lithium aluminum hydride, also known as LAH, is a powerful reducing agent widely used in organic chemistry. It can reduce aldehydes and ketones to primary alcohols, carboxylic acids and esters to secondary alcohols, amides, nitriles, nitro compounds and alkyl azides to amines, epoxides to alcohols and lactones to diols.
LiAlH4 crystal structure consists of five AlH4 tetrahedra and a Li+ centre surrounded by each of these tetrahedra, forming a bipyramid arrangement. The hydride, H- ions are coordinated to the Al3+ ions and hybridization of central Al is sp3.
In a three step reaction mechanism, amides and nitriles are reduced by adding a polar CN bond to the carbonyl oxygen and then transferring the resulting hydride from the AlH3- group. The final protic workup converts the amide to the corresponding primary amine.
This reagent can also be used to convert haloalkanes and haloarenes to their corresponding hydrocarbons. It is a very strong reducing agent and should be handled in inert and dry surroundings.
It can be obtained by the reaction of lithium hydride and aluminium chloride. It is a white solid but commercial samples are usually grey due to impurities and should be filtered before use.
Reactivity with water produces hydrogen gas, and the reagent should be stored in tightly sealed containers away from moisture and combustible materials. It should be disposed of according to local waste disposal regulations.
If LAH is spilled, clean up with soap and water, and wash the area with copious amounts of water for 15 minutes (lifting upper and lower lids occasionally). Inhaled or swallowed lithium aluminum hydride may cause serious or fatal health effects.