Lithium amide

Lithium amide
Names
IUPAC name
Lithium amide
Other names
Lithamide
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.029.062
Properties
LiNH
2
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) decomposes
reacts
Solubility slightly soluble in ethanol
insoluble in ammonia
Thermochemistry
-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 oilHealth code 3: Short exposure could cause serious temporary or residual injury. E.g., chlorine gasReactivity code 2: Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. E.g., phosphorusSpecial hazard W: Reacts with water in an unusual or dangerous manner. E.g., cesium, sodiumNFPA 704 four-colored diamond
1
3
2
Except where otherwise noted, 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

The anionic conjugate bases of amines are known as amides. Thus a lithium amide may also refer to any compound in the class of the lithium salt of an amine. These chemicals have the general form Li+NR2−, with the chemical lithium amide itself as the parent structure. Common lithium amides include lithium diisopropylamide (LDA), Lithium tetramethylpiperidide (LiTMP), and lithium hexamethyldisilazide (LiHMDS).


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, they can also act as nucleophiles.

Examples

Lithium tetramethylpiperidide has been crystallised as a tetramer.[1] On the other hand, the lithium derivative of bis(1-phenylethyl)amine crystallises as a trimer:[2]

Tetrameric lithium tetramethylpiperidide
Trimeric lithium bis(1-phenylethyl)amide

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; 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; R. Snaith (1999). "Structural studies of the chiral lithium amides [{PhC(H)Me}2NLi] and [PhCH2{PhC(H)Me}NLi·THF] derived from α-methylbenzylamine". Dalton Transactions: 4063–4068. doi:10.1039/A904725E.
  3. ↑ K.W. Henderson, D.S. Walther & 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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