Novel solid-state synthesis of halide free alane

Abstract

The traditional aluminum hydride (alane, AlH3) synthesis involves reacting AlCl3 and LiAlH4 in diethyl ether, resulting in the formation of the alane etherate adduct, AlH3·h[(C2H5)2O]. The desired crystallized, stable a-AlH3 can only be obtained by either extensive vacuum distillation and heating of the etherate or by a crystallization process involving a large, heated bath of a benzene/toluene solution. These processes tend to be costly due to the several hours of vacuum pumping and/or heating required as well as dangerously using large amounts of flamable, toxic solvents. It is demonstrated here that a-AlH3 can be obtained by simply mixing AlCl3 and LiAlH4 in the solid state and slowly heating to 75° C. The a-AlH3 product can be washed with minimal solvents to remove the LiCl bi-product, leading to zero formation of any alane adducted materials. Although simple mixing and heating the reactants can provide a 40% yield of alane, the application of moderate pressure while heating increases this yield to over 60 % of cvrystalline a-AlH3.