Oxidation reactions of some natural volatile aromatic compounds: Anethole and eugenol

trans-Anethole [1-methoxy-4-(trans-prop-1-en-1-yl)benzene] was isolated from anise seed oil (Pimpinella anisum). Its photochemical oxidation with hydrogen peroxide gave the corresponding epoxy derivative together with 4-methoxybenzaldehyde. The thermal oxidation of trans-anethole with 3-chloroperoxybenzoic acid at room temperature resulted in the formation of dimeric epoxide, 2,5-bis(4-methoxyphenyl)-3,6-dimethyl-1,4-dioxane, as the only product. Photochemical oxygenation of trans-anethole in the presence of tetraphenylporphyrin, Rose Bengal, or chlorophyll as sensitizer led to a mixture of 1-(4-methoxyphenyl)prop-2-en-1-yl hydroperoxide and 4-methoxybenzaldehyde. Eugenol was isolated from clove oil [Eugenia caryophyllus (Spreng.)]. It was converted into 2-methoxy-4-(prop-2-en-1-yl)phenyl hydroperoxide by oxidation with hydrogen peroxide under irradiation. Thermal oxidation of eugenol with 3-chloroperoxypenzoic acid at room temperature produced 2-methoxy-4-(oxiran-2-ylmethyl)phenol, while sensitized photochemical oxygenation (in the presence of Rose Bengal or chlorophyll) gave 4-hydroperoxy-2-methoxy-4-(prop-2-en-1-yl)cyclohexa-2,5-dien-1-one.