Oxidation of Phenols Quinones

Phenols are more easily oxidized than alcohols, and a large number of inorganic oxidizing agents have been used for this purpose. The phenol oxidations that are of the most use to the organic chemist are those involving derivatives of 1,2-benzenediol (pyrocatechol) and 1,4-benzenediol (hydroquinone). Oxidation of compounds of this type with silver oxide or with chromic acid yields conjugated dicarbonyl compounds called quinones. 

Siiver oxide is a weak oxidizing agent. AgcO ether 0 

Quinones are colored p-benzoquinone, for example, is yellow. Many occur naturally and have been used as dyes. Alizarin is a red pigment extracted from the roots of the madder plant. Its preparation from anthracene, a coal tar derivative, in 1868 was a significant step in the development of the synthetic dyestuff industry. 

Quinones that are based on the anthracene ring system are caiied anthraquinones. Aiizarin is one exampie of an anthraquinone dye. 

The oxidation-reduction process that connects hydroquinone and benzoquinone involves two 1-electron transfers  

The ready reversibility of this reaction is essential to the role that qninones play in cellular respiration, the process by which an organism uses molecular oxygen to convert its food to carbon dioxide, water, and energy. Electrons are not transferred directly from the substrate molecule to oxygen but instead are transferred by way of an electron transport chain involving a succession of oxidation-reduction reactions. A key component of this electron transport chain is the substance known as ubiquinone, or coenzyme Q  

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Oxidation of Phenols Quinones 932 Spectroscopic Analysis of Phenols 933 Summary 935... 

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