Editing Picric acid (section)

== Synthesis ==
The aromatic ring of [[phenol]] is activated towards electrophilic substitution reactions, and attempted nitration of phenol, even with dilute nitric acid, results in the formation of high molecular weight tars. In order to minimize these side reactions, anhydrous phenol is [[sulfonated]] with [[fuming sulfuric acid]], and the resulting sulfonic acid is then nitrated with concentrated [[nitric acid]]. During this reaction, [[Nitro compound|nitro]] groups are introduced, and the [[sulfonic acid]] group is displaced. The reaction is highly [[exothermic]], and careful temperature control is required. Synthesis routes that nitrate [[aspirin]] or [[salicylic acid]] can also be used to mitigate tar formation. Carbon dioxide is lost from the former via [[decarboxylation]], while both acetic acid and carbon dioxide are lost from the latter.<ref>{{Cite web |title=λ » LambdaSyn – Synthese von Pikrinsäure |url=https://www.lambdasyn.org/synfiles/pikrinsaeure.htm |access-date=2024-08-01 |website=www.lambdasyn.org}}</ref> Another method of picric acid synthesis is direct nitration of [[2,4-Dinitrophenol|2,4-dinitrophenol]] with nitric acid.<ref>{{cite book|url=https://books.google.com/books?id=2B4VqK18VOUC&q=picric+acid+synthesis+further+nitration+dinitrophenol&pg=PA132|title=Organic Chemistry of Explosives|last1=Agrawal|first1=Jai Prakash|last2=Hodgson|first2=Robert|date=2007-01-11|publisher=John Wiley & Sons|isbn=9780470059357}}</ref><ref>{{cite web|url=https://patents.google.com/patent/US1299171|title=Manufacture of picric acid. US Patent US1299171A|last=Green|first=Arthur George|date=1919-04-01|website=patents.google.com|access-date=2018-08-26}}</ref> It crystallizes in the orthorhombic space group ''Pca''2<sub>1</sub> with a = 9.13 Å, b = 18.69 Å, c = 9.79 Å and α = β = γ = 90°.<ref name="Bertolasi">V. Bertolasi, P. Gilli, G. Gilli: ''Hydrogen Bonding and Electron Donor-Acceptor (EDA) Interactions Controlling the Crystal Packing of Picric Acid and Its Adducts with Nitrogen Bases. Their Rationalization in Terms of the p''K''<sub>a</sub> Equalization and Electron-Pair Saturation Concepts.'' In: ''[[Cryst. Growth Des.]]'' 2011, 11, 2724–2735, [[doi:10.1021/cg101007a]].</ref>