Ethyne

Ethyne or Acetylene, colourless, odourless, flammable gas, HC:CH, slightly lighter than air. As ordinarily prepared it has an unpleasant odour due to impurities. Ethyne can be prepared from any of various organic compounds by heating them in the absence of air, but it is usually made commercially by the reaction of calcium carbide with water. Although ethyne can be liquefied at ordinary temperatures with high pressure, it is violently explosive as a liquid. Ethyne gas is usually stored in metal tanks, under pressure, dissolved in liquid propanone (acetone). When ethyne is bubbled through a solution of ammonia and copper (I) chloride, copper carbide, a reddish precipitate, is formed. This is used as a test for ethyne. Copper carbide is explosive when dry.

Ethyne burns in air with a hot and brilliant flame. It was formerly much used as an illuminant and is now mainly used in the oxyacetylene torch, in which ethyne is burned in oxygen, producing a very hot flame used for welding and cutting metal. Ethyne is also used in chemical synthesis, particularly in the manufacture of chloroethene (vinyl chloride) for plastics, ethanal (acetaldehyde), and the neoprene type of synthetic rubber. Ethyne has a melting point of -81° C (-113.8° F) and a boiling point of -57° C (-70.6° F).