Preparation of Alcohols by Reduction of Carbonyl Compounds

Aldehydes and ketones are reduced to alcohols by lithium aluminium hydride (LiAlH4) in a solvent such as tetrahydrofuran (THF), followed by hydrolysis; unlike Raney nickel or Na-Hg/H2O, LiAlH4 does NOT reduce a carbon-carbon double bond present in the same molecule, so it is the reagent of choice for making unsaturated alcohols from unsaturated carbonyl compounds (e.g. crotonaldehyde, CH3-CH=CH-CHO, reduces cleanly to crotyl alcohol, CH3-CH=CH-CH2-OH, i.e. but-2-en-1-ol). Acetone gives propan-2-ol; benzoic acid gives benzyl alcohol; ethyl ethanoate gives two moles of ethanol. When a molecule carries both a carbonyl and a carboxyl group, the milder reagent sodium borohydride (NaBH4 …