Question

Predict the product(s) and provide the mechanism for each reaction below. What does each mechanism have in common?

b.

c.

d.

Short answer

a.

b.

c.

d.

Step-by-step solution

Hydrolysis of imines and enamines

Aldehydes and ketones on reaction with primary amines forms imine derivatives (Schiff bases), and elimination of water occurs in the reaction. Most aldehydes and ketones react with secondary amines to give products known as enamines (alkene+ amine). Now, thus formed imines and enamines can be converted back into corresponding aldehydes or ketones by imine or enamine hydrolysis in presence of an acid.

a. Hydrolysis of imines

The reaction involves the same intermediates as were in the formation of imines, just that steps are reversed starting from protonation of the nitrogen converting the imine into iminium ion which is then attacked by water.

After a proton transfer from the oxygen to nitrogen, an oxonium ion is obtained which after deprotonation gives desired ketone.

b. Hydrolysis of enamine

First protonation involving double-bonded carbon occurs. Then C=O carbon is attacked by water forming an intermediate. After this protonation of nitrogen occurs forming a good leaving group which is expelled out by lone pair of oxygen. Now after deprotonation of oxonium ion corresponding ketone is obtained.

Mechanism (a)

Mechanism (b)

Mechanism (c)

Mechanism

Mechanism (d)

Mechanism

All these reactions follow the same mechanistic pathway.