l-buten-3-yne (HC≡C—CH=CH2), the simplest unsaturated hydrocarbon containing double and triple carbon-carbon bonds. Colorless gas. Boiling point, 5.5° C; density at 0° C, 0.6867 g/cm3.
Vinyl acetylene is obtained by dimerization of acetylene in the presence of copper salts in an ammonium chloride solution (50°-100° C):
Vinyl acetylene is very reactive; the hydrogen atom of the terminal CH group can be replaced by a metal, a halogen (MgX, where X is a halogen), and so on. The most important reaction of vinyl acetylene is with HCl, yielding chloroprene, CH2=CCl—CH=CH2, which is used to make chloroprene rubbers. Vinyl acetylene oxidizes and polymerizes readily.