Illustrated Glossary of Organic Chemistry

Arndt-Eistert Reaction: A reaction sequence to convert an ester into a homolog having one additional carbon. The new carbon is inserted adjacent to the carboxyl group of the starting carboxylic acid.

	SOCl2		CH2N2		Ag2O
Benzoic acid A carboxylic acid		Benzoyl chloride An acid chloride		α-Diazoacetophenone A diazoketone		Phenylacetic acid A benzoic acid homolog

In this Arndt-Eistert reaction, benzoic acid (PhCO₂H) is converted into phenylacetic acid (PhCH₂CO₂H) by insertion of a methylene group between the benzene ring and carboxyl group of benzoic acid.