Of polycyclic aromatic

Dewar and his co-workers, as mentioned above, investigated the reactivities of a number of polycyclic aromatic compounds because such compounds could provide data especially suitable for comparison with theoretical predictions ( 7.2.3). This work was extended to include some compounds related to biphenyl. The results were obtained by successively compounding pairs of results from competitive nitrations to obtain a scale of reactivities relative to that of benzene. Because the compounds studied were very reactive, the concentrations of nitric acid used were relatively small, being o-i8 mol 1 in the comparison of benzene with naphthalene, 5 x io mol 1 when naphthalene and anthanthrene were compared, and 3 x io mol 1 in the experiments with diphenylamine and carbazole. The observed partial rate factors are collected in table 5.3. Use of the competitive method in these experiments makes them of little value as sources of information about the mechanisms of the substitutions which occurred this shortcoming is important because in the experiments fuming nitric acid was used, rather than nitric acid free of nitrous acid, and with the most reactive compounds this leads to a... 

TABLE 5.3 The nitration of polycyclic aromatic compounds in solutions of acetyl nitrate in acetic anhydride... 

Reactivity numbers of the most reactive positions have been used to correlate the reactivities in nitration (see below) and other substitutions of a series of polycyclic aromatic hydrocarbons, and they give somewhat better correlations than any of the other commonly used indices of reactivity. The relationship shown below, which was discussed earlier ( 7.1.1),... 

Under different conditions [PdfOAcj2, K2CO3, flu4NBr, NMP], the 1 3 coupling product 86 with 4-aryl-9,10-dihydrophenanthrene units was obtained. The product 86 was transformed into a variety of polycyclic aromatic compounds such as 87 and 88[83], The polycyclic heteroarene-annulated cyclopen-tadicnc 90 is prepared by the coupling of 3-iodopyridine and dicyclopentadiene (89), followed by retro-Diels Alder reaction on thermolysis[84]. 

A large number of polycyclic aromatic hydrocarbons are known Many have been synthesized m the laboratory and several of the others are products of com bustion Benzo[a]pyrene for example is present m tobacco smoke contaminates food cooked on barbecue grills and collects m the soot of chimneys Benzo[a]pyrene is a carcinogen (a cancer causing substance) It is converted m the liver to an epoxy diol that can induce mutations leading to the uncontrolled growth of certain cells... 

Wingen, L. M. Low, J. C. Pinlayson-Pitts, B. J. Chromatography, Absorption, and Pluorescence A New Instrumental Analysis Experiment on the Measurement of Polycyclic Aromatic Hydrocarbons in Cigarette Smoke, ... 

ACID-BASED SURFACTANT CLOUD POINT EXTRACTION AND PRECONCENTRATION OF POLYCYCLIC AROMATIC HYDROCARBONS PRIOR TO FLUORESCENCE DETERMINATION... 

Fluorescence scanning of chromatograms of polycyclic aromatic compounds is a vivid example of their employment. A careful choice of the wavelengths of exci-... 

Fig. 29 Fluorescence scans of polycyclic aromatic hydrocarbons at various excitation wavelengths in combination with various secondary filters.

Fig. 42 Chromatogram of polycyclic aromatic hydrocarbons on caffeine-impregnated precoated silica gel 60 HPTLC plates with concentrating zone (Merck). The following can be recognized in increasing Rf value. — 1. benzo(ghi)perylene, 2. indeno(l,2,3-cd)pyrene, 3 benzo(a)pyrene, 4. benzo(b)fluoranthene, 5. benzo(k)fluoranthene, 6. fluoranthene.

Reduction of fullerenes to fullerides — Reversible electrochemical reduction of Ceo in anhydrous dimethylformamide/toluene mixtures at low temperatures leads to the air-sensitive coloured anions Qo" , ( = 1-6). The successive mid-point reduction potentials, 1/2, at -60°C are -0.82, -1.26, -1.82, -2.33, —2.89 and —3.34 V, respectively. Liquid NH3 solutions can also be used. " Ceo is thus a very strong oxidizing agent, its first reduction potential being at least 1 V more positive than those of polycyclic aromatic hydrocarbons. C70 can also be reversibly reduced and various ions up to... 

On the basis of the reaction of alkyl radicals with a number of polycyclic aromatics, Szwarc and Binks calculated the relative selectivities of several radicals methyl, 1 (by definition) ethyl, 1.0 n-propyl, 1.0 trichloromethyl, 1.8. The relative reactivities of the three alkyl radicals toward aromatics therefore appears to be the same. On the other hand, quinoline (the only heterocyclic compound so far examined in reactions with alkyl radicals other than methyl) shows a steady increase in its reactivity toward methyl, ethyl, and n-propyl radicals. This would suggest that the nucleophilic character of the alkyl radicals increases in the order Me < Et < n-Pr, and that the selectivity of the radical as defined by Szwarc is not necessarily a measure of its polar character. 

R. Eener, J. E. Belrtam and J. Guiteras, Mathematical procedure for the detennination of the breaktlirough volumes of polycyclic aromatic hydrocarbons . Anal. Chim. Acta 346 253-258(1997). 

An alternative way of eliminating water in the RPLC eluent is to introduce an SPE trapping column after the LC column (88, 99). After a post-column addition of water (to prevent breakthrough of the less retained compounds), the fraction that elutes from the RPLC column is trapped on to a short-column which is usually packed with polymeric sorbent. This system can use mobile phases containing salts, buffers or ion-pair reagents which can not be introduced directly into the GC unit. This system has been successfully applied, for example, to the analysis of polycyclic aromatic hydrocarbons (PAHs) in water samples (99). 

J. L. Bernal, M. J. Nozal, L. Toribio, M. L. Serna, F. Bonnll, R. M. Marce and E. Pocumll, Determination of polycyclic aromatic hydi ocarbons in waters by use of supercritical fluid cliromatography coupled on-line to solid-phase exti action with disks , ]. Chromatogr. 778 321-328 (1997). 

E. R. Brouwer, A. N. J. Elermans, El. Lingeman and U. A. Th Briknman, Determination of polycyclic aromatic hydrocarbons in surface water by column liquid cliromatogr a-phy with fluorescence detection, using on-line micelle-mediated sample preparation , J. Chromatogr. 669 45-57 (1994). 

Epoxides are often encountered in nature, both as intermediates in key biosynthetic pathways and as secondary metabolites. The selective epoxidation of squa-lene, resulting in 2,3-squalene oxide, for example, is the prelude to the remarkable olefin oligomerization cascade that creates the steroid nucleus [7]. Tetrahydrodiols, the ultimate products of metabolism of polycyclic aromatic hydrocarbons, bind to the nucleic acids of mammalian cells and are implicated in carcinogenesis [8], In organic synthesis, epoxides are invaluable building blocks for introduction of diverse functionality into the hydrocarbon backbone in a 1,2-fashion. It is therefore not surprising that chemistry of epoxides has received much attention [9]. 

Dihydrovinylphenanthrenes are more reactive than the corresponding vinyl phenanthrenes and undergo Diels-Alder reactions easily. They have been used in the synthesis of polycyclic aromatic compounds and helicenes. Examples of cycloaddition reactions of the 3,4-dihydro-1-vinylphenanthrene (70), [61] 3,4-dihydro-2-vinylphenanthrene (71) [68] and l,2-dihydro-4-vinylphenanthrene (72) [69] are reported in Equation 2.22 and Schemes 2.27 and 2.28. 

Pressure influences the regioselectivity and the endo-exo diastereoselectivity of the cycloadditions. All the cycloadducts were converted into polycyclic aromatic hydrocarbons by treatment over a Pd/charcoal catalyst. This approach provides a new and efficient route to a broad variety of polycyclic aromatic hydrocarbons [36]. 

The environmental occurrence of polycyclic aromatic hydrocarbons is mainly associated with dispersion of oil products and with various types of combustion. For these chemicals a kind of pre-industrial background exists, due to forest fires or to domestic wood burning. The sediments of the deepest strata were certainly deposited in the nineteenth century, when no significant industrial activities had been initiated. The ratio between PAH concentrations found in the sediments dated to this century, and the deepest ones, vary from 1.7 to 30, increasing from the beginning of the... 

Table 2. Bromination of Polycyclic Aromatic Hydrocarbons with CuBr2/Al2033)... 

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. 

Table VII. Standard Reference Materials (SRM s) for the Determination of Polycyclic Aromatic Hydrocarbons (PAH s) ...

Vol. 101. Chemical Analysis of Polycyclic Aromatic Compounds. Edited by Tuan Vo-Dinh... 

The largest releases of polycyclic aromatic hydrocarbons (PAHs) are due to the incomplete combustion of organic compounds during the course of industrial processes and other human activities. Important sources include the combustion of coal, crude oil, and natural gas for both industrial and domestic purposes, the use of such materials in industrial processes (e.g., the smelting of iron ore), the operation of the internal combustion engine, and the combustion of refuse (see Environmental Health Criteria 202, 1998). The release of crude oil into the sea by the offshore oil industry and the wreckage of oil tankers are important sources of PAH in certain areas. Forest hres, which may or may not be the consequence of human activity, are a signihcant... 

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. 

KAYALI-SAYADI M N, RUBIO-BARROSO S, CUESTA-JIMENEZ M P and PALO-DIEZ L M (1998) Rapid determination of polycyclic aromatic hydrocarbons in tea infusion samples by high-performance liquid chromatography and fluorimetric detection based on solid-phase extraction , 123, 2145-8. 

Lagadec AJM, DJ Miller, AV Lilke, SB Hawthorne (2000) Pilot-scale subcritical water remediation of polycyclic aromatic hydrocarbon- and pesticide-contaminated soil. Environ Sci Technol 34 1542-1548. 

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). 

Bnmpus JA (1989) Biodegradation of polycyclic aromatic hydrocarbons by Phanerochaete chrysosporium. Appl Environ Microbiol 55 154-158. 

MacGillivray AR, MP Shiaris (1993) Biotransformation of polycyclic aromatic hydrocarbons by yeasts isolated from coastal sediments. Appl Environ Microbiol 59 1613-1618. 

Sarma PM, D Bhattacharya, S Krishnan, B Lai (2004) Degradation of polycyclic aromatic hydrocarbons by a newly discovered enteric bacterium Leclercia adecaroxylata. Appl Environ Microbiol 70 3163-3166. 

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