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Diacetylene with the formula C4H2, is a highly unsaturated
Alkynes are hydrocarbons that have a triple bond between two carbon atoms, with the formula CnH2n-2. Alkynes are traditionally known as acetylenes, although the name acetylene also refers specifically to C2H2, known formally as ethyne using IUPAC nomenclature...


 that contains three single bonds and two triple bond
Triple bond

s. It is the first in the series of polyyne
The polyynes are a group of organic compounds with alternating single and triple bonds. The simplest example is diacetylene or buta-1,3-diyne, HC≡C-C≡CH....



Diacetylene has been identified in the atmosphere of Titan
Titan (moon)

 and in the protoplanetary nebula
Protoplanetary nebula
A protoplanetary nebula or preplanetary nebula is an astronomical object which is at the short-lived episode during a star's rapid stellar evolution between the late asymptotic giant branch phase and the subsequent planetary nebula phase. A PPN emits strongly in infrared radiation, and is a...

 CRL 618 by its characteristic vibrational modes. The molecule is most likely to have formed in Titan's atmosphere by a reaction between acetylene
Acetylene is the chemical compound with the formula C2H2. It is a hydrocarbon and the simplest alkyne. This colorless gas is widely used as a fuel and a chemical building block. It is unstable in pure form and thus is usually handled as a solution.As an alkyne, acetylene is unsaturated because...

 and the ethynyl radical
Ethynyl radical
The ethynyl radical, with chemical formula C2H, is an abundant interstellar polyatomic molecule that does not occur naturally on Earth. It was first observed by electron spin resonance isolated in a solid argon matrix at liquid helium temperatures in 1963 by Cochran and coworkers at the Johns...

 C2H, which is produced when acetylene undergoes photolysis. This radical can in turn attack the triple bond in acetylene and react efficiently even at cold temperatures. Diacetylene has also been found on the Moon



This compound may be made by the dehydrohalogenation of 1,4-dichloro-2-butyne by potassium hydroxide at low temperature:

The bis(trimethylsilyl
A trimethylsilyl group is a functional group in organic chemistry. This group consists of three methyl groups bonded to a silicon atom [−Si3], which is in turn bonded to the rest of a molecule...

)-protected derivative may be prepared by the Hay coupling of (trimethylsilyl)acetylene:
2 (tms)C≡CH → (tms)C≡C-C≡CH