Wikipedia:WikiProject Chemicals/Chembox validation/VerifiedDataSandbox and Picric acid: Difference between pages

{{short description|Explosive chemical compound}}

{{redirect|Lyddite|the rock type|Lydite}}

{{Chembox

| Watchedfields = changed

| verifiedrevid = 477229220

| ImageFile1 = Pikrinsäure.svg

| ImageFile3 = Pikriinhape54.jpg

| ImageFile2 =246trinitrophenol-3D-vdW.png

| PIN = 2,4,6-Trinitrophenol<ref name=iupac2013>{{cite book |title=Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013 (Blue Book) |publisher=[[Royal Society of Chemistry]] |location=Cambridge |date=2014 |page=691 |isbn=978-0-85404-182-4 |doi=10.1039/9781849733069-FP001}}</ref>

| SystematicName = 2,4,6-Trinitrobenzenol

| OtherNames = Picric acid<ref name=iupac2013 /><br />Carbazotic acid<br />Phenol trinitrate<br />Picronitric acid<br />Trinitrophenol<br />2,4,6-Trinitro-1-phenol<br />2-Hydroxy-1,3,5-trinitrobenzene<br />TNP<br />Melinite<br />Lyddite

|Section1={{Chembox Identifiers

| Abbreviations =

| EINECS =

| =

| RTECS =TJ7875000

| KEGG =

}}

|Section2={{Chembox Properties

| MolarMass = 229.10&nbsp;gmol^&minus;1

| Appearance =Colorless to yellow solid

| Density = 1.763&nbsp;gcm^&minus;3, solid

| = 122.5

| =

| BoilingPt= >

| BoilingPtC = 300

| BoilingPt_notes = Detonates

| Solubility = 12.7&nbsp;g·L^&minus;1

| =

| Solvent =

| pKb =

| VaporPressure = 1 mmHg (195 °C)<ref name=PGCH/>

| MagSus = -84.34·10⁻⁶ cm³/mol

}}

|Section7={{Chembox Hazards

| MainHazards = explosive

| NFPA-F =

| NFPA- =

| = {{}}{{}}{{}}

| = {{}}

| PPhrases = {{P-phrases|210|212|230|233|280|370+380+375|501}}

| =

| FlashPt_ref = <ref name=PGCH/>

| =

| =

| IDLH = 75 mg/m³<ref name=PGCH>{{PGCH|0515}}</ref>

| REL = TWA 0.1 mg/m³ ST 0.3 mg/m³ [skin]<ref name=PGCH/>

| PEL = TWA 0.1 mg/m³ [skin]

| LDLo = 100 mg/kg (guinea pig, oral)<br/>250 mg/kg (cat, oral)<br/>120 mg/kg (rabbit, oral)<ref>{{IDLH|88891|Picric acid}}</ref>

}}

|Section8={{Chembox Explosive

| ShockSens =

| FrictionSens =

| DetonationV = 7,350&nbsp;m·s^&minus;1 at ρ 1.70

| REFactor = 1.20}}

'''Picric acid''' is an [[organic compound]] with the formula (O₂N)₃C₆H₂OH. Its [[IUPAC name]] is '''2,4,6-trinitrophenol''' ('''TNP'''). The name "picric" comes from {{lang-el|πικρός}} (''pikros''), meaning "bitter", due to its bitter taste. It is one of the most [[acid]]ic [[phenols]]. Like other strongly [[nitration|nitrate]]d organic compounds, picric acid is an [[Explosive material|explosive]], which is its primary use. It has also been used as medicine ([[antiseptic]], burn treatments) and as a dye.

== History ==

Picric acid was probably first mentioned in the [[alchemical]] writings of [[Johann Rudolf Glauber]]. Initially, it was made by [[nitrating]] substances such as animal horn, [[silk]], [[indigo dye|indigo]], and natural [[resin]], the synthesis from indigo first being performed by [[Peter Woulfe]] in 1771.<ref>Peter Woulfe (1771) [https://books.google.com/books?id=nEJWAAAAYAAJ&pg=PA14 "Experiments to shew the nature of aurum mosaicum,"] ''Philosophical Transactions of the Royal Society of London'', '''61''': 114–130. See pages 127–130: "A method of dying wool and silk, of a yellow colour, with indigo; and also with several other blue and red colouring substances." and "Receipt for making the yellow dye." — where Woulfe treats indigo with nitric acid ("acid of nitre").</ref> The German chemist [[Justus von Liebig]] had named picric acid {{lang|de|Kohlenstickstoffsäure}} (rendered in French as {{lang|fr|acide carboazotique}}). Picric acid was given that name by the French chemist [[Jean-Baptiste Dumas]] in 1841.<ref>{{cite journal |last=Dumas |first=J. |title=Quatrième mémoire sur les types chimiques |journal=Annales de Chimie et de Physique |date=1841 |volume=2 |pages=204–232 |url=https://babel.hathitrust.org/cgi/pt?id=hvd.hx3dxf&view=1up&seq=208 |series=3rd series |trans-title=Fourth memoir on chemical types |language=fr}} From p. 228: ''"C'est sous ce nom que j'ai désigné l'acide carboazotique, ..."'' (It is by this name [i.e., picric acid] that I designated carboazotic acid, ... )</ref> Its synthesis from [[phenol]], and the correct determination of its formula, were accomplished during 1841.<ref>Auguste Laurent (1841) [http://gallica.bnf.fr/ark:/12148/bpt6k6568619q/f199.image.langEN "Sur le phényle et ses dérivés"] (On phenol and its derivatives), ''Annales de Chimie et de Physique'', series 3, '''3''': 195–228; see especially pages 221–228.</ref> In 1799, French chemist Jean-Joseph Welter (1763–1852) produced picric acid by treating silk with nitric acid; he found that potassium picrate could explode.<ref>{{cite journal |last=Welter |first=Jean-Joseph |title=Sur quelques matières particulières, trouvées dans les substances animals, traitées par l'acide nitrique |journal=Annales de Chimie et de Physique |date=1799 |volume=29 |pages=301–305 |url=https://babel.hathitrust.org/cgi/pt?id=pst.000067418503&view=1up&seq=305 |series=1st series |trans-title=On some particular materials, found in animal substances, treated with nitric acid |language=fr}} From p. 303: ''"Le lendemain je trouvai la capsule tapisée de cristaux dorés qui avoient la finesse de la soie, qui détonoient comme la poudre à canon, et qui, à mon avis, en auroient produit l'effet dans une arme à feu."'' (The next day, I found the crucible covered with golden crystals which had the fineness of silk, which detonated like gun powder, and which, in my opinion, would produce the same effect in a firearm.) Welter named picric acid ''amer'' (bitter): from p. 304: ''" ... je nommerai ''amer''."'' ( ... I will name it "bitter".)</ref> Not until 1830 did chemists think to use picric acid as an [[Explosive material|explosive]]. Before then, chemists assumed that only the [[Salt (chemistry)|salt]]s of picric acid were explosive, not the acid itself.<ref>A theory to explain why picrate salts detonated whereas picric acid itself didn't, was proposed by the French chemists [[Antoine François, comte de Fourcroy|Antoine Fourcroy]] and [[Louis Nicolas Vauquelin|Louis Vauquelin]] in 1806 and reiterated by the French chemist [[Michel Eugène Chevreul|Michel Chevreul]] in 1809. Picric acid evidently contained enough oxygen within itself — i.e. it was "super-oxygenated" (''suroxigéné'') (Fourcroy and Vauquelin, 1806), p. 543; (Chevreul, 1809), p. 129) — to combust completely even in the absence of air (because even in the absence of air, heat could transform it completely into gases, leaving no carbon). ((Fourcroy and Vauquelin, 1806), pp. 542–543); (Chevreul, 1809), pp. 127–128) However, when picric acid was burned, the heat that was generated caused some of the acid to evaporate, dissipating so much heat that only burning, not detonation, occurred. In contrast, picrate salts were solids that did not sublimate, and thus did not dissipate heat; hence, they did detonate.((Fourcroy and Vauquelin, 1806), p. 542); (Chevreul, 1809), pp. 129–130) See:

* {{cite journal |last1=Fourcroy |last2=Vauquelin |title=Mémoire sur la découverte d'une nouvelle matière inflammable et détonnante, formée par l'action de l'acide nitrique sur l'indigo et les matières animales |journal=Mémoires de l'Institute des Sciences et Arts |date=1806 |volume=6 |pages=531–543 |url=https://www.biodiversitylibrary.org/item/86732#page/657/mode/1up |trans-title=Memoir on the discovery of a new flammable and explosive substance, formed by the action of nitric acid on indigo and animal substances |language=fr}}

* {{cite journal |last1=Chevreul |title=Extrait d'un mémoire sur les substances amères formées par la réaction de l'acide nitrique sur l'indigo |journal=Annales de Chimie et de Physique |date=1809 |volume=72 |pages=113–142 |url=https://babel.hathitrust.org/cgi/pt?id=pst.000067418718&view=1up&seq=459 |trans-title=Extract from a memoir on the bitter substances formed by the reaction of nitric acid with indigo |language=fr}}</ref> In 1871 [[Hermann Sprengel]] proved it could be detonated<ref>Note:

* In March 1871, Sprengel detonated picric acid at the gunpowder works of John Hall & Sons in Faversham in Kent, England.

* Sprengel filed patents in Britain for "safety explosives" (i.e., stable explosives) on April 6, 1871 (no. 921), and on October 5, 1871 (no. 2642); in the latter patent, Sprengel proposed using picric acid dissolved in nitric acid as an explosive.

* Hermann Sprengel (1873) "On a new class of explosives which are non-explosive during their manufacture, storage, and transport", ''Journal of the Chemical Society'', '''26''' : 796–808 {{doi|10.1039/js8732600796}}.

* Hermann Sprengel, [http://babel.hathitrust.org/cgi/pt?id=nyp.33433090730692;view=1up;seq=35 ''The Discovery of Picric Acid (Melinite, Lyddite) "As a Powerful Explosive"'' ...], 2nd ed. (London: Eyre & Spottiswoode, 1903). This pamphlet is a collection of (splenetic) letters in which Sprengel defends his priority in the use of picric acid as a high explosive.</ref> and afterwards most [[military]] powers used picric acid as their main [[high explosive]] material. A full synthesis was later found by Leonid Valerieovich Kozakov.

Picric acid was the first strongly explosive nitrated [[organic compound]] widely considered suitable to withstand the shock of firing in conventional [[artillery]]. [[Nitroglycerine]] and [[nitrocellulose]] (guncotton) were available earlier, but shock sensitivity sometimes caused [[detonation]] in an artillery barrel at the time of firing. In 1885, based on research of Hermann Sprengel, French chemist [[Eugène Turpin]] patented the use of pressed and cast picric acid in [[Rock blasting|blasting]] charges and [[artillery shell]]s. In 1887 the French government adopted a mixture of picric acid and guncotton with the name '''Melinite'''. In 1888, Britain started manufacturing a very similar mixture in [[Lydd]], Kent, with the name '''Lyddite'''. Japan followed with an alternative stabilization approach known as '''[[Shimose powder]]''' which, instead of attempting to stabilize the material itself, removed its contact with metal by coating the inside of the shells with layer(s) of resin and wax.<ref>Koike, Shigeki (2006). "The Russo-Japanese War and the system of SHIMOSE gunpowder" (PDF). Bulletin of Papers (in Japanese). Takasaki City University of Economics. 1 (49).</ref> In 1889, a mixture of [[ammonium cresylate]] with [[trinitrocresol]], or an ammonium salt of trinitrocresol, started to be manufactured with the name '''[[Ecrasite]]''' in [[Austria-Hungary]]. By 1894 Russia was manufacturing artillery shells filled with picric acid. Ammonium picrate (known as '''Dunnite''' or [[explosive D]]) was used by the United States beginning in 1906. However, shells filled with picric acid become unstable if the compound reacts with the metal shell or [[fuze]] casings to form metal [[picrate]]s which are more sensitive than the parent phenol. The sensitivity of picric acid was demonstrated by the [[Halifax Explosion]].

[[File:The French Munitions Industry, 1914-1918 Q19175.jpg|thumb|left|300px|Workers filling shells with liquid melinite at a French munitions factory during WWI]]

Picric acid was used in the [[Battle of Omdurman]],<ref name="Brown">{{cite book |last=Brown |first=G.I. |title=The big bang: a history of explosives |publisher=Sutton Pub |location=Stroud, UK |year=1998 |pages=151–163 |isbn=0-7509-1878-0 |oclc=40348081}}</ref> the [[Second Boer War]],<ref>{{cite book |last=Wisser |first=John Philip |author-link=John Philip Wisser |title=The second Boer War, 1899–1900 |publisher=Hudson-Kimberly |year=1901|page=243|url=https://archive.org/stream/secondboerwar18900wissrich#page/243/mode/1up|access-date=2009-07-22}}</ref> the [[Russo-Japanese War]],<ref>[https://timesmachine.nytimes.com/timesmachine/1907/08/18/104992996.pdf Dunnite Smashes Strongest Armor], ''[[The New York Times]]'', August 18, 1907</ref> and [[World War I]].<ref>Marc Ferro. ''The Great War''. London and New York: Routeladge Classics, p. 98.</ref> Germany began filling artillery shells with [[trinitrotoluene]] (TNT) in 1902. [[Toluene]] was less readily available than phenol, and TNT is less powerful than picric acid, but the improved safety of munitions manufacturing and storage caused the replacement of picric acid by TNT for most military purposes between the World Wars.<ref name="brown">Brown, G.I. (1998), ''The Big Bang: a History of Explosives'', Sutton Publishing {{ISBN|0-7509-1878-0}} pp.151–163</ref>

Efforts to control the availability of [[phenol]], the precursor to picric acid, emphasize its importance in [[World War I]]. Germans are [[Great Phenol Plot |reported]] to have bought US supplies of phenol and converted it to [[acetylsalicylic acid]] ([[aspirin]]) to keep it from the Allies. At the time, phenol was obtained from [[coal]] as a co-product of [[Coke (fuel)|coke]] ovens and the manufacture of gas for [[gas lighting]]. [[Laclede Gas]] reports being asked to expand production of phenol (and [[toluene]]) to assist the war effort.<ref name="Beck">Beck, Bill (2007) ''Laclede Gas and St. Louis: 150 Years Working Together, 1857–2007'', Laclede Gas Company, {{ISBN|978-0-9710910-1-6}} p. 64</ref> Both [[Monsanto]]<ref name="Forrestal">Forrestal, Dan J. (1977), ''Faith, Hope & $5000: The Story of Monsanto'', Simon & Schuster, {{ISBN|0-671-22784-X}}[2] p. 24</ref> and [[Dow Chemical]]<ref name="Brandt">Brandt, E.N. (1997), ''Growth Company: Dow Chemical's First Century'', Michigan State University, {{ISBN|0-87013-426-4}} p. 77, 97 and 244</ref> began manufacturing synthetic phenol in 1915, with Dow being the main producer. Dow describes picric acid as "the main battlefield explosive used by the French. Large amounts [of phenol] also went to Japan, where it was made into picric acid sold to the Russians."<ref>Brandt, E.N. (1997), ''Growth Company: Dow Chemical's First Century'', Michigan State University, {{ISBN|0-87013-426-4}} p. 97</ref>

[[File:Stumps and rocks on farms shown here being removed by Picric acid LCCN2016891950.jpg|thumb|Photograph showing the use of picric acid on a farm to remove stumps and rocks.]]

[[Thomas Edison]] needed phenol to manufacture [[phonograph]] records. He responded by undertaking production of phenol at his [[Silver Lake, Essex County, New Jersey|Silver Lake, New Jersey]], facility using processes developed by his chemists.<ref>Conot, Robert (1979), A Streak of Luck: The Life & Legend of Thomas Alva Edison, Seaview Books, NY, p 413-4</ref> He built two plants with a capacity of six tons of phenol per day. Production began the first week of September, one month after hostilities began in Europe. He built two plants to produce the raw material [[benzene]] at [[Johnstown, Pennsylvania]], and [[Bessemer, Alabama]], replacing supplies previously from Germany. Edison manufactured [[aniline dyes]], which had previously been supplied by the [[IG Farben|German dye trust]]. Other wartime products included [[xylene]], [[p-phenylenediamine]], [[shellac]], and [[pyrophyllite]]. Wartime shortages made these ventures profitable. In 1915, his production capacity was fully committed by midyear.{{cn|date=March 2023}}

== 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''2₁ 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''_a Equalization and Electron-Pair Saturation Concepts.'' In: ''[[Cryst. Growth Des.]]'' 2011, 11, 2724–2735, [[doi:10.1021/cg101007a]].</ref>

== Uses ==

By far the greatest use of picric acid has been in [[ammunition|ammunitions]] and explosives. [[Explosive D]], also known as Dunnite, is the [[ammonium]] salt of picric acid. Dunnite is more powerful but less stable than the more common explosive [[TNT]] (which is produced in a similar process to picric acid but with toluene as the feedstock). Picramide, formed by aminating picric acid (typically beginning with Dunnite), can be further aminated to produce the very stable explosive [[TATB]].

It has found some use in organic chemistry for the preparation of crystalline salts of organic bases (picrates) for the purpose of identification and characterization.

=== Optical metallography ===

In [[metallurgy]], a 4% picric acid in ethanol etch, termed "picral", has been commonly used in optical [[metallography]] to reveal prior [[austenite]] grain boundaries in ferritic steels. The hazards associated with picric acid have meant it has largely been replaced with other chemical etchants. However, it is still used to etch [[magnesium alloy]]s, such as AZ31.

=== Histology ===

[[Bouin solution]] is a common picric-acid–containing [[Fixation (histology)|fixative]] solution used for [[histology]] specimens.<ref>{{cite book |title=Histotechnology: A Self-Instructional Text |edition=3 |last1=Carson |first1=Freida L. |last2=Hladik |first2=Christa |year=2009 |publisher=[[American Society for Clinical Pathology]] Press |location=Hong Kong |isbn=978-0-89189-581-7 |page=19}}</ref> It improves the staining of acid dyes, but it can also result in [[hydrolysis]] of any DNA in the sample.<ref>{{cite web |last=Llewellyn |first=Brian D |title=Picric Acid |url=http://stainsfile.info/StainsFile/prepare/fix/agents/picric_acid.htm |work=StainsFile |access-date=28 September 2012 |date=February 2009 |archive-url=https://web.archive.org/web/20150531030210/http://stainsfile.info/StainsFile/prepare/fix/agents/picric_acid.htm |archive-date=31 May 2015 |url-status=dead}}</ref>

Picric acid is used in the preparation of [[Sirius Red|Picrosirius red]], a histological stain for [[collagen]].<ref>{{cite journal|vauthors=Lattouf R, Younes R, Lutomski D, Naaman N, Goudeau G, Senni K, Changotade S|year=2014|volume=62|issue=10|journal=Journal of Histochemistry & Cytochemistry|doi=10.1369/0022155414545787|doi-access=free|title=Picrosirius Red Staining: A Useful Tool to Appraise Collagen Networks in Normal and Pathological Tissues|pmid=25023614|pages=751–758}}</ref><ref>{{cite journal|vauthors=Junqueira LC, Bignolas G, Brentani RR|title=Picrosirius staining plus polarization microscopy, a specific method for collagen detection in tissue sections|journal=The Histochemical Journal|year=1979|volume=11|issue=4|pages=447–455|doi=10.1007/BF01002772|pmid=91593}}</ref>

=== Blood tests ===

Clinical chemistry laboratory testing utilizes picric acid for the [[Jaffe reaction]] to test for [[creatinine]]. It forms a colored complex that can be measured using spectroscopy.<ref>{{cite web |url=http://www.cimascientific.com/2600.htm |title=Creatinine Direct Procedure, on CimaScientific |access-date=2011-03-26 |archive-date=2020-08-06 |archive-url=https://web.archive.org/web/20200806152607/http://www.cimascientific.com/2600.htm |url-status=dead}}</ref>

Picric acid forms red isopurpurate with hydrogen cyanide (HCN). By photometric measurement of the resulting dye, picric acid can be used to quantify hydrogen cyanide.<ref>[https://lernvorsprung.at/wp-content/uploads/2019/04/QUANTIFICATION_OF_TOTAL_CYANIDE_CONTENT_IN_STONE_-FRUIT_KERNELS.pdf Quantification of total cyanide content in stone fruit kernels.] {{webarchive |url=https://web.archive.org/web/20190430065823/https://lernvorsprung.at/wp-content/uploads/2019/04/QUANTIFICATION_OF_TOTAL_CYANIDE_CONTENT_IN_STONE_-FRUIT_KERNELS.pdf |date=2019-04-30}} pdf, Pg.33</ref>

During the early 20th century, picric acid was used to measure blood [[glucose]] levels. When glucose, picric acid and [[sodium carbonate]] are combined and heated, a characteristic red color forms. With a calibrating glucose solution, the red color can be used to measure the glucose levels added. This is known as the Lewis and Benedict method of measuring glucose.<ref>2{{cite web|title=Measuring blood glucose levels in the 1920s|url=https://tacomed.com/chapter-4-measuring-blood-glucose-levels-in-the-1920s/the-lewis-and-benedict-method-of-measuring-glucose/|website=Tacomed.com|access-date=13 June 2017|archive-date=16 December 2018|archive-url=https://web.archive.org/web/20181216215037/https://tacomed.com/chapter-4-measuring-blood-glucose-levels-in-the-1920s/the-lewis-and-benedict-method-of-measuring-glucose/|url-status=dead}}</ref>

=== Skin dye ===

Much less commonly, wet picric acid has been used as a skin dye, or temporary branding agent.{{citation needed|date=July 2023}} It reacts with proteins in the skin to give a dark brown color that may last as long as a month.{{citation needed|date=July 2023}}

=== Antiseptic ===

During the early 20th century, picric acid was stocked in pharmacies as an [[antiseptic]] and as a treatment for [[burn]]s, [[malaria]], [[herpes]], and [[smallpox]]. Picric-acid–soaked [[gauze]] was commonly stocked in [[first aid kit]]s from that period as a burn treatment. It was notably used for the treatment of burns suffered by victims of the [[Hindenburg disaster]] in 1937. Picric acid was used as a treatment for [[trench foot]] suffered by soldiers stationed on the [[Western Front (World War I)|Western Front]] during [[World War I]].<ref>(1922) [http://babel.hathitrust.org/cgi/pt?id=uc1.b2943177;view=1up;seq=201] ''History of the Great War - Surgery of the War, Vol. 1'', Pg. 175.</ref>

Picric acid has been used for many years by [[Fly tying|fly tyers]] to dye [[mole skin]]s and feathers a dark [[olive green]] for use as fishing lures. Its popularity has been tempered by its toxic nature.{{cn|date=March 2023}}

==Safety==

Modern safety precautions recommend storing picric acid wet, to minimize the danger of explosion. Dry picric acid is relatively sensitive to [[Shock (mechanics)|shock]] and [[friction]], so laboratories that use it store it in bottles under a layer of [[water (molecule)|water]], rendering it safe. Glass or plastic bottles are required, as picric acid can easily form metal [[picrate]] salts that are even more sensitive and hazardous than the acid itself. Industrially, picric acid is especially hazardous because it is volatile and slowly sublimes even at room temperature. Over time, the buildup of picrates on exposed metal surfaces can constitute an explosion hazard.<ref>{{cite web |title=Picric Acid, Wet |website=hazard.com |date=21 April 1998 |url=http://hazard.com/msds/mf/baker/baker/files/p4556.htm |access-date=13 April 2021}}</ref>

Picric acid gauze, if found in antique first aid kits, presents a safety hazard because picric acid of that vintage (60–90 years old) will have become crystallized and unstable,<ref>{{cite news |last1=Harding |first1=Evan |last2=Searle |first2=Jamie |date=7 July 2021 |title=Potentially explosive substance was in Catlins museum for decades |url=https://www.stuff.co.nz/national/125677951/potentially-explosive-substance-was-in-catlins-museum-for-decades |work=Stuff |access-date=20 July 2021}}</ref> and may have formed metal picrates from long storage in a metal first aid case.

[[Bomb disposal]] units are often called to dispose of picric acid if it has dried out.<ref>{{cite web|url= http://www.irishtimes.com/newspaper/breaking/2010/1001/breaking49.html|title= Bomb squad called to Dublin lab|date= 1 October 2010|work= irishtimes.com|publisher= Irish Times|access-date= 22 July 2011|archive-date= 22 October 2012|archive-url= https://web.archive.org/web/20121022045304/http://www.irishtimes.com/newspaper/breaking/2010/1001/breaking49.html|url-status= dead}}</ref><ref>{{cite web |url= http://www.rte.ie/news/2010/1103/teagasc.html|title= Unstable chemicals made safe by army|date= 3 November 2010|work= rte.ie|publisher= RTÉ News|access-date=22 July 2011}}</ref> In the United States there was an effort to remove dried picric acid containers from high school laboratories during the 1980s.

[[Munitions]] containing picric acid may be found in sunken [[warships]]. The buildup of metal picrates over time renders them shock-sensitive and extremely hazardous. It is recommended that [[shipwreck]]s that contain such munitions not be disturbed in any way.<ref name="allbright78">Albright, p.78</ref> The hazard may subside when the shells become corroded enough to admit [[seawater]] as these materials are water-soluble.<ref name="allbright78" /> Currently there are various fluorescent probes to sense and detect picric acid in very minute quantity.<ref>{{cite journal |last1=Arunkumar |first1=Chellaiah |last2=Sujatha |first2=Subramaniam |title=Protonation and axial ligation intervened fluorescence turn-off sensing of picric acid in freebase and tin(iv) porphyrins |journal=RSC Advances |date=26 Oct 2015 |volume=5 |issue=113 |page=93243 |doi=10.1039/C5RA18310C |bibcode=2015RSCAd...593243S |url=https://pubs.rsc.org/en/content/articlelanding/2015/ra/c5ra18310c}}</ref>

==See also==

*[[Shellite (explosive)]], an explosive containing picric acid, formerly used in naval shells.

*[[Table of explosive detonation velocities]]

*[[RE factor]]

*[[Verhoeff's stain]]

*[[Styphnic acid]]

==References==

{{reflist}}

==Further reading==

* {{cite book |title=Cleanup of Chemical and Explosive Munitions: Location, Identification and Environmental Remediation |publisher=William Andrew |author=Albright, Richard |year=2011}}

* {{cite journal |last1=Brown |first1=David K. |last2=McCallum |first2=Iain |year=2001 |title=Ammunition Explosions in World War I |journal= Warship International |publisher=International Naval Research Organization |volume=XXXVIII |issue=1 |pages=58–69 |issn=0043-0374}}

* Cooper, Paul W., ''Explosives Engineering'', New York: Wiley-VCH, 1996. {{ISBN|0-471-18636-8}}

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* [https://www.cdc.gov/niosh/npg/npgd0515.html CDC - NIOSH Pocket Guide to Chemical Hazards]

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[[Category:Explosive chemicals]]

[[Category:Nitrophenols]]

[[Category:Organic acids]]