Alkynes: Introduction and Nomenclature
Alkynes are hydrocarbons containing one or more C≡C triple bonds.
According to IUPAC conventions, the names of alkynes are derived from those of the corresponding alkanes by changing the infix -an to -yn which indicates a triple bond. A side chain containing a triple bond, for example in ethynylyclohexane, is commonly called an alkynyl group.
A H-C≡C-CH2 group is called a propargyl group; e.g. H-C≡C-CH2-OH, propargyl alcohol. For comparison purposes, the group names are listed below.
Until the 50s, because side reactions were rare,was used in medicine as an anesthetic agent under the trade name narcyclen. However, the gaseous agent in a mixture with oxygen for breathing purposes had to contain 60% of highly purified ethyne. After several explosions had occured in operating rooms, the method was finally abandoned.
Ethyne ( acetylene) was first discovered in 1836 by the Irish chemist Edmund Davy (1785-1857, a cousin of Sir H. Davy) as a by-product during the preparation of metallic potassium by heating a mixture of calcinated potassium tartrate with charcoal. In 1862, F. Wöhler synthesized ethyne by treating calcium carbide with water. Since Davy described his observations only in his laboratory journal, the discovery of ethyne is generally attributed to Wöhler. In the same year, Berthelot synthesized ethyne from carbon and hydrogen. Formerly, ethyne was mainly used for illumination purposes and burned in mobile acetylene gas lamps or carbide lamps, for example in bicycle lamps. It was generated by dropping water onto calcium carbide. In the chemical industry, ethyne became a very important starting material in organic synthesis after the development of acetylene chemistry by Reppe. However, its importance as feedstock in petrochemistry is constantly decreasing when compared to ethene.
On a large-scale technical basis, ethyne was formerly synthesized exclusively by hydrolysis of calcium carbide (CaC2 ), which was prepared from calcium oxide (lime) and coke in an electric arc furnace at ca. 2200 °C (2475 K) (Wöhler, 1862).