Return to Contents  Chapter 20: Carboxylic Acid Derivatives. Nucleophilic Acyl Substitution  Ch 20 contents

Reactions of RLi or RMgX with Nitriles

reaction of RLi or RMgX with nitriles
Reaction usually in Et2O or  THF

Reaction type:  Nucleophilic Acyl Substitution then Nucleophilic Addition

Summary:

addition of a Grignard to a nitrile giving the ketone
MECHANISM FOR THE REACTION OF RMgX WITH A NITRILE
Step 1:
The nucleophilic C in the organometallic reagent adds to theelectrophilic C in the polar nitrile group. Electrons from the C≡N move to the electronegative N creating an intermediate imine salt complex.
addition of Grignard reagent to an nitrile
Step 2:
An acid/base reaction. On addition of aqueous acid, the intermediate salt protonates giving the imine.
Step 3:
An acid/base reaction. Imines undergo nucleophilic addition, but require activation by protonation (i.e. acid catalysis).
Step 4:
Now the nucleophilic O of a water molecule attacks the electrophilicCwith the π bond breaking to neutralise the change on the N.
Step 5:
An acid/base reaction. Deprotonate the O from the water molecule to neutralise the positive charge.
Step 6:
An acid/base reaction. Before the N system leaves, it needs to be made into a better leaving group by protonation.
Step 7:
Use the electrons on the O in order to push out the N leaving group, a neutral molecule of ammonia.
Step 8:
An acid/base reaction. Deprotonation reveals the carbonyl group ofthe ketone product.

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© Dr. Ian Hunt, Department of Chemistry, University of Calgary