Naphthacene radical cation

The structures of the radical anion of dibenzo[a,c]naphthacene (135) and the corresponding radical cation were investigated by ESR and proton-ENDOR spectroscopies. ... 

Reaction of Sodium Salt of Naphthacene Dianions with Na-phthacene. An example of electron transfer that reveals the role of solvation in such a process is the reaction of the sodium salt of naphthacene dianions (Nap2-) with naphthacene (Nap) in benzene (15). To increase the solubility of this salt in benzene, small amounts of THF are added to the solution. Apparently, more molecules of THF solvate the Na+ cations associated with naphthacene radical anions (Nap -) than the Na+ cations aggregated with Nap2- dianions. Hence, the disproportionation equilibrium for this system is described by the following reaction ... 

The plot of log Kdispa versus log [THF] shown in Figure 11 is linear and has a slope of -2. This result implies that m - n = 1, that is, one additional molecule of THF solvates each Na+ cation as the dianions of naphthacene are converted into radical anions. 

Polarographic reduction of aromatic cation radicals (e.g. perylene, naphthacene, anthracene, pyrene and others) in trifluoracetic acid-boron trifluoride leads to the formation of the radical ArH2 [eqns (5)-(7)] and has shown that reduction of the cation radical (5) is... 

Knowledge of how aluminum chloride oxidizes aromatics to cation radicals is practically non-existent. At one time it seemed that a nitro compound was a necessary co-acceptor (Buck et al., 1960) and that, whereas with mononuclear alkylaromatics, the Lewis acid-nitro compound pair formed only charge transfer complexes (Brown and Grayson, 1953), complete electron transfer occurred with more easily oxidized aromatics. But, cation-radical formation from perylene, anthracene, and chrysene was found to occur in carbon disulfide, chloroform, and benzene solutions, too (Rooney and Pink, 1961) and even occurs on warming anthracene and naphthacene with solid aluminum chloride (Sato and Aoyama, 1973). There is no doubt that a nitro compound enhances electron transfer, however (Sullivan and Norman, 1972). Cation radical formation in AlCl3-nitromethane has been estimated as approximately 100% as compared with 1% in sulfuric acid oxidation of dialkoxybenzenes (Forbes and Sullivan, 1966). Unfortunately, aluminum halide salts have not been isolated and, therefore, even the beginnings of analytical data have yet to be collected. There is no definite knowledge of either the nature of the counter ion or the fate of the electrons in these cation-radical formations. 

Among other Lewis acids, sulfur trioxide in dimethyl sulfate solution oxidizes perylene to the cation radical. Naphthacene is so easily oxidized that the dication is formed (Aalbersberg et al., 1959b). 

Some aromatic hydrocarbons (e.g. perylene) give cation radicals in (neat) antimony trichloride solutions at 75° (Porter et al., 1970 Johnson, 1971). However, the cation radicals are not formed in the absence of oxygen. In fact, molten antimony trichloride can be used as a solvent at 99° for the anodic oxidation of perylene, naphthacene, and other polynuclear aromatics, provided that the electrolyte (e.g. KC1) is highly dissociated (Bauer et al., 1971). When a more covalent electrolyte (e.g. A1C13) is used, the solvent system itself becomes the oxidant [(17) and (18)]. 

Polynuclear aromatic hydrocarbons are the most easily oxidized on catalyst surfaces. Perylene and anthracene have been the most commonly used hydrocarbons, and their cation radicals have been characterized in such work by esr and absorption spectroscopy. Naphthalene (Rooney and Pink, 1962) and naphthacene (Flockhart et al., 1966) have been used, but their oxidation to the cation radical goes only poorly. 

Formation of dicationic dimers (90) has been longer known than formation of the monocationic type (89), no doubt because of the availability of and interest in the very stable Wurster Salts. Hausser and Murrell (1957) proposed that the long wave-length absorption band (near 800 nm) of Wurster s Blue perchlorate in ethanol at —90° was caused by two associated, cation radicals lying in parallel planes. Since that time a considerable number of workers have explored the dimerization of Wurster and analogous cation radicals, (e.g. Kawamori et al., 1966 Kimura et al., 1968). Not only does Wurster s Blue cation radical (i.e. TMPD +) associate with itself, but it also forms a spin paired dimer with p-phenylenediamine cation radical (PD +). In fact, Takimoto et al. (1968) conclude from absorption spectroscopy that solutions of TMPD + and PD + in ethanol-ether at —195° contain (PD"+)2 and (PD"+-TMPD +)2 but very little of (TMPD +)2. Dimerization of unlike cation radicals is known in other systems too. Perylene" and naphthacene4-each forms an (M"+)2 dimer in sulfuric acid at reduced temperatures (Kimura et al., 1971). Mixtures of the two cation radicals in sulfuric acid leads to a mixed dimer too, (Perylene "+, naphthacene +), the heat of formation of which (—7-7 kcal mole-1) incidentally, lies between that of the perylene"+ (—8-8) and naphthaccne + (— 5 6) dimers (Yamazakiand Kimura, 1972). 

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