Chapter 22: Amines

Reactions of Secondary Amine Derivatives with Aldehydes and Ketones
(review of Chapter 17)

enamine

Summary

• Secondary amines, R₂NH, react with aldehydes or ketones to give carbinolamines which then dehydrate to give enamines.
• The carbinolamine in these reactions can only eliminate to give a C=C since there is no N-H in the carbinolamine.
• The products are called enamines because they are "alkene amines".
• Enamines are useful reagents in synthetic organic chemistry and biochemical transformations.

• Formation of Acetals
• Dehydration of Alcohols
• Formation of Imines

NUCLEOPHILIC ADDITION OF A SECONDARY AMINE GIVING AN ENAMINE.
Step 1: An acid/base reaction. Protonation of the carbonyl activates it and makes it more susceptible to attack by a neutral nucleophilic like the N of a secondary amine.
Step 2: Attack of the N nucleophile at the electrophilic C of the C=O group with the electrons from the π bond going to the +ve O.
Step 3: An acid/base reaction. Removal of the proton neutralises the +ve charge on the N and forms the carbinolamine intermediate.
Step 4: To form the enamine we need to dehydrate. However, before -OH leaves it needs to be protonated, so a simple acid/base reaction.
Step 5: Removal of a proton from an adjacent C allows the π bond to form and loss of the leaving group, a neutral water molecule, creating the enamine.

© Dr. Ian Hunt, Department of Chemistry