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Lithium amide

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Lithium amide
Names
IUPAC name
Lithium amide
Other names
Lithamide
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.029.062 Edit this at Wikidata
  • InChI=1S/Li.H2N/h;1H2/q+1;-1 checkY
    Key: AFRJJFRNGGLMDW-UHFFFAOYSA-N checkY
  • InChI=1/Li.H2N/h;1H2/q+1;-1
    Key: AFRJJFRNGGLMDW-UHFFFAOYAO
  • [Li+].[NH2-]
Properties
LiNH2
Molar mass 22.96 g/mol
Appearance white solid
Density 1.178 g/cm3
Melting point 390 °C
Boiling point 430 °C
decomposes
Hazards
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 1: Exposure would cause irritation but only minor residual injury. E.g. turpentineFlammability 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g. canola oilInstability 2: Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. E.g. white phosphorusSpecial hazard W: Reacts with water in an unusual or dangerous manner. E.g. sodium, sulfuric acid
1
1
2
W
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
checkY verify (what is checkY☒N ?)

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 crystallised as a tetramer:

Tetrameric lithium amide.[1]

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

Trimeric lithium amide.[2]

It is also possible to make mixed oligomers of metal alkoxides and amides. [3] These are related to the superbases 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.

See also

References

  1. ^ M.F. Lappert, M.J. Slade, A. Singh, J.L. Atwood, R.D. Rogers and R. Shakir (1983). "Structure and reactivity of sterically hindered lithium amides and their diethyl etherates: crystal and molecular structures of [Li{N(SiMe3)2}(OEt2)]2 and tetrakis(2,2,6,6-tetramethylpiperidinatolithium)". Journal of the American Chemical Society. 105 (2): 302–304. doi:10.1021/ja00340a031.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  2. ^ D.R. Armstrong, K.W. Henderson, A.R. Kennedy, W.J. Kerr, F.S. Mair, J.H. Moir, P.H. Moran and R. Snaith, Dalton Transactions, 1999, 4063.
  3. ^ K.W. Henderson, D.S. Walther and P.G. Williard (1995). "Identification of a Unimetal Complex of Bases by 6Li NMR Spectroscopy and Single-Crystal Analysis". Journal of the American Chemical Society. 117 (33): 8680–8681. doi:10.1021/ja00138a030.


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