Chapter 21, Problem 21.31P

Interpretation Introduction

Interpretation:

A synthesis of $\text{pent-4-enoic acid}$ from either acetoacetic ester or malonic ester is to be outlined.

Concept introduction:

In case of active methylene compounds, the protons on $\text{α}$ ${\text{CH}}_{\text{2}}$ group, which is flanked between the two electron-withdrawing groups, are significantly more acidic than normal ketones and esters. It is because the enolate conjugate base formed is stabilized by resonance as well as inductive effect. This negatively charged enolate anion is highly nucleophilic and reacts with electrophiles. This enolate anion reacts with an alkyl halide to produce the alkylated product via ${\text{S}}_{\text{N}}\text{2}$ reaction. An ester on acid or base-catalyzed hydrolysis produces corresponding carboxylic acid. $\text{β-carbonyl}$ acid, on heating, undergoes decarboxylation reaction to produce the corresponding carbonyl compound, and gaseous carbon dioxide (${\text{CO}}_{\text{2}}$) is liberated from the solution.