Dissolve 10 g of copper(I) chloride in 100 mL of 20 % ammonia solution, start passing through acetylene gas until no more red copper acetylide precipitates. Filter and wash with 200ml of water, store under water. Do not let to dry.
C2H2 + 2 CuCl (NH4OH) = Cu2C2 + 2 HCl + (NH4OH)
Bubbling acetylene through the solution
Pure copper acetylide