Oxidation of anthrone

Moro-Oka et al. (1976) have reported that the oxidation of 9,10-dihydroanthracene by K02 solubilized in DMSO by 18-crown-6 gives mainly the dehydrogenated product, anthracene. Under the same conditions, 1,4-hexadiene is dehydrogenated to benzene. The authors proposed a mechanism in which the superoxide ion acts as a hydrogen-abstracting agent only. The oxidations of anthrone (to anthraquinone), fluorene (to fluorenone), xanthene (to xanthone) and diphenylmethane (to benzophenone) are also initiated by hydrogen abstraction. 

Hydrolysis of the oxidate of anthrone resulted in the precipitation of anthraquinone (m.p. 263-268°C.). Extraction of the aqueous filtrate with chloroform yielded the DMSO adduct (1 to 1) of anthraquinone (m.p. 158-158.5°C.) (recrystallized from a chloroform-cyclohexane mixture). 

A sample of the monohydroperoxide, previously reported by Bickel and Kooyman (2), was obtained by autoxidation of 9,10-dihydroanthra-cene in benzene under ultraviolet irradiation. When this compound was treated under nitrogen with benzyltrimethylammonium hydroxide, it decomposed to give a mixture of anthracene and anthrone. (Under acidic conditions, it decomposed entirely to anthracene.) A fresh sample of the hydroperoxide was then oxidized. The physical appearance of the reaction mixture was similar to that in the oxidation of anthrone. The product was analyzed, and the conversion to anthraquinone was only 59%. Again, other oxidation products or anthrone may have contributed to the anthraquinone estimate. 

The catalytic activity of alkylamines in the oxidation of anthrone by 2 in DMS decreased in the order primary > secondary > tertiary amines. The order of reaction for each of the reagents was determined, and the formation of complexes between anthrone and amines were confirmed and their formation constants and rate constant were determined. ... 

Kinetic evidence of the influence of the structure of aliphatic amines on their catalytic activity in the O2 oxidation of anthrone in DMSO has been compared with results of quantum-chemical calculations amine catalytic activity was directly related to an increase in the absolute value of the heat of formation of the corresponding ammonium cation. ... 

Emodins with both aromatic rings hydroxylated are synthesised exclusively by the polyketide pathway as octaketides. Biosynthesis of bianthrones and other condensed emodin derivatives occurs by one-electron oxidation of anthrone derivatives (anthranols) to radicals, which are joined to form bianthrones. 

Phosphazenes has also been used as catalysts in several other reactions including asymmetric Mannich reaction,ring-opening polymerization of rac-lactide and cyclic esters as well as in the oxidation of anthrones. Luminescence of room temperature ionic liquids containing triallyl-(pentafluorocyclotriphosphazenyl)ammonium moieties (180) was studied. They all revealed blue-luminescence under an excitation of... 

In pulp and paper processing, anthraquinone (AQ) accelerates the delignification of wood and improves liquor selectivity. The kinetics of the liquid-phase oxidation of anthracene (AN) to AQ with NO2 in acetic acid as solvent has been studied by Rodriguez and Tijero (1989) in a semibatch reactor (batch with respect to the liquid phase), under conditions such that the kinetics of the overall gas-liquid process is controlled by the rate of the liquid-phase reaction. This reaction proceeds through the formation of the intermediate compound anthrone (ANT) ... 

In 2006, Tan and co-workers reported the first asymmetric guanidine catalyzed Diels-Alder addition of anthrone to maleimides (Scheme 75) [130], The authors observed very high yields and enantioselectivities using a derivative of Corey s C2-symmetric bicyclic gnanidine catalyst. The addition of anthrones to maleimide also worked well for snbstitnted anthrones. Interestingly, the anthors observed the oxidized prodnct when the anthrone was substituted at the meto-positions (Scheme 76). 

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. 

Oxidation of Related Compounds. Several other compounds related to dihydroanthracene in structure were oxidized in pyridine solvent (Table VI). No attempt was made to optimize the yields in any instance except with dihydroanthracene. It was surprising that anthrone reacted much more slowly than dihydroanthracene and that only a 40% yield of anthraquinone was obtained. 

Dr. Russell Is it possible that the oxidation of 9,10-dihydroanthra-cene is more exothermic than that of anthrone and that the heat generated could have accounted for the high yield of anthraquinone in the 2-hour reaction ... 

Dr. Schowalter It appears that this is another mechanism that could account for the oxidation of dihydroanthracene without intermediate anthrone formation. 

The oxidation of 10 with chromic anhydride in aqueous acetic acid leads to anthrone 218 and to anthraquinone 219 with excess oxidant. According to the authors opinion (54JOC1533), the oxidation process was supposed to include the primary formation of diketone 9 it was this compound, but not the initial salt 10, which was oxidized to anthrone 218. 

Hydroxylation at the benzylic position is encountered very rarely. An example is the oxidation of 10-methylanthrone to lO-hydroxy-lO-methyl-anthrone in 67% yield on treatment with 30% hydrogen peroxide in 10% sodium hydroxide in hot ethanol for 3 min (equation 164) [1126]. 

Chemical and biochemical reactions can be viewed by diffraction methods provided the reactions are slow and the techniques for measuring them are rapid. For example, Lonsdale and coworkers studied the conversion of a photo-oxide of anthracene on exposure to Cu Ka or Mo Ka X rays at room temperature. A single mixed crystal of anthraquinone and anthrone is formed which still shows crystallinity. The crystal does not change in appearance, and the space group remains P2i/a, but the unit-cell dimensions change ... 

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). 

The use of fresh bark, which contains free anthrones, may cause severe vomiting, intestinal cramping, and possibly spasms (Anonymous, 1996). Therefore, the bark requires either storage for at least 1 yr before use or artificial conversion by heat to allow oxidation of the harsh laxative constituents, the emodin glycosides (anthrones), to less active monomeric forms (Tyler, 1994 Anonymous, 1996). 

Anthralin, Fig. (18) is the most common therapeutic agent among a small number of pro-oxidant 9-anthrones, effective in the topical treatment of psoriasis. However, the usefulness of this drug is diminished by toxic side effects, including skin irritation and inflammation. Several studies suggest... 

Little is known about the biosynthetic origin of hypericin(s) they are related to the anthranoid metabolism and emodin anthrone is possibly their precursor. Synthesis in vitro of hypericin following alkaline dimerization of emodin and oxidation of its reduction derivative, emodine anthrone, has in fact been demonstrated [35,36]. 

Oxidative dimerization of anthrone and its derivatives can be effected by oxygen,286 aromatic nitro compounds,287 diazomethane,288 or oxygen in the presence of palladium.289 The following procedure is for the use of nitrobenzene 287... 

Under certain conditions, oxanthrone can also be formed during the hydrogenation process (Scheme 14.3). Oxanthrone is not reoxidized in the autoxidation process, and further hydrogenation of oxanthrone leads to anthrone, tetrahy-droanthrones, and dianthrones (the latter via oxidative dimerization of anthrone)... 

Oxidation of anthracene is interesting from the viewpoint of obtaining anthraquinone, a valuable product. The oxidation can actually be carried out by a non-catalytic method using any oxidant, but the non-catalytic process requires rigid conditions and is accompanied by formation of a number of side products, especially anthrone and bianthrone (Eq. 12-27). 

TLC has been useful also for following the fermentative oxidation of rhein-anthrone to rhein and rhein-dianthrone [136] solvent II on silica gel G was used. 

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