Anthrone, from anthraquinone

Benzanthrone, in turn, is obtained from anthraquinone by reaction with glycerine and sulfuric acid in the presence of a reducing agent such as iron. Anthraquinone is initially reduced to anthrone, which is condensed with acrolein. Acrolein, on the other hand, is an intermediate of the reaction between glycerine and sulfu-... 

Preparation of nearly all important anthraquinones starts from the following key intermediates anthraquinonesulfonic acids, nitroanthraquinones, and the products of nucleus synthesis, 1,4-dihydroxy-, 2-methyl-, and 2-chloroanthraquinone. The only exceptions are derivatives with condensed rings, e.g., benzan-throne and derived products, which are prepared directly from anthraquinone via anthrone. 

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. 

Figure 2. (A) Structures of aromatic polyketides produced by A. arborescens. (B) Khellin andvisnagin in Ammi visnaga. (C) A hypothetical scheme for the involvement of OKS and as yet unidentified ketoreductase in the biosynthesis of anthrones and anthraquinones. In the absence of interactions with the reductase, OKS Just affords SEK4/SEK4b as shunt products, (Adapted from reference 7b, Copyright 2005 American Chemical Society,)...

This synergistic effect in mice results from synergistic stimulation of large intestinal transit and large intestinal water secretion [15,16], Recently, several investigations have been performed to determine whether intracaecally administered rhein-anthrone and anthraquinones such as aloe-emodin, Fig. 

Anthrone and anthraquinone derivatives are used as laxatives (F 2). The compounds formed in plants may repel potential predators (E 5.5.3). Hypericin, a photodynamic compound, is a feeding deterrent from Hypericum perforatum St. Johns wort, E 5.5.3). 

Benzanthrone (6.73) is the source of various commercially important violet, blue and green vat dyes. This tetracyclic system can be prepared from a mixture of anthraquinone and propane-1,2,3-triol (glycerol) by heating with iron powder in concentrated sulphuric acid. The reaction involves reduction of anthraquinone to anthrone (6.74) followed by condensation (Scheme 6.14) with propenal (acrolein), the latter compound being generated... 

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. 

The direct reaction of oxygen with the carbanion from dihydroanthracene does not seem likely. Russell (5) has indicated a preference for a one-electron transfer process to convert the carbanion to a free radical, which then reacts with oxygen to form an oxygenated species. Therefore, we considered a mechanism involving one-electron transfer to form a free radical from the carbanion, which would lead to the formation of anthraquinone and anthracene without having either the hydroperoxide or anthrone as an intermediate. 

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... 

Baughman (1992) measured the disappearance rate constants for a number of solvent and disperse azo, anthraquinone, and quinoline dyes in anaerobic sediments. The half-lives ranged from 0.1 to 140 days. Product studies of the azo dyes showed that reduction of the azo linkages and nitro groups resulted in the formation of substituted anilines. The 1,4-diaminoanthraquinone dyes underwent complex reactions thought to involve reduction and replacement of amino with hydroxy groups. Demethylation of methoxyanthraquinone dyes and reduction of anthraquinone dyes to anthrones also was observed. 

From 1, 1.4,10,10-tetrafluoro-9(10F/)-anthrone (5 %) and l,4-difluoro-9,10-anthraquinone arc obtained as byproducts. 2-Fluoro-1,3.5-trinitrobenzene (picryl fluoride, 4) has been synthesized from pyridinium pierate (3) by the use of diethylaminosulfur trifluoride (DAST).175... 

Aromatic natural products of polyketide origin are less prevalent in plants compared with microorganisms. The majority of the plant constituents that contain aromatic stmctures are known to arise from the shikimate pathway (see below). Unlike those derived from the shikimate pathway, aromatic products of the polyketide pathway invariably contain a meta oxygenation pattern because of their origin from the cyclization of polyketides. Phenolic compounds such as chrysophanol-anthrone (Bl), and emodin-anthrone (B2), and the anthraquinones, aloe-emodin (B3) and emodin (B4) (Fig. 2), are products of the polyketide pathway and are found to occur in some plants of the genera Cassia (Leguminosae) (21), Rhamnus (Rhamnaceae) (22), and Aloe (Liliaceae) (23). The dimer of emodin-anthrone (B2), namely hypericin, (B5) is a constituent of the antidepressant herbal supplement, St. John s wort (Hypericumperforatum, Hy-pericaceae) (24). 

Unfortunately anthrahydroquinone is not very stable under acid conditions, which are needed for a reversible cyclization of the benzoquinone derivatives. There is an early preparative observation on the rapid formation of anthraquinone (AQ) 3 and anthrone (Ant) 4 from anthrahydroquinone (AQH2) 1 in cold concentrated sulfuric acid [83] according the overall reaction... 

Adinolfi, M, Lanzetta, R, Marciano, C E, Parrilli, M, Giuliu, A D, A new class of anthraquinone-anthrone-C-glycosides from Asphodelus ramosus tubers. Tetrahedron, Al, 4435-4440, 1991. 

In practice, the anthraquinone process is much more complicated than has been de.scribed above, in that byproducts such as 1,2,3,4-tetrahydroanthraquinone are formed, particularly in the hydrogenation step. These behave similarly to anthrahydroquinones, but their further hydrogenation leads to octahydroanthrahydroquinones which are unusable in this process. Other byproducts such as oxanthrones and anthrones can only be partially regenerated. These unusable byproducts have to be removed from the process. 

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