Formation polycyclic aromatic hydrocarbons

A very comprehensive analysis of hydrocarbons (linear, acyclic and cyclic - steranes, hopanes etc.- isoprenoids) carboxylic acids, aldehydes, ketones and amines of the Vale do Paraiba and Marau oil shales was made by Chicarelli (27). An extremely careful quantitative and qualitative analysis of hydrocarbons (n-, iso-and anteiso-paraffins, isoprenoids, steranes and triterpanes) and carboxylic acids of Irati oil shale was presented by Carvalhaes (28). Nooner Oro (29) also reported data on the hydrocarbons pres ent in the Irati Formation. Polycyclic aromatic hydrocarbons in I-rati were determined by Youngblood Blumer (40). 

The polycyclic aromatic hydrocarbons such as naphthalene, anthracene, and phenan-threne undergo electrophilic aromatic substitution and are generally more reactive than benzene. One reason is that the activation energy for formation of the c-complex is lower than for benzene because more of the initial resonance stabilization is retained in intermediates that have a fused benzene ring. 

The branched oligo(arylene)s 37 and 40 can undeigo a further oxidative cyclization with copper(ll) chloride or triflate/aluminum trichloride leading to the formation of large, hitherto unknown polycyclic aromatic hydrocarbons PAHs 41 and 42. 

Major unknowns in the mechanism by which a hydrocarbon fuel bums concern the pyrosynthesis reactions that lead to the formation of polycyclic aromatic hydrocarbons (PAHs) and soot and the oxidation chemistry of atoms other than carbon and hydrogen (heteroatoms) in the fuel, particularly nitrogen, sulfur, and halogens. 

FIGURE 7.9 Mechanism of formation of polycyclic aromatic hydrocarbons (PAHs) during combustion. 

Polycyclic aromatic hydrocarbons, indole and quinoline derivatives, naphthylamines, azulenes Silica gel G Formation of oxidation products via the initially formed iodine complexes [15]... 

Richter, H. and Howard, J.B., Formation of polycyclic aromatic hydrocarbons and their growth to soot—a review of chemical reaction pathways, Prog. Energy Combust. Sci., 26,565,2000. 

The recommended method of trichloroethylene disposal is incineration after mixing with a combustible fuel (Sittig 1985). Care should be taken to carry out combustion to completion in order to prevent the formation of phosgene (Sjoberg 1952). Other toxic byproducts of incomplete combustion include polycyclic aromatic hydrocarbons and perchloroaromatics (Blankenship et al. 1994 Mulholland et al. 1992). An acid scrubber also must be used to remove the haloacids produced. 

The metabolic activity of other white-rot fungi including Phanerochaete chrysosporium and Pleurotus ostreacus has been discussed in the context of polycyclic aromatic hydrocarbons. For example, the mineralization potential of the manganese peroxide system fmmNematolomafrowardii for a number of substrates has been demonstrated (Hofrichter et al. 1998) the formation of CO2 from labeled substrates ranged from 7% (pyrene) to 36% (pentachlorophenol), 42% (2-amino-4, 6-dinitrotoluene), and 49% (catechol). 

One of the more significant classes of compounds resulting from and emitted by combustion sources include polycyclic aromatic hydrocarbons (PAHs) these species serve as nuclei for the formation of soot particles. Past studies have concluded that 85% of... 

Metabolites of carcinogenic polycyclic aromatic hydrocarbons (PAH) such as ( ) trans-7,8-dihydroxy-anti-9,10-epoxy-7,8,9,10-tetrahy-drobenzo[a]pyrene (BPDE) and 7,8,9,10-tetrahydroxytetrahydroben-zo[ a] pyrene (BPT) participate in tt binding interactions with nucleotide bases (1-19) which lead to the reversible formation of... 

NRCC (1983) Polycyclic aromatic hydrocarbons in the aquatic environment Formation, sources, fate and effects on aquatic biota. NRCC/CNRC, Ottawa, Canada. 

Landrum, P.F. 1983. The effect of co-contaminants on the bioavailability of polycyclic aromatic hydrocarbons to Pontoporeia hoyi. Pages 731-743 in M. Cooke and AJ. Dennis (eds.). Polynuclear Aromatic Hydrocarbons Formation, Metabolism and Measurement. Battelle Press, Columbus, OH. 

Pal, K. 1984. The relationship between the levels of DNA-hydrocarbon adducts and the formation of sister-chromatid exchanges in Chinese hamster ovary cells treated with derivatives of polycyclic aromatic hydrocarbons. Mutat. Res. 129 365-372. 

It is sometimes assumed that every phenol metabolite indicates the formation of an arene oxide intermediate however, as discussed above, arene oxides are not obligate intermediates in the formation of phenols. This is an important distinction because arene oxides and other epoxides are reactive intermediates that can be toxic or even carcinogenic, e.g., epoxides of some polycyclic aromatic hydrocarbons. The question of whether their formation is obligatory is significant for drug design and development and has implications for toxicity as discussed in Chapter 8. 

In many mammals induction of monooxygenation by polycyclic aromatic hydrocarbons is accompanied by the formation of a hemoprotein not seen to any appreciable extent in non-induced animals. This leads to an alteration in the microsomal hemoprotein populations, a change in the metabolic activity of the microsomes and, hence, possible alterations in the toxicity of other chemicals (27, 8). 

In the pH range of 5 - 10, H20-catalyzed hydrolysis is the predominant mechanism (see Fig. 10.11, Pathway b), resulting in the formation of the (8R,9R)-dihydrodiol (10.133, Fig. 10.30). Thus, aflatoxin B1 exo-8,9-epoxide is possibly the most reactive oxirane of biological relevance. Such an extreme reactivity is mostly due to the electronic influence of 0(7), as also influenced by stereolectronic factors, i.e., the difference between the exo- and endo-epoxides. The structural and mechanistic analogies with the dihydro-diol epoxides of polycyclic aromatic hydrocarbons (Sect. 10.4.4) are worth noting. 

PCDD/F and other chlorinated hydrocarbons observed as micropollutants in incineration plants are products of incomplete combustion like other products such as carbon monoxide, polycyclic aromatic hydrocarbons (PAH), and soot. The thermodynamically stable oxidation products of any organic material formed by more than 99% are carbon dioxide, water, and HCl. Traces of PCDD/F are formed in the combustion of any organic material in the presence of small amounts of inorganic and organic chlorine present in the fuel municipal waste contains about 0.8% of chlorine. PCDD/F formation has been called the inherent property of fire. Many investigations have shown that PCDD/Fs are not formed in the hot zones of flames of incinerators at about 1000°C, but in the postcombustion zone in a temperature range between 300 and 400°C. Fly ash particles play an important role in that they act as catalysts for the heterogeneous formation of PCDD/Fs on the surface of this matrix. Two different theories have been deduced from laboratory experiments for the formation pathways of PCCD/F ... 

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