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 gre ...

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 was ...

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

precipitate In an aqueous solution, precipitation is the process of transforming a dissolved substance into an insoluble solid from a super-saturated solution. The solid formed is called the precipitate. In case of an inorganic chemical reaction leading ...

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 exp ...

, more thermally sensitive than

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 ...

. 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 pinkis ...

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 Petrochemicals (sometimes abbreviated as petchems) are the chemical products obtained from petroleum by refining. Some chemical compounds made from petroleum are also obtained from other fossil fuels, such as coal or natural gas, or renewable sou ...

can also possess a degree of risk under certain conditions.

Reactions

Copper acetylide is the substrate of

Glaser coupling The Glaser coupling is a type of coupling reaction. It is by far the oldest acetylenic coupling and is based on cuprous salts like copper(I) chloride or copper(I) bromide and an additional oxidant like oxygen. The base in its original scope is amm ...

for the formation of polyynes. 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 d ...

to and forms a blue soluble

complex Complex commonly refers to: * Complexity, the behaviour of a system whose components interact in multiple ways so possible interactions are difficult to describe ** Complex system, a system composed of many components which may interact with each ...

with the

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

carbyne In organic chemistry, a carbyne is a general term for any compound whose structure consists of an electrically neutral carbon atom connected by a single covalent bond and has three non-bonded electrons. The carbon atom has either one or thre ...

, 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, known as allotropes of the elements. Allotropes are different structural modifications of an element: the ...

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 Acid strength is the tendency of an acid, symbol ...

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 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 In organometallic chemistry, acetylide refers to chemical compounds with the chemical formulas and , where M is a metal. The term is used loosely and can refer to substituted acetylides having the general structure (where R is an organic side c ...

anions in the solid into

-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

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