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. Silver acetylide is a high explosive.

Silver acetylide
Names
Preferred IUPAC name
Silver acetylide
Systematic IUPAC name
Silver(I) ethynediide
Other names
Silver percarbide
Silver carbide
Silver dicarbide
Argentous acetylide
Argentous ethynediide
Argentous percarbide
Argentous carbide
Argentous dicarbide
Identifiers
3D model (JSmol)
Properties
C2Ag2
Molar mass 239.758 g·mol−1
Appearance gray or white solid
Melting point 120 °C (248 °F; 393 K)
Boiling point decomposes
insoluble
Hazards
Main hazards High Explosive, Toxic
NFPA 704 (fire diamond)
Flammability code 3: Liquids and solids that can be ignited under almost all ambient temperature conditions. Flash point between 23 and 38 °C (73 and 100 °F). E.g. gasolineHealth code 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasReactivity code 4: Readily capable of detonation or explosive decomposition at normal temperatures and pressures. E.g. nitroglycerinSpecial hazards (white): no code
3
3
4
Flash point 77 °C (171 °F; 350 K)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Synthesis

Silver acetylide can be produced by passing acetylene gas through a solution of silver nitrate:[1]

2 AgNO
3 (aq) + C
2H
2 (g) → Ag
2C
2 (s) + 2 HNO
3 (aq)

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.[2]

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.

Explosive character

Pure silver acetylide is a heat- and shock-sensitive high explosive. For a long time, it was assumed to have the unusual property that on ignition it does not evolve any gas, only decomposing through the reaction:

Ag
2C
2 (s) → 2 Ag (s) + 2 C (s)

However, it has been shown that some gaseous products do form, containing water, carbon dioxide, carbon monoxide, hydrogen, and methane.

The detonation velocity of the silver acetylide-silver nitrate double salt is 1980 m/s, while that of pure silver acetylide is 1200 m/s.[3]

Solubility

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

References
  1. G.-C. Guo; Q.-G. Wang; G.-D. Zhou; T. C. W. Mak (1998). "Synthesis and characterization of Ag2C2·2AgClO4·2H2O: a novel layer-type structure with the acetylide dianion functioning in a 6-η1,η1:η2,η2:η2,η2 bonding mode inside an octahedral silver cage". Chem. Commun. (3): 339–340. doi:10.1039/a708439k.
  2. M. P. Berthelot (1866). "Ueber eine neue Klasse zusammengesetzter metallhaltiger Radicale (A new class of combined metallic radicals)". Annalen der Chemie. 138 (2): 245–253. doi:10.1002/jlac.18661380215.
  3. Matyáš, Robert; Pachman, Jiří (2013). Primary Explosives. Berlin, Heidelberg: Springer Berlin Heidelberg. doi:10.1007/978-3-642-28436-6. ISBN 9783642284359.
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