Lithium carbide

Lithium carbide
Preferred IUPAC name Lithium carbide
Systematic name Dilithium(1+) ethyne
Other names Dilithium acetylide Lithium dicarbon Lithium percarbide
Identifiers
CAS number	1070-75-3
ChemSpider	59503 Y
EC number	213-980-1
Jmol-3D images	Image 1
SMILES [Li+].[Li+].[C-]#[C-]
InChI InChI=1S/C2.2Li/c1-2;;/q-2;2*+1 Y Key: ARNWQMJQALNBBV-UHFFFAOYSA-N Y InChI=1S/C2.2Li/c1-2;;/q-2;2*+1 Key: ARNWQMJQALNBBV-UHFFFAOYSA-N InChI=1/C2.2Li/c1-2;;/q-2;2*+1 Key: ARNWQMJQALNBBV-UHFFFAOYAB
Properties
Molecular formula	Li2C2
Molar mass	37.9034 g/mol
Density	1.3 g/cm³[1]
Melting point	> 550°C
Y carbide (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Lithium carbide, Li₂C₂, 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. Li₂C₂ is one of an extensive range of lithium-carbon compounds which include the lithium-rich Li₄C, Li₆C₂, Li₈C₃, Li₆C₃, Li₄C₃, Li₄C₅, and the graphite intercalation compounds LiC₆, LiC₁₂, and LiC₁₈.
Li₂C₂ is the thermodynamically-stable lithium-rich compound and is the only one of them that can be obtained directly from the elements. It was first produced by Moissan, in 1896^[2] 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, Li₂CO₃, because of the similarity of its name.

Structure

Li₂C₂ is a salt formulated 2Li⁺C₂²⁻. It has a similar structure to that of edit] Preparation and chemistry

To prepare pure samples in the laboratory molten lithium + graphite are reacted at high temperature. Li₂C₂ can also be prepared by reacting CO₂ with molten lithium. It is reactive and hydrolyses very readily to form acetylene gas, C₂H₂, and LiOH.

Use in radiocarbon dating

Main article: 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.^[4] The outcome is the same: Li₂C₂ is produced, which can then be used to create species easy to mass, like acetylene and benzene.^[5] Note that lithium nitride may be formed and this produces ammonia when hydrolyzed, which contaminates the acetylene gas.

References

1. ^ R. Juza; V. Wehle; H.-U. Schuster (1967). "Zur Kenntnis des Lithiumacetylids". Zeitschrift für anorganische und allgemeine Chemie 352: 252. doi:10.1002/zaac.19673520506. 
2. ^ H. Moissan Comptes Rendus hebd. Seances Acad. Sci. 122, 362 (1896)
3. ^ 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. 
4. ^ 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. 
5. ^ University of Zurich Radiocarbon Laboratory webpage