Copper(I) acetylide
Chemical compound
From Wikipedia, the free encyclopedia
Copper(I) acetylide, copper carbide or cuprous acetylide, is claimed to be a chemical compound with the formula Cu2C2. It is proposed to consists of Cu+ cations and acetylide anions −C≡C−, with the triple bond between the two carbon atoms. Although never characterized by X-ray crystallography, the material has been claimed at least since 1856.[2] One form is claimed to be a monohydrate with formula Cu2C2·H2O. It is a reddish-brown explosive powder.
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| Names | |
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| IUPAC name
Dicuprous acetylide | |
Other names
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| Identifiers | |
3D model (JSmol) |
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| ChemSpider | |
PubChem CID |
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| Properties | |
| Cu2C2 | |
| Molar mass | 151.114 g·mol−1 |
| Appearance | red-brown powder |
| Hazards | |
| Occupational safety and health (OHS/OSH): | |
Main hazards |
explosive |
| NIOSH (US health exposure limits): | |
PEL (Permissible) |
TWA 1 mg/m3 (as Cu)[1] |
REL (Recommended) |
TWA 1 mg/m3 (as Cu)[1] |
IDLH (Immediate danger) |
TWA 100 mg/m3 (as Cu)[1] |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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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.[3]
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.[4] This led to abandonment of copper as a construction material in such facilities.[5] Copper catalysts used in the chemical industry can also possess a degree of risk under certain conditions.[6]
Reactions
"Copper(I) acetylide" is claimed to be a precursor to polyynes. Treatment of Cu2C2·H2O with ammonia in air leaves a black solid residue, claimed to be carbyne, an elusive allotrope of carbon:[7]
- Cu+(−C(≡C−C≡)nC−)Cu+
This interpretation has been disputed.[8]
Freshly prepared "copper(I) acetylide" reacts with hydrochloric acid to form acetylene and copper(I) chloride.[citation needed] 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 hydrochloric acid. 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 C2−2 in the solid into carbyne-type anions. −C(≡C−C≡)nC− or cumulene-type anions 2−C(=C=C=)nC2−.[2]
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 (−C≡C−)n rather than graphite as expected.[2]
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 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.
Related compounds
Although Cu2C2 remains weakly characterized, complexes with a Cu−C≡C−Cu linkage are known.[9]