Silver acetylide


Silver acetylide is an inorganic chemical compound with the formula Ag2C2, a metal acetylide. The compound can be regarded as a salt of the weak acid, acetylene. The salt's anion consists of two carbon atoms linked by a triple bond. The alternate name "silver carbide" is rarely used, although the analogous calcium compound CaC2 is called calcium carbide.
Pure silver acetylide is a heat- and shock-sensitive high explosive with the unusual property that on ignition it does not evolve any gas:
A common misconception about the "silver acetylide" used in commercial explosives is that it explodes without the evolution of gaseous products and that its chemical formula is. In reality, it is a double salt with the silver salt it was produced from, usually silver nitrate. The anion of the parent compound acts as the oxidizer in the decomposition reaction.
The detonation velocity of the mixture silver acetylide: silver nitrate is 3460 m/s. That of pure silver acetylide is 4000 m/s. Other authors report values of only 1980 and 1200 m•s⁻¹ respectively.

Synthesis

Silver acetylide can be produced by passing acetylene gas through a solution of silver nitrate:
The reaction product is a greyish to white precipitate. This is the same synthesis from Berthelot in which he first found silver acetylide in 1866.
The double salt is formed in acidic or neutral silver nitrate solutions. Performing the synthesis in basic ammonia solution does not allow the double salt to form, producing pure silver acetylide. To properly form the double salt, acetylene gas is passed through dilute silver nitrate and nitric acid solution. Instead of the conventional synthesis of passing acetylene gas through silver nitrate solution, an amateur chemist by the username fdnjj6 discovered that a purer and whiter precipitate can be formed by passing acetylene gas through acetone and adding the acetylene solution drop-wise to a dilute silver nitrate and nitric acid solution. The reaction was performed at ambient room temperature.
Silver acetylide can be formed on the surface of silver or high-silver alloys, e.g. in pipes used for transport of acetylene, if silver brazing was used in their joints.

Solubility

Silver acetylide is not soluble in water and is not appreciably soluble in any other solvent.