9,10-dihydroanthracene hydrogenation

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. 

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. 

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. 

The photo-oxidation of n-butane has been modelled by ab initio and DFT computational methods, in which the key role of 1- and 2-butoxyl radicals was confirmed.52 These radicals, formed from the reaction of the corresponding butyl radicals with molecular oxygen, account for the formation of the major oxidation products including hydrocarbons, peroxides, aldehydes, and peroxyaldehydes. The differing behaviour of n-pentane and cyclopentane towards autoignition at 873 K has been found to depend on the relative concentrations of resonance-stabilized radicals in the reaction medium.53 The manganese-mediated oxidation of dihydroanthracene to anthracene has been reported via hydrogen atom abstraction.54 The oxidation reactions of hydrocarbon radicals and their OH adducts are reported.55... 

In a non-planar dihydroanthracene molecule, two types of geometrically distinct carbon-hydrogen bonds can be distinguished in the meso position. These types of bonds have been designated lin (for linear, since they lie almost along the line of the C9- -C10 direction) and perp (for perpendicular, since they lie almost perpendicular to the C9- C10 direction). The conformational implications of this on 9,10-dialkyl-9,10-dihydroanthracenes have been discussed by Beckett and Mulley (1955). 

Hydrogenation with the use of H-donating compounds 9,10-dihydroanthracene (DHA), diimide N2H2, hydroboration. 

Miyazawa et al. (92) related rates of decrease of aliphatic hydrogen protons during pyrolysis of ethylene tar pitch to formation of mesophase. Yokono et al, (93) used the model compound anthracene to monitor the availability of transferable hydrogen. Co-carboniza-tions of pitches with anthracene suggested that extents of formation of 9,10-dihydroanthracene could be correlated with size of optical texture. The method was then applied to the carbonization behaviour of hydrogenated ethylene tar pitch (94). This pitch, hydrogenated at 573 K, had a pronounced proton donor ability and produced, on carbonization, a coke of flow-type anisotropy compared with the coarse-grained mosaics (<10 ym dia) of coke from untreated pitch. 

Obara et al. (95) co-carbonized a petroleum pitch which gave a coke of mosaic size of optical texture with the strong Lewis acid catalyst, aluminium chloride,which promoted the size of the optical texture and extents of hydrogen transfer to added anthracene. A correlation was established between size of optical texture of the resultant cokes and extents of formation of 9,10-dihydroanthracene plus evolved hydrogen gas. 

Another significant technique developed by Sanada s group is the characterization of pitch for its electron donor ability, which is estimated by the amount of hydrogen transferred from pitch to anthracene after the mixture has been heated to 400°C (22). The present authors later showed that the electron acceptor ability of pitch can be estimated in a similar manner by using a mixture of pitch and dihydroanthracene (23). The details of hydrogen transfer between pitch molecules is an important topic for study to understand the initial stages of carbonization processes. 

Dihydroanthracene is obtained in high yield in the hydrogenation over copper-chromium oxide in ethanol at 100°C (eq. 11.79)254 or in decalin at 150°C.255 Tetrahydroanthracene is obtained in high yield in the hydrogenation over copper-chromium oxide at 240-260°C and 9.5 MPa H2.255... 

---