Claisen by condensing ethoxymethylene aceto-acetic esters and similar compounds with /3-ketonic esters and with 1.3 diketones.
The 2.6-diketo-tetrahydropyrimidines or uracils may be considered as the ureides of /-aldehydo, and 0-ketonic acids.
The carbonyl group is not ketonic in character since it yields neither an oxime nor hydrazone.
Compounds containing an oxy in addition to an aldehydic or ketonic group) undergo both condensation and oxidation when treated with phenylhydrazine, forming compounds known as osozones; these are of great importance in characterizing the sugars (q.v.).
The remaining oxygen atom is aldehydic or ketonic, for the sugars combine with hydrocyanic acid, hydroxylamine and phenylhydrazine.