AbstractThe hydroperoxides in oxidised methyl oleate can be converted in high yield into the dinitro‐phenylhydrazones of aldehydes and aldehyde esters by reaction on a Celite/dinitrophenylhydrazine‐hydrochloric acid column. The aldehydes and aldehyde esters formed are the same as those produced during the thermal decomposition of methyl oleate hydroperoxide.The dinitrophenylhydrazones of unsaturated conjugated C18keto esters are also for