Arenes cerium ammonium nitrate

The direct oxidation of arenes to quinones is a reaction with a limited scope [41], Only substrates that form stable quinones give good yields. For example, oxidation of anthracene to stable 9,10-anthraquinone with chromic acid is practiced on industrial scale. Such oxidations are believed to proceed through a series of one-electron oxidation/solvolysis steps. Yields and selectivity may be improved by using a strong one-electron oxidant such as cerium ammonium nitrate (CAN), as in the oxidation of phenanthrene to phenanthrenequinones (Eq. 9) [42]. 

Different from the hydroxyalkylation reactions using carbonyl compounds as substrates, Nicolaou s and Macmillan s groups developed independently the intramolecular asymmetric Friedel-Crafts-type a-arylation of aldehydes with electron-enriched arenes based on the SOMO activation strategy. Using chiral imidazolidione as catalyst, a series of cyclic aldehydes were obtained in good yields and enantioselectivities with cerium ammonium nitrate (CAN) as single electron transfer oxidant [46]. 

Recently it was pointed out [6] that potassium and sodium bromate oxidize arenes in good yields in a 3 2 dioxane-water solution by using cerium ammonium nitrate (CAN) as catalyst. Toluene derivatives are oxidized to ca. 1 1 mixture of benzaldehydes and benzoic acids, while ethylbenzenes are converted to acetophenones. According to the proposed mechanistic scheme, water either influences the polarity of the reaction medium or acts as the reagent, reacting with the intermediate benzylic carbonium ion to give a hydroxy derivative, which is oxidized from either Ce or BrOa ions. 

Catechols and hydroquinones can be converted (91-98%) into quinones by cerium(IV) salts coated onto silica as free-flowing yellow powder from impregnation with cerium(IV) ammonium nitrate. This reaction is usually performed in the presence of magnesium sulfate. The same (NH4)2Ce(N03)6 SiQ2 reagent in the dry state effects oxidative nitrations of arenes. For example a-mq>hthol is converted to the Orth) (42%) and the para (38%) nitro compounds, while its metiiyl or ethyl ethers give exclusively the para nitration product (equation 4). In solution, the products are cmtaminated with the products of dinitration and of oxidation into quinones. ... 

Silica gel supported cerium(IV) ammonium nitrate (CAN) has been employed for controlled nitration of some naphthalene derivatives. While treatment of hydroxynaphthalenes and polynuclear arenes with cerium(IV) ammonium nitrate absorbed on silica gel without a solvent affords mononitro derivatives, the reaction of the same substrates with cerium(IV) ammonium nitrate in solution alfords a considerable per-... 

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