Carboxylic Acid Reactions: Carboxylic acids Reduction to form Alcohol with LiAlH4

Primary alcohols can be formed from carboxylic acids using a strong reducing agent called Lithium aluminum hydride (abbreviated as LiAlH4):

This reaction is pretty straight forward; the double bonded O gets removed. There aren’t any “trick” reactions with this reagent and functional group; if there is a carboxylic acid group simply remove the double bonded Ol.

The reaction mechanism is depicted below:

In the first step, the hydride (H-) from LiAlH4 attacks the proton on the carboxylic acid group, forming a carboxylate ion (COO-).

In the second step, another equivalent of LiAlH4 has its hydride attack the carbon, breaking the double bond between the carbon and oxygen, sending the electrons to the oxygen.

In the third step, the lone pair electrons on the oxygen return to form a double bond, thereby “kicking” the other oxygen atom off the molecule.

In the fourth step, a third equivalent of LiAlH4 has its hydride attack the same carbon, once again shifting the electrons from the double bond to the oxygen atom..

In the fifth step, the lone pair electrons on the oxygen attack a proton on a nearby H3O+ molecule, completing the reaction.

This reduction only occurs on the carboxylic acid group; alkenes and benzene rings will not be reduced.