meta nitroaniline. In this reaction the fast-reacting and activating aniline (ArNH<sub>2</sub>) is in equilibrium with the more abundant but less reactive and deactivating anilinium ion (ArNH<sub>3</sub><sup>+</sup>), which may explain this reaction product distribution. According to another source <ref>Web source: [http://orgchem.colorado.edu/courses/3381manualS06/AMSLM81S06.pdf Link]</ref> 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 nitroamide back to the nitroamine.
In the [[Wolfenstein-Boters reaction]], [[benzene]] reacts with nitric acid and mercury nitrate to give picric acid.
== References ==
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[[Category:Substitution reactions]]
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[[he:ניטרציה]]
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[[ru:Нитрование]]
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[[zh:硝化反应]]