Aromatizations cerium ammonium sulfate

Ammonium cerium sulfate (ceric ammonium sulfate), (NH4)2Ce-(804)4 2(NH4)2S04 2H20, converts aromatic polynuclear hydrocarbons into quinones [429]. 

Quinones (Table 6.10, item 4) are formed only with difficulty from benzene (CfiH ) itself. However, as shown in Equations 6.77 and 6.78, on oxidation in solution with, for example, ammonium cerium(IV) sulfate [ceric ammonium sulfate, Ce(NHi)4(S04)4], naphthalene (CioHg) and anthracene (C14H10) yield p-quinones and phenanthrene (C14H10), an isomer of the latter (Equation 6.79), yields an o-quinone much more readily. It has been argued that maintaining aromaticity in portions of each of these polynuclear systems aids in making the oxidation reaction much more facile. Similar oxidation patterns are common in naturally occurring quinones. 

Phenols (e.g., phenol itself [CeHs-OH or Ar-OH], Table 6.10, item 2) and their esters (e.g., the trifluoroacetate ester of phenol [C6H5-O2CCF3 or Ar02CCH3], Table 6.10, item 3) have been oxidized with air and oxygen (O2), in neutral and alkaUne solutions, with and without ionic and/or radical catalysts and/or irradiation and in a variety of solvents. Enzymes (this chapter and Chapter 12) from a wide variety of sources have also been used. Frequently, oxidation of aromatic systems to phenols cannot be stopped before quinones and products of ring fragmentation occur and numerous, sometimes ill-defined, products result. Thus, as shown in Equation 6.80, oxidation of the polynuclear hydrocarbon chrysene with anunonium cerium(IV) sulfate [ceric ammonium sulfate, Ce(NH,)4(S04)4] is reported to produce 6H-benzo[d]naphtho[l,2-/>]pyran-6-one (8% yield) and a quinone (23% yield). The remainder of the product(s) (69%) was unidentified. 

Mehta et al. (1976) reported on the use of this reagent for the Baeyer-Villiger oxidation of polycyclic ketones like 1,3-bishomocubanone and 1,4-bishomocubanone into lactones. Ammonium tetrasulfatocerate(IV) dissolved in a mixture of dilute sulfuric acid and acetonitrile was applied as a reagent to transform polycyclic aromatic compounds into quinones (Peri-asamy and Bhatt, 1977a, 1977b). Skarzewski (1984) oxidized polycyclic aromatics with this reagent in a two-phase system with sodium dodecyl sulfate as a surfactant. CAS could be used in catalytic amounts if an excess of ammonium persulfate was present to steadily reconvert cerium(III) in cerium(IV). 

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