Acetylenedicarboxylic acid

Acetylenedicarboxylic acid
Names
	Preferred IUPAC name But-2-ynedioic acid
	Other names 2-Butynedioic acid
Identifiers
CAS Number	142-45-0 ;
3D model (JSmol)	Interactive image; Interactive image;
Beilstein Reference	878357
ChEBI	CHEBI:30781 ;
ChemSpider	362 ;
ECHA InfoCard	100.005.033
EC Number	205-536-0;
Gmelin Reference	26624
KEGG	C03248 ;
PubChem CID	371;
UNII	2D2OJ4KO44;
CompTox Dashboard (EPA)	DTXSID3059715 ;
	InChI InChI=1S/C4H2O4/c5-3(6)1-2-4(7)8/h(H,5,6)(H,7,8) Key: YTIVTFGABIZHHX-UHFFFAOYSA-N ; InChI=1/C4H2O4/c5-3(6)1-2-4(7)8/h(H,5,6)(H,7,8) Key: YTIVTFGABIZHHX-UHFFFAOYAA;
	SMILES C(#CC(=O)O)C(=O)O; O=C(O)C#CC(=O)O;
Properties
Chemical formula	H2C4O4
Molar mass	114.056 g·mol−1
Appearance	Crystalline solid
Melting point	175 to 176 °C (347 to 349 °F; 448 to 449 K) (decomposes); 180–187 °C (decomposes)
Conjugate base	Hydrogen acetylenedicarboxylate (chemical formula HC4O−4)
Hazards
	GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H301, H314, H315, H319, H335
Precautionary statements	P260, P264, P270, P271, P280, P301+P310, P301+P330+P331, P302+P352, P303+P361+P353, P304+P340, P305+P351+P338, P310, P312, P321, P330, P332+P313, P337+P313, P362, P363, P403+P233, P405, P501 Preview warning: Omit Rules: keep P260, omit P261
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

Acetylenedicarboxylic acid or butynedioic acid is an organic compound (a dicarboxylic acid) with the formula H₂C₄O₄ or HO−C(=O)−C≡C−C(=O)−OH. It is a crystalline solid that is soluble in diethyl ether.

The removal of two protons yields the acetylenedicarboxylate dianion C₄O2−4, which consists only of carbon and oxygen, making it an oxocarbon anion. Partial ionization yields the monovalent hydrogen acetylenedicarboxylate anion HC₄O−4.

The acid was first described in 1877 by Polish chemist Ernest Bandrowski. It can be obtained by treating α,β-dibromosuccinic acid with potassium hydroxide KOH in methanol or ethanol. The reaction yields potassium bromide and potassium acetylenedicarboxylate. The salts are separated and the latter is treated with sulfuric acid.

Acetylenedicarboxylic acid is used in the synthesis of dimethyl acetylenedicarboxylate, an important laboratory reagent. The acid is commonly traded as a laboratory chemical. It can also be reacted with sulfur tetrafluoride to produce hexafluoro-2-butyne, a powerful dienophile for use in Diels-Alder reactions.

Fatty alcohol esters of acetylenedicarboxylic acid can be used for the preparation of phase change materials (PCM).