Lithium amide

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Lithium amide
Identifiers
CAS number 7782-89-0 YesY
PubChem 24532
ChemSpider 22939 YesY
Jmol-3D images Image 1
Properties
Molecular formula LiNH2
Molar mass 22.96 g/mol
Appearance white solid
Density 1.178 g/cm3
Melting point 375 °C (707 °F; 648 K)
Boiling point 430 °C (806 °F; 703 K) decomp
Solubility in water reacts
Solubility slightly soluble in ethanol
insoluble in ammonia
Thermochemistry
Std enthalpy of
formation
ΔfHo298
-182 kJ/mol
Hazards
NFPA 704
Flammability code 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g., canola oil Health code 3: Short exposure could cause serious temporary or residual injury. E.g., chlorine gas Reactivity code 2: Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. E.g., phosphorus Special hazard W: Reacts with water in an unusual or dangerous manner. E.g., cesium, sodiumNFPA 704 four-colored diamond
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

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[edit]

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[edit]

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[edit]

References[edit]

  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. 
  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. 

External links[edit]