Lithium aluminium hydride

Lithium aluminium hydride

LiAlH4 being poured from its container
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
Chemical formula	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
Solubility in water	Reacts
Solubility	Soluble in ethers Slightly soluble in dibutyl ether Insoluble in toluene, xylene
Solubility in diethyl ether	11.2332 g/100 ml
Solubility in tetrahydrofuran	39.5 g/100 ml
Vapor pressure	~0 mmHg
Thermochemistry
Std molar entropy (So298)	87.9 J·mol-1K-1
Std enthalpy of formation (ΔfHo298)	-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. Can also be found on eBay.

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. THF can also be used as solvent.

Projects

• Reducing esters to alcohols
• Reduce amides to amines
• Source of hydrogen

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. Wear proper protection, like gloves, when handling this compound.

Storage

LAH is 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 can be 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

• Lithium hydride
• Sodium borohydride

References

Relevant Sciencemadness threads

• Synthesis of LiAlH4 Starting from "Scratch"
• For sale: Lithium Aluminum Hydride 99% (pelletized)
• heating lithium aluminum hydride with heating mantle
• Lithium Al Hydride quick question
• LAH storage
• Storage of LiAlH4