Chapter 18, Problem 18.86P

Interpretation Introduction

Interpretation:

A detailed mechanism for the reaction, in which, treatment of a nitrile with base followed by acid hydrolysis yields a $\text{β-keto nitrile}$ as shown, is to be provided.

Concept introduction:

By counting the carbons, we can see that two molecules of the nitrile are joined by an Aldol-type reaction. $\text{α-Carbon}$ of one nitrile is attached to the terminal $\text{C1}$ of the other nitrile molecule. In the mechanism, ethoxide removes an $\text{α-}$ proton from the nitrile to make a carbanion nucleophile. The carbanion nucleophile attacks another molecule of nitrile. Under these basic conditions, no strong acid should appear. Upon addition of acid, a $\text{C=N}$ group is formed, which is hydrolysed to make $\text{C=O}$. Under these acidic conditions, no strong base should appear.