AQA A Level Chemistry复习笔记7.2.2 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: