Anthraquinone, from anthracene oxidation

The use of mild oxidizing agents or operation under mild conditions usually results in products other than anthraquinone from the oxidation of anthracene. Tints, oxidation with tin oxide, manganese oxide, cerium acetate, or vanadium pentoxide in glacial acetic add results in the formation of a mixture of acetates.258 ... 

Also important is the choice of a suitable redox system for the indirect electroreaction of particular substrates. For instance, toluene can be oxidized with Mn(III) or Ce(IV) to benzaldehyde, whilst with Cr(VI) benzoic acid is obtained. On the other hand, anthraquinone is commercially prepared from anthracene by employing chromic acid oxidation. 

Anthrone did not react with DMSO under the reaction conditions. However, 9,10-anthraquinone (2 mmoles) in 25 ml. of DMSO (80%)-terf-butyl alcohol (20% ) containing potassium tert-butoxide (4 mmoles) gave a deep red solution at 25°C., from which 60% of the adduct could be isolated after 1 hour and 88% after 3 hours. This adduct was isolated from the oxidate of 9,10-dihydroanthracene (after hydrolysis, acidification, and filtrations of anthracene) by extraction of the aqueous filtrate by chloroform. Xanthone and thioxanthone failed to form isoluble adducts with DMSO in basic solution. 

The autoxidation mechanism by which 9,10-dihydroanthra-cene is converted to anthraquinone and anthracene in a basic medium was studied. Pyridine was the solvent, and benzyl-trimethylammonium hydroxide was the catalyst. The effects of temperature, base concentration, solvent system, and oxygen concentration were determined. A carbanion-initi-ated free-radical chain mechanism that involves a singleelectron transfer from the carbanion to oxygen is outlined. An intramolecular hydrogen abstraction step is proposed that appears to be more consistent with experimental observations than previously reported mechanisms that had postulated anthrone as an intermediate in the oxidation. Oxidations of several other compounds that are structurally related to 9,10-dihydroanthracene are also reported. 

Anthraquinone was produced in 96% yield from the oxidation of anthracene with TBHP in the presence of RhC (PPh1)3 catalyst (equation 93).266 Oxidation of cylic alkenes, e.g. cyclopentene, cyclohexene, cycloheptene, by TBHP in the presence of Rh2(OAc)4 results in the formation of a,/3-unsaturated ketones and allylic acetates as the major products (equation 94).267... 

Anthraquinone is being made at pilot plant scale from anthracene. The Ce3+/4+ couple is used with methane sulfonic acids. The steps involve anodic oxidation of Ce3+ and the use of Ce4+ outside the cell to convert naphthalene to napthaquinone, which is then converted to anthraquinone via a step involving butadiene. 

The direct synthesis of anthraquinone from phthalic anhydride and benzene has been reported to proceed over zeolite Beta [50] in a shape selective manner. In a conventional anthraquinone synthesis, anthracene is used as a feedstock for oxidation. Once there is a shortage of it in the market, additional anthracene could be produced by isomerization of its isomer, viz. phenanthrene. This, however, is not possible by direct isomerization of the trinuclear aromatic system but involves the partially (symmetrically) hydrogenated species. Consequently, isomerization of symmetrical octahydrophenanthrene to symmetrical octahydro-anthracene was studied by Song and Moffatt [51]. As sketched in Figure 3, a high yield of symmetrical octahydroanthracene can be obtained over zeolite H-mordenite (ngj/nyy = 8) at 250 °C (liquid phase, decalin as solvent). These examples show that (shape selective) catalysis on zeolites is more and more expanding into the conversion of polycyclic aromatics, and we foresee continued interest and success in this field of zeolite catalysis. 

The net result of the process is that impure or partly purified anthracene may be oxidized directly to anthraquinone. From tire standpoint of eouioment cost it does not matter whether two single catalytic converters... 

When mixtures of anthracene and phenanthrene, such as are obtained by removing carbazole from anthracene press cake by caustic fusion, arc oxidized, mixtures of phthalic anhydride and anthraquinone result. A separation of these valuable products is effected by washing out the acids with an alkali solution and recovering as sodium salts or as acids by addification subsequent to removal of anthraquinone by filtration. The products may be distilled or sublimed to separate from any unoxidized material that may be present. Maleic acid may also be present in the products to a small extent and is recovered with the phthalic anhydride from which it must be removed as an impurity.88... 

In the conversion of anthracene into anthraquinone, the para bond between the two carbon atoms involved in the oxidation is broken, but no change takes place in the benzene rings present in the compound. The synthesis of anthraquinone from phthalic anhydride confirms this view of its structure. When the anhydride is heated with benzene in the presence of a dehydrating agent, such as aluminium chloride, one molecule of water is lost and anthraquinone is formed —... 

On the other hand, quinones such as 9,10 anthraquinone made from the oxidation of anthracene contains double bonds that are part of an aromatic system and therefore it could not act as a dienophile in a Diels-Alder reaction. This is because the disruption of the double bond loses the extra stability of aromatic compounds. 

In Europe, where an abundant supply of anthracene has usually been available, the preferred method for the manufacture of anthraquinone has been, and stiU is, the catalytic oxidation of anthracene. The main problem has been that of obtaining anthracene, C H q, practically free of such contaminants as carbazole and phenanthrene. Many processes have been developed for the purification of anthracene. Generally these foUow the scheme of taking the cmde anthracene oil, redistilling, and recrystaUizing it from a variety of solvents, such as pyridine (22). The purest anthracene may be obtained by azeotropic distillation with ethylene glycol (23). 

Has been purified by co-distillation with ethylene glycol (boils at 197.5°), from which it can be recovered by additn of water, followed by crysm from 95% EtOH, benzene, toluene, a mixture of benzene/xylene (4 1), or EtjO. It has also been chromatographed on alumina with pet ether in a dark room (to avoid photo-oxidation of adsorbed anthracene to anthraquinone). Other purification methods include sublimation in a N2 atmosphere (in some cases after refluxing with sodium), and recrystd from toluene [Gorman et al. J Am Chem Soc 107 4404 1985]. 

Anthraquinone itself is traditionally available from the anthracene of coal tar by oxidation, often with chromic acid or nitric acid a more modern alternative method is that of air oxidation using vanadium(V) oxide as catalyst. Anthraquinone is also produced in the reaction of benzene with benzene-1,2-dicarboxylic anhydride (6.4 phthalic anhydride) using a Lewis acid catalyst, typically aluminium chloride. This Friedel-Crafts acylation gives o-benzoylbenzoic acid (6.5) which undergoes cyclodehydration when heated in concentrated sulphuric acid (Scheme 6.2). Phthalic anhydride is readily available from naphthalene or from 1,2-dimethylbenzene (o-xylene) by catalytic air oxidation. 

Although most of the experiments were carried out using p-xylene as substrate, several exploratory runs were made using other aromatic hydrocarbons. These are summarized in Table I. Maximum yields were not determined. Alkylnaphthalenes gave highly colored oxidates, from which only small amounts of naphthoic and naphthalic acids could be isolated. Oxidation of anthracene gave virtually quantitative yields of anthraquinone under extremely mild conditions (10). 

Methyl anthraquinone has been obtained by the oxidation of /3-methyl anthracene by several investigators 1 and material of the same origin, obtained by the benzene-extraction of crude commercial anthraquinone,2 has been fully described. As regards the synthesis from phthalic anhydride and toluene, both the preparation and properties of />-toluyl-o-benzoic acid 3 and the complete synthesis 4 have been the subject of several papers. This acid has also been prepared from o-carbomethoxy benzoyl chloride and toluene.5 The phthalic anhydride synthesis of anthraquinone derivatives in general has received considerable attention. An account of this work, together with extensive references, is given by Barnett.6... 

Quinones of the more reactive, polycyclic, aromatic systems can usually be obtained by direct oxidation, which is best carried out with chromium(vi) compounds under acidic conditions. In this way 1,4-naphthoquinone, 9,10-anthraquinone and 9,10-phenanthraquinone are prepared from naphthalene, anthracene and phenanthrene respectively (Expt 6.128). Also included in this section is the reduction of anthraquinone with tin and acid to give anthrone, probably by the sequence of steps formulated below. 

Despite the ionic reactions, other reactions (presented in Scheme 44) show that free-radical mechanisms can also take place. Catalyzed by ebselen, TBHP oxidation of alkylarenes to alkyl aryl ketones (141) [240], anthracene to anthraquinone (142), 1,4-dimethoxyarenes to 1,4-quinones (e.g., menadione 143) [244], and oxidative coupling of 2-aminophenol to phenoxazinone (144) [245] gave results similar to these when one-electron oxidants such as Ce(IV), Ag(II), or Mn(III) were the reagents. Moreover, oxidation of azine derived from 2-acetylpyridine gave a mixture of ketone (145) and condensed triazole (146) [240], The same result was found when cerium ammonium nitrate was used as the reagent. This suggests that the... 

Air, often in the presence of a catalyst. Examples of this method are the preparation of phthalic anhydride from naphthalene by air and vanadium oxide (Wohl s method, page 171), and the analogous oxidation of anthracene to anthraquinone. In the latter case, anthracene which is not entirely pure can be used. 

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