- Chlorination increases the persistence of semiquinone free radicals derived from polychlorinated biphenyl hydroquinones and quinones
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(Chemical Equation Presented) Polychlorinated biphenyls (PCBs) comprise a group of persistent organic pollutants that differ significantly in their physicochemical properties, their persistence, and their biological activities. They can be metabolized via
- Song, Yang,Buettner, Garry R.,Parkin, Sean,Wagner, Brett A.,Robertson, Larry W.,Lehmler, Hans-Joachim
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supporting information; experimental part
p. 8296 - 8304
(2009/04/11)
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- Reactions of dimethoxycarbene with cyclic perchlorinated olefins and ketones
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Reactions of dimethoxycarbene (2), a carbonyl group equivalent, with perchlorinated olefins and ketones were investigated. Thermolysis of 2,2- dimethoxy-5,5-dimethyl-Δ3-1,3,4-oxadiazoline (1) at 110 °C generated 2, which reacted with hexachlorocyclopentadiene (4), octachlorocycloheptatriene (12), octachlorobicyclo[3.2.0]hepta-3,6-diene (24), hexachlorotropone (28), hexachlorobicyclo[3. 2.0]-hepta-3,6-dien-2-one (32), and tetrachloro-1,4- benzoquinone (35). Reactions of 2 with perchlorinated olefins 4, 12, and 24 led to esters or, in the case of 12, to a ketene acetal. Their formation is rationalized in terms of Michael-like addition and displacement (S(N)2' or S(N)2', if concerted) of allylic chlorine atoms by 2, yielding ion pairs that either dechloromethylate to esters or dechlorinate to a ketene acetal. In contrast, the reactions of 2 with unsaturated perchloroketones 28, 32, and 35 led to ring contraction, ring expansion, and aromatization, respectively. The products from these reactions are consistent with nucleophilic addition of 2 at the carbonyl moiety rather than Michael-type addition. Dimethoxycarbene- d3 was used to show that demethylation in the latter reaction was intermolecular. Mechanisms for the different reaction courses are proposed.
- Dunn, James A.,Pezacki, John Paul,McGlinchey, Michael J.,Warkentin, John
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p. 4344 - 4352
(2007/10/03)
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- Oxidative Dealkylation of Hydroquinone Ethers with Nitrogen Dioxide in the Convenient Preparation of Quinones
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Various Hydroquinone dialkyl ethers (R2Q) are effectively converted by nitrogen dioxide into the corresponding quinone (Q) and alkyl nitrite (RONO) in dichloromethane at room temperature or below.The preparative procedure for the isolation of crystalline quinones in quantitative yield merely involves the convenient removal of the low boiling solvent in vacuo.Isotopic labelling studies demonstrate that the oxidative dealkylation proceeds via alkoxy scission of the labile cation radical (R2Q-cation radical) formed via the oxidation of the hydroquinone ether by nitrogen dioxide ( as the disproportionated ion pair NO+NO3-).The electron-transfer mechanism is confirmed by the spectral observation of R2Q-cation radical (identified by the isolation of the crystalline salt R2Q-cation radical-SbCl6-) and its rapid conversion into quinone and alkyl nitrite by combination with nitrate (NO3-) and nitric oxide (NO).
- Rathore, Rajendra,Bosch, Eric,Kochi, Jay K.
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p. 1157 - 1166
(2007/10/02)
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- 13C and 17O NMR Study of Methoxy Groups in Chlorinated Di- and Trimethoxybenzenes
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13C and 17O NMR data for the methoxy groups in isomeric 1,2-, 1,3- and 1,4-dimethoxybenzenes, 1,2,3-trimethoxybenzenes and most of their chlorinated derivatives and some related brominated compounds were measured for CDCl3 solutions.The 17O NMR chemical shifts show up to 60 ppm dispersion.Comparison between the compounds with and without adjacent chlorine atoms (2,6-di- and 2,4,6-trisubstitution) also showed a clear methoxy carbon chemical shift change.The number and position of the chlorine atoms in the aromatic ring give small but observable effects on the 17O NMR chemical shifts of the methoxy group if it is coplanar with the aromatic plane.Similarly, the degree and nature of the substitution have a minor effect (about 1 Hz) on the 1J(CH) direct coupling values.
- Knuutinen, J.,Kolehmainen, E.
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p. 315 - 317
(2007/10/02)
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- Facile Synthesis of Chloro-substituted Aromatic Ethers by Use of Benzyltrimethylammonium Tetrachloroiodate
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The reaction of aromatic ethers with a calculated amount of benzyltrimethylammonium tetrachloroiodate in acetic acid (or dichloromethane) under mild conditions gave, selectively, the objective chloro-substituted aromatic ethers in good yields.
- Kajigaeshi, Shoji,Shinmasu, Youichi,Fujisaki, Shizuo,Kakinami, Takaaki
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p. 415 - 418
(2007/10/02)
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