Aluminum hydride
[CAS# 7784-21-6]

Identification

• Classification: Inorganic chemical industry >> Inorganic salt >> Hydride, nitride, azide
• Name: Aluminum hydride
• Synonyms: Alane
• Molecular Formula: AlH₃
• Molecular Weight: 30.01
• CAS Registry Number: 7784-21-6
• EC Number: 232-053-2
• SMILES: [AlH3]

Properties

• Density: 1.45 g/mL
• Melting point: 660 °C (Expl.)
• Boiling point: 2056 °C (Expl.)

Safety Data

• Hazard Symbols: GHS02;GHS05;GHS07 Danger
• Risk Statements: H260-H314-H318-H335
• Safety Statements: P223-P231+P232-P260-P261-P264-P264+P265-P271-P280-P301+P330+P331-P302+P335+P334-P302+P361+P354-P304+P340-P305+P354+P338-P316-P317-P319-P321-P363-P370+P378-P402+P404-P403+P233-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Skin corrosion	Skin Corr.	1B	H314
Substances or mixtures which in contact with water emit flammable gases	Water-react.	1	H260

Discovery and Applications

Aluminum hydride, also known as alane, is an inorganic compound with the chemical formula AlH₃. It is a covalent hydride of aluminum that exists as a colorless to white solid under standard conditions. Aluminum hydride was first reported in the early 20th century and has since become important in both academic research and industrial applications due to its strong reducing properties and high hydrogen content.

The discovery of aluminum hydride dates back to the 1940s when it was first prepared by the reaction of lithium aluminum hydride with aluminum chloride. Its structure consists of aluminum atoms bonded to hydrogen atoms in a polymeric network, giving it unique properties compared to other metal hydrides.

One of the primary applications of aluminum hydride is as a reducing agent in organic synthesis. It is capable of selectively reducing a wide range of functional groups including aldehydes, ketones, carboxylic acids, esters, and lactones to their corresponding alcohols or hydrocarbons. Compared to other hydride reagents such as lithium aluminum hydride or sodium borohydride, aluminum hydride offers advantages in selectivity and handling for certain substrates.

In addition to its role in organic chemistry, aluminum hydride has been explored as a potential hydrogen storage material due to its high gravimetric hydrogen content, approximately 10% by weight. This has driven research into its decomposition behavior and regeneration, aiming at applications in fuel cells and clean energy technologies. However, challenges remain in controlling its stability and hydrogen release properties for practical use.

Aluminum hydride is usually handled under inert atmosphere conditions because it reacts violently with water and moisture, releasing hydrogen gas and forming aluminum hydroxides. It is typically prepared and stored in dry organic solvents or as stabilized complexes to improve safety and usability.

From a physical perspective, aluminum hydride can exist in several polymorphic forms, which differ in crystalline structure and stability. These polymorphs influence its reactivity and handling characteristics.

Safety considerations are important when working with aluminum hydride due to its flammability and vigorous reactivity with water and air. Proper protective equipment, dry handling techniques, and storage under inert atmospheres are necessary to prevent accidents.

Overall, aluminum hydride is a valuable reagent in synthetic chemistry and a subject of ongoing research in materials science for hydrogen storage. Its discovery and development have contributed to advances in selective reduction methods and the pursuit of alternative energy carriers.

References

2024. Ultra-fast response behavior of aluminum hydride (AlH3) in a quasi-detonation environment. Journal of Materials Science, 59(7).
DOI: 10.1007/s10853-023-09318-1

2024. Dependence of the TNT Equivalent of an Underwater Explosion on the Content of Aluminum Hydride in an Energy Material. Russian Journal of Physical Chemistry B, 18(1).
DOI: 10.1134/s1990793124010147

2024. Hollow structured Fe@C nanorods for boosting dehydrogenation properties of α-AlH3. Nano Research, 17(8).
DOI: 10.1007/s12274-024-6867-z