Question

In Beckmann rearrangement, Cyclohexanone oxime and its Rearrangement to  ε-caprolactam why do we use hydroxylamine hydrochloride but not hydroxylamine? And why do we add sodium acetate?

Answer 1

In Beckmann rearrangement, cyclohexanone is converted to ε-caprolactam via cyclohexanone oxime.

For this reaction to proceed smoothly hydroxylamine hydrochloride and sodium acetate are used as reagents.

First, hydroxylamine reacts with cyclohexanone to form cyclohexanone oxime. Now, HCl provides the acidic conditions needed for the hydroxyl group to become good leaving group and get eliminated as water. Now, sodium acetate along with HCl buffer the reaction mixture and maintain the acidic nature of the reaction so it goes to completion.

The role of HCl is to help remove the hydroxyl group from the oxime and the role of sodium acetate is to buffer the reaction mixture so the acidic conditions are maintained.