Question

Question: Propose mechanisms for the three imine-forming reactions just shown.

Short answer

Answer

(a)

(b)

(c)

Step-by-step solution

Formation of imines

In imine forming reactions, carbonyl compounds act as an electrophile while the amines act as a nucleophile.The mechanism for the imine formation canbe divided into two parts. First part is the acid-catalyzed addition of the amine to the carbonyl group in which protonation of the carbonyl takes place followed by addition of the amine and deprotonation. Second part is the acid-catalyzed dehydration in which protonation of the group followed by loss of water and deprotonation.

Mechanism for the imine formation in (a)

(a) Acid-catalyzed addition of takes place to the carbonyl group of cyclohexanone. This results in protonation of the carbonyl followed by the addition of amine and deprotonation. Again, acidcatalyzed dehydration takes place where protonation of the group occurs followed by the loss of water and deprotonation which gives the desired imine.

Mechanism for the imine formation

Mechanism for the imine formation in (b)

(b) Acid-catalyzed addition of aniline takes place to the carbonyl group of cyclopentanone. This results in protonation of the carbonyl followed by the addition of amine and deprotonation. Again, acidcatalyzed dehydration takes place where protonation of the group occurs followed by the loss of water and deprotonation which gives the desired imine.

Mechanism for the imine formation

Mechanism for the imine formation in (c)

(c) Acid-catalyzed addition of methylamine takes place to the carbonyl group of benzaldehyde. This results in protonation of the carbonyl followed by the addition of amine and deprotonation. Again, acidcatalyzed dehydration takes place where protonation of the group occurs followed by the loss of water and deprotonation which gives the desired imine.

Mechanism for the imine formation