|Preferred IUPAC name
|Systematic IUPAC name
3D model (Jmol)
|Molar mass||37.9034 g/mol|
|Melting point||> 550°C|
|Solubility||insoluble in organic solvents|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
|what is ?)(|
Lithium carbide, Li
2, often known as dilithium acetylide, is a chemical compound of lithium and carbon, an acetylide. It is an intermediate compound produced during radiocarbon dating procedures. Li
2 is one of an extensive range of lithium-carbon compounds which include the lithium-rich Li
5, and the graphite intercalation compounds LiC
12, and LiC
2 is the most thermodynamically-stable lithium-rich compound and the only one that can be obtained directly from the elements. It was first produced by Moissan, in 1896 who reacted coal with lithium carbonate. The other lithium-rich compounds are produced by reacting lithium vapor with chlorinated hydrocarbons, e.g. CCl4.
Lithium carbide is sometimes confused with the drug lithium carbonate, Li
3, because of the similarity of its name.
Preparation and chemistry
In the laboratory samples may be prepared by bubbling acetylene through a solution of lithium dissolved in liquid ammonia.
2 + 2 Li → Li
2 + H2
Lithium carbide prepared in this manner generally has very poor crystallinity, being essentially amorphous. Purer samples may be prepared by a reaction between molten lithium and graphite at over 1000 °C. Li2C2 can also be prepared by reacting CO2 with molten lithium.
2 is a Zintl phase compound and exists as a salt, 2Li+
. Its reactivity, combined with the difficulty in growing suitable single crystals, has made the determination of its crystal structure difficult. It adopts a distorted anti-fluorite crystal structure, similar to that of rubidium peroxide (Rb
2) and caesium peroxide (Cs
2). Each Li atom is surrounded by six carbon atoms from 4 different acetylides, with two acetylides co-ordinating side -on and the other two end-on. The observed C-C distance of 120 pm indicates the presence of a C≡C triple bond. At high temperatures Li
2 transforms reversibly to a cubic anti-fluorite structure.
Use in radiocarbon dating
There are a number of procedures employed, some that burn the sample producing CO2 that is then reacted with lithium, and others where the carbon containing sample is reacted directly with lithium metal. The outcome is the same: Li2C2 is produced, which can then be used to create species easy to mass, like acetylene and benzene. Note that lithium nitride may be formed and this produces ammonia when hydrolyzed, which contaminates the acetylene gas.
- 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.
- 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)
- Juza, Robert; Opp, Karl (November 1951). "Metallamide und Metallnitride, 24. Mitteilung. Die Kristallstruktur des Lithiumamides". Zeitschrift für anorganische und allgemeine Chemie (in German). 266 (6): 313–324. doi:10.1002/zaac.19512660606.
- U. Ruschewitz; R. Pöttgen (1999). "Structural Phase Transition in Li
2". 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. doi:10.1007/BF02146038.
- University of Zurich Radiocarbon Laboratory webpage