Dicyanoacetylene

 ( Conjugated Nitriles ) 

Dicyanoacetylene, also called carbon subnitride or but-2-ynedinitrile (IUPAC), is a compound of carbon and nitrogen with chemical formula . At room temperature, dicyanoacetylene is a colorless volatile liquid. It has a linear molecular structure, (often abbreviated as ), with alternating triple and single . It can be viewed as acetylene with the two hydrogen atoms replaced by cyanide groups.

Because of its high endothermic heat of formation, dicyanoacetylene can explode to carbon powder and nitrogen gas, and it burns in oxygen with a bright blue-white flame at a temperature of , the hottest flame in oxygen; burned in ozone at high pressure the flame temperature exceeds . Dicyanoacetylene polymerizes at room temperature into a dark solid.

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Synthesis Dicyanoacetylene can be prepared by passing nitrogen gas over a sample of graphite heated to temperatures between . It may also be synthesized via a reaction between a dihaloacetylene and a cyanide salt:

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As a reagent in organic chemistry Dicyanoacetylene is a powerful dienophile because the cyanide groups are electron-withdrawing, so it is a useful reagent for Diels–Alder reactions with unreactive . It even adds to the aromaticity compound durene (1,2,4,5-tetramethylbenzene) to form a substituted bicyclooctatriene. Only the most reactive of dienophiles can attack such aromatic compounds.

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In outer space Solid dicyanoacetylene has been detected in the atmosphere of Titan by infrared spectroscopy. As the seasons change on Titan, the compound condenses and evaporates in a cycle, which allows scientists on Earth to study Titanian meteorology.

, the detection of dicyanoacetylene in the interstellar medium has been impossible, because its symmetry means it has no rotational microwave spectrum. However, similar asymmetric molecules like cyanoacetylene have been observed, and its presence in those environments is therefore suspected.

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See also

• Cyanogen, N≡C−C≡N
• Diacetylene, H−C≡C−C≡C−H

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