Lithium aluminum hydride reaction with protic solvents

Sodium metal in conjunction with a protic solvent such as an alcohol is sometimes used as a less expensive substitute for lithium aluminum hydride for reducing esters to alcohols in an industrial setting. This is the Bouveault-Blanc reaction. A modem version of this old reaction employs sodium-in-silica-gel (Na-SG), a safe fi ee-flowing powder, instead of the bulk metal (B. S. Bodnar, P. F. Vogt, J. Org. Chem. 2009, 74, 2598-2600) ... 

Lithium aluminum hydride is commonly abbreviated either as LAH or as LiAlH4. It is also a delivery agent of H=, but it is a much stronger reagent. It reacts violendy vith water, and therefore, a protic solvent cannot be present together with LAH in the reaction flask. First the ketone or aldehyde is treated with LAH, and then, in a separate step, the proton source is added to the reaction flask. Water (H2O) can serve as a proton source, although H3O can also be used as a proton source ... 

Reaction of Lithium Aluminum Hydride with Protic Solvents... 

Both aluminum hydride and borohydride react with protic solvents such as water and ethanol. Lithium aluminum hydride reacts violently with water to form hydrogen gas, which may burn explosively because of the heat generated in the reaction. Therefore, lithium aluminum hydride can only be used in aprotic solvents such as diethyl ether. 

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