Acetylenedicarboxylic acid

Acetylenedicarboxylic acid

Names
IUPAC name But-2-ynedioic acid
Other names 2-Butynedioic acid
Identifiers
CAS Number	142-45-0 N
3D model (JSmol)	Interactive image Interactive image
ChEBI	CHEBI:30781 Y
ChemSpider	362 Y
ECHA InfoCard	100.005.033
KEGG	C03248 Y
PubChem CID	371
InChI InChI=1S/C4H2O4/c5-3(6)1-2-4(7)8/h(H,5,6)(H,7,8) Y Key: YTIVTFGABIZHHX-UHFFFAOYSA-N Y 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	C4H2O4
Molar mass	114.06 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)
Hazards
R-phrases (outdated)	R25 R36/37/38
S-phrases (outdated)	S26 S45
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N  (what is YN ?)
Infobox references

Acetylenedicarboxylic acid or butynedioic acid is an organic compound (a dicarboxylic acid) with the formula C₄H₂O₄ or HO₂C-C≡C-CO₂H. It is a crystalline solid that is soluble in diethyl ether.

The removal of two protons yields the acetylenedicarboxylate dianion C₄O₄²⁻, which consists only of carbon and oxygen, making it an oxocarbon anion. Partial ionization yields the monovalent hydrogenacetylenedicarboxylate anion HC₄O₄⁻.

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. Both the acid and the monobasic salt potassium hydrogenacetylenedicarboxylate KC₄HO₄ are commonly traded as laboratory chemicals. It can also be reacted with sulfur tetrafluoride to produce hexafluoro-2-butyne, a powerful dienophile for use in Diels-Alder reactions.