Reaction of Esters with Lithium Aluminum Hydride

13 Reaction of Esters with Lithium Aluminum Hydride 

Section 15.3 described the reduction of carboxylic acids to primary alcohols with lithium aluminum hydride. Esters are more easily reduced than carboxylic acids. Two alcohols are formed from each ester molecule, with cleavage of the acyl group of the ester giving a primary alcohol. 

Ethyl benzoate reacts with lithium aluminum hydride to give benzyl alcohol and ethanol. 

The mechanism for the reduction of esters with lithium aluminum hydride involves the addition of hydride to the ester carbonyl group to give a tetrahedral intermediate, which undergoes elimination to produce an aldehyde. 

Aldehydes react rapidly with lithium aluminum hydride to give primary alcohols (Section 15.2). The aldehyde produced during the reduction of the ester reacts with a second equivalent of hydride, to give the primary alcohol. One mole of lithium aluminum hydride reduces two moles of ester to alcohol. 

---