Anthraquinones, by oxidation

Graebe and Liebermann378 converted anthracene into anthraquinone by oxidation with chromic acid in glacial acetic acid, although it is preferable379 to use sodium chlorate and vanadium pentoxide as catalysts. However, anthraquinone can also be prepared in good yield by use of potassium permanganate ... 

Another important group of dienophiles of the a,p-unsaturated carbonyl class are quinones. 1,4-Benzoquinone reacts readily with butadiene at room temperature to give a high yield of the mono-adduct, tetrahydronaphthaquinone (3.8) under more vigorous conditions a bis-adduct is obtained which can be converted into anthraquinone by oxidation of an alkaline solution with atmospheric oxygen. As with other dienophiles, alkyl substitution on the double bond leads to a decrease in activity and cycloaddition of monoalkyl 1,4-benzoquinones with dienes occurs preferentially at the unsubstituted double bond. In addition to steric effects, electronic effects can play a part, such that cycloaddition occurs at the more electron-deficient double bond of the benzoquinone. The first step in an approach to the steroid ring system makes use of such selectivity (3.9). ... 

Prepared by condensing p-chlorophenol with phlhalic anhydride in sulphuric acid solution in the presence of boric acid. The chlorine atom is replaced by hydroxyl during the condensation. It can also be prepared by oxidation of anthraquinone or 1-hydroxyanthraquinone by means of sulphuric acid in the presence of mercury(ll) sulphate and boric acid. 

Although considered an active participant in the process cycle, the tetrahydroaLkylanthraquinone (10) may not be a significant part of the catalytic hydrogenation because, dependent on the concentration in the working solution, these could all be converted to the hydroquinone by the labile shift per equation 17 and not be available to participate. None of the other first- or second-generation anthraquinone derivatives produce hydrogen peroxide, but most are susceptible to further reaction by oxidative or reductive mechanisms. 

SuIfona.tlon, Sulfonation is a common reaction with dialkyl sulfates, either by slow decomposition on heating with the release of SO or by attack at the sulfur end of the O—S bond (63). Reaction products are usually the dimethyl ether, methanol, sulfonic acid, and methyl sulfonates, corresponding to both routes. Reactive aromatics are commonly those with higher reactivity to electrophilic substitution at temperatures > 100° C. Tn phenylamine, diphenylmethylamine, anisole, and diphenyl ether exhibit ring sulfonation at 150—160°C, 140°C, 155—160°C, and 180—190°C, respectively, but diphenyl ketone and benzyl methyl ether do not react up to 190°C. Diphenyl amine methylates and then sulfonates. Catalysis of sulfonation of anthraquinone by dimethyl sulfate occurs with thaHium(III) oxide or mercury(II) oxide at 170°C. Alkyl interchange also gives sulfation. 

Quinizarin has been prepared by heating /)-chlorophenol, phthalic anhydride, and sulfuric acid by heating hydroquinone with phthalic anhydride - by heating hydroquinone, phthalic anhydride and c.i>. sulfuric acid by oxidizing anthraquinone... 

Figure 2.6 Anthraquinone derivatives can photoreactively couple to substrates by means of a free radical generation process. The reactive intermediate also can be regenerated back to the initial anthraquinone by proton abstraction and oxidation, resulting in the possibility of again being photolyzed and successfully coupled to the substrate.

The anthronylidenes lp-lr are easily matrix-isolated by photolysis of the corresponding diazo compounds 2 (Scheme 17).99 The reaction of the carbenes with molecular oxygen results in the formation of anthraquinone 0-oxides 7,... 

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. 

Kagedal, K., Bironaite, D., and Olhnger, K., 1999, Anthraquinone cytotoxicity and apoptosis in primary cultures of hepatocytes. Free Rad. Res. 31 419-428 Kagedal, K., Johansson, U., and Olhnger, K., 2001, The lysosomal protease cathepsin D mediates apoptosis induced by oxidative stress. FASEB J. (May 18, 2001) 10.1096/. 00-0708fje... 

The methyl substituent of 2-methyl-4,8-dihydrobenzo[l,2- 5,4-. ]dithiophene-4,8-dione 118 undergoes a number of synthetic transformations (Scheme 8), and is therefore a key intermediate for the preparation of a range of anthraquinone derivatives <1999BMC1025>. Thus, oxidation of 118 with chromium trioxide in acetic anhydride at low temperatures affords the diacetate intermediate 119 which is hydrolyzed with dilute sulfuric acid to yield the aldehyde 120. Direct oxidation of 118 to the carboxylic acid 121 proceeded in very low yield however, it can be produced efficiently by oxidation of aldehyde 120 using silver nitrate in dioxane. Reduction of aldehyde 120 with sodium borohydride in methanol gives a 90% yield of 2-hydroxymethyl derivative 122 which reacts with acetyl chloride or thionyl chloride to produce the 2-acetoxymethyl- and 2-chloromethyl-4,8-dihydrobenzo[l,2-A5,4-3 ]-dithiophene-4,8-diones 123 and 124, respectively. 

Anthraquinone. Anthraquinone an important intermediate used extensively in the dye industry can be manufactured through the oxidation of anthracene.1041,1042 Almost all anthraquinone is currently produced by oxidation with Cr03 in the liquid phase (50-100°C) with selectivity better than 90% at complete conversion. 

Anthraquinone is obtained by oxidation of anthracene using sodium bichromate plus sulfuric add, and is purified by dissolving in concentrated sulfuric acid at 130 Cl and pouring into boiling water, whereupon anthraquinone separates as pure solid, and is recovered by filtration, Further... 

The following unimportant preparative methods may be mentioned the production of /3-methyl anthraquinone by the reduction of 2-bromo-3-methyl anthraquinone 7 the oxidation of /3-methyl anthracene-7-carboxylic acid 8 and the reduction of 2-methyl anthraquinonyl-i-diazonium sulfate.9... 

Anthracene can be selectively oxidized to anthraquinone by molecular oxygen in the presence of copper(II) bromide in an ethylene glycol solution. Ethylene glycol (EG) acts as a bidendate ligand for copper and prevents the formation of bromoanthracene as a by-product (equation 267).596... 

Although many substances have been produced by oxidation methods anthraquinone, vanillin, saccharin oxidation is not so easily graduated as the reduction processes. The overvoltage of oxygen is relatively high at most anodes, and frequently the compound to be oxidised is decomposed during treatment and carbon dioxide formed. 

Anthraquinone vat dyes containing a thia-zole ring include C.I. Vat Yellow 2, the synthesis of which is shown in Fig. 13.125. In this case, at least two approaches are possible. In the first, 2,6-diaminoanthraquinone is condensed with benzotrichloride in the presence of sulfur and the initial product is oxidized without isolation to give the target dye. Alternatively, the starting diamine can be chlorinated and converted to the corresponding dithiol (47). At this point condensation with benzaldehyde followed by oxidation (e.g. air or dichromate) gives the dye. 

For the manufacture of alizarin on a large scale a very pure anthraquinone is required, and this is generally prepared by oxidation of anthracene with sodium bichromate and dilute sulphuric acid. The anthracene is generally a 50-per-cent, product which has oeen converted into a soft powder by subliming with superheated steam. The oxidation takes place in lead-lined vessels in which the mixture is heated by direct steam. By employing a pure anthracene and a not too concentrated oxidation-mixture, the anthraquinone separates as soft grey powder, which is freed from acid by washing wdth water. The crude product is then dried, dissolved in concentrated sulphuric acid, and precipitated with water. A further purification is effected by sublimation with superheated steam. 

Substituted orthoquiiutnes. Crude phenanthrenequinone prepared by oxidation of technical (90%) phenanthrene can be freed from anthraquinone and other contaminants by triturating it with 4-6 portions of hot 40% bisulfite solution, filtering, cooling, collecting the adduct, and adding hydrochloric acid to a suspension in water."... 

The second product identified by Meyer, oxanthrone acetate (5, better 10-acetoxy-9-anthrone), was obtained in moderate amount by oxidation of 9-acetoxy-anthracene (3) with lead tetraacetate in acetic acid. Oxidation of (3) in refluxing benzene resulted in 1,4-addition to give the triacetoxy compound (4). This substance when heated in acetic acid is converted largely into lO-acetoxy-9-anthrone (5) by loss of acetic anhydride and to a lesser extent into 9,10-diacetoxyanthracene (7) by loss of acetic acid. If (4) is an intermediate in the oxidation of (3) in acetic acid lo (5), the acetoxy group in the product (5) must be attached to a different meso carbon atom (5) than in (3), and this inference was shown to be correct by oxidation of 2-methyl-9-acetoxyanthracene and identification of the product as 2-methyl-I O-acetoxy-9-anthrone by synthesis. Both (5) and (7) on further oxidation with lead tetraacetate in acetic acid yield anthraquinone, probably via the products of acetoxylation of (5) and 1,4-addition to (7). 

Anthracene was oxidized to anthraquinone by warming a mixture of 90 g. of finely powdered hydrocarbon, 0.5 g. of vanadium pentoxide, 76 g. of sodium chlorate, 1 1. of acetic acid, and 200 ml. of 2% sulfuric acid under reflux until a vigorous reaction set in. After eventual brief refluxing, anthraquinone was obtained in 88-91% yield. The method is not suitable for the oxidation of hydrocarbons of the naphthalene or phenanthrene series to the quinones or for oxidation of acenaphthene or fluorene. 

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