With ascaridole (1) as reference compound the reaction mechanism of th
e peroxide reagent by Huber and Frohlke was investigated. A blue dye f
ormed was isolated and its structure elucidated. By modification of th
e reagent, the application for the densitometric assay of 1 in chenopo
dium oil and of the allergen alpha-peroxyachifolid in yarrow (Achillea
millefolium L.) is reported.