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AQA A Level Chemistry復習筆記7.2.2 Reduction of Carbonyls

Category: A-level課程, 教材筆記, 福利干貨 Date: 2022年7月4日上午11:08

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:

7-2-2-reduction-of-a-carboxylic-acid

Aldehyde to a primary alcohol:
Ketone to a secondary alcohol:

7.2.2-Reduction-of-a-ketone

Exam Tip

In theory the reduction of a carboxylic acid is a two stage process, from the carboxylic acid to the aldehyde and then further reduction from the aldehyde to the primary alcohol. In reality however, the reaction would really go from the carboxylic acid straight to the primary alcohol. Be careful and check the wording of the question when asked about the reduction of a carboxylic acid!