Question

Give the expected products of lithium aluminum hydride reduction of the following compounds (followed by hydrolysis).

a) Alcohols
b) Aldehydes
c) Ketones
d) Carboxylic acids

Answer 1

Lithium aluminum hydride (LiAlH4) reduces aldehydes and ketones to primary and secondary alcohols respectively, and carboxylic acids to primary alcohols; alcohols are generally not further reduced by LiAlH4.

Step-by-step explanation:

Lithium aluminum hydride (LiAlH4) is a strong reducing agent widely used in organic chemistry for the reduction of various functional groups following by hydrolysis. The expected products after the reduction and subsequent hydrolysis are:

• Alcohols: Reduction of alcohols with LiAlH4 generally does not proceed, as alcohols are already in a relatively reduced state.
• Aldehydes: Aldehydes are reduced by LiAlH4 to primary alcohols.
• Ketones: Ketones are reduced by LiAlH4 to secondary alcohols.
• Carboxylic acids: Carboxylic acids are reduced by LiAlH4 to primary alcohols.

The overall process involves the nucleophilic addition reaction of hydride ion from LiAlH4 to the electrophilic carbon atom of the carbonyl (C=O) group in aldehydes and ketones or to the carbon atom of the carboxyl (C=O) group in carboxylic acids, reducing them to their corresponding alcohols. Typically, hydrolysis is performed by adding water after the reduction step to ensure full conversion to the alcohol product.