Copper(I) acetylide

Synthesis

Materials purported to be copper acetylide can be prepared by treating acetylene with a solution of copper(I) chloride and ammonia: : This reaction produces a reddish solid precipitate.

Properties

When dry, "copper acetylide" is a heat and shock sensitive primary explosive, more sensitive than silver acetylide.

In acetylene manufacturing plants, copper acetylide is thought to form inside pipes made of copper or an alloy with high copper content, which may result in violent explosion. This led to abandonment of copper as a construction material in such facilities. Copper catalysts used in the chemical industry can also possess a degree of risk under certain conditions.

Reactions

"Copper(I) acetylide" is claimed to be a precursor to polyynes. Treatment of with ammonia in air leaves a black solid residue, claimed to be carbyne, an elusive allotrope of carbon:Franco Cataldo (1999), A study on the structure and electrical properties of the fourth carbon allotrope: carbyne. Polymer International, volume 44, issue 2, pages 191–200. : This interpretation has been disputed. H. Kroto (2010), Carbyne and other myths about carbon. RSC Chemistry World, November 2010.

Freshly prepared "copper(I) acetylide" reacts with hydrochloric acid to form acetylene and copper(I) chloride. Samples that have been aged with exposure to air or to copper(II) ions liberate also higher polyynes , with n from 2 to 6, when decomposed by hydrochloric acid. A "carbonaceous" residue of this decomposition also has the spectral signature of chains. It has been conjectured that oxidation causes polymerization of the acetylide anions in the solid into carbyne-type anions. or cumulene-type anions . Franco Cataldo (1999), From dicopper acetylide to carbyne.Polymer International, volume 48, issue 1, pages 15-22.

Thermal decomposition of "copper(I) acetylide" in vacuum is not explosive and leaves copper as a fine powder at the bottom of the flask, while depositing a fluffy very fine carbon powder on the walls. On the basis of spectral data, this powder was claimed to be carbyne rather than graphite as expected.

Applications

Though not practically useful as an explosive due to high sensitivity, it is interesting as a curiosity because it is one of the very few explosives that do not liberate any gaseous products upon detonation.

The formation of copper(I) acetylide when a gas is passed through a solution of copper(I) chloride is used as a test for the presence of acetylene.

Reactions between and alkynes occur only if a terminal hydrogen is present (as it is slightly acidic in nature). Thus, this reaction is used for identification of terminal alkynes.

Related compounds

Although Cu2C2 remains weakly characterized, complexes with a linkage are known.

References

References

1. {{PGCH. 0150
2. (2007). "Synthesis, Structure and Thermal Properties of Copper and Silver Polyynides and Acetylides". Journal of Inorganic and Organometallic Polymers and Materials.
3. "Mine Safety and Health Administration (MSHA) - Accident Prevention Program - Miner's Tips - Hazards of Acetylene Gas".
4. "Copper".
5. "The Safe Use of Copper -Containing Catalysts in Ethylene Plants".
6. (1996). "Synthesis, Structure, Photophysics, and Excited-State Redox Properties of the Novel Luminescent Tetranuclear Acetylidocopper(I) Complex [Cu₄(μ-DPPM)₄(μ₄-η¹,η²-CC-)](BF₄)₂". Angewandte Chemie International Edition in English.