Anthrone, oxidation

K. A. Schowaiter Our data indicate that both the hydroperoxide and anthrone oxidize at a slower rate than dihydroanthracene in our... 

Accordingly, the cyclopropenylidene anthrones 190/198 were converted by ferric chloride in hydroxylic solvents to the allene ketal 466, whose hydrolysis gives the allenic ketone 46 7288. The dioxolane 468 was obtained from the alkyl-substituted quinocyclopropene 190 in glycol and the ketone 467 in methanol. Apparently FeCl3 served not only as an oxidant, but also as a Lewis acid assisting solvent addition to C1 2 of the triafulvene. 

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) ... 

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. 

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). 

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). 

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. 

If the 9,10-dihydro-9-anthranyl carbanion were to react directly with oxygen, 9,10-dihydro-9-anthranylhydroperoxide would be formed. This could decompose to give anthrone and/or anthracene. Anthrone, which would exist mainly as anthranol in a basic medium, generally is oxidized easily to anthraquinone. The following equations illustrate this reaction. 

However, when anthrone was oxidized under the same conditions as the dihydroanthracene, the conversion to anthraquinone was estimated to be only 40%, and that value was probably high because of interference by unreacted anthrone during analysis. Anthrone, then, was not readily oxidized, contrary to expectation if it were the intermediate to the quinone. 

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. 

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. 

Significant impact on the environment and generation of wastes (mainly associated with the less than 100% selectivity in the reduction and oxidation steps - formation ofhydroxyanthrones, anthrones, anthracenes, and epoxide, some solvent stripping by air used in the oxidation step, and in the crude H202 stream). 

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. 

Anthraquinones. A new regioselective route to highly substituted anthraquinones (4) involves the reaction of diketene in the presence of sodium hydride with ethyl 4-uryl-3-oxobutanoates (1) prepared as shown from arylacetic acids. The products, after mcthylation, are cyclized to anthrones (3), which are oxidized to anthraquinones.1... 

If a very simple reagent such as trichlorosilane (2) is applied to phenylphosphin-oxides (e. g. 9-phenyl-9-phospha-9,10-anthraquinone) the corresponding phenylphos-phine93,94 [e. g., 9-phenyl-9-phospha-anthrone (134)] is obtained (see Scheme 15). 

The phenomena occurring with these oxidations were later more accurately investigated by Perlin.3 From anthraquinone in 92% sulphuric acid 90 to 96% dioxyanthraquinones and a small quantity of monoanthraquinones were obtained. Besides a- and / -monooxyanthraquinone, quinizarin, alizarin, and pur-purin could be isolated. If the anthraquinone-sulphuric acid solution is employed as cathode fluid, anthranols, anthrones, and hydroanthranols are formed. If the sulphuric-acid concentration of the anode solution is increased, there are formed sulphurated oxyanthraquinones. 

This benzannelation provides the key step in a synthesis of the anthracycline 5. Thus reaction of the complex 2 with the acetylene 3 provides, after oxidation, the tetrahy-dronaphthol 4. The fourth ring of 5 is formed by ring closure to an anthrone followed by air oxidation (Triton B) to an anthraquinone. ... 

A rare example of photochemical cycloaddition to a C=N group is provided by the formation of benzoxazole (19) from pentachloro-phenol in acetonitrile. The photoconversion of 2-methylbenzo-phenone into the anthrone (20) involves two sequential photoprocesses via the E-enol (21) which under the influence of high intensity laser light absorbs a second photon to give the cyclized intermediate (22) which undergoes air-oxidation to (20) (Wilson et al.). 

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