- Birch-Type Photoreduction of Arenes and Heteroarenes by Sensitized Electron Transfer
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The direct reduction of arenes and heteroarenes by visible-light irradiation remains challenging, as the energy of a single photon is not sufficient for breaking aromatic stabilization. Shown herein is that the energy accumulation of two visible-light photons allows the dearomatization of arenes and heteroarenes. Mechanistic investigations confirm that the combination of energy-transfer and electron-transfer processes generates an arene radical anion, which is subsequently trapped by hydrogen-atom transfer and finally protonated to form the dearomatized product. The photoreduction converts planar aromatic feedstock compounds into molecular skeletons that are of use in organic synthesis.
- Chatterjee, Anamitra,K?nig, Burkhard
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supporting information
p. 14289 - 14294
(2019/08/30)
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- Characterization of polycyclic aromatic hydrocarbon particulate and gaseous emissions from polystyrene combustion
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The partitioning of polycyclic aromatic hydrocarbons (PAHs) between the particulate and gaseous phases resulting from the combustion of polystyrene was studied. A vertical tubular flow furnace was used to incinerate polystyrene spheres (100-300 μm) at different combustion temperatures (800- 1200 °C) to determine the effect of temperature and polystyrene feed size on the particulate and gaseous emissions and their chemical composition. The furnace reactor exhaust was sampled using real-time instruments (differential mobility particle sizer and/or optical particle counter) to determine the particle size distribution. For chemical composition analyses, the particles were either collected on Teflon filters or split into eight size fractions using a cascade impactor with filter media substrates, while the gaseous products were collected on XAD-2 adsorbent. Gas chromatography/mass spectroscopy (GC/MS) was used to identify and quantify the specific PAH species, their partitioning between the gas and particulate phases, and their distribution as a function of emission particle size. The total mass and number of PAH species in both the particulate and gas phases were found to decrease with increasing incineration temperature and decreasing polystyrene feed size, while the mean diameter of the particles increases with increasing incineration temperature and decreasing feed size. In addition, the PAH species in the particulate phase were found to be concentrated in the smaller aerosol sizes. The experimental results have been analyzed to elucidate the formation mechanisms of PAHs and particles during polystyrene combustion. The implications of these results are also discussed with respect to the control of PAH emissions from municipal waste-to-energy incineration systems. The partitioning of polycyclic aromatic hydrocarbons (PAHs) between particulate and gaseous phases resulting from the combustion of polystyrene was studied. A vertical tubular flow furnace was used to incinerate polystyrene spheres to determine the effect of temperature and polystyrene feed size on the particulate and gaseous emissions and their chemical composition. The furnace reactor exhaust was sampled using real-time instruments to determine the particle size distribution. The total mass and number of PAH species in both the particulate and gas phases were found to decrease with increasing incineration temperature and decreasing polystyrene feed size, while the mean diameter of the particles increases with increasing incineration temperature and decreasing feed size. In addition, the PAH species in the particulate phase were found to be concentrated in the smaller aerosol sizes.
- Durlak, Susan K.,Biswas, Pratim,Shi, Jichun,Bernhard, Mary Jo
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p. 2301 - 2307
(2007/10/03)
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- Partial Hydrogenation of Polycyclic Aromatic Hydrocarbons by Electroreduction in Protic Solvents
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Polycyclic aromatic hydrocarbons (PAH) such as anthracene (1), phenanthrene (5), acenaphthylene (15), pyrene (17), chrysene (22), and fluoranthene (28) are selectively hydrogenated upon electroreduction at a lead cathode in ethanolic solution. The degree of hydrogenation and the structure of the products depend on the reaction conditions, in particular on the applied reduction potential.
- Anowski,Voss
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p. 337 - 344
(2007/10/03)
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- Relative Reactivities of Some Polycyclic Aromatic Hydrocarbons in Catalytic Hydrogenation over Raney Nickel
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Catalytic hydrogenation of 9H-fluorene (10), phenanthrene (2), 4H-cyclopentaphenanthrene (3), pyrene (4), and fluoranthene (5) was carried out over Raney nickel (W-7) at 323 K under 608 kPa of hydrogen.The order of the reaction rate was 5>4>3>2>1.The adsorption equilibrium constant of the substrates decreased in the order 4 > or = 5 >> 2 > 3 >> 1.
- Minabe, Masahiro,Urushibara, Shuuichi,Mishina, Fumihiko,Kimura, Takao,Tsubota, Motohiro
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p. 670 - 672
(2007/10/02)
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- Mechanisms of Electrochemical Hydrogenation of Fluoranthene in HMPA with Ethanol and Aqueous HCl as Proton Donors
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The electrochemical hydrogenation of the non-alternant aromatic hydrocarbon fluoranthene has been investigated in LiClO4-hexamethylphosphoric triamide; it has been found that hydrogenation cannot be achieved satisfactorily, not even to the dihydro derivative, when ethanol is used as the proton donor, whether present during or added after electrolysis.On the other hand, reaction of a stock of fluoranthene dianion with aqueous hydrochloric acid proves to be a clean, easy way to prepare 1,2,3,10b-tetrahydrofluoranthene, a product which requires donation of four electrons to fluoranthene.A mechanism is discussed to account for such a transfer of electrons.
- Dassas, Yves,Boue, Stephane,Fontana, Andre
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p. 613 - 617
(2007/10/02)
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- REMARKABLE ABILITY OF TETRAHYDROFLUORANTHRENE IN THE LIQUEFACTION OF A SUB-BITUMINOUS COAL AT UNUSUALLY HIGH TEMPERATURE UNDER A MODERATE PRESSURE
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An Australian sub-vbituminous coal was effectively liquefied under high temperature short contact time conditions at about 30 kg/cm2 using 1,2,3,3a-tetrahydrofluoroanthrene (4HFL) as the solvent.The yields of the oil and asphaltene, the target products, were as high as 54 and 16percent, respectively, for a reaction at 560 deg C with zero contact time. 4HFL was principally converted into fluoranthrene together with some undefined four ring aromatic compounds.The efficacy of the present liquefaction procedures is introduced.
- Mochida, Isao,Otani, Kazumasa,Korai, Yozo
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p. 1461 - 1464
(2007/10/02)
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