Sodium aluminium hydride

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Sodium aluminium hydride
Names
IUPAC name
Sodium aluminium hydride
Systematic IUPAC name
Sodium alumanuide
Other names
Sodium tetrahydroaluminate
Identifiers
3D model (JSmol)
ECHA InfoCard 100.033.986 Edit this at Wikidata
EC Number
  • 237-400-1
UN number 2835
  • InChI=1S/Al.Na.4H/q-1;+1;;;;
  • [Na+].[AlH4-]
Properties
AlH4Na
Molar mass 54.003 g·mol−1
Appearance White or gray crystalline solid
Density 1.24 g/cm3
Melting point 178 °C (352 °F; 451 K)
Solubility soluble in THF (16 g/100 mL at room temperature)
Hazards
GHS labelling:
GHS02: FlammableGHS05: CorrosiveGHS07: Exclamation mark
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasFlammability 2: Must be moderately heated or exposed to relatively high ambient temperature before ignition can occur. Flash point between 38 and 93 °C (100 and 200 °F). E.g. diesel fuelInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazard W: Reacts with water in an unusual or dangerous manner. E.g. sodium, sulfuric acid
3
2
0
W
Flash point −22 °C; −7 °F; 251 K
185 °C (365 °F; 458 K)
Lethal dose or concentration (LD, LC):
740 mg/kg (oral, mouse)
Safety data sheet (SDS) Fisher Scientific
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Sodium aluminium hydride or sodium alumanuide 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 AlH−
4 anions.[1]

Structure, preparation, and reactions

Sodium tetrahydroaluminate adopts the structure of (is isostructural with) calcium tungstate. As such, the tetrahedral AlH−
4 centers are linked with eight-coordinate Na+ cations.[1] 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" + 4 H2

Applications

Hydrogen storage

Sodium alanate[3] has been explored for hydrogen storage in hydrogen tanks.[4] The relevant reactions are:

3 NaAlH4 → Na3AlH6+ 2 Al + 3 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, with several minutes being required to fill a tank. Both release and uptake are catalysed by titanium.[5]

Reagent in organic chemistry

Sodium aluminium hydride is a strong reducing agent, very similar in reactivity to lithium aluminium hydride (LAH) and, to some extent, Diisobutylaluminium hydride (DIBAL) in organic reactions.[6] 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

References

  1. ^ a b J. W. Lauher, D. Dougherty P. J. Herley "Sodium tetrahydroaluminate" Acta Crystallogr. 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. ^ Computational Study of Pristine and Titanium-doped Sodium Alanates for ...
  4. ^ 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.
  5. ^ "Researchers Solve Decade-Old Mystery of Hydrogen Storage Material". Phys.Org. 2008-02-27.
  6. ^ Melinda Gugelchuk "Sodium Aluminum Hydride" Encyclopedia of Reagents for Organic Synthesis, 2001, John Wiley. doi:10.1002/047084289X.rs039
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