Sodium aluminium hydride

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Sodium aluminium hydride
Names
IUPAC name
Sodium aluminium hydride
Other names
Sodium tetrahydroaluminate
Identifiers
13770-96-2 YesY
EC number 237-400-1
Jmol-3D images Image
PubChem 26266
Properties
H4AlNa
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)
Hazards
MSDS External MSDS
Flash point −22 °C; −7 °F; 251 K
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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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 considered 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.[1]

Preparation and reactions[edit]

The compound is prepared from the elements under high pressures of H2 at 200 °C using triethylaluminium catalyst:[2]

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" + 2 H2

Applications[edit]

Hydrogen storage[edit]

Sodium alumate has been explored for hydrogen storage in hydrogen tanks.[3] 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.[4]

Reagent in organic chemistry[edit]

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.[5] 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[edit]

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[edit]

References[edit]

  1. ^ J. W. Lauher, D. Dougherty P. J. Herley "Sodium tetrahydroaluminate" Acta Cryst. 1979, volume B35, pp.1454-1456. doi:10.1107/S0567740879006701
  2. ^ Peter Rittmeyer, Ulrich Wietelmann "Hydrides" in Ullmann's Encyclopedia of Industrial Chemistry, 2002, Wiley-VCH, Weinheim. doi:10.1002/14356007.a13_199
  3. ^ Zaluska, A.; Zaluski, L.; Ström-Olsen, J. O. (2000). "Sodium Alanates for Reversible Hydrogen Storage". Journal of Alloys and Compounds 298 (1–2): 125–134. doi:10.1016/S0925-8388(99)00666-0. 
  4. ^ "Researchers Solve Decade-Old Mystery of Hydrogen Storage Material". Phys.Org. 2008-02-27. 
  5. ^ Melinda Gugelchuk "Sodium Aluminum Hydride" Encyclopedia of Reagents for Organic Synthesis, 2001, John Wiley. doi:10.1002/047084289X.rs039