Silver acetylide

Silver acetylide is an inorganic chemical compound with the formula Ag₂C₂, a metal acetylide. The compound can be regarded as a silver salt of the weak acid, acetylene. The salt's anion consists of two carbon atoms linked by a triple bond, thus, its structure is [Ag⁺]₂[⁻C≡C⁻]. The alternate name "silver carbide" is rarely used, although the analogous calcium compound CaC₂ is called calcium carbide. Silver acetylide is a primary 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
CAS Number	7659-31-6 Y
3D model (JSmol)	Interactive image
CompTox Dashboard (EPA)	DTXSID30904769
InChI InChI=1S/C2.2Ag/c1-2;;/q-2;2*+1 Key: FIDGMLJJLFFOEI-UHFFFAOYSA-N
SMILES [Ag+].[Ag+].[C-]#[C-]
Properties
Chemical formula	Ag2C2
Molar mass	239.758 g·mol−1
Appearance	gray or white solid
Density	4.47 g/cm3[1]
Melting point	120 °C (248 °F; 393 K)
Boiling point	decomposes
Solubility in water	insoluble
Hazards
Occupational safety and health (OHS/OSH):
Main hazards	highly sensitive primary explosive
NFPA 704 (fire diamond)	3 3 4
Flash point	77 °C (171 °F; 350 K)
Thermochemistry
Std enthalpy of formation (ΔfH⦵298)	357.6±5.0 kJ/mol[2]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

Synthesis

Silver acetylide can be produced by passing acetylene gas through a solution of silver nitrate:^[3]

2 AgNO₃(aq) + C₂H₂(g) → Ag₂C₂(s) + 2 HNO₃(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.^[4]

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, 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 primary explosive. Silver acetylide decomposes through the reaction:

Ag₂C₂(s) → 2 Ag(s) + 2 C(s)

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.^[5]

Solubility

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

References

1. McCowan, J. D. (1963). "Decomposition of silver acetylide". Transactions of the Faraday Society. 59: 1860–1864. doi:10.1039/tf9635901860.
2. Finch, Arthur; Gardner, Peter J.; Head, Arthur J.; Majdi, Hassan S. (1991). "The standard enthalpy of formation of silver acetylide". Thermochimica Acta. 180: 325–330. doi:10.1016/0040-6031(91)80402-5.
3. 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.
4. 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.
5. Matyáš, Robert; Pachman, Jiří (2013). Primary Explosives. Berlin, Heidelberg: Springer Berlin Heidelberg. doi:10.1007/978-3-642-28436-6. ISBN 9783642284359. S2CID 199492549.