Phenols cerium ammonium nitrate

Oxidation of 1-(4-methoxyphenyl)-2-( -substituted phenyl) et hands, 6, by Cerium(IV). Dehydration prevented the oxidative-cleavage study of l-(4-hydroxyphenyl)-2-(4,-substituted phenyl)ethanols, 4, (8). As an alternative study, the oxidation of these phenolic compounds using the homolytic oxidant ceric ammonium nitrate (CAN) in an acidic environment was initiated. However, preliminary oxidations of these compounds were unsuccessful due to the apparent formation of complexes of cerium(IV) with the phenolic hydroxyl groups. 

Quinones can he prepared hy the oxidation of phenols, dihydroxy-henzenes, dimethoxyhenzenes and anilines. For example, 1,4-dihydroxy-henzene (hydroquinone) can he oxidized in good yield using sodium chlorate in dilute sulfuric acid in the presence of vanadium pentoxide and also hy manganese dioxide and sulfuric acid and hy chromic acid. Other reagents which convert hydroquinones to quinones include Fremy s salt [potassium nitrosodisulfonate, (KS03)2N0] and cerium(IV) ammonium nitrate [CAN, Ce(NH4)2(N03)J. 

Cerium is a member of the lanthanides in the Periodic Table and adopts tetra- and tripositive states in its electronic configuration. Among cerium reagents, ceric ammonium nitrate (CAN) is most widely used in organic synthesis. It is well known to convert phenol derivatives to quinones in high yields under mild conditions. An excellent review on cerium(IV) oxidation of organic compounds is available, and only a few examples will be described herein. 

N03)j, a newcomer to the arena of oxidants, is useful for the acetoxylation of aromatic side chains in benzylic positions [415, 416] and for the oxidation of methylene or methyl groups that are adjacent to aromatic rings to carbonyl groups [238, 415, 417]. The reagent also oxidizes alcohols to aldehydes [418, 419, 420, 421] and phenols to quinones [422, 423], cleaves vicinal diols to ketones and a-hydroxy ketones to acids [424, 425], and converts diaryl sulfides into sulfoxides [426]. A specialty of ammonium cerium nitrate is the oxidative recovery of carbonyl compounds from their oximes and semicarbazones [422, 427] and of carboxylic acids from their hydrazides [428] under mild conditions. 

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