Chemistry:Dilithium acetylide
LiC≡CLi
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| Names | |
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| Preferred IUPAC name
Lithium acetylide | |
| Systematic IUPAC name
Lithium ethynediide | |
Other names
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3D model (JSmol)
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PubChem CID
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| Properties | |
| Li 2C 2 | |
| Molar mass | 37.9034 g/mol |
| Appearance | Powder |
| Density | 1.3 g/cm3[1] |
| Melting point | 452°C[2] |
| Reacts | |
| Solubility | insoluble in organic solvents |
| Related compounds | |
Related compounds
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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 | |
Dilithium acetylide is an organometallic compound with the formula Li2C2. It is typically derived by double deprotonation of acetylene. X-ray crystallography confirms the presence of C≡C subunits attached to lithium, resulting in a polymeric structure.[3] Li
2C
2 is one of an extensive range of lithium-carbon compounds, which include the lithium-rich Li
4C, Li
6C
2, Li
8C
3, Li
6C
3, Li
4C
3, Li
4C
5, and the graphite intercalation compounds LiC
6, LiC
12, and LiC
18. It is an intermediate compound produced during radiocarbon dating procedures.
Li
2C
2 is the most thermodynamically-stable lithium-rich carbide[3] and the only one that can be obtained directly from the elements. It was first produced by Moissan, in 1896[4] who reacted coal with lithium carbonate.
- Li
2CO
3 + 4 C → Li
2C
2 + 3 CO
The other lithium-rich compounds are produced by reacting lithium vapor with chlorinated hydrocarbons, e.g. CCl
4. Lithium carbide is sometimes confused with the drug lithium carbonate, Li
2CO
3, because of the similarity of its name.
Preparation and reactions
In the laboratory samples may be prepared by treating acetylene with butyl lithium:[5]
- C
2H
2 + 2 BuLi → Li
2C
2 + BuH
Instead of butyl lithium, a solution of lithium in ammonia can be used to prepare Li
2C
2. In this case, a transient adduct Li
2C
2 · C
2H
2 · 2NH
3 if formed. It decomposes with release of ammonia at room temperature.
Samples prepared from acetylene generally are poorly crystalline. Crystalline samples may be prepared by a reaction between molten lithium and graphite at over 1000 °C.[3] Li
2C
2 can also be prepared by reacting CO
2 with molten lithium.[citation needed]
- 10 Li + 2 CO
2 → Li
2C
2 + 4 Li
2O
Other method for production of Li
2C
2 is heating of metallic lithium in atmosphere of ethylene. Lithium hydride is a coproduction:
- 6 Li + C
2H
4 → Li
2C
2 + 4 LiH
Lithium carbide hydrolyzes readily to form acetylene as well as Lithium hydroxide:
- Li
2C
2 + 2 H
2O → 2 LiOH + C
2H
2
Lithium hydride reacts with graphite at 400°C forming lithium carbide.[6]
- 2 LiH + 4 C → Li
2C
2 + C
2H
2
Lithium carbide reacts with acetylene in liquid ammonia rapidly to give a lithium hydrogen acetylide.
- LiC≡CLi + HC≡CH → 2 LiC≡CH
Preparation of the reagent in this way sometimes improves the yield in an ethynylation over that obtained with reagent prepared from lithium and acetylene.[citation needed]
Structure
Li
2C
2 could be viewed as a Zintl phase. It is not a salt. It adopts a distorted anti-fluorite crystal structure, similar to that of rubidium peroxide (Rb
2O
2) and caesium peroxide (Cs
2O
2). Each lithium atom is surrounded by six carbon atoms from 4 different acetylide anions, with two acetylides co-ordinating side -on and the other two end-on.[3][7] The relatively short C-C distance of 120 pm indicates the presence of a C≡C triple bond. At high temperatures Li
2C
2 transforms reversibly to a cubic anti-fluorite structure.[8]
Use in radiocarbon dating
There are a number of procedures employed, some that burn the sample producing CO
2 that is then reacted with lithium, and others where the carbon containing sample is reacted directly with lithium metal.[9] The outcome is the same: Li
2C
2 is produced, which can then be used to create species easy to use in mass spectroscopy, like acetylene and benzene.[10] Note that lithium nitride may be formed and this produces ammonia when hydrolyzed, which contaminates the acetylene gas.
References
- ↑ R. Juza; V. Wehle; H.-U. Schuster (1967). "Zur Kenntnis des Lithiumacetylids". Zeitschrift für anorganische und allgemeine Chemie 352 (5–6): 252. doi:10.1002/zaac.19673520506.
- ↑ Savchenko, A.P.; Kshnyakina, S.A.; H.-Majorova, A.F. (1997). "Thermal properties of lithium carbide and lithium intercalation compounds of graphite". Neorganicheskie Materialy 33 (11): 1305–1307.
- ↑ 3.0 3.1 3.2 3.3 Ruschewitz, Uwe (September 2003). "Binary and ternary carbides of alkali and alkaline-earth metals". Coordination Chemistry Reviews 244 (1–2): 115–136. doi:10.1016/S0010-8545(03)00102-4.
- ↑ H. Moissan Comptes Rendus hebd. Seances Acad. Sci. 122, 362 (1896)
- ↑ Walton, D.R.M.; Waugh, F. (1972). "Friedel–Crafts reactions of bis(trimethylsilyl)polyynes with acyl chlorides; a useful route to terminal-alkynyl ketones". Journal of Organometallic Chemistry 37: 45–56. doi:10.1016/S0022-328X(00)89260-8.
- ↑ Konar, Sumit; Häusserman, Ulrich; Svensson, Gunnar (2015-04-14). "Intercalation Compounds from LiH and Graphite: Relative Stability of Metastable Stages and Thermodynamic Stability of Dilute Stage Id". Chemistry of Materials 27 (7): 2566–2575. doi:10.1021/acs.chemmater.5b00235. ISSN 0897-4756. https://doi.org/10.1021/acs.chemmater.5b00235.
- ↑ Juza, Robert; Opp, Karl (November 1951). "Metallamide und Metallnitride, 24. Mitteilung. Die Kristallstruktur des Lithiumamides" (in German). Zeitschrift für anorganische und allgemeine Chemie 266 (6): 313–324. doi:10.1002/zaac.19512660606.
- ↑ U. Ruschewitz; R. Pöttgen (1999). "Structural Phase Transition in Li2C2". Zeitschrift für anorganische und allgemeine Chemie 625 (10): 1599–1603. doi:10.1002/(SICI)1521-3749(199910)625:10<1599::AID-ZAAC1599>3.0.CO;2-J.
- ↑ Swart E.R. (1964). "The direct conversion of wood charcoal to lithium carbide in the production of acetylene for radiocarbon dating". Cellular and Molecular Life Sciences 20: 47–48. doi:10.1007/BF02146038.
- ↑ University of Zurich Radiocarbon Laboratory webpage
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