Polycyclic aromatic hydrocarbons, reduction

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... 

Li, H. and Westerholm, R., Determination of mono- and di-nitro polycyclic aromatic hydrocarbons by on-line reduction and high-performance liquid chromatography with chemiluminescence detection, /. Chromatogr. A, 664,177, 1994. 

Bioventing technology was developed by the U.S. EPA Risk Reduction Engineering Laboratory to treat soil contaminated by numerous industrial wastes, which is subjected to aerobic microbial degradation, especially to promote the degradation of polycyclic aromatic hydrocarbons.65 It uses a series of air injection probes, each of which is attached to a low-pressure air pump. The air pump operates at extremely low pressures to allow the inflow of oxygen without volatilization of contaminants. Additional additives such as ozone or nutrients may also be supplied to stimulate microbial growth.77... 

McCarthy, J.F., Jimenez, B.D. (1985) Reduction in bioavailability to bluegills of polycyclic aromatic hydrocarbons bound to dissolved humic material. Environ. Toxicol. Chem. 4, 511-521. 

On treatment with a base such as NaOMe or even LLAIH4, mono-cycloadducts of mesitonitrile oxide and polycyclic aromatic hydrocarbons have been cleaved to yield the corresponding oximes, which are oxidized to ketones by the Dess— Martin method. The same ketones have been obtained by reductive ring opening of the mono-cycloadducts with Raney Ni (438). 

One consequence of the uptake of some contaminants is a reduction in the ability of lysosomes to retain the dye Neutral Red. As a consequence, the Neutral Red retention time has been developed as an index of lysosomal membrane fragility and thus of toxicity. The test has been used on the digestive cells involved with intracellular digestion of endocytosed food following administration of organic contaminants, such as polycyclic aromatic hydrocarbons [71]. The phenomenon has been reported many times after exposure to... 

Grundy, M. M., Moore, M. N., Howell, S. M. and Ratcliffe, N. A. (1996). Phagocytic reduction and effects on lysosomal membranes by polycyclic aromatic hydrocarbons, in haemocytes of Mytilus edulis, Aquat. Toxicol., 34, 273-290. 

Reduction potentials for polycyclic aromatic hydrocarbons in rigorously dried... 

The delocalised radical formed by protonation of the radical-anion is more easily reduced than the starting arene. For some polycyclic aromatic hydrocarbons, the redox potential for this radical species can be determined using a cyclic voltammetry technique [10]. Reduction in dimethylformamide is carried out to the potential for formation of the dianion. The dianion undergoes rapid monoprotonation and on the reverse sweep at a fast scan rate, oxidation of the monoanion to the radical can be observed. The radical intermediate from pyrene has E° = -1.15 V vs. see in dimethylformamide compared to E° = -2.13 V vs. see for pyrene,... 

Baek, S. O., M. E. Goldstone, P. W. W. Kirk, J. N. Lester, and R. Perry, Concentrations of Particulate and Gaseous Polycyclic Aromatic Hydrocarbons in London Air Following a Reduction in the Lead Content of Petrol in the United Kingdom, Sci. Total Environ., Ill, 169-199 (1992). 

Jung, H., A. U. Shaikh, R. H. Heflich, and P. P. Fu, Nitro Group Orientation, Reduction Potential, and Direct-Acting Mutagenicity of Nitro-Polycyclic Aromatic Hydrocarbons, Environ. Mol. Mutagen., 17, 169-180 (1991). 

Baud-Gasset, F., Safferman, S. I., Baud-Gasset, S. Lamar, R. T. (1994). Demonstration of soil bioremediation and toxicity reduction by fungal treatment. In Bioremediation of Chlorinated and Polycyclic Aromatic Hydrocarbon Compounds, ed. R. E. Hinchee et al., pp. 496-500. Boca Raton, FL CRC Press. 

Although Table I is generally self-explanatory, the carbonaceous material measurements require comment. Because of its chemical complexity, carbonaceous material is frequently characterized only on the basis of carbon measurements. These measurements attempt to divide the carbonaceous material into organic C and elemental C . Carbon present in carbonate salts, frequently a minor contributor to the total particulate carbon, can be determined independently. Elemental carbon is among the most important pollutants in visibility reduction. Polycyclic aromatic hydrocarbons (PAHs) are relatively minor constituents of the particulate carbon but are of great interest in health effects studies. PAHs can also serve as model compounds in developing improved sampling techniques for semivolatile carbonaceous materials. 

Polycyclic aromatic hydrocarbons contain extended conjugated rc-electron systems and are electroactive within the cathodic potential window of many organic sol-vent/tetraalkylammonium electrolyte combinations. For many of them reduction potentials were measured and reported. It is important to note that the reduction of polycyclic aromatics involves consecutive electron-transfers and protonations. The nature of the product depends on the number of electrons and protons consumed and higher numbers result in more hydrogenated, less conjugated and thus less electroactive products. A simplified reduction scheme for polycyclic aromatics is shown below. The products are divided into three groups (A) are reduced within the potential window and (B) require drastic reduction conditions as those described for the substrates in Chapt. 3. 

A new synthetic approach to polycyclic aromatic compounds has been developed based on double Suzuki coupling of polycyclic aromatic hydrocarbon bis(boronic acid) derivatives with o-bromoaryl aldehydes to furnish aryl dialdehydes. These are then converted to larger polycyclic aromatic ring systems by either (a) conversion to diolefins by Wittig reaction followed by photocyclization, or (b) reductive cyclization with trifluoromethanesulfonic acid and 1,3-propanediol (Eq. (12)) [30]. 

In this absence of evidence for increased radical density, one could postulate the presence of spin-paired, diamagnetic, dianions in the reduced coal. However, using the chemistry of polycyclic aromatic hydrocarbons as a model, we find hat such dianions are neither expected to be statistically abundant (24, 25) nor, as good bases, to be inert to the reductive system on a time scale of 100 hours (26). 

Supercritical fluid extraction (SFE) is a suitable process for many separation problems. The regeneration of the supercritical fluid is as important as the extraction step itself Therefore this paper presents a method to do this in a more isobaric way than the customary pressure reduction regeneration. For the example of soil remediation we have investigated the activated carbon regeneration of supercritical carbon dioxide loaded with the low-volatile polycyclic aromatic hydrocarbon (PAH) pyrene. Characteristics of supercritical fluid extraction for soil remediation are elevated temperatures and pressures up to 370 K and 300 bar. For this reason adsorption isotherms of pyrene on activated carbon up to these conditions are measured first. Subsequently this method is used to regenerate carbon dioxide in a closed solvent cycle plant with a 4 1 extractor. An economic analysis using these results indicate that the soil remediation costs will decrease for about 20 - 30 % by means of an activated carbon adsorber. 

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