Lithium carbide

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Lithium carbide
Wireframe model of lithium carbide
Identifiers
CAS number 1070-75-3 YesY
PubChem 66115
ChemSpider 59503 YesY
EC number 213-980-1
Jmol-3D images Image 1
Properties
Molecular formula Li
2
C
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 are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 YesY (verify) (what is: YesY/N?)
Infobox references

Lithium carbide, Li
2
C
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
C
2
is one of an extensive range of lithium-carbon compounds which include the lithium-rich Li
4
C
, Li
6
C
2
, Li
8
C
3
, Li
6
C
3
, Li
4
C
3
, Li
4
C
5
, and the graphite intercalation compounds LiC
6
, LiC
12
, and LiC
18
.
Li
2
C
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
2
CO
3
, because of the similarity of its name.

Structure[edit]

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

Preparation and chemistry[edit]

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[edit]

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[edit]

  1. ^ 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. 
  2. ^ H. Moissan Comptes Rendus hebd. Seances Acad. Sci. 122, 362 (1896)
  3. ^ U. Ruschewitz, R. Pöttgen (1999). "Structural Phase Transition in Li
    2
    C
    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.
     
  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