Elbs peroxydisulfate oxidation

Behrman and Pitt306 have applied the Elbs peroxydisulfate oxidation to the pyridine series, obtaining, for instance, 2,5-pyridinediol in 42% yield from 2-pyridinol. 

Pyridone, 4-pyridone, and 3-pyridinol undergo the Elbs peroxydisulfate oxidation, a reaction characteristic of phenols and aromatic amines. A bimolecular ionic reaction in which the 2-pyridyloxy ion attacks the peroxy-bond of the persulfate ion with displacement of sulfate ion to give 2-pyridone-5-sulfate is consistent with the observations. ... 

Preparative methods based on oxidations by peroxydisulfate have long been known. Peroxydisulfate ions are capable of oxidizing virtually all functional groups, even hydrocarbons. The oxidation of phenol using potassium peroxydisulfate in alkaline solution, to yield a 1,2- or 1,4-dihydroxybenzene, is called the Elbs reaction and it had been already reported in 1893 (equation 12) . 

Recently, Behiman and coworkers discussed the mechanism of the Elbs oxidation reaction and explained why the para product predominates over the ortho product in this oxidation. According to the authors, semiempirical calculations show that the intermediate formed by the reaction between peroxydisulfate anion and the phenolate ion is the species resulting from reaction of the tautomeric carbanion of the latter rather than by the one resulting from the attack by the oxyanion. This is confirmed by the synthesis of the latter intermediate by the reaction between Caro s acid dianion and some nitro-substituted fluorobenzenes. An example of oxidative functionalization of an aromatic compound is the conversion of alkylated aromatic compound 17 to benzyl alcohols 20. The initial step in the mechanism of this reaction is the formation of a radical cation 18, which subsequently undergoes deprotonation. The fate of the resulting benzylic radical 19 depends on the conditions and additives. In aqueous solution, for example, further oxidation and trapping of the cationic intermediate by water lead to the formation of the benzyl alcohols 20 (equation 13) . ... 

A number of other aromatic oxidations involving peroxygen species have been documented. Probably the best known of these is the hydroxylation of phenols using alkaline peroxydisulfates, known as the Elbs reaction.490 This... 

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