A similar reaction occur with hydrogen bromide at 100 degC. Reaction with hydrogen chloride occurs very slowly. The products obtained by polymerising ethyne depend on the conditions used. When ethyne is passed through a glass tube at 4000C a little benzene is formed. This linear polymerisation can be extended by altering the conditions of reaction. The reactions of ethynes indicate acidic properties for the hydrogens which are attached to the carbon atoms involved in the triple bond.
Ethynes readily form compounds with metal.
When ethyne is passed through a solution of sodium in liquid ammonia then sodium acetylide is formed and hydrogen is liberated. The other hydrogen atom in ethyne can be similarly replaced. When ethyne is passed into a solution of cuprous chloride in ammonia, cuprous acetylide is produced. CuCCCu Copper Acetylide Silver acetylide is formed when ethyne is passed into an ammoniacal solution of silver nitrate. These substitution reactions which ethynes undergo to form compounds with metals are not occur with the alkenes.