Sodium hydride



Sodium hydride
Identifiers
CAS number 7646-69-7
Properties
Molecular formula NaH
Molar mass 23.99 g/mol
Appearance colorless to gray solid
Density 1.396 g/cm³, solid
Melting point

800 °C with decomp.

Solubility in water Reacts
Hazards
MSDS External MSDS
EU classification Flammable (F)
NFPA 704
3
3
2
 
R-phrases R15
S-phrases S42
Related Compounds
Other cations Potassium hydride
Related compounds Sodium borohydride
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)
Infobox disclaimer and references

Sodium hydride is the ammonia and water. It is an ionic material that is insoluble in organic solvents (although apparently soluble in molten Na), consistent with the fact that H− remains an unknown anion in solution. Because of the insolubility of NaH, all reactions involving NaH occur at the surface of the solid.

Basic properties and structure

NaH is produced by the direct reaction of hydrogen and liquid sodium.[1] Pure NaH is colorless, although samples generally appear gray. NaH is ca. 40% more dense than Na (0.968 g/cm³).

NaH, like LiH, crystal structure. In this motif, each Na+ ion is surrounded by six H− centers in an octahedral geometry. The ionic radii of H− (146 pm in NaH) and F− (133 pm) are comparable, as judged by the Na−H and Na−F distances.[2]

Applications in organic synthesis

First and foremost, NaH is a base of wide scope and utility in organic chemistry.[3] It is capable of deprotonating a wide range of even weak thiols.

NaH most notably is employed to deprotonate carbon acids such as 1,3-dicarbonyls and analogues such as DMSO.

In an illustrative reaction, NaH is used to make ylides, which in turn are used to convert ketones into epoxides. Also, it is used in one synthesis of the dithioimidodiphosphinates which are an interesting class of acac like ligands in inorganic chemistry.

NaH reduces Si-Si and S-S bonds in disilanes and disulfides. Otherwise, NaH rarely exhibits the reducing qualities of Na itself.

Practical considerations

Sodium hydride is sold by many chemical suppliers such as THF; THF resists deprotonation but solvates many organo sodium compounds.

Safety

NaH can ignite in air, especially upon contact with water. The reaction gives off base.

References

  1. ^ Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.
  2. ^ Wells, A.F. (1984). Structural Inorganic Chemistry, Oxford: Clarendon Press
  3. ^ Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. DOI: 10.1002/047084289.
 
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