Reduction of Carbonyls (AQA A Level Chemistry)

Reduction of Carbonyls

Reduction of Carbonyls

• There are a large number of reducing agents which will reduce both an aldehyde and a ketone to an alcohol

• Aldehydes are reduced to primary alcohols and ketones are reduced to secondary alcohols

• Possibly the most common reducing agent for this is sodium tetrahydridoborate, NaBH₄

  • You may also see this named as sodium borohydride in some sources

• In an aqueous solution, NaBH₄ generates the hydride ion nucleophile, :H^-

• The hydride ion will reduce a carbonyl group in an aldehyde or a ketone, but is not strong enough to reduce a C=C double bond

  • This is because it is attracted to the C in the C=O bond, but is repelled by the high electron density of the C=C bond

• When this reaction takes place, it is an example of a nucleophilic addition reaction

Reduction Reactions

• Carboxylic acid to a primary alcohol:

• Aldehyde to a primary alcohol:

  

• Ketone to a secondary alcohol: