Chapter 16, Problem 76P

Interpretation Introduction

Interpretation:

The reaction mechanism for the formation of an anhydride from the reaction of butanedioic acid and thionyl chloride has to be proposed.

Concept introduction:

Dicarboxylic acid reacts with thionyl chloride and undergoes nucleophilic substitiution reaction at one carboxylic group to form acyl chloride.

Acyl chloride is the most reactive carboxylic derivative functional group and hence nucleophilic $\text{OH}$ group of the second carboxylic group attacks the carbonyl of the acyl group. Chloride ion leaves as the leaving group and cyclic anhydride product from the dicarboxylic acid is formed.