Alkene are hydrocarbons that contain a carbon—carbon triple bond. Acetylene, H-C/// C-H, the simplest alkyne, was once widely used in industry as the staring material for the preparation of acetaldehyde, acetic acid, vinyl choride, and other high-volume chemicals, but more efficient routes to these substances using ethylene as starting material are now available. Acetylene is still use in the preparation of acrytic polymers, however, and is prepared industrially by high-temperature decomposition (pyrolysis) of methane. The method is of no use in the laboratory, however.