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Sodium hydride

Sodium hydride
Sodium hydride
Sodium-hydride-3D-vdW.png
Identifiers
7646-69-7 YesY
3D model (Jmol) Interactive image
ChemSpider 23144 YesY
ECHA InfoCard 100.028.716
EC Number 231-587-3
PubChem 24758
Properties
NaH
Molar mass 23.99771 g/mol
Appearance white or grey solid
Density 1.396 g/cm3
Melting point 300 °C (572 °F; 573 K) decomposes
Reacts with water
Solubility insoluble in ammonia, benzene, CCl4, CS2
1.470
Structure
fcc (NaCl), cF8
Fm3m, No. 225
a = 498 pm
Octahedral (Na+)
Octahedral (H−)
Thermochemistry
36.4 J/mol K
40 J·mol−1·K−1
−56.4 kJ·mol−1
-33.5 kJ/mol
Hazards
Safety data sheet External MSDS
GHS pictograms Water-react. 1
GHS signal word DANGER
H260
NFPA 704
Flammability code 3: Liquids and solids that can be ignited under almost all ambient temperature conditions. Flash point between 23 and 38 °C (73 and 100 °F). E.g., gasoline) 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
Flash point combustible
Related compounds
Other cations
Lithium hydride
Potassium hydride
Related compounds
 Sodium borohydride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N  (what is YesYN ?)
Infobox references

Sodium hydride is the chemical compound with the empirical formula NaH. This alkali metal hydride is primarily used as a strong, yet combustible base in organic synthesis. NaH is representative of the saline hydrides, meaning it is a salt-like hydride, composed of Na+ and H− ions, in contrast to the more molecular hydrides such as borane, methane, ammonia and water. It is an ionic material that is insoluble in organic solvents (although 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.

NaH is produced by the direct reaction of hydrogen and liquid sodium. Pure NaH is colorless, although samples generally appear grey. NaH is ca. 40% denser than Na (0.968 g/cm3).

NaH, like LiH, KH, RbH, and CsH, adopts the NaCl 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.

A very unusual situation occurs in a compound dubbed "inverse sodium hydride", which contains Na− and H+ ions. Na− is an alkalide, and this compound differs from ordinary sodium hydride in having a much higher energy content due to the net displacement of two electrons from hydrogen to sodium. A derivative of this "inverse sodium hydride" arises in the presence of the base adamanzane. This molecule irreversibly encapsulates the H+ and shields it from interaction with the alkalide Na−. Theoretical work has suggested that even an unprotected protonated tertiary amine complexed with the sodium alkalide might be metastable under certain solvent conditions, though the barrier to reaction would be small and finding a suitable solvent might be difficult.


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