Polynuclear aromatic hydrocarbon radical

Odd-Alternate Polynuclear Aromatic Hydrocarbon Radicals. Substantial evidence supports the contention that the stable free radicals formed during the pyrolysis of polynuclear aromatic compounds are odd-alternate hydrocarbon radicals. As an example, the phenalenyl radical (5) is formed during pyrolysis of a number of organic compounds including acenaphthylene (3) and dihydronaphthalene (4) (24) (see Scheme III). The... 

More recently it has become apparent that proton equilibria and hence pH can be equally important in aprotic and other non-aqueous solvents. For example, the addition of a proton donor, such as phenol or water, to dimethylformamide has a marked effect on the i-E curve for the reduction of a polynuclear aromatic hydrocarbon (Peover, 1967). In the absence of a proton donor the curve shows two one-electron reduction waves. The first electron addition is reversible and leads to the formation of the anion radical while the second wave is irreversible owing to rapid abstraction of protons from the solvent by the dicarbanion. 

Many chemicals are metabolized to carcinogens by processes that do not seem to involve free radicals a well-understood example is the oxidation of benzo(a)pyrene [B(a)P] to the diol epoxide by the cytochrome P450 system. However, the oxidation of B(a)P and other polynuclear aromatic hydrocarbons (PAH) to carcinogenic compounds can involve radicals. This statement, while once controversial, now has ample evidence (12.,22,25.). Although it is clear that some products arise from radical-mediated metabolism of PAH, the involvement of these products in tumorigenesis is less clear nevertheless, I believe that such evidence does now exist (12,12). 

It is now well established that a variety of organic molecules such as polynuclear aromatic hydrocarbons with low ionization energies act as electron donors with the formation of radical cations when adsorbed on oxide surfaces. Conversely, electron-acceptor molecules with high electron affinity interact with donor sites on oxide surfaces and are converted to anion radicals. These surface species can either be detected by their electronic spectra (90-93, 308-310) or by ESR. The ESR results have recently been reviewed by Flockhart (311). Radical cation-producing substances have only scarcely been applied as poisons in catalytic reactions. Conclusions on the nature of catalytically active sites have preferentially been drawn by qualitative comparison of the surface spin concentration and the catalytic activity as a function of, for example, the pretreatment temperature of the catalyst. Only phenothiazine has been used as a specific poison for the butene-1 isomerization on alumina [Ghorbel et al. (312)). Tetra-cyaonoethylene, on the contrary, has found wide application as a poison during catalytic reactions for the detection of active sites with basic or electron-donor character. This is probably due to the lack of other suitable acidic probe or poison molecules. 

Composition of Parent Pitch. Once the chemical composition of the carbonizing system moves away from the comparative simplicity of polynuclear aromatic hydrocarbons to that of industrial pitches, then the pyrolysis chemistry incorporates effects caused by the presence of heteroatoms (0, N and S) and alkyl and naphthenic groups. In general terms, the system becomes more Reactive creating higher concentrations of radicals detectable by ESR. This in turn, leads to enhanced cross-linkages and polymerization of molecular constituents of any mesophase which is formed, and this causes enhanced viscosity and a reduction in size of optical texture. 

Sullivan PD, Calle LM, Shafer K, et al. 1978. Effects of antioxidants of benzo[a]pyrene free radicals. In Freudenthal RI. Jones PW, eds. Polynuclear aromatic hydrocarbons 2nd International Symposium on Analysis. Chemistry, and Biology (Carcinogenesis-a comprehensive survey). Vol. 3. New York, NY Raven Press. 1-3. 

The PANs are known to be quite sensitive to walls in laboratory studies, and therefore are likely to react on aerosol surfaces. The PANs are very soluble in nonpolar organics. PANs can undergo important oxidation reactions on soot surfaces, leading to the formation of oxidized and nitrated polynuclear aromatic hydrocarbons which can be highly mutagenic. " The measurement of the PANs, as well as more usual oxidants such as O3, nitrate radical, and hydroxyl radical, is an important part of the characterization of potentially hazardous air pollutants. 

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. 

Although many polynuclear aromatic hydrocarbons give stable cation radical solutions (e.g. in sulfuric acid), not many give stable... 

The PET-generated arene radical cations also undergo nucleophilic substitution via the a-complex. Photocyanation of arenes may be cited in this context as a very early example [139], where hydrogen served as the group undergoing displacement. This concept is further extended [140] for the direct amination of polynuclear aromatic hydrocarbons with ammonia or primary amines via the arene radical cation produced by irradiating arenes in die presence of DCNB. Another potentially useful application of this methodology is... 

Arene radical anions, particularly from polynuclear aromatic hydrocarbons (e.g., phenanthrene, anthracene, and pyrene), generated by ET using amines as the electron donor has been shown [165] to undergo carboxylation reaction (e.g., Phen->189) by the electrophilic addition of CO2, followed by the termination of the resultant radical species by H-abstraction from the solvent (Scheme 39). A laser flash photolysis study [166] has recently confirmed the involvement of arene radical anions in this reaction. 

The nature of the reactions of hydroxyl radicals with polynuclear aromatic hydrocarbons is illustrated by studies of products observed with naphthalene (Fig. 6.25)." Addition of the hydroxyl radical to the aromatic ring produces ring opening with the... 

Reductive Remediation of Nonhalogenated Molecules. Na/NHa treatments can also destroy nonhalogenated hazardous conqraunds. Three classes pollutants will be mentioned here polynuclear aromatic hydrocarbons (PNAs), nitro- and nitrate-type explosive wastes and chemical warfare agents. The treatment of neat sanq>les of PNAs leads to destmction efficiencies of 99.99% for many of these conq)ounds including such examples as acenaphthene, benzo[a]anthracene, benzo[b]fluoranthene, benzo[g,h,l]perylene, chrysene, fluorandiene, fluorine, naphdialene and phenanthrene. With the exception of naphthalene and anthracene, conq)lex product mixtures are formed. Radical anion formation followed by protonation occurs sequentially leading to dihydro, tetrahydro and further reduced products (see Scheme 3). Depending on the reaction conditions, dimerization of intermediate radicals can occur to give dimers in various states of reduction. 

Polymer or radical molecules with n, j, s, or r polymerization degree Polynuclear aromatic hydrocarbons... 

Between 1961 and 1967 the electrochemical generation method has been used to obtain, identify, and investigate free radicals derived from about 400 different organic compounds, such as unsaturated acyclic and alicyclic hydrocarbons, condensed and noncondensed polynuclear aromatic hydrocarbons, heterocyclic compounds, quinones, carbonyl compounds, nitriles, nitroso and nitro derivatives, and carboxylic esters. 

Aromatic Hydrocarbons. There is no information on the production of free radical ions of benzene by the electrochemical method. From noncondensed polynuclear aromatic systems radical anions of diphenyl [62] and of stilbene [116] have been generated. 

The reagent alkali metal/naphthalene in tetrahydrofuran reacts with graphite, polynuclear aromatics, and various coals to form chemically reduced products. In the present paper, we emphasize the use of electron paramagnetic resonance data, in the form of g values, linewidths, radical densities, and saturation characteristics, to analyze the reduced coal products and to infer certain differences between the reduced coals and the anions of graphite and simple aromatic hydrocarbons. Additionally, because the interaction of coals with alkali metal/naph-thalene requires much time for completion, we have investigated internal decomposition pathways for the... 

So far, only a few examples of cationic photopolymerizations using PET corresponding to Scheme 3 have been described [10,13,165]. In the ternary system cyclohexene oxide, 9.10-dicyano anthracene and polynuclear aromatics, the polymerization of the former is initiated by the radical cations of the aromatic hydrocarbons formed via the PET with the dicyano compound. 

Three studies on radical cations discuss the characterization of polynuclear aromatic radical cation salts as organic metals (8), the reactions of cation radicals with neutral radicals (9), and the magnetic-electrical properties of perfluoroaromatic radical-cation salts (10). Chapters on polynuclear aromatic compounds in nonvolatile petroleum products (II) and in coal-based materials (12) present reviews of the subject and new findings. The remaining chapters in this book discuss the thermal conversion of polynuclear aromatic compounds to carbon (13), the nitration of pyrene by mixtures of N02 and N204 (14), the spectra, structures, and chromatographic retention times of large polycyclic aromatic hydrocarbons (15), the desulfurization of polynuclear thiophenes correlated with tt electron densities (16) and simple theoretical methods to predict and correlate polynuclear benzenoid aromatic hydrocarbon reactivities (IT). 

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