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Aldehydes, Ketones and Carboxylic Acids
Preparation of Ketones from Nitriles
1 question from 1 paper, each with its answer.
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Concepts tested
- Grignard reagent with nitrile gives ketone
All Questions
2002 AIPMT 1 question
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The reaction of m-methoxybenzonitrile ($m-CH_3OC_6H_4CN$) with $CH_3MgBr$ followed by $H_3O^+$ gives product P :
A Grignard reagent adds once to the C$\equiv$N group of a nitrile, forming an imine magnesium salt:
$ArC\equiv N + CH_3MgBr \rightarrow Ar-C(CH_3)=N-MgBr$
Acid hydrolysis converts this imine salt into a ketone:
$Ar-C(CH_3)=NMgBr \xrightarrow{H_3O^+} Ar-CO-CH_3 + NH_3 + Mg(OH)Br$
Here Ar is the m-methoxyphenyl group, so P is m-methoxyacetophenone, $m-CH_3OC_6H_4COCH_3$.
(The ketone is not attacked further because it is formed only during the hydrolysis, after the Grignard reagent has been destroyed.)