White crystalline powder when pure; monoclinic crystals; grey in the presence of aluminum impurity; stable below 120°C in dry air; turns grey on standing; hygroscopic; density 0.917 g/cm3; melts at 190°C (decomposes); reacts with water and alcohols; soluble in diethylether and tetrahydrofuran (about 30 and 13 g/100g, respectively at 25°C; also soluble in dimethylcellosolve; sparingly soluble in dibutylether; slightly soluble in dioxane (1g/L) and practically insoluble in hydrocarbons; can be solubilized in benzene by crown ether.
Lithium aluminum hydride is prepared by reaction of lithium hydride with aluminum chloride in diethylether:
4LiH + AlCl3 →(C2H5)2O→LiAlH4+3LiCl
A powerful reagent and reducing agent.
Air & Water Reactions
Reacts with water vigorously attaining incandescence and ignition of evolved hydrogen [Kelen, Cahiers, 1977, (86), 100]. Reactions with water or moist air (or heated air) are violent and may be explosive [Schmidt, D.L., et al. Inorg. Synth. 1973. p. 14, 51].
Lithium aluminum hydride is among the most important industrial reducingagents. It is used extensively in organic syntheses and also in catalytichydrogenation. Reactant or reagent for:
1. The preparation of thermoplastic polyester polyamides from oleic acid
2. Lithium-polymer batteries
3. Hydrodefluorination of gem-difluoromethylene derivatives
4. Asymmetric aldol reactions
5. Synthesis of Li-Al-N-H composites with hydrogen absorption / desorption properties
6. LAH is a powerful reducing agent for many different reduction reactions such as that of ketones to alcohols
Lithium aluminum hydride is a flammable substance. It ignites spontaneously on grinding and reacts violently with water and many organic substances. Diethyl ether, tetrahydrofuran or another suitable solvent should be used in its synthetic applications. Dry or powdered limestone is an appropriate fire extinguishing agent.
Lithium aluminium hydride is a powerful reducing agent. React violently on contact with many oxidizing agents. Ignites by friction, especially if powdered. Reacts vigorously with hydroxy compounds such as water, alcohols, carboxylic acids [Mellor 2 Supp. 2:142. 1961]. Caused a violent explosion when used to dry diethylene glycol dimethyl ether: Ignition may have been caused by heat from reaction with impurity water or perhaps decomposition of peroxides in the ether. About 75% of the ether had been removed when the explosion occurred [MCA Case History 1494. 1968]. Reduces carbon dioxide or sodium hydrogen carbonate to methane and ethane at elevated temperatures. These flammable or explosive gases can form when CO2 extinguishers are used to fight hydride fires. Forms explosive complexes with ether, dimethylamine and various tetrazoles. Tetrazoles include, 2-methyl, 2-ethyl, 5-ethyl, 2-methyl-5-vinyl, 5-amino-2-ethyl [US Pat. 3 396 170, 1968].
Behavior in Fire: Decomposes at 257°F to form hydrogen gas. The heat generated may cause ignition and/or explosion.
Reducing agent; in preparation of other hydrides.
Contact of solid with eyes and skin causes severe burns similar to those caused by caustic soda.
Extract it with Et2O, and, after filtering, the solvent is removed under vacuum. The residue is dried at 60o for 3hours, under high vacuum [Ruff J Am Chem Soc 83 1788 1961]. It is a strong reducing agent. It IGNITES in the presence of a small amount of water and reacts with it EXPLOSIVELY. [Becher in Handbook of Preparative Inorganic Chemistry (Ed. Brauer) Academic Press Vol I p 805 1963.]
A white powder that turns gray on standing. If spread out over a large flat combustible surface, friction can cause ignition. Used to make other chemicals, as a polymerization catalyst, as a hydrogen source, and as a propellant.