Preparative conversion of oximes to parent carbonyl compounds by cerium(IV) oxidation

Abstract

Oximes and semicarbazones are oxidized by ceric ammonium nitrate to the parent carbonyl compound in good yield. Suitable solvent systems include aqueous alcohols, acetonitrile, and acetic acid. The reaction is rapid at 0° or below. This procedure for regeneration of aldehydes and ketones from these derivatives may be preferable to the well-known hydrolytic procedures in some cases. The stoichiometry of the reaction was studied by isothermal calorimetry; two equivalents of oxidant are consumed by one mole of oxime evolving approximately 40 kcal/mole. A smaller consumption of oxidant by hexane-2,5-dione dioxime was attributed to stabilization of the monoxime as a nitroso chelate. Gaseous products were studied by infrared spectroscopy and nitrous oxide was identified as the sole product absorbing between 3 and 15 μ. A reaction mechanism is proposed involving one-electron oxidation to the iminoxy radical, oxidized by a second one-electron step to the α-hydroxy nitroso compound. Dimerization and elimination of hyponitrous acid gives the carbonyl compound. Nitrocyclohexane was absent from the oxidation product from cyclohexanone oxime. Carvone oxime was oxidized to carvone without racemization or significant attack of the olefin groups.