Chapter 18, Problem 18.85P

Interpretation Introduction

(a)

Interpretation:

The HO- cannot be used as a base is to be explained.

Concept introduction:

The aldol addition reaction with deprotonated imine, which contains a polar $\text{π}$ bond, has acidic alpha hydrogen. Every aldol addition produces a $\text{β-hydroxycarbonyl}$ compound. Like the enolate anion of ketone and aldehydes, this deprotonated imine can act as a nucleophile. The acidity of $\text{α}$ hydrogen of an imine is much less acidic than that of ketone or aldehyde. So hydroxide is simply not a strong enough base to generate the enolate anion. The hydrolysis takes place under acidic condition to convert imine into an aldehyde.

Interpretation Introduction

(b)

Interpretation:

The detailed mechanism for the given reaction, including the structure of the intermediate species not shown there, is to be drawn.

Concept introduction:

The aldol addition reaction with deprotonated imine, which contains a polar $\text{π}$ bond, has acidic alpha hydrogen. Every aldol addition produces a $\text{β-hydroxycarbonyl}$ compound. Like the enolate anion of ketone and aldehydes, this deprotonated imine can act as a nucleophile. The acidity of $\text{α}$ hydrogen of an imine is much less acidic than that of ketone or aldehyde. So hydroxide is simply not a strong enough base to generate the enolate anion. The hydrolysis takes place under acidic condition to convert imine into an aldehyde.