{{chembox | Name = Tetrolic acid | ImageFile = Tetrolic Acid Structural Formula.svg | ImageSize = 240px | ImageAlt = Skeletal formula of tetrolic acid | ImageFile2 = Tetrolic acid (2-butynoic acid) crystals.jpg | ImageSize2 = 240px | ImageAlt2 = Crystals of tetrolic acid | PIN = But-2-ynoic acid | OtherNames = 2-Butynoic acid<br />Butynoic acid |Section1={{Chembox Identifiers | ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}} | ChemSpiderID = 61810 | PubChem = 68535 | SMILES1 = CC#CC(=O)O | CASNo = 590-93-2 | UNII_Ref = {{fdacite|correct|FDA}} | UNII = W3AM9ANZ22 | InChI = 1S/C4H4O2/c1-2-3-4(5)6/h1H3,(H,5,6) | InChIKey = LUEHNHVFDCZTGL-UHFFFAOYSA-N }} |Section2={{Chembox Properties | Formula = {{chem2|CH3C\tCCO2H}} | C=4|H=4|O=2 | Density = 0.9641 g/cm<sup>3</sup><ref name=b92/> | MeltingPtC = 78 | MeltingPt_ref = <ref name=b92>{{RubberBible92nd|page=3.88}}</ref> | BoilingPtC = 203 | BoilingPt_ref = <ref name=b92/> }} | Section8 = {{Chembox Related | OtherCompounds = {{ubl|[[but-3-enoic acid]]}} }} }} '''Tetrolic acid''' ('''2-butynoic acid''') is a short-chain unsaturated [[carboxylic acid]], described by the formula {{chem2|CH3\sC\tC\sCO2H}}. [[Salts]] and [[esters]] of tetrolic acid are known as '''tetrolates'''.
== History == The first reported synthesis<ref>{{cite journal|last=Geuther|first=A.|author-link=Johann Georg Anton Geuther|title=Ethyldiacetic Acid and some of its Derivatives|journal=[[J. Chem. Soc.]]|year=1871|volume=24|pages=812–837|doi=10.1039/JS8712400808 }}</ref> of tetrolic acid is believed to be by German chemist [[Johann Georg Anton Geuther]] in 1871 as part of his work investigating the derivatives of [[ethyl acetoacetate]].
== Production == Tetrolic acid is manufactured<ref>Smith, W. (1973) "Preparation of tetrolic acid" {{US Patent|3752848A}}</ref> on a commercial scale by treatment of [[propyne]] with a strong base (to form an [[acetylide]]), followed by [[carbon dioxide]]: [[File:Synthesis of tetrolic acid.png|Scheme2|left|500px]] {{Clear left}} Strong bases such as [[n-Butyllithium|''n''-BuLi]]<ref>{{cite journal|doi = 10.1039/P19940002525|first1 = Basil|last1 = Hartzoulakis|first2 = David|last2 = Gani|title = Synthesis of (2''S'', 3''R'')- and (2''S'', 3''S'')-3-methylglutamic acid|journal = [[J. Chem. Soc., Perkin Trans. 1]]|pages = 2525–2531|volume = 1994|issue = 18|year = 1994}}</ref> and {{chem2|[[sodium amide|NaNH2]]}}<ref>{{OrgSynth|doi = 10.15227/orgsyn.042.0097|title = Tetrolic Acid (2-Butynoic Acid)|volume = 42|pages = 97|year = 1962|collvol = 5|collvolpages = 1043|prep = CV5P1043|first1 = J. C.|last1 = Kauer|first2 = M.|last2 = Brown}}</ref> can be used.
== Properties == Tetrolic acid is highly soluble in polar solvents ([[water]], [[ethanol]]) and can be recrystallized from non-polar solvents (such as [[heptane]], [[hexane]] or [[toluene]]). The compound is a white crystalline solid which can exist in two polymorphous crystalline forms.<ref>{{cite journal|doi=10.1016/j.chemphys.2008.01.035|journal=[[Chemical Physics (journal)|Chemical Physics]]|year=2008|volume=345|issue=1|pages=49–64|title= Effects of "excessive" exciton interactions in polarized IR spectra of the hydrogen bond in 2-butynoic acid crystals: Proton transfer induced by dynamical co-operative interactions involving hydrogen bonds|last1= Flakus|first1= Henryk T.|last2= Hachuła|first2= Barbara|bibcode=2008CP....345...49F}}</ref>
The [[proton nuclear magnetic resonance]] (<sup>1</sup>H-NMR) spectrum in deuterated [[dimethyl sulfoxide]] shows a characteristic singlet peak at 1.99 ppm corresponding to the –{{chem2|CH3}} protons.
Tetrolic acid [[Sublimation (phase transition)|sublimes]] at temperatures above 20 °C, so it is typically stored in a sealed container in a refrigerator.<ref name="stability">{{cite journal|last1=Golden|first1=M.|date=2019|title=Thermal Stability of 2-Butynoic Acid (Tetrolic acid)|journal=Org. Process Res. Dev.|volume=23|issue=5|pages=1101–1104|doi=10.1021/acs.oprd.9b00106|s2cid=146028375 }}</ref>
Accelerated rate [[calorimetry]] (ARC) showed exothermic onset from 135 °C, precluding short-path distillation as a means of purification.<ref name="stability" />
== References == {{Commons category|Tetrolic acid}} {{reflist}}
[[Category:Alkynoic acids]]