Abstract

In an attempt to prepare an azo ester by coupling benzendiazonium chloride with ethyl-2-methylacetoacetate, Japp and Klingemann obtained a product, which was soon recognized as the phenylhydrazone of ethyl pyruvate. It thus appears that the acetyl group is displaced, actually the coupling product was unstable under the conditions of its formation, undergoing hydrolytic scission of the acetyl group and rearrangement of the azo structure. It was later discovered that, if the substituted acetoacetic ester was saponified and the cocoupling carried out on the sodium salt, the carboxylic function rather than the acetyl group, was lost and the product isolated was the phenylhydrazone of biacetyl. This reaction was extended to other systems containing methinyl groups.