Aromatic compounds to quinones

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]. 

Thallium trinitrate, TI(N03)3 3H20 (mp 102-105 C), oxidizes phenols and dihydroxy aromatic compounds to quinones [409, acetylenes to a-hydroxy ketones, a-diketones, or carboxylic acids 413] and methyl ketones to a-keto acids [414],... 

The reagent potassium nitrosodisulfonate (33), known as Fremy s salt, was first prepared in 1845. Its use as a chemoselective oxidizing agent has been reviewed extensively by Zimmer [59a] and Parker [59b] and will only be mentioned briefly here. While it is most widely known for its use in the oxidation of various heteroatom-substituted aromatic compounds to quinones [59], it has also been used in the selective oxidation of benzylic alcohols to ketones [60] and the oxidation of a-amino and a-hydroxy acids to a-keto acids [61]. 

Ceric ammonium nitrate converts a 1,4-dimethoxy aromatic compound to the quinone, which is reduced with sodium dithionite to give a depro-tected hydroquinone. ... 

The Gomberg-Bachmann reaction is a method for arylation of aromatic compounds and quinones (Gomberg and Bachmann, 1924). Originally this reaction involved adding aqueous sodium hydroxide slowly to an intimate mixture of an aqueous solu-... 

The interstellar dust was shown to contain quinone derivatives as well as oxygen-rich condensed aromatic compounds the quinones were present in both hydrated and carboxylated form. Very little nitrogen was present in the compounds detected. The cometary material, however, contained condensed nitrogen heterocycles. Hardly any oxygen was detected in the solid phase of the cometary dust it possibly evaporates from the tail of the comet in the form of water or oxidized carbon compounds. The authors assume that these analytical results could lead to a reconsideration of the current biogenesis models (Kissel et al 2004 Brownlee, 2004). 

Nuclear oxidations of aromatic compounds to form quinones (Table 3) have been performed technically in the case of anthraquinone using electrochemically regenerated Ce(IV) or Cr(VI) as redox catalysts This technique has, however, become less... 

Collie s hypothesis that aromatic compounds are made biologically from ethanoic acid was greatly expanded by A. J. Birch to include an extraordinary number of diverse compounds. The generic name acetogenin has been suggested as a convenient classification for ethanoate (acetate)-derived natural products, but the name polyketides also is used. Naturally occurring aromatic compounds and quinones are largely made in this way. An example is 2-hydroxy-6-methylbenzoic acid formed as a metabolite of the mold Penicillium urticae ... 

The Dess-Martin periodinane 8 is also able to oxidize aromatic compounds to the corresponding quinones. The presence of water is important and, starting from anilides 42 substituted in the 2-position, the rare class of ortho-imido-quinones 43 is accessible, Scheme 21. It has been shown that compounds of type 43 are interesting building blocks and can lead to polycyclic molecules of diverse molecular architecture [95,96]. They can undergo subsequent Diels-Alder reactions and intramolecular versions have been used for a rapid access to natural products and for synthesis of scaffolds for further manipulation.para-Quinones 45 are also easily accessible, however, only in modest yields by reacting 4-sub-stituted anilines 44 under the same reaction conditions, Scheme 21 [97]. 

The domain of oxidations with silver oxide includes the conversion of aldehydes into acids [63, 206, 362, 365, 366, 367 and of hydroxy aromatic compounds into quinones [171, 368, 369]. Less frequently, silver oxide is used for the oxidation of aldehyde and ketone hydrazones to diazo compounds [370, 371], of hydrazo compounds to azo compounds [372], and of hydroxylamines to nitroso compounds [373] or nitroxyls [374] and for the dehydrogenation of CH-NH bonds to -C=N- [375]. Similar results with silver carbonate are obtained in oxidations of alcohols to ketones [376] or acids [377] and of hydroxylamines to nitroso compounds [378]. 

Sodium dichromate hydroxylates tertiary carbons [620] and oxidizes methylene groups to carbonyls [622, 623, 625, 626, 631] methyl and methylene groups, especially as side chains in aromatic compounds, to carboxylic groups [624, 632, 633, 634, 635] and benzene rings to quinones [630, 636, 637] or carboxylic acids [638]. The reagent is often used for the conversion of primary alcohols into aldehydes [629, 630, 639] or, less frequently, into carboxylic acids or their esters [640] of secondary alcohols into ketones [621, 629, 630, 641, 642, 643, 644] of phenylhydroxylamine into nitroso-benzene [645] and of alkylboranes into carbonyl compounds [646]. 

Zinc dichromate tiihydrate, ZnCr207<3H20, is obtained as an orange-red solid by adding zinc carbonate to a cold solution of chromium trioxide in dilute sulfuric acid [660]. The applications are oxidations of acetylenes lo a-diketones, of aromatic hydrocarbons to quinones, of alcohols to aldehydes, and of ethers to esters and the oxidative regeneration of carbonyl compounds from their oximes [660]. 

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]. 

Sodium iodate, NalOj, is used rarely its applications are limited to the oxidation of aromatic polyhydroxy compounds to quinones [753, 754]. 

The oxidative cleavage of carbon-carbon bonds in vicinal diols [756, 759] is a reaction widely used in saccharide chemistry. Besides its application in this reaction, periodic acid achieves the oxidative coupling [757] or oxidation to quinones [758] of polynuclear aromatic hydrocarbons, the oxidation of methyl groups in aromatic compounds to carbonyl groups [760], the conversion of epoxides into dicarbonyl compounds [761], and the oxidative cleavage of trimethylsilyl ethers of acyloins to carboxylic acids [755]. 

The applications of ruthenium tetroxide range from the common types of oxidations, such as those of alkenes, alcohols, and aldehydes to carboxylic acids [701, 774, 939, 940] of secondary alcohols to ketones [701, 940, 941] of aldehydes to acids (in poor yields) [940] of aromatic hydrocarbons to quinones [942, 943] or acids [701, 774, 941] and of sulfides to sulfoxides and sulfones [942], to specific ones like the oxidation of acetylenes to vicinal dicarbonyl compounds [9JS], of ethers to esters [940], of cyclic imines to lactams [944], and of lactams to imides [940]. 

Silver oxide and sodium sulfate are frequently used to oxidize 1,2-dihydroxy aromatic compounds to orf/io-quinones. Phenanthrene furnishes, after being shaken for 15 s with the mixture in ether at room temperature, a 65% yield of 3,4-phenanthrenequinone [171]. Another oxidant used to prepare orfho-quinones is sodium iodate (equation 321) [754],... 

Among electron carriers used for indirect oxidation reactions, cerium salts [Ce -t- e Ce E° = -t-1.44 V vs. NHE] appear to be of particular interest when a mild oxidation has to be considered. Substituted toluenes and methylaryl compounds are easily functionalized to the corresponding aldehydes in high yields [125-129]. Acidic solutions are required (such as aqueous AcOH, aqueous methane sulfonic acid, or aqueous trifluorosulfonic acid). The conversion of aromatic compounds into quinones may also be conducted by means of electrogenerated ceric ions (see Table 3). Let us stress the example... 

Thallium carboxylates, particularly the acetate and trifluoroacetate, which can be obtained by dissolution of the oxide in the acid, are extensively used in organic chemistry.14 Both Tl metal and Tl1 salts such as the acetylaceton-ate also have specific uses. One example is the use of thallium(m) acetate in controlled bromination of organic substances such as anisole. The trifluoroacetate will directly thallate (cf. aromatic mercuration, Section 18-9) aromatic compounds to give aryl thallium ditrifluoroacetates, e.g., C6H5Tl(OOCCF3)2. It also acts as an oxidant, inter alia converting para-substituted phenols into p-quinones. 

Sulfide. This is used mainly for the partial reduction of pol3mitro aromatic compounds to nitroamines and for the reduction of nitroanthra-quinones to aminoanthraquinones. 

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