Answer :
Final answer:
Grignard reagents react with ketones to produce tertiary alcohols by adding two alkyl groups. They react with nitriles to form ketones by adding one alkyl group and hydrolyzing the imine salt intermediate. Preparation of an aldehyde from an N,N-dialkylalkanamide requires controlled conditions.
Explanation:
Reaction of Grignard Reagents with Ketones and Nitriles
Grignard reagents are well-known for their ability to form new carbon-carbon bonds. When a Grignard reagent reacts with a ketone, it adds to the carbonyl carbon to form a new C-C bond, creating an alkoxide intermediate. After the subsequent acid work-up, this intermediate is protonated to produce a tertiary alcohol. The final product is a tertiary alcohol because two alkyl groups are introduced from the Grignard reagent, and the ketone already carries one alkyl group (assuming this is a carbon group).
Conversely, when a Grignard reagent reacts with a nitrile, the nucleophilic carbon of the Grignard adds to the electrophilic carbon in the nitrile forming an imine salt, which upon hydrolysis gives a ketone. This is because only one alkyl group is introduced from the Grignard reagent.
For the preparation of an aldehyde from an N,N-dialkylalkanamide, a careful choice of Grignard reagent and control of conditions must be made to ensure that only one equivalent of Grignard is added, stopping the reaction at the aldehyde stage before further addition occurs.
