Lithium carbide

Template:Chembox new Lithium carbide, Li₂C₂, often known as dilithium acetylide, is a chemical compound of lithium and carbon. 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 who reacted coal with lithium carbonate. The other lithium rich compounds are produced by reacting lithium vapour with chlorinated hydrocarbons e.g. CCl₄. Lithium carbide is sometimes confused with the drug lithium carbonate, Li₂CO₃, because of the similarity of its name.

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.

Structure

Li₂C₂ is an ionic salt and is formulated 2Li+ C₂²⁻. It has a similar structure to Rb₂O₂ and Cs₂O₂. At high temperatures Li₂C₂ 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 prior 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. Note that lithium nitride may be formed and this produces ammonia when hydrolysed, which contaminates the acetylene gas.

General references

• Structural Phase Transition in Li₂C₂ U. Ruschewitz R Pottgen Zeitschrift für anorganische und allgemeine Chemie Volume 625, Issue 10 , Pages 1599 - 1603