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The alkyne compounds are Hydrocarbure S having a non-saturation characterized by the presence of triple bond between two atoms of Carbone. Two carbons are hybrid sp. Triple connection is the combination of two connections π and a connection σ. The electronic density of the molecule is distributed in a cylindrical way along axis DC.

It is said that one deals with true alkyne compound if R or R' is a hydrogen.

Alkyne compounds, or acetylenic hydrocarbons, have as a general formula: CnH2n-2.

And are characterized by the presence in their molecule of triple connection and a possible coexistence of double connections.

Nomenclature

The alkyne compounds are named like the Alcène S correspondents, by replacing the termination “- ene” by the termination “- yne”. Except nomenclature IUPAC, the first term, C2H2, are also called Acétylène. The linear alkyne compounds have as a general formula CnH2n-2.

Examples:

  • éthyne (acetylene)
  • goal-1-yne
  • goal-2-yne

Physical properties

General properties

The alkyne compounds are characterized by infra-red spectra (band of absorbtion 2.100 - 2.300 Nm). Acetylene, propyne and the butyne-1 are gases at the ordinary temperature; the other terms are liquid then solid, as their molecular weight increases to be solid starting from C15.

They are present, in small quantity, in the Pétrole S and the natural gases.

Chemical properties

It is advisable to distinguish those from triple connection, which are common to all alkyne compounds, and the properties from the contiguous hydrogen to triple connection, which are particular with “true” alkyne compounds. Triple connection presents the same type of reactivity as the double connection, but with a sometimes different intensity. Like it, it lends itself to reactions of addition and of polymerization and it constitutes a point of less resistance of the chain. The alkyne compounds are insoluble in water but soluble in alcohol, the ether, the Solvant S organics Apolaire S.

In addition to reactions of hydration (Acetaldehyde), the alkyne compounds are easily hydrogenated in Alcanes or in Alcène S. the choice of catalyst makes it possible to differentiate the Isomère S Cis or Trans to be produced. Thus one can obtain Propane starting from the Propyne by a reaction of Hydrogénation with like catalyst the Platine or the Nickel.

Acetylene

The Acétylène is not very water soluble, but much more in the Acétone. Its formation starting from its elements is endothermic, it absorbs 230 kJ/mole.

Acetylene is unstable, for this reason, and tends to break up in a sometimes violent way, especially if it is compressed or liquefied. This characteristic a long time obstructed the use of acetylene in various applications which it can receive. One can however transport it without danger in the form of solution in the Acétone, and use it under a light pressure in the industrial syntheses with the proviso of diluting it with an inert gas (nitrogenizes) and of displacing air of the installations completely.

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