Lithium carbide

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Lithium carbide
Lithium carbide.png
Names
Preferred IUPAC name
Lithium acetylide
Systematic IUPAC name
Lithium ethynediide
Other names
  • Dilithium acetylide
  • Lithium dicarbon
  • Lithium percarbide
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.012.710 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 213-980-1
PubChem CID
UNII
  • InChI=1S/C2.2Li/c1-2;;/q-2;2*+1 Yes check.svgY
    Key: ARNWQMJQALNBBV-UHFFFAOYSA-N Yes check.svgY
  • 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
  • [Li+].[Li+].[C-]#[C-]
Properties
Li2C2
Molar mass 37.9034 g/mol
AppearancePowder
Density 1.3 g/cm3 [1]
Melting point 452°C [2]
Reacts
Solubility insoluble in organic solvents
Related compounds
Related compounds
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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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.

Contents

Li2C2 is the most thermodynamically-stable lithium-rich carbide [3] and the only one that can be obtained directly from the elements. It was first produced by Moissan, in 1896 [4] who reacted coal with lithium carbonate.

Li2CO3 + 4 C → Li2C2 + 3 CO

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.

Preparation and chemistry

In the laboratory samples may be prepared by treating acetylene with a solution of lithium in ammonia, on −40°C, with creation of adduct of Li2C2· C2H2 ·2NH3 that decomposes in stream of hydrogen at room temperature giving white powder of Li2C2.

C2H2 + 2 Li → Li2C2 + H2

Samples prepared in this manner generally are poorly crystalline. Crystalline samples may be prepared by a reaction between molten lithium and graphite at over 1000 °C. [3] Li2C2 can also be prepared by reacting CO2 with molten lithium.

10 Li + 2 CO2 → Li2C2 + 4 Li2O

Other method for production of Li2C2 is heating of metallic lithium in atmosphere of ethylene.

6 Li + C2H4 → Li2C2 + 4 LiH

Lithium carbide hydrolyzes readily to form acetylene:

Li2C2 + 2 H2O → 2 LiOH + C2H2

Lithium hydride reacts with graphite at 400°C forming lithium carbide.

2 LiH + 4 C → Li2C2 + C2H2

Also Li2C2 can be formed when organometallic compound n-butyllithium reacts with acetylene in THF or Et2O used as a solvent, reaction is rapid and highly exothermic.

C2H2 + 2 CH3CH2CH2CH2Li → Li2C2 + 2 CH3CH2CH2CH3

Lithium carbide reacts with acetylene in liquid ammonia rapidly to give a clear solution of lithium hydrogen acetylide.

Li+[C≡C]Li+ + HC≡CH → 2 Li+[C≡CH]

Preparation of the reagent in this way sometimes improves the yield in an ethynylation over that obtained with reagent prepared from lithium and acetylene.

Structure

Li2C2 is a Zintl phase compound and exists as a salt, with the formula [Li+]2[C≡C]. Its reactivity, combined with the difficulty in growing suitable single crystals, has made the determination of its crystal structure difficult. It adopts a distorted anti-fluorite crystal structure, similar to that of rubidium peroxide (Rb2O2) and caesium peroxide (Cs2O2). Each lithium atom is surrounded by six carbon atoms from 4 different acetylide anions, with two acetylides co-ordinating side -on and the other two end-on. [3] [5] The observed relatively short C-C distance of 120 pm indicates the presence of a C≡C triple bond. At high temperatures Li2C2 transforms reversibly to a cubic anti-fluorite structure. [6]

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. [7] The outcome is the same: Li2C2 is produced, which can then be used to create species easy to use in mass spectroscopy, like acetylene and benzene. [8] Note that lithium nitride may be formed and this produces ammonia when hydrolyzed, which contaminates the acetylene gas.

Related Research Articles

<span class="mw-page-title-main">Acetylene</span> Hydrocarbon compound (HC≡CH)

Acetylene is the chemical compound with the formula C2H2 and structure H−C≡C−H. It is a hydrocarbon and the simplest alkyne. This colorless gas is widely used as a fuel and a chemical building block. It is unstable in its pure form and thus is usually handled as a solution. Pure acetylene is odorless, but commercial grades usually have a marked odor due to impurities such as divinyl sulfide and phosphine.

<span class="mw-page-title-main">Calcium carbide</span> Chemical compound

Calcium carbide, also known as calcium acetylide, is a chemical compound with the chemical formula of CaC2. Its main use industrially is in the production of acetylene and calcium cyanamide.

In organometallic chemistry, acetylide refers to chemical compounds with the chemical formulas MC≡CH and MC≡CM, where M is a metal. The term is used loosely and can refer to substituted acetylides having the general structure RC≡CM. Acetylides are reagents in organic synthesis. The calcium acetylide commonly called calcium carbide is a major compound of commerce.

Iodine pentafluoride is an interhalogen compound with chemical formula IF5. It is one of the fluorides of iodine. It is a colorless liquid, although impure samples appear yellow. It is used as a fluorination reagent and even a solvent in specialized syntheses.

<span class="mw-page-title-main">Silver acetylide</span> Chemical compound

Silver acetylide is an inorganic chemical compound with the formula Ag2C2, a metal acetylide. The compound can be regarded as a silver salt of the weak acid, acetylene. The salt's anion consists of two carbon atoms linked by a triple bond, thus, its structure is [Ag+]2[C≡C]. The alternate name "silver carbide" is rarely used, although the analogous calcium compound CaC2 is called calcium carbide. Silver acetylide is a primary explosive.

Copper(I) acetylide, Kupfercarbid or cuprous acetylide, is a chemical compound with the formula Cu2C2. Although never characterized by X-ray crystallography, the material has been claimed at least since 1856. One form is claimed to be a monohydrate with formula Cu
2
C
2
.H
2
O
is a reddish-brown explosive powder.

<span class="mw-page-title-main">Lithium tetrachloroaluminate</span> Chemical compound

Lithium tetrachloroaluminate is an inorganic compound with the formula Li[AlCl4]. It consists of lithium cations Li+ and tetrahedral tetrachloroaluminate anions [AlCl4].

<span class="mw-page-title-main">Acetylenediol</span> Chemical compound

Acetylenediol, or ethynediol, is a chemical substance with formula HO−C≡C−OH (an ynol). It is the diol of acetylene. Acetylenediol is unstable in the condensed phase, although its tautomer glyoxal (CHO)2 is well known.

<span class="mw-page-title-main">Potassium amide</span> Chemical compound

Potassium amide is an inorganic compound with the chemical formula KNH2. Like other alkali metal amides, it is a white solid that hydrolyzes readily. It is a strong base.

The nitridoborates are chemical compounds of boron and nitrogen with metals. These compounds are typically produced at high temperature by reacting hexagonal boron nitride with metal nitrides or by metathesis reactions involving nitridoborates. A wide range of these compounds have been made involving lithium, alkaline earth metals and lanthanides, and their structures determined using crystallographic techniques such as X-ray crystallography. Structurally one of their interesting features is the presence of polyatomic anions of boron and nitrogen where the geometry and the B–N bond length have been interpreted in terms of π-bonding.

<span class="mw-page-title-main">Barium carbide</span> Chemical compound

Barium carbide is a chemical compound in the carbide family having the chemical formula BaC2.

<span class="mw-page-title-main">Vanadium(II) iodide</span> Chemical compound

Vanadium(II) iodide is the inorganic compound with the formula VI2. It is a black micaceous solid. It adopts the cadmium iodide structure, featuring octahedral V(II) centers. The hexahydrate [V(H2O)6]I2, an aquo complex, is also known. It forms red-violet crystals. The hexahydrate dehydrates under vacuum to give a red-brown tetrahydrate with the formula V(H2O)4I2.

<span class="mw-page-title-main">Hydromelonic acid</span> Chemical compound

Hydromelonic acid, is an elusive chemical compound with formula C
9
H
3
N
13
or (HNCN)
3
(C
6
N
7
)
, whose molecule would consist of a heptazine H3(C
6
N
7
)
molecule, with three cyanamido groups H–N=C=N– or N≡C–NH– substituted for the hydrogen atoms.

The inorganic imide is an inorganic chemical compound containing

<span class="mw-page-title-main">Europium(II) chloride</span> Chemical compound

Europium(II) chloride is an inorganic compound with a chemical formula EuCl2. When it is irradiated by ultraviolet light, it has bright blue fluorescence.

A chloride nitride is a mixed anion compound containing both chloride (Cl) and nitride ions (N3−). Another name is metallochloronitrides. They are a subclass of halide nitrides or pnictide halides.

Phosphide carbides or carbide phosphides are compounds containing anions composed of carbide (C4−) and phosphide (P3−). They can be considered as mixed anion compounds. Related compounds include phosphide silicides, germanide phosphides, arsenide carbides, nitride carbides and silicide carbides.

An iodide nitride is a mixed anion compound containing both iodide (I) and nitride ions (N3−). Another name is metalloiodonitrides. They are a subclass of halide nitrides or pnictide halides. Some different kinds include ionic alkali or alkaline earth salts, small clusters where metal atoms surround a nitrogen atom, layered group 4 element 2-dimensional structures, and transition metal nitrido complexes counter-balanced with iodide ions. There is also a family with rare earth elements and nitrogen and sulfur in a cluster.

Carbide chlorides are mixed anion compounds containing chloride anions and anions consisting entirely of carbon. In these compounds there is no bond between chlorine and carbon. But there is a bond between a metal and carbon. Many of these compounds are cluster compounds, in which metal atoms encase a carbon core, with chlorine atoms surrounding the cluster. The chlorine may be shared between clusters to form polymers or layers. Most carbide chloride compounds contain rare earth elements. Some are known from group 4 elements. The hexatungsten carbon cluster can be oxidised and reduced, and so have different numbers of chlorine atoms included.

Strontium carbide (also more precisely known as strontium acetylide or strontium dicarbide) is a salt with chemical formula SrC2. It was first synthesized by Moissan in 1894.

References

  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. Savchenko, A.P.; Kshnyakina, S.A.; H.-Majorova, A.F. (1997). "Thermal properties of lithium carbide and lithium intercalation compounds of graphite". Neorganicheskie Materialy . 33 (11): 1305–1307.
  3. 1 2 3 Ruschewitz, Uwe (September 2003). "Binary and ternary carbides of alkali and alkaline-earth metals". Coordination Chemistry Reviews. 244 (1–2): 115–136. doi:10.1016/S0010-8545(03)00102-4.
  4. H. Moissan Comptes Rendus hebd. Seances Acad. Sci. 122, 362 (1896)
  5. Juza, Robert; Opp, Karl (November 1951). "Metallamide und Metallnitride, 24. Mitteilung. Die Kristallstruktur des Lithiumamides". Zeitschrift für anorganische und allgemeine Chemie (in German). 266 (6): 313–324. doi:10.1002/zaac.19512660606.
  6. 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.
  7. 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: 47–48. doi:10.1007/BF02146038. S2CID   31319813.
  8. University of Zurich Radiocarbon Laboratory webpage Archived 2009-08-01 at the Wayback Machine