Anthracene, hydrogen transfer

In summary, the A1- and A2-dialin isomers have been shown to be appreciably more active than etralin (and decalin) in transferring hydrogen to anthracene and phenanthrene. The observed selectivity of this hydrogen transfer is in accord with the Woodward-Hoffman rules for group transfer reactions, anthracene conversions being in the ratio ( 3 / 0 ) = 12/1 >> 1 while phenanthrene conversions are in the ratio ( 0/(33 ) = 0.6/1 < 1. The quantitative differences in the selectivities observed with anthracene and phenanthrene are being further explored. 

At typical coal liquefaction conditions, namely temperatures from 300 to 400 C and reaction times on the order of 1 hr, hydrogen transfer from model CIO donors, the A1- and A2-dialins, to model C14 acceptors, anthracene and phenanthrene, occurs in the sense allowed by the Woodward-Hoffman rules for supra-supra group transfer reactions. Thus, in the conversion of the C14 substrates to their 9, 10 dihydro derivatives the dialins exhibited a striking reversal of donor activity, the A dialin causing about twice as much conversion of phenanthrene but only one-tenth as much conversion of anthracene as did A2-dialin. 

In the case of anthracene, An-02 is converted to 10-hydroxyanthrone, which is further oxidized to yield the final six-electron oxidation product, i.e. anthraqui-none, accompanied by generation of H202 with the further photoirradiation (2 > 430 nm) of an 02-saturated CD3CN solution of An-02 and Acr+-Mes [61]. When the reaction is started from the isolated An-02, no photochemical reaction has occurred without Acr+-Mes or no thermal reaction has taken place with Acr+-Mes [61]. Under photoirradiation in the presence of Acr+-Mes, electron transfer from An-02 to the Mes + moiety of Acr -Mes+ results in 0-0 bond cleavage of An-02+, followed by facile intramolecular hydrogen transfer to produce the 10-hydroxyanthrone radical cation as shown in Scheme 13.4 [61]. The back electron transfer from the Acr moiety to 10-hydroxyanthrone radical cation affords 10-hy-... 

In another example, the hexaacetylene 109 - after deprotection with potassium carbonate in methanol - is subjected to typical Bergman trapping conditions, resulting in the formation of the anthracene derivative 110 [61]. As a third, more complex illustration, the aroma-tization of the triacetylene 111 may be considered. Here, the 1,4-diradical intermediate faces another triple bond as an internal trap, and, after hydrogen transfer from 1,4-cyclohexadiene, the tricyclic allylic alcohol 112 is produced [61]. 

Virk and Garry (24a) have recently investigated hydrogen transfer from cyclohexanol to anthracene and phenanthrene and have reported well-behaved second-order kinetics. These workers suggest that this reaction may occur by a concerted molecular H2-transfer. Simple second-order kinetic behavior, however, is also consistent with molecular disproportionation (and also with hydride, H, transfer). However, if it is assumed that (k, /k ) = 0.1, predicted rates are only 1/100... 

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. 

The results of this investigation of hydrogen transfer are presented in table 9.3. The experiment with thermal treatment of pure anthracene (E.l) demonstrated that a significant amount of dihydroanthracene was found in the used anthracene after thermal treatment. Therefore, it is important to use this fact in the discussion of the results. Experiment RE.3 is a reproducibility experiment in comparison with E.3. It is evident that the experimental method has a good reproducibility (relative divergence 4%). 

The 9-(aminoalkyl)anthracenes 67 and 68 also undergo intramolecular addition upon irradiation in benzene solution to yield the 1.4-adducts 69 and 70, respectively. The formation of these adducts is proposed to occur via photoinduced electron transfer followed by N-H proton transfer to yield 10-anthryI-aniIino biradical intermediates (Scheme 9). In the case of the biradical from 68, C-N bond formation affords adduct 70. The biradical from 67 undergoes C-C bond formation at the ortho position of the anilino radical, followed by hydrogen transfer to yield 69, rather than C-N bond formation to form the highly strained lower homolog of 70. The formation of 62 from the intramolecular reaction of 58 and of 5 from the iniermolecular reaction of anthracene and dimethylaniline may also occur via C-C bond formation in the biradical or radical pair intermediates. 

The crude tar is not completely inert during distillation, and some aromatics such as acenapthylene, anthracene and indene are partially converted into the corresponding hydroaromatics by hydrogen transfer from the pitch. 

The quality of anthracene obtained by this method is sufficient for the manufacture of anthraquinone by the usual processes. Because of hydrogen transfer during coal tar refining, the fore-runnings which arise during the distillation of the anthracene cake are enriched with 9,10-dihydroanthracene, which can be converted into anthracene by oxidation with air. This anthracene, recoverable by subsequent crystallization, is distinguished by an exceptionally low nitrogen content. 

SCHEME 6.4 Concerted hydrogen transfer reaction and aromatization in anthracene-cyclohexadiene system. 

Stein, S.E. Griffith, L.L. Bilhners, R. Chen, R.H. Hydrogen transfer between anthracene structures, J. Phys. Chem., 1986, 90, 517. 

Most often, these radicals are unstable and can exist only while adsorbed on the electrode, although in the case of polycyclic aromatic compounds (e.g., the derivatives of anthracene), they are more stable and can exist even in the solution. The radicals formed first can undergo a variety of chemical or electrochemical reactions. This reaction type is the analog of hydrogen evolution, where electron transfer as the first step produces an adsorbed hydrogen atom, which is also a radical-type product. 

Several methods can be employed to convert coal mto liquids, with or without the addition of a solvent or vehicle. Those methods which rely on simple pyrolysis or carbonization produce some liquids, but the main product is coke or char Extraction yields can be dramatically increased by heating the coal over 350°C in heavy solvents such as anthracene or coal-tar oils, sometimes with applied hydrogen pressure, or the addition of a catalyst Solvent components which are especially beneficial to the dissolution and stability of the products contain saturated aromatic structures, for example, as found in 1,2,3,4 tetrahydronaphthalene Ilydroaromatic compounds are known to transfer hydrogen atoms to the coal molecules and, thus, prevent polymerization... 

The main features of the chemiluminescence mechanism are exemplarily illustrated in Scheme 11 for the reaction of bis(2,4,6-trichlorophenyl)oxalate (TCPO) with hydrogen peroxide in the presence of imidazole (IMI-H) as base catalyst and the chemiluminescent activators (ACT) anthracene, 9,10-diphenylanthracene, 2,5-diphenyloxazole, perylene and rubrene. In this mechanism, the replacement of the phenolic substituents in TCPO by IMI-H constitutes the slow step, whereas the nucleophilic attack of hydrogen peroxide on the intermediary l,l -oxalyl diimidazole (ODI) is fast. This rate difference is manifested by a two-exponential behavior of the chemiluminescence kinetics. The observed dependence of the chemiexcitation yield on the electrochemical characteristics of the activator has been rationalized in terms of the intermolecular CIEEL mechanism (Scheme 12), in which the free-energy balance for the electron back-transfer (BET) determines whether the singlet-excited activator, the species responsible for the light emission, is formed ... 

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