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Nitration
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==Scope== Selectivity can be a challenge. Often alternative products act as contaminants or are simply wasted. Considerable attention thus is paid to optimization of the reaction conditions. For example, the mixed acid can be derived from phosphoric or [[perchloric acid]]s in place of sulfuric acid.<ref name="Booth"/> [[Regioselectivity]] is strongly affected by substituents on aromatic rings (see [[electrophilic aromatic substitution]]). For example, nitration of nitrobenzene gives all three isomers of [[dinitrobenzene]]s in a ratio of 93:6:1 (respectively meta, ortho, para).<ref>{{March6th|page=665}} </ref> Electron-withdrawing groups such as other [[nitro compound|nitro]] are [[Deactivating group|deactivating]]. Nitration is accelerated by the presence of [[activating group]]s such as [[amino]], [[Hydroxyl|hydroxy]] and [[methyl]] groups also [[amide]]s and [[ether]]s resulting in para and ortho isomers. In addition to regioselectivity, the degree of nitration is of interest. [[Fluorenone]], for example, can be selectively trinitrated<ref>{{OrgSynth | title = 2,4,7-Trinitrofluorenone | author = E. O. Woolfolk and Milton Orchin | collvol = 3 | collvolpages = 837 | prep=cv3p0837}}</ref> or tetranitrated.<ref>{{OrgSynth | title = 2,4,5,7-Tetranitrofluorenone | author = Melvin S. Newman and H. Boden | collvol = 5 | collvolpages = 1029 | prep=cv5p1029}}</ref> 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 warren-wilson.edu] {{Webarchive|url=https://web.archive.org/web/20120320060521/http://www.warren-wilson.edu/~research/Undergrad_Res/nss97-98/abstrspr98.htm |date=2012-03-20 }}</ref> results in a 50/50 mixture of ''para''- and ''meta''-nitroaniline isomers. In this reaction the fast-reacting and activating aniline (ArNH<sub>2</sub>) exists in equilibrium with the more abundant but less reactive (deactivated) anilinium ion (ArNH<sub>3</sub><sup>+</sup>), which may explain this reaction product distribution. According to another source,<ref>''Mechanism and synthesis'' Peter Taylor, Royal Society of Chemistry (Great Britain), Open University</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 amide back to the nitrated aniline. ===Alternatives to nitric acid=== Mixture of nitric and acetic acids or nitric acid and acetic anhydride is commercially important in the production of [[RDX]], as amines are destructed by sulfuric acid. [[Acetyl nitrate]] had also been used as a nitration agent.<ref>Louw, Robert "Acetyl nitrate" e-EROS Encyclopedia of Reagents for Organic Synthesis 2001, 1-2. {{doi| 10.1002/047084289X.ra032}}</ref><ref>{{cite journal |doi=10.1021/jo981557o |title=A Novel Method for the Nitration of Simple Aromatic Compounds |date=1998 |last1=Smith |first1=Keith |last2=Musson |first2=Adam |last3=Deboos |first3=Gareth A. |journal=The Journal of Organic Chemistry |volume=63 |issue=23 |pages=8448–8454 }}</ref> In the [[Wolffenstein–Böters reaction]], [[benzene]] reacts with nitric acid and [[mercury(II) nitrate]] to give [[picric acid]]. In the second half of the 20th century, new reagents were developed for laboratory usage, mainly N-nitro heterocyclic compounds.<ref>{{Cite journal |last=Yang |first=Tao |last2=Li |first2=Xiaoqian |last3=Deng |first3=Shuang |last4=Qi |first4=Xiaotian |last5=Cong |first5=Hengjiang |last6=Cheng |first6=Hong-Gang |last7=Shi |first7=Liangwei |last8=Zhou |first8=Qianghui |last9=Zhuang |first9=Lin |date=2022-09-26 |title=From N–H Nitration to Controllable Aromatic Mononitration and Dinitration─The Discovery of a Versatile and Powerful N -Nitropyrazole Nitrating Reagent |url=https://pubs.acs.org/doi/10.1021/jacsau.2c00413 |journal=JACS Au |language=en |volume=2 |issue=9 |pages=2152–2161 |doi=10.1021/jacsau.2c00413 |issn=2691-3704 |pmc=9516713 |pmid=36186553}}</ref> ===Ipso nitration=== With aryl chlorides, [[triflate]]s and nonaflates, [[Arene substitution pattern#Ipso.2C meso.2C and peri substitution|ipso]] nitration may also take place.<ref>{{Cite journal| doi = 10.1002/anie.200906940| pmid = 20146295| year = 2010| last1 = Prakash | first1 = G.| last2 = Mathew | first2 = T.| title = Ipso-Nitration of Arenes| volume = 49| issue = 10| pages = 1726–1728| journal = Angewandte Chemie International Edition in English }}</ref> The phrase '''ipso nitration''' was first used by Perrin and Skinner in 1971, in an investigation into chloroanisole nitration.<ref>{{Cite journal| doi = 10.1021/ja00743a015| title = Directive effects in electrophilic aromatic substitution ("ipso factors"). Nitration of haloanisoles| year = 1971| last1 = Perrin | first1 = C. L.| last2 = Skinner | first2 = G. A.| journal = Journal of the American Chemical Society| volume = 93| issue = 14| pages = 3389 }}</ref> In one protocol, 4-chloro-''n''-butylbenzene is reacted with [[sodium nitrite]] in [[tert-butanol|''t''-butanol]] in the presence of 0.5 mol% [[Tris(dibenzylideneacetone)dipalladium(0)|Pd<sub>2</sub>(dba)<sub>3</sub>]], a biarylphosphine ligand and a [[phase-transfer catalyst]] to provide 4-nitro-''n''-butylbenzene.<ref>{{Cite journal| doi = 10.1021/ja905768k| pmid = 19737014| year = 2009| last1 = Fors | first1 = B.| last2 = Buchwald | first2 = S.| title = Pd-Catalyzed Conversion of Aryl Chlorides, Triflates, and Nonaflates to Nitroaromatics| journal = Journal of the American Chemical Society| volume = 131| issue = 36| pages = 12898–12899| pmc = 2773681}}</ref>
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