Copper(I) acetylide, or cuprous acetylide, is a

chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...

with the formula Cu₂ C₂. Although never characterized by

X-ray crystallography X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angles ...

, the material has been claimed at least since 1856. One form is claimed to be a mono

hydrate In chemistry, a hydrate is a substance that contains water or its constituent elements. The chemical state of the water varies widely between different classes of hydrates, some of which were so labeled before their chemical structure was understo ...

with formula .. It is a reddish solid, that easily explodes when dry.

Synthesis

Materials purported to be copper acetylide can be prepared by treating

acetylene Acetylene ( systematic name: ethyne) is the chemical compound with the formula and structure . It is a hydrocarbon and the simplest alkyne. This colorless gas is widely used as a fuel and a chemical building block. It is unstable in its pure ...

with a solution of

copper(I) chloride Copper(I) chloride, commonly called cuprous chloride, is the lower chloride of copper, with the formula CuCl. The substance is a white solid sparingly soluble in water, but very soluble in concentrated hydrochloric acid. Impure samples appear g ...

and

ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous ...

: :C₂H₂ (g) + 2 CuCl (s) → Cu₂C₂ (s) + 2 HCl (g) This reaction produces a reddish solid precipitate.

Properties

When dry, copper acetylide is a heat and shock sensitive

high explosive An explosive (or explosive material) is a reactive substance that contains a great amount of potential energy that can produce an explosion if released suddenly, usually accompanied by the production of light, heat, sound, and pressure. An ...

, more thermally sensitive than silver acetylide. Copper acetylide is thought to form inside pipes made of

copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pink ...

or an alloy with high copper content, which may result in violent explosion. This was found to be the cause of explosions in acetylene plants, and led to abandonment of copper as a construction material in such plants. Copper

catalyst Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...

s used in petrochemistry can also possess a degree of risk under certain conditions.

Reactions

Copper acetylide is the substrate of Glaser coupling for the formation of

polyyne In organic chemistry, a polyyne () is any organic compound with alternating single and triple bonds; that is, a series of consecutive alkynes, with ''n'' greater than 1. These compounds are also called polyacetylenes, especially in the natural ...

s. In a typical reaction, a suspension of . in an amoniacal solution is treated with air. The copper is

oxidized Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a ...

to and forms a blue soluble complex with the

, leaving behind a black solid residue. The latter has been claimed to consist of carbyne, an elusive

allotrope Allotropy or allotropism () is the property of some chemical elements to exist in two or more different forms, in the same physical State of matter, state, known as allotropes of the elements. Allotropes are different structural modifications o ...

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. : ⁻C(≡C−C≡)_nC⁻ This interpretation has been disputed. H. Kroto (2010)
''Carbyne and other myths about carbon''
RSC Chemistry World, November 2010. Freshly prepared copper acetylide reacts with

hydrochloric acid Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid. It is a component of the gastric acid in the dige ...

to form acetylene and copper(I) chloride. Samples that have been aged with exposure to air or to copper(II) ions liberate also higher

s H(−C≡C−)_nH, with ''n'' from 2 to 6, when decomposed by

. A "carbonaceous" residue of this decomposition also has the spectral signature of (−C≡C−)_''n'' chains. It has been conjectured that oxidation causes polymerization of the acetylide anions in the solid into carbyne-type anions .C(≡C−C≡)_nC²⁻ or polycumulene-type anions C(=C=C=)_mC⁴⁻. Franco Cataldo (1999), ''From dicopper acetylide to carbyne''.Polymer International, volume 48, issue 1, pages 15-22. Thermal decomposition of copper 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 C(−C≡C−)_''n''C rather than graphite as expected.

Applications

Though not practically useful as an explosive due to high sensitivity and reactivity towards water, 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 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 Cu⁺ 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.

References

{{Copper compounds Copper(I) compounds Acetylides Explosive chemicals

Synthesis

Properties

Reactions

Applications

See also

References