Lithium amide

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IUPACName = Lithium amide
OtherNames = Lithamide
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CASNo = 7782-89-0
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Section2 = Chembox Properties
Formula = LiNH₂
MolarMass = 22.96 g/mol
Appearance = white solid
Density = 1.178 g/cm³
MeltingPt = 380 - 400 °C
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Solubility = Reacts vigorously in water
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Lithium amide is an inorganic compound with the chemical formula Li⁺NH₂^-, i.e. it is composed of a lithium cation, and the conjugate base of ammonia. It is a white solid with a tetragonal crystal structure.

Lithium amides

The anionic conjugate bases of amines are known as amides. Thus lithium amide may also refer to lithium salts of amines e.g. Li⁺NR₂^-. An example of a lithium amide is lithium diisopropylamide (LDA), which is quite commonly used.

Lithium amide can be made by adding lithium metal to liquid ammonia:

:2Li + 2NH₃ → 2LiNH₂ + H₂

Lithium amides in general can be similarly formed, substituting ammonia with the appropriate amine:

:2Li + 2R₂NH → 2LiNR₂ + H₂

Lithium amides are very reactive compounds and can act as strong bases. Unless the nitrogen atom is hindered, as in the case of LDA, they can also act as nucleophiles.

Examples

The lithium salt of 2,2,6,6-tetramethylpiperidine has been crystalised as a tetramer:

On the other hand, the lithium derivative of di-(1-phenylethyl)amine crystallises as a trimer:

It is also possible to make mixed oligomers of metal alkoxides and amides. [cite journal | author=K.W. Henderson, D.S. Walther and P.G. Williard | journal=Journal of the American Chemical Society | date= 1995 | volume=117 | issue=33 | pages= 8680–8681 | title=Identification of a Unimetal Complex of Bases by 6Li NMR Spectroscopy and Single-Crystal Analysis | doi=10.1021/ja00138a030 ] These are related to the super bases which are mixtures of metal alkoxides and alkyls. The cyclic oligomers form when the nitrogen of the amide forms a sigma bond to a lithium while the nitrogen lone pair binds to another metal centre.

Other organolithium compounds (such as BuLi) are generally considered to exist in and function via high-order, aggregated species.

ee also

* Sodium amide
* Butyllithium
* Lithium hexamethyldisilazide

References

* "Merck Index", 11th Edition, 5398.

External links