Sodium aluminium hydride

Sodium aluminium hydride

Names
IUPAC name Sodium aluminium hydride
Other names Sodium tetrahydroaluminate
Identifiers
CAS Number	13770-96-2 Y
EC Number	237-400-1
Jmol 3D model	Interactive image
PubChem	26266
InChI InChI=1S/Al.Na.4H/q-1;+1;;;;
SMILES [Na+].[AlH4-]
Properties
Chemical formula	AlH4Na
Molar mass	54.00 g·mol−1
Appearance	White crystalline solid
Density	1.24 g/cm3
Melting point	183 °C (361 °F; 456 K) (decomposes)
Solubility	soluble in THF (16 g/100 mL at room temperature)
Vapor pressure	{{{value}}}
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)
Infobox references

Sodium aluminium hydride or sodium alanate is an inorganic compound with the chemical formula NaAlH₄. It is a white pyrophoric solid that dissolves in tetrahydrofuran (THF), but not in diethyl ether or hydrocarbons. It has been evaluated as an agent for the reversible storage of hydrogen and it is used as a reagent for the chemical synthesis of organic compounds. Similar to lithium aluminium hydride, it is a salt consisting of separated sodium cations and tetrahedral AlH₄⁻ anions.

Structure, preparation, and reactions

Sodium tetrahydroaluminate adopts the structure of (is isostructural with) calcium tungstate. As such, the tetrahedral AlH₄^- centers are linked with eight-coordinat Na+ cations. The compound is prepared from the elements under high pressures of H₂ at 200 °C using triethylaluminium catalyst:

Na + Al + 2 H₂ → NaAlH₄

As a suspension in diethyl ether, it reacts with lithium chloride to give the popular reagent lithium aluminium hydride:

LiCl + NaAlH₄ → LiAlH₄ + NaCl

The compound reacts rapidly, even violently, with protic reagents, such as water, as described in this idealized equation:

4 H₂O + NaAlH₄ → "NaAl(OH)₄" + 4 H₂

Applications

Hydrogen storage

Sodium alanate has been explored for hydrogen storage in hydrogen tanks. The relevant reactions are:

3 NaAlH₄ → Na₃AlH₆+ Al + H₂

Na₃AlH₆ → 3 NaH + Al + 3/2 H₂

Sodium tetrahydroaluminate can release up to 7.4 wt % of hydrogen when heated at 200 °C (392 °F). absorption can be slow, several minutes being required to fill a tank. Both release and uptake are catalysed by titanium.

Reagent in organic chemistry

Sodium aluminium hydride is a strong reducing agent, very similar in reactivity to lithium aluminum hydride (LAH) and, to some extent, Diisobutylaluminium hydride (DIBAL) in organic reactions. It is much more powerful reducing agent than sodium borohydride due to the weaker and more polar Al-H bond compared to the B-H bond. Like LAH, it reduces esters to alcohols.

Safety

Sodium aluminium hydride is highly flammable. It does not react in dry air at room temperature but is very sensitive to moisture. It ignites or explodes on contact with water.

See also

• Complex metal hydride