Oxidation of Aromatic Amines to Quinones

The presence of an amino group on an aromatic ring often results in oxidation of the ring to a quinone. The classical and industrial method is the treatment of anilines with potassium dichromate and sulfuric acid. Thus, aniline at room temperature is converted into p-benzoquinone in 86% yield [647], and 2,5-dimethylaniline at 80 °C gives a 55% yield of p-xyloquinone [648. A specific reagent for such oxidations is the Fremy salt, potassium nitrosodisulfonate (equation 528) [490. The oxidation of the amino group takes place even if it is acylated (equation 529) [1190.  

Such oxidations are especially easy, if electron-releasing groups such as hydroxyls or amino groups are located in para or ortho positions with respect to the amino groups. 3-Chloro-4-aminophenol stirred with sodium dichromate and sulfuric acid at a temperature below 35 °C gives a 58-63% yield of chloro-p-benzoquinone after the reaction mixture is allowed to stand at room temperature for 1 h [6J7]. Aminothymol is converted into thymoquinone on warming for 30 min with dilute sulfuric acid and sodium nitrite (equation 530) [451], 

Diaminodurene in the form of its hexachlorostannate is oxidized to duroquinone with ferric chloride (equation 531) [908]. 

Aminonaphthols are converted into naphthoquinones [1191, 1192, 1193 by nitric acid [1193], by potassium dichromate [1191, or by ferric chloride [1192 (equations 532 and 533). 

Several other examples of the oxidation of hydroxyamino and diamino aromatic compounds with silver oxide [368, lead dioxide [368], lead tetraacetate [441], and sodium hypochlorite [694] are documented in equations 534-536. 

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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]. 

Sodium hypochlorite is used for the epoxidation of double bonds [659, 691] for the oxidation of primary alcohols to aldehydes [692], of secondary alcohols to ketones [693], and of primary amines to carbonyl compounds [692] for the conversion of benzylic halides into acids or ketones [690] for the oxidation of aromatic rings to quinones [694] and of sulfides to sulfones [695] and, especially, for the degradation of methyl ketones to carboxylic acids with one less carbon atom [655, 696, 697, 695, 699] and of a-amino acids to aldehydes with one less carbon [700]. Sodium hypochlorite is also used for the reoxidation of low-valence ruthenium compounds to ruthenium tetroxide in oxidations by ruthenium trichloride [701]. 

Secondary alcohols have been oxidized to ketones with excess ferf-butylhydroperoxide in up to 93-99% yields using a zirconium catalyst.250 Zirconium catalysts have also been used with ferf-butylhydroperoxide in the oxidation of aromatic amines to nitro compounds and of phenols to quinones. Allylic oxidation of steroids in 75-84% yields has been performed with ferf-butylhydroperoxide and cop-... 

The scope of the catalytic potential of the cerium(III) ion was intimated by Pratt (1962) in an investigation of the addition of aromatic amines to quinones. Use of hydrated cerous chloride in place of cupric acetate as an oxygen carrier in the oxidation of byproduct hydroquinone resulted in improved yields and easier product separation from metal complexes. 

Tyrosinase catalyzes the reactions other than those shown in eq. (28), e.g, stepwise oxidation of aromatic amines to o-aminophenols and o-quinone imines as shown in eq. (29) [244]. Products were isolated as quinone anils or phenoxazones. The reaction is different from those by other oxidizing agents, because of the regiospecific hydroxylation of the ortho position and further oxidation of the intermediate -aminophenol. The... 

The nitrosodisulfonate salts, particularly the dipotassium salt called Fremy s salt, are useful reagents for the selective oxidation of phenols and aromatic amines to quinones (the Teuber reaction). - Dipotassium nitrosodisulfonate has been prepared by the oxidation of a hydroxylaminedisulfonate salt with potassium permanganate, " with lead dioxide, or by electrolysis. This salt is also available commercially. The present procedure illustrates the electrolytic oxidation to form an alkaline aqueous solution of the relatively soluble disodium nitrosodisulfonate. This procedure avoids a preliminary filtration which is required to remove manganese dioxide formed when potassium permanganate is used as the oxidant. " ... 

Oxidation of Phenols and Aromatic Amines to Quinones 1/0,6/ O-Dihydro-elimination... 

Azo Coupling. The coupling reaction between an aromatic diazo compound and a coupling component is the single most important synthetic route to azo dyes. Of the total dyes manufactured, about 60% are produced by this reaction. Other methods include oxidative coupling, reaction of arylhydrazine with quinones, and oxidation of aromatic amines. These methods, however, have limited industrial applications. 

The relationship of quinones to aromatic compounds is revealed by their preparation by the oxidation of aromatic hydrocarbons, phenols or amines (Scheme 3.52). 

Barium manganate, BaMn04, is commercially available. The dark-blue crystals are obtained from aqueous solutions of barium chloride and potassium permanganate [552, 555]. It oxidizes alcohols, especially benzylic alcohols, to carbonyl compounds [552, 555] hydroquinone to quinone [555] benzylamines to benzaldehydes [555] aromatic amines to azo compounds [555] and phosphines to phosphine oxides [555],... 

Introduction. The quinones are intermediate products in the oxidation of the aromatic nucleus. They may be prepared in some cases by the direct oxidation of aromatic hydrocarbons. For example, anthracene, naphthalene, and phenanthrene are oxidized to the corresponding quinones by chromic acid mixtures. Quinones are prepared more conveniently by oxidation of primary aromatic amines, particularly the p-substituted amines. p-Benzoquinone is obtained by the oxidation of aniline, p-toluidine, sulfanilic acid, p-aminophenol, and other similar compounds. Similarly the a-naph-thoquinone is obtained by oxidation of 1,4-aminonaphthol, and /9-naphthoquinone by the oxidation of 1,2-aminonaphthol. In the laboratory, although it is possible to prepare p-benzoquinone by the oxidation of aniline with acid-dichromate mixture, the method is tedious and the yield poor. Since hydroquinone is used extensively as a photographic developer and is made industrially, it is more convenient to prepare quinone by its oxidation. 

Peroxides [1] e.g. hydrogen peroxide, per acids, diacylperoxides, hydroperoxides, ketone peroxides [1] Under the influence of peroxides aromatic amines (color developer 3) react with phenols to yield quinone imines [1]. Oxidizing agent Aromatic amine -l- 1-Naohthol Quinone imine dyestuff. 

If >>c(oo-)o-h = 75 kcal mole-1, then q = 30 kcal mole-1. Therefore, hyroxyperoxy radicals, in contrast to alkylperoxy radicals, display a dual reactivity. They can take part both in oxidation and in reduction reactions and they would be expected to react not only with radicals but with molecules of the oxidizing agent, with quinones for example. The kinetics of 2-propanol oxidation in the presence of benzoquinone has been studied [80], Quinones are known to terminate chains in hydrocarbon oxidation only by reactions with alkyl radicals [1]. In alcohol oxidation, quinone terminates chains by reaction with hydroxyalkyl as well as with hydroxyperoxy radicals [80]. At 71°C and PQl = 760 torr, 86% of chain termination is due to the reaction >C)0H)00- + quinone. The rate coefficient is M>C(0H)00- + quinone) = 3.2 X 1031 mole-1 s-1 and kQ/kp = 1.0 X 104. Just as in the case of aromatic amines, f> 2 f= 23 for quinone, i.e. quinone is regenerated in the reactions... 

Oxidative coupling reactions of p-phenylenedia-mines with amines and phenols are widely used. As can be seen in Scheme 1 p-phenylene diamine is oxidized to its quinone diimine (QDI) by potassium hexacyanoferrate(III) or a similar oxidant in a weakly basic medium. In the rate-limiting step, QDI reacts with the amine or phenol to give leuco-indamines (indophenols), which are rapidly oxidized to colored indamines (indophenols) with the aid of a QDI molecule. This reaction is chiefly used for resolving a large variety of mixtures of aromatic amines, phenols, and chlorophenols. 

On the other hand, there is at least one case of an aromatic amine without a hydroxy group in the 2-position, namely 1-aminophenazine (2.29) which, after the initial diazotization, is oxidized within minutes by air or additional nitrous acid to the quinone diazide 2.31 (Olson, 1977). 

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