Chemistry:Copper(I) acetylide
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| Names | |
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| IUPAC name
Dicuprous acetylide
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| Identifiers | |
3D model (JSmol)
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| ChemSpider | |
PubChem CID
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| Properties | |
| C2Cu2 | |
| Molar mass | 151.114 g·mol−1 |
| Appearance | red-brown powder |
| Hazards | |
| Main hazards | explosive |
| NIOSH (US health exposure limits): | |
PEL (Permissible)
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TWA 1 mg/m3 (as Cu)[1] |
REL (Recommended)
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TWA 1 mg/m3 (as Cu)[1] |
IDLH (Immediate danger)
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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). | |
 verify (what is   ?)
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| Infobox references | |
Copper(I) acetylide, or cuprous acetylide, is a chemical compound with the formula Cu2C2. 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 is a reddish-brown explosive powder.
Synthesis
Materials purported to be copper acetylide can be prepared by treating acetylene with a solution of copper(I) chloride and ammonia:
- 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 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 acetylide is the substrate of Glaser coupling for the formation of polyynes. In a typical reaction, a suspension of Cu2C2.H2O in an amoniacal solution is treated with air. The copper is oxidized to Cu2+ and forms a blue soluble complex with the ammonia, leaving behind a black solid residue. The latter has been claimed to consist of carbyne, an elusive allotrope of carbon:[7]
- Cu+ −C(≡C−C≡)nC− Cu+
This interpretation has been disputed.[8]
Freshly prepared copper 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 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≡)nC2− or polycumulene-type anions C(=C=C=)mC4−.[2]
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−)nC 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 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.
See also
- Carbide
- Walter Reppe
- Ethynylation
References
- ↑ 1.0 1.1 1.2 NIOSH Pocket Guide to Chemical Hazards. "#0150". National Institute for Occupational Safety and Health (NIOSH). https://www.cdc.gov/niosh/npg/npgd0150.html.
- ↑ 2.0 2.1 2.2 Franco Cataldo (1999), From dicopper acetylide to carbyne.Polymer International, volume 48, issue 1, pages 15-22. doi:10.1002/(SICI)1097-0126(199901)48:1
- ↑ Cataldo, Franco; Casari, Carlo S. (2007). "Synthesis, Structure and Thermal Properties of Copper and Silver Polyynides and Acetylides". Journal of Inorganic and Organometallic Polymers and Materials 17 (4): 641–651. doi:10.1007/s10904-007-9150-3. ISSN 1574-1443.
- ↑ "Mine Safety and Health Administration (MSHA) - Accident Prevention Program - Miner's Tips - Hazards of Acetylene Gas". http://www.msha.gov/Accident_Prevention/Tips/acetylenegas.htm. Retrieved 2008-06-08.
- ↑ "Copper". Archived from the original on October 1, 2007. https://web.archive.org/web/20071001010729/http://www.ilo.org/encyclopedia/?print&nd=857200158. Retrieved February 8, 2013.
- ↑ "The Safe Use of Copper -Containing Catalysts in Ethylene Plants". http://aiche.confex.com/aiche/s06/preliminaryprogram/abstract_43768.htm. Retrieved 2008-06-08.
- ↑ 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. doi:10.1002/(SICI)1097-0126(199710)44:2
- ↑ H. Kroto (2010), Carbyne and other myths about carbon. RSC Chemistry World, November 2010.
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