9.10- Dihydroanthracene reactions

With the above procedure, variables such as reaction temperature, mole ratio of catalyst to dihydroanthracene, reaction solvent, and oxygen concentration were examined. 

The hydroperoxide radical reacts with another molecule of oxygen (Reaction 5) to give the hydroperoxide-peroxy radical. This radical in turn reacts with a molecule of dihydroanthracene (Reaction 6), to give the dihydroperoxide and generate a radical to propagate the chain. However, the hydroperoxide radical formed in Reaction 4 may be decomposed by a carbanion to the anthracene diradical (Reaction 7). [An example of the decomposition of an unstable hydroperoxide by reaction with an anion is found in the basic autoxidation of 2-nitropropane (3).]... 

In the following preparation, this reaction is exemplified by the union of anthracene with maleic anhydride, to form 9,io-dihydroanthracene-9,io-e do-a -succinic anhydride note that as a result of this reaction both the outer rings of the anthracene system become truly aromatic in character. 

Examples include luminescence from anthracene crystals subjected to alternating electric current (159), luminescence from electron recombination with the carbazole free radical produced by photolysis of potassium carba2ole in a fro2en glass matrix (160), reactions of free radicals with solvated electrons (155), and reduction of mtheiiium(III)tris(bipyridyl) with the hydrated electron (161). Other examples include the oxidation of aromatic radical anions with such oxidants as chlorine or ben2oyl peroxide (162,163), and the reduction of 9,10-dichloro-9,10-diphenyl-9,10-dihydroanthracene with the 9,10-diphenylanthracene radical anion (162,164). Many other examples of electron-transfer chemiluminescence have been reported (156,165). 

The reaction of benzyl radicals wdth several heterocyclic compounds W as more extensively studied by Waters and Watson, " - who generated benzyl radicals by decomposing di-tert-butyl peroxide in boiling toluene. The products of the reaction with acridine, 5-phenyl-acridine, 1 2- and 3 4-benzacridine, and phenazine were studied. Acridine gives a mixture of 9-benzylacridine (17%) (28) and 5,10-dibenzylacridan (18%) (29) but ho biacridan, w hereas anthracene gives a mixture of 9,10-dibenzyl-9,10-dihydroanthracene and 9,9 -dibenzyl-9,9, 10,10 -tetrahydrobianthryl. This indicates that initial addition must occur at the meso-carbon and not at the nitrogen atom. (Similar conclusions were reached on the basis of methylations discussed in Section III,C.) That this is the position of attack is further supported by the fact that the reaction of benzyl radicals with 5-... 

In some model compound studies with the i-PrOH/KOH system we found that anthracene was converted to 9,10-dihydroanthracene in 64% yield. Benzyl phenyl ether was also studied and was converted to a polymeric material under the reaction conditions. There were no traces of phenol nor toluene, the expected reduction products. 

Model compound studies were also carried out in MeOH/KOH, and the results are shown in Table VI. Phenanthrene and biphenyl were quantitatively recovered unchanged by the reactions, and bibenzyl was recovered in 95% yield, with small amounts of toluene observed. Anthracene and diphenyl ether, on the other hand, were converted respectively to 9,10-dihydroanthracene and a mixture of polymethyl-phenols similar to that observed in the work with coal. The cleavage of diphenyl ether via hydrogenolysis should yield both benzene and phenol as products we saw no benzene in our study, and our... 

Kwok, E.S.C., Atkinson, R., Arey, J. (1997) Kinetic of the gas-phase reactions of indan, indene, fluorene, and 9,10-dihydroanthracene with OH radicals, NOs radicals, and 03. Int. J. Chem. Kinet. 29, 299-309. 

Howard and Ingold studied this equilibrium reaction in experiments on the oxidation of tetralin and 9,10—dihydroanthracene in the presence of specially added triphenylmethyl hydroperoxide[41]. They estimated the equilibrium constant K to be equal to 60 atm-1 (8 x 103 L mol-1, 303 K). This value is close to T=25atm-1 at 300 K (A/7=38kJ mol-1), which was found in the solid crystal lattice permeable to dioxygen [84], The reversible addition of dioxygen to the diphenylmethyl radical absorbed on MFI zeolite was evidenced and studied recently by the EPR technique [85],... 

Reactions of phenoxyl and aminyl radicals with RH and ROOH are chain propagation steps in oxidation inhibited by phenols and amines (see Chapter 14). Both reactions become important when their rates are close to the initiation rate (see Chapter 14). Mahoney and DaRooge [57] studied the oxidation of 9,10-dihydroanthracene inhibited by different phenols. He went on to estimate the values of rate constants ratio of the reaction of ArO with RH and the reaction In + In (reactions (9) and (10), see Chapter 14) by the kinetic study. The values of kw for the reaction... 

Isolation of Oxidation Products. After oxygen absorption had ceased, or reached the desired value, the oxidates were poured into water. In many cases the reaction product could be removed by filtration in high yield. In this manner xanthone (m.p. 172-174°C.), was isolated from oxidations of xanthene or xanthen-9-ol thioxanthone (m.p. 208-210°C.), from thioxanthene acridine (m.p. 107-109°C.), from acridan anthracene (m.p. 216-217°C.), from 9,10-dihydroanthracene phenanthrene (m.p. 95-99°C.), from 9,10-dihydrophenanthrene pyrene (m.p. 151-152.5°C.) (recrystallized from benzene) from 1,2-dihydropyrene and 4-phenan-throic acid (m.p. 169-171 °C.) (recrystallized from ethanol) by chloroform extraction of the hydrolyzed and acidified oxidate of 4,5-methyl-enephenanthrene. 

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. 

A homogeneous reaction system was used in which benzyltrimethyl-ammonium hydroxide was the base and pyridine the solvent. An oxidation mechanism is proposed that is consistent with observations on the reaction variables and possible oxidation intermediates of dihydroanthracene. 

Table I. Effect of Initial Reaction Temperature on Oxidation of Dihydroanthracene to Anthraquinone0...

Reaction mixture and conditions anhydrous pyridine, 50 ml., benzyltrimethylammonium hydroxide, dihydroanthracene, 9.0 grams, 50 mmoles reaction time, 2 hrs. 

Solvent Effects. The conversion of dihydroanthracene could be increased by adding water to the pyridine solvent (Table III). An 86% conversion to anthraquinone was obtained when 95% aqueous pyridine was used as the solvent. Furthermore, methanol could be substituted for the water with equivalent results. Other solvents were tried in place of pyridine (Table IV). The data indicate that 95% aqueous pyridine gave the best yields, although aniline gave nearly similar results. When acetonitrile and dimethylformamide were used, the large amounts of unreacted starting material indicate that these solvents may have deactivated the base by undergoing a hydrolysis reaction. 

Mechanism for Base-Catalyzed Autoxidation of 9,10-Dihydroanthracene. The autoxidation of 9,10-dihydroanthracene in pyridine as the solvent and in the presence of benzyltrimethylammonium hydroxide, a strong base, is believed to involve the reaction of a carbanion and molecular oxygen. Indirect evidence of the existence of the carbanion of dihydroanthracene in pyridine solution comes from the color that forms in the presence of the base. When dihydroanthracene is added to a pyridine solution of the base, a deep blood-red color develops immediately. This color is not completely attributable to carbanions since a trace of anthra-quinone alone will produce it. However, under an inert atmosphere (nitrogen) in which no anthraquinone can be formed, a deep red color is also formed. 

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. 

An attempt was made to determine the amount of hydrogen peroxide formed and correlate it with the amount of anthracene. An experiment was made with oxygen at atmospheric pressure and a reaction temperature of —20°C., so that any hydrogen peroxide formed would be less likely to decompose. The solid product (88% recovery of dihydroanthracene) was isolated and found to contain 1 mmole of anthracene. The... 

This study indicates that the oxidation of dihydroanthracene in a basic medium involves the formation of a monocarbanion, which is then converted to a free radical by a one-electron transfer step. It is postulated that the free radical reacts with oxygen to form a peroxy free radical, which then attacks a hydrogen atom at the 10-position by an intramolecular reaction. The reaction then proceeds by a free-radical chain mechanism. This mechanism has been used as a basis for optimizing the yield of anthraquinone and minimizing the formation of anthracene. 

Mahoney studied this kinetics by the oxidation of 9,10-dihydroanthracene inhibited by several substituted phenols [23,31,32,37,38,49]. 9,10-Dihydroanthracene possesses weak C—H bonds that are easily attacked not only by peroxyl radicals but also by phenoxyl radicals as well (for the rate constants of reaction (10), see Chapter 15). 

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