Lithium aluminium hydride

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Lithium aluminium hydride
Names
IUPAC name
Lithium aluminium hydride
Preferred IUPAC name
Lithium tetrahydridoaluminate(III)
Systematic IUPAC name
Lithium alumanuide
Other names
LAH
Lithal
Lithium aluminium hydride
Lithium alanate
Lithium aluminohydride
Lithium tetrahydridoaluminate
Properties
LiAlH4
Appearance White or grayish crystals
Odor Odorless
Density 0.917 g/cm3
Melting point 150 °C (302 °F; 423 K) (decomposes)
Boiling point Decomposes
Reacts
Solubility Slightly soluble in dibutyl ether
Insoluble in toluene
Solubility in diethyl ether 11.2332 g/100 ml
Solubility in tetrahydrofuran 39.5 g/100 ml
Thermochemistry
87.9 J·mol-1K-1
-117 kJ/mol
Hazards
Safety data sheet AcrosOrganics
Flash point 125 °C
Related compounds
Related compounds
Lithium borohydride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Lithium aluminium hydride, commonly abbreviated to LAH is an inorganic compound with the chemical formula LiAlH4. It is a strong reducing agent used in organic chemistry.

Properties

Chemical

LAH is sensitive to water, and reacts vigorously to release hydrogen.

LiAlH4 + H2O → LiOH + Al(OH)3 + 4 H2

LAH is metastable at room temperature. During prolonged storage it slowly decomposes to Li3AlH6 and LiH.

LAH is a strong reducing agent, it will convert esters, carboxylic acids, acyl chlorides, aldehydes, and ketones into the corresponding alcohols. Similarly, it converts amide, azide, imine, nitrile, nitro and oxime compounds into amines. LAH is most commonly used for the reduction of esters and carboxylic acids to primary alcohols.

Physical

LAH is a white solid, however commercial samples are usually gray due to impurities. It can be purified by recrystallization from diethyl ether. The pure powdered material is pyrophoric, but its large crystals are not. LAH will react with water to release hydrogen, so samples are usually stored is airtight bags, away from any moisture. LAH is soluble in many ethereal solutions, but is more stable in THF than diethyl ether, even though it's less soluble in the former than the latter.

Availability

LAH is somewhat hard to find, due its sensitivity to air and water. Some people have been able to purchase LAH from Alibaba, from certain chemical sellers.

Preparation

LAH can be prepared by reacting LiH with anhydrous aluminium chloride, in an aprotic solvent such as diethyl ether. The product is purified by recrystallizing it from diethyl ether.[1] THF can also be used as solvent.

Projects

  • Reducing esters to alcohols
  • Reduce amides to amines

Handling

Safety

LAH will react with water to produce lithium hydroxide which is corrosive. It will react with both liquid water as well as the moisture from air.

Storage

It's best stored in a dry airtight container or bags, under inert or reducing conditions if possible. LAH is also a fire hazard, and in its powdered form it's pyrophoric.

Disposal

The byproducts or neutralizing LAH are lithium and aluminium compounds, usually lithium hydroxide or carbonate and aluminium oxide. They can either be recycled (lithium especially) or disposed in centers that accept aluminium wastes.

See also

References

  1. J. Am. Chem. Soc., 1947, 69 (5), pp 1199–1203

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