Lithium carbide

Lithium carbide

Names
Preferred IUPAC name Lithium carbide
Systematic IUPAC name Dilithium(1+) ethyne
Other names Dilithium acetylide Lithium dicarbon Lithium percarbide
Identifiers
CAS Registry Number	1070-75-3 Y
ChemSpider	59503 Y
EC number	213-980-1
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
Jmol-3D images	Image
PubChem	66115
SMILES [Li+].[Li+].[C-]#[C-]
Properties
Chemical formula	Li 2C 2
Molar mass	37.9034 g/mol
Density	1.3 g/cm³[1]
Melting point	> 550°C
Solubility	insoluble in organic solvents
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

Lithium carbide, Li
2C
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
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.
Li
2C
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^[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, Li
2CO
3, because of the similarity of its name.

Structure

Li
2C
2 is a salt formulated 2Li+
C
22−
. It has a structure similar to that of rubidium peroxide|Rb
2O
2 and caesium peroxide|Cs
2O
2. At high temperatures Li
2C
2 transforms reversibly to a cubic anti-fluorite structure.^[3]

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

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