View source for Lithium carbide

{{Chembox new
|   Name = '''Lithium carbide'''
|   ImageFile = lithium carbide.png
|   ImageSize = 120px
|   ImageName = Lithium carbide
|   OtherNames = dilithium acetylide
| Section1 = {{Chembox Identifiers
|   CASNo = 1070-75-3
  }}
| Section2 = {{Chembox Properties
|   Formula = Li<sub>2</sub>C<sub>2</sub>
|   MolarMass = 37.9034 g/mol
|   Density = 1.3 g/cm³<ref>''Zur Kenntnis des Lithiumacetylids''  R Juza V Wehle H-U Schuster Z Anorg Allgem chem.  (1967) 352, 252</ref> 
|   Solvent = 
|   SolubleOther = 
|   MeltingPt = > 550°C
|   BoilingPt = }}
}}
'''Lithium carbide''', Li<sub>2</sub>C<sub>2</sub>, often known as dilithium acetylide, is a chemical compound of [[lithium]] and [[carbon]]. It is an intermediate compound produced during [[radiocarbon dating]] procedures. Li<sub>2</sub>C<sub>2</sub> is one of an extensive range of lithium<nowiki>&minus;</nowiki> carbon compounds which include the lithium rich; Li<sub>4</sub>C, Li<sub>6</sub>C<sub>2</sub>, Li<sub>8</sub>C<sub>3</sub>, Li<sub>6</sub>C<sub>3</sub>, Li<sub>4</sub>C<sub>3</sub>, Li<sub>4</sub>C<sub>5</sub>, and the [[graphite intercalation compound]]s LiC<sub>6</sub>, LiC<sub>12</sub>, and LiC<sub>18</sub>.<br /> Li<sub>2</sub>C<sub>2</sub> 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 [[Henri Moissan|Moissan]], in 1896<ref> H. Moissan Comptes Rendus hebd. Seances Acad. Sci. 122, 362 (1896)</ref> who reacted coal with [[lithium carbonate]]. The other lithium rich compounds are produced by reacting lithium vapour with chlorinated hydrocarbons e.g. [[carbon tetrachloride|CCl<sub>4</sub>]].
Lithium carbide is sometimes confused  with the drug [[lithium carbonate]], Li<sub>2</sub>CO<sub>3</sub>, 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. Li<sub>2</sub>C<sub>2</sub> can also be prepared by reacting CO<sub>2</sub> with molten lithium. It is reactive and hydrolyses very readily to form [[acetylene]] gas , C<sub>2</sub>H<sub>2</sub>, and [[LiOH]].

===Structure===
Li<sub>2</sub>C<sub>2</sub> is an ionic salt and is formulated 2Li+ C<sub>2</sub><sup>2<nowiki>&minus;</nowiki></sup>. It has a similar structure to Rb<sub>2</sub>O<sub>2</sub> and Cs<sub>2</sub>O<sub>2</sub>. At high temperatures Li<sub>2</sub>C<sub>2</sub> 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 [[carbon dioxide|CO<sub>2</sub>]] prior that is then reacted  with lithium, and others where the carbon containing sample is reacted directly with lithium metal.<ref>''The direct conversion of wood charcoal to lithium carbide in the production of acetylene for radiocarbon dating'' Swart E.R., Cellular and Molecular Life Sciences  Volume 20, Number 1 (1964), 47-48  DOI: 10.1007/BF02146038</ref>. The outcome is the same, Li<sub>2</sub>C<sub>2</sub> 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 Li<sub>2</sub>C<sub>2</sub>''  U. Ruschewitz R Pottgen Zeitschrift für  anorganische und allgemeine Chemie Volume  625, Issue 10 , Pages 1599 - 1603

==Footnotes==
{{reflist|2}}

[[Category:Lithium compounds]]
[[Category:carbides]]

[[pt:Carbeto de lítio]]