Oxidation of Aromatic Compounds to Quinones

The oxidation of benzene to p-benzoquinone is impractical, because benzoquinone is obtained from other compounds [647. Condensed aromatic hydrocarbons are oxidized to quinones by many reagents [429, 758, 802], most frequently by the compounds of hexavalent chromium [1121] (equation 150). 

Alkylnaphthalenes are converted into alkyl-1,4-naphthoquinones with peroxyacetic acid [139] or chromic add [557]. Under the conditions of these reactions (equation 151), the alkyl groups resist oxidation to carboxyl groups. 

The oxidation of anthracene to anthraquinone takes place in positions 9 and 10 [5, 249, 509, 630, 660, 663] and has industrial application in the synthesis of lake and vat dyes (equation 152). 

Na2Cr207, H2SO4, BU4NHSO4, 70 °C, 2 min 82-92% ZnCr207.3H20, CCI4, RT, 3.5 h 80% 

10-Anthraquinone is also formed from 9-methylanthracene on refluxing with sodium dichromate in acetic acid for 30 min (yields are 97% of crude product and 88% of pure product) [1122]. 

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Table 3. Indirect electrochemical oxidation of aromatic compounds to quinones using metal salts as redox catalysts... 

Oxidations by oxygen and catalysts are used for the conversion of alkanes into alcohols, ketones, or acids [54]-, for the epoxidation of alkenes [43, for the formation of alkenyl hydroperoxides [22] for the conversion of terminal alkenes into methyl ketones [60, 65] for the coupling of terminal acetylenes [2, 59, 66] for the oxidation of aromatic compounds to quinones [3] or carboxylic acids [65] for the dehydrogenation of alcohols to aldehydes [4, 55, 56] or ketones [56, 57, 62, 70] for the conversion of alcohols [56, 69], aldehydes [5, 6, 63], and ketones [52, 67] into carboxylic acids and for the oxidation of primary amines to nitriles [64], of thiols to disulfides [9] or sulfonic acids [53], of sulfoxides to sulfones [70], and of alkyl dichloroboranes to alkyl hydroperoxides [57]. 

The most important applications of peroxyacetic acid are the epoxi-dation [250, 251, 252, 254, 257, 258] and anti hydroxylation of double bonds [241, 252, the Dakin reaction of aldehydes [259, the Baeyer-Villiger reaction of ketones [148, 254, 258, 260, 261, 262] the oxidation of primary amines to nitroso [iJi] or nitrocompounds [253], of tertiary amines to amine oxides [i58, 263], of sulfides to sulfoxides and sulfones [264, 265], and of iodo compounds to iodoso or iodoxy compounds [266, 267] the degradation of alkynes [268] and diketones [269, 270, 271] to carboxylic acids and the oxidative opening of aromatic rings to aromatic dicarboxylic acids [256, 272, 271, 272,273, 274]. Occasionally, peroxyacetic acid is used for the dehydrogenation [275] and oxidation of aromatic compounds to quinones [249], of alcohols to ketones [276], of aldehyde acetals to carboxylic acids [277], and of lactams to imides [225,255]. The last two reactions are carried out in the presence of manganese salts. The oxidation of alcohols to ketones is catalyzed by chromium trioxide, and the role of peroxyacetic acid is to reoxidize the trivalent chromium [276]. 

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