- Facile Synthesis of a Fully Fused, Three-Dimensional ?-Conjugated Archimedean Cage with Magnetically Shielded Cavity
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The synthesis of molecular cages consisting of fully fused, ?-conjugated rings is rare due to synthetic challenges including preorganization, large strain, and poor solubility. Herein, we report such an example in which a tris-2-aminobenzophenone precursor undergoes acid-mediated self-condensation to form a truncated tetrahedron, one of the 13 Archimedean solids. Formation of eight-membered [1,5]diazocine rings provides preorganization and releases the strain while still maintains weak ?-conjugation of the backbone. Thorough characterizations were performed by X-ray, NMR, and UV-vis analysis, assisted by theoretical calculations. The cage exhibits a rigid backbone structure with a well-defined cavity that confines a magnetically shielded environment. The solvent molecule, o-dichlorobenzene, is precisely encapsulated in the cavity at a 1:1 ratio with multiple ?···?, C-H···?, and halogen···πinteractions with the cage skeleton, implying its template effect for the cage closing reaction. Our synthetic strategy opens the opportunity to access more complex, fully fused, three-dimensional ?-conjugated cages.
- Han, Yi,Jiao, Tianyu,Li, Zhengtao,Ni, Yong,Wu, Jishan,Wu, Shaofei,Zhang, Qiuyu,Zhu, Jun
-
supporting information
p. 14314 - 14321
(2021/09/13)
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- Dechlorination of hexachlorobenzene by nano zero-valent iron/activated carbon composite: Iron loading, kinetics and pathway
-
Nano zero-valent iron (nZVI) and activated carbon composites were synthesized and employed to remove hexachlorobenzene (HCB). Methods of impregnation and adsorption were employed to firstly load iron salt onto activated carbon, and thus loaded iron was then reduced to form zero valent iron. Results indicate that the method of iron loading significantly impacted the amount of iron and HCB dechlorination. In general, nZVI/activated carbon composite synthesized using an adsorption method showed considerably higher removal efficiency and dechlorination capability. More than 80% of the HCB was dechlorinated after 48 h. The dechlorination of HCB followed a stepwise pathway: HCB (hexachlorobenzene) → PCB (pentachlorobenzene) → 1,2,4,5 TeCB (tetrachlorobenzene) → TriCB (trichlorobenzene) → 1,4 DCB (dichlorobenzene) → MCB (monochlorobenzene). Compared with activated carbon or nZVI, nZVI/activated carbon composite showed much higher HCB removal. Analysis of mass partition on solid and aqueous phases indicates that most of the HCB and its dechlorination intermediates were retained on solids probably due to the strong adsorption on activated carbon. In summary, activated carbon performs three important functions: it alleviated the limitation of nZVI agglomeration, contributed to HCB removal due to its own adsorption capability and increased the resistance of nZVI against pH change. This journal is
- Chen, Wei-Fang,Pan, Ling,Chen, Li-Fang,Wang, Qiong,Yan, Chang-Cheng
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p. 46689 - 46696
(2014/12/11)
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- Selective C-F/C-H bond activation of fluoroarenes by cobalt complex supported with phosphine ligands
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The reactions of pentafluoropyridine C5NF5, hexafluorobenzene C6F6, and perfluoronaphthalene C 10F8 with cobalt(0) complex, Co(PMe3) 4, were investigated. The Co(i) complexes (4-C5NF 4)Co(PMe3)3 (1), (C6F 5)Co(PMe3)3 (2), (C10F 7)Co(PMe3)3 (3), (4-C5NF 4)Co(PMe3)4 (4) and (C10F 7)Co(PMe3)4 (6) were obtained by selective activation of the C-F bonds. The reactions of 1 and 2 with CO afforded dicarbonyl cobalt(i) complexes (4-C5NF4)Co(CO) 2(PMe3)2 (7), (C6F 5)Co(CO)2(PMe3)2 (8). Under similar reaction conditions, 2 as a C-H bond activation product was obtained from the reaction of pentafluorobenzene, C6F5H, with Co(PMe 3)4. The byproducts, hydrodefluorination product 1,2,4,5-C6F4H2 and F2PMe3 from the reaction of C6F5H and Co(PMe3) 4 were also observed. The reaction mechanism of C6F 5H with Co(PMe3)4 is proposed and partly-experimentally verified. The reaction of C6F5H with Co(PMe3)4 under 1 bar of CO at room temperature afforded hydrido dicarbonyl cobalt(ii) complex (C6F5)Co(H)(CO) 2(PMe3)2 (11). Treatment of the mixtures of C6F5H/Co(PMe3)4 with hexachlorobenzene, C6Cl6, resulted in (C6F 5)CoCl(PMe3)3 (12) via C-H bond cleavage with the hydrodechlorination product pentachlorobenzene, C6Cl 5H, and 1,2,4,5-tetrachlorobenzene, C6Cl4H 2. The structures of complexes 1, 2, 6, 7, 8, 11 and 12 were determined by X-ray diffraction.
- Li, Junye,Zheng, Tingting,Sun, Hongjian,Xu, Wengang,Li, Xiaoyan
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p. 5740 - 5748
(2013/07/11)
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- Efficient oxidative chlorination of aromatics on saturated sodium chloride solution
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An efficient metal-free system using saturated aqueous sodium chloride/aqueous ammonium chloride solution as chlorine source and potassium persulfate as a cheap oxidant for the chlorination of various aromatic compounds including deactivated ones has been developed that proceeds without any acid additive in an excellent regioselective manner. The easy-to-handle aqueous solution/acetonitrile biphasic system as solvent and no need for precautionary measures make this process very practical. Copyright
- Gu, Liuqun,Lu, Ting,Zhang, Mingyun,Tou, Lijuan,Zhang, Yugen
-
supporting information
p. 1077 - 1082
(2013/05/21)
-
- New look into the synthesis of polyhalogenoarylphosphanes
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The present study shows new aspects of the synthesis of polyhalogenoarylphosphanes. The sterically hindered anions Ph(R)P-Y- (1a-c, Y = O, lone pair; R = Ph, But) have been used to show the complexity of the reaction between phosphorus nucleophiles and hexahalogenobenzenes or 9-bromofluorene (E3). The Ph(But)P-O-(1a) anion reacts with hexachlorobenzene (E1), hexafluorobenzene (E2), or E3 to give Ph(R)P(O)X (4a-c, X = F, Cl, Br) with the release of the corresponding carbanion as a nucleofuge, followed by side reactions. In contrast, the lithium phosphides Ph(R)PLi (1b,c) react with hexahalogenobenzenes to give the corresponding diphosphanes 5a,b as the main product and traces of P-arylated products, i.e., Ph(R)P-C6X 5 (10a,b, X = Cl, F). Unexpectedly, Ph(But)PLi (1b) reacts with an excess of 9-bromofluorene to give only halogenophosphane Ph(Bu t)P-X. Taylor & Francis Group, LLC.
- Nycz, Jacek E.
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experimental part
p. 2605 - 2612
(2010/08/06)
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- Thermolysis of hexachlorocyclohexane in a flow-through packed reactor
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Thermolysis of hexachlorocyclohexane in a flow-through packed system in an inert gas atmosphere was studied.
- Kut'in,Gubanova,Zorin,Zanozina,Markova,Suprunova,Bykova
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p. 1518 - 1522
(2007/10/03)
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- Identification of surrogate compounds for the emission of PCDD/F (I-TEQ value) and evaluation of their on-line realtime detectability in flue gases of waste incineration plants by REMPI-TOFMS mass spectrometry
-
Correlations between products of incomplete combustion (PIC), e.g., chloroaromatic compounds, can be used to characterise the emissions from combustion processes, like municipal or hazardous waste incineration. A possible application of such relationships may be the on-line real-time monitoring of a characteristic surrogate, e.g., with Resonance-Enhanced Multiphoton Ionization-Time-of-Flight Mass Spectrometry (REMPI-TOFMS). In this paper, we report the relationships of homologues and individual congeners of chlorinated benzenes (PCBz), dibenzo-p-dioxins (PCDD), dibenzofurans (PCDF) and phenols (PCPh) to the International Toxicity Equivalent (I-TEQ) of the PCDD/F (I-TEQ value) in the flue gas and stack gas of a 22 MW hazardous waste incinerator (HWI). As the REMPI detection sensitivity is decreasing with the increase of the degree of chlorination, this study focuses on the lower chlorinated species of the compounds mentioned above. Lower chlorinated species, e.g., chlorobenzene (MCBz), 1,4-dichlorobenzene, 2,4,6-trichlorodibenzofuran or 2,4-dichlorophenol, were identified as I-TEQ surrogates in the flue gas. In contrast to the higher chlorinated phenols, the lower chlorinated phenols (degree of chlorination 4) were not reliable as surrogates in the stack gas. The identified surrogates are evaluated in terms of their detectability by REMPI-TOFMS laser mass spectrometry. The outcome is that MCBz is the best suited surrogate for (indirect) on-line measuring of the I-TEQ value in the flue gas by REMPI-TOFMS. The correlation coefficient r of the MCBz concentration to the I-TEQ in the flue gas was 0.85.
- Blumenstock,Zimmermann,Schramm,Kettrup
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p. 507 - 518
(2007/10/03)
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- Hydrodechlorination of polychlorinated benzenes in the presence of a bimetallic catalyst in combination with a phase-transfer catalyst
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Bimetallic supported catalysts (Pd-Ni/C and Ni-Cu/C) in combination with a phase-transfer catalyst were found efficient and selective in the liquid-phase hydrodechlorination of polychlorinated benzenes under mild conditions.
- Simagina,Stoyanova
-
-
- Reactions of 2,4,6-trichlorophenol on model fly ash: Oxidation to CO and CO2, condensation to PCDD/F and conversion into related compounds
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Thermal treatment of 2,4,6-trichlorophenol on a magnesium silicate-based model fly ash in the temperature range between 250°C and 400°C leads predominantly to carbon monoxide and carbon dioxide. The fraction of 2,4,6-trichlorophenol which is oxidized to CO and CO2 increases from 3% at 250°C to 75% at 400°C. Further products are polychlorinated benzenes, dibenzo-p-dioxins, dibenzofurans and phenols. The homologue and isomer patterns of the chlorobenzenes suggest chlorination in the ipso-position of the trichlorophenol. The formation of PCDD from 2,4,6-trichlorophenol and 2,3,4,6-tetrachlorophenol on municipal solid waste incinerator fly ashes and model fly ash were compared and the reaction order calculated.
- Hell,Stieglitz,Altwicker,Addink,Will
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p. 697 - 702
(2007/10/03)
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- Catalytic Dehalogenation of Highly Chlorinated Benzenes and Aroclors Using PdCl2(dppf) and NaBH4: Efficiency, Selectivity, and Base Support
-
Reported herein is a convenient one-pot system that can dehalogenate highly chlorinated benzenes at room temperature with reasonable conversion rates using PdCl2(dppf) (dppf = 1,1′-bis-(diphenylphosphino)ferrocene) as catalyst, NaBH4 as reducing agent, TMEDA (N,N,N',N'-tetra-methyl-1,2-ethylenediamine) as supporting base, and THF as solvent. Total conversion of substrate to less chlorinated isomers is achieved within 200 h when hexachloro-, pentachloro-, and tetrachlorobenzenes are used. Degradation to benzene is not achievable, but the efficiency shown in the partial dechlorination is encouraging. A pronounced selectivity is accomplished with removal of meta-substituted chlorines being preferred over ortho- or para-substituted Cl atoms. The sequence in which reagents are added is also critical, thus indicating a protective role of the base. The effectiveness of the method was tested on the PCB mixtures Aroclor 1242, 1248, and 1254. Dechlorination efficiency at 67 °C is satisfactory.
- Lassová, Luisa,Lee, Hian Kee,Hor, T.S. Andy
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p. 3538 - 3543
(2007/10/03)
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- Methanesulfonylation of deactivated aromatics with superelectrophilic CH3so2F·3SbF5 and (CH3so2)2O-2CF3so 3H/B(O3SCF3)3 systems
-
Methanesulfonylation of various deactivated arenes, including tri- and tetrafluorobenzenes, was achieved in good yield under mild conditions using superelectrophilic CH3SO2F/3SbF5 and (CH3SO2O)2O/2CF3SO 3H-B(O3SCF3)3 reagent systems. 1998 MAHK "Hayka/Interperiodica".
- Olah,Orlinkov,Oxyzoglou,Prakash, G.K. Suria
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p. 1573 - 1578
(2007/10/03)
-
- Reaction of Hexachlorobenzene and (Pentachlorophenyl)lithium with α-Arylacetonitriles
-
(Pentachlorophenyl)lithium (2) reacts with α-lithio-α-arylacetonitriles (4) at -70 deg C to room temperature to supply α-aryl-α-(2,3,5,6-tetrachlorophenyl)acetonitriles 7.Small amounts of 1,2,4,5-tetrachlorobenzene (8) and trans-1,2-dicyano-1,2-diarylethylenes 9 are also obtained; however, no α-tetrachloroarylated nitriles 6 from 3,4,5,6-terachlorobenzyne were detected.Similar treatment of hexachlorobenzene (1) and 4 afforded α-aryl-α-(2,3,4,5,6-pentachlorophenyl)acetonitriles 10.The addition of 2 to 4 at tetrachlorobenzyne-generating temperatures (0-20 deg C) gave a complex mixture containing mainly dimeric and polymeric materials; 6 was not found.A mechanism is proposed for the reaction of 2 and 4 which suggests that nitriles 7 are formed by the condensation of 2 and 4 via a four-centered transition state and that alkenes 9 are supplied by a base-mediated dimerization of α-chloro-α-arylacetonitriles 13, formed by a lithium-chlorine exchange between 2 and 4.Nitriles 10 most likely are provided from the reaction of 1 and 4 by the usual aromatic nucleophilic substitution pathway.
- Refat, Hala Mohammed,Waggenspack, John,Dutt, Mahesh,Zhang, Hongming,Fadda, A. A.,Biehl, Ed
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p. 1985 - 1989
(2007/10/02)
-
- Photoinduced Charge Separation in Rigid Bichromophoric Compounds and Charge Transfer State Electron Transfer Reactivity
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Bichromophoric compounds giving, after photoexcitation, a locally excited state (LE) rapidly followed by an intramolecular charge transfer (CT) state were designed using a Paddon-Row type synthesis.The electron-accepting end of the CT state is chosen in order to play the role of an electron relay versus external acceptors.In this way, electron transfer photosensitization is made available by using the CT state of bichromophores.The photophysics of the synthesized bichromophores is discussed, and the reductive dechlorination of polychlorinated benzenes is used as a test reaction.The bichromophoric sensitizer is unexpectedly found to be totally regenerated: the reaction is shown to be initiated by an electron transfer from the CT state to the chlorinated quencher.A rapidly breaking radical anion leads to the dechlorination, while the recombination of the sensitizer radical cation with the released chloride anion opens the way to the sensitizer recovery.
- Jiwan, J. L. Habib,Soumillion, J. Ph.
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p. 14223 - 14230
(2007/10/02)
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- Dechlorination of chlorinated benzenes by an anaerobic microbial consortium that selectively mediates the thermodynamic most favorable reactions
-
A chlorinated benzene dechlorinating anaerobic microbial consortium was obtained by selective enrichment with hexachlorobenzene (HCB) and lactate from a freshwater sediment sample that originated from an area with proven in situ HCB dechlorination. The consortium was used to determine compound selectivity and relative dechlorination rates by incubation with the individual chlorinated benzenes under methanogenic conditions. The selectivity of the enrichment culture showed an interesting correlation with the thermodynamics of the various dechlorination steps: from the 19 dechlorination reactions possible with benzenes that contain at least two chlorines, only the seven reactions with the highest energy release took place. -from Authors
- Beurskens,Dekker,Van Den Heuvel,Swart,De Wolf,Dolfing
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p. 701 - 706
(2007/10/03)
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- Photodechlorination of polychlorobenzene congeners in surfactant micelle solutions
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Photochemical reactions of polychlorobenzene congeners in aqueous solutions containing surfactant micelles have been investigated. Photoreduction through photodechlorination was shown to be the main decay pathway in which lesser chlorinated congeners and benzene were formed as intermediates. Final products included H+ and Cl- in approximately stoichiometric amounts. Several hydrogen sources were investigated with sodium borohyride shown to be a promising rate enhancer at elevated concentrations. -Authors
- Wei Chu,Jafvert
-
p. 2415 - 2422
(2007/10/03)
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- DEHALOGENATION OF CHLOROBENZENES WITH SODIUM DIHYDRIDOBIS(2-METHOXYETHOXO)ALUMINATE
-
The dehalogenation of a series of 9 mono- to pentachlorinated benzenes with the title hydride in toluene has been found to be first order in the substrate and half order in the hydride.The reactivities of the chlorobenzenes, expressed by rate constants for the first-step dehalogenation, increased with increasing number of chlorine atoms over three orders of magnitude.The rate data revealed the unexpected acceleration of benzene formation during exhaustive dehalogenation of the higher chlorinated benzenes.For comparison, dehalogenation of several isomeric dibromobenzenes and bromochlorobenzenes with the same hydride and the product distribution for the dehalogenation of some chlorobenzenes with LiAlH4 are also reported.
- Vcelak, Jaroslav,Friesova, Anna,Rericha, Roman,Hetflejs, Jiri
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p. 1368 - 1383
(2007/10/02)
-
- Photochemistry of Polyhaloarenes. 12. The Photochemistry of Pentachlorobenzene in Micellar Media
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The dependence of the reciprocal of the quantum yield for the photohydrodechlorination of pentachlorobenzene (1) in aqueous 0.100 M hexadecyltrimethylammonium bromide (CTAB) solution upon the reciprocal of the microconcentration of 1 and upon the reciprocal of the probability for excited state 1 reacting with ground-state 1 provides a linear correlation at high microconcentrations of 1.The regiochemistry of the photohydrodechlorination process in CTAB favors formation of 1,2,4,5-tetrachlorobenzene to a significantly smaller extent than is observed in the analogous process in acetonitrile solution in the presence of triethylamine.The bromotetrachlorobenzene byproduct is formed in the photolysis in the following composition: 1-bromo-2,3,4,5-tetrachloro- (5) : 2-bromo-1,3,4,5-tetrachloro- (6) : 3-bromo-1,2,4,5-tetrachlorobenzene (7) = 9.7 : 66.7 : 23.3.In a trapping experiment carried out during an irradiation of 1 in CH3CN/ H2O (8:2) in the presence of excess KBr at 254 nm, bromotetrachlorobenzenes (5:6:7) were formed in a ratio of 11.3 : 66.8 : 21.9.These experiments are rationalized by proposing that product in these micellar photohydrodechlorination reactions is formed by fission of triplet-state 1 and a competing process which involves conversion of triplet-state 1 to triplet excimer which then undergoes fragmentation.
- Freeman, Peter K.,Lee, Youn-Sik
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p. 2846 - 2850
(2007/10/02)
-
- Photochemistry of Polyhaloarenes. 8. The Photodechlorination of Pentachlorobenzene
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Measurements of the intersystem crossing yield of pentachlorobenzene triplet, the quenching of photodechlorination of pentachlorobenzene with fumaronitrile, the dependence of the fluorescence lifetime, and the quantum yield of photodechlorination of pentachlorobenzene upon substrate concentration and the dependence of relative product concentration upon light intensity provide evidence for three pathways to product: direct fission of singlet and triplet and fragmentation of triplet excimer.
- Freeman, Peter K.,Ramnath, N.,Richardson, Alan D.
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p. 3643 - 3646
(2007/10/02)
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- Photochemistry of Polyhaloarenes. 7. Photodechlorination of Pentachlorobenzene in the Presence of Sodium Borohydride
-
The mechanism of photodechlorination of pentachlorobenzene (1) in acetonitrile has been examined.The quantum yield of reaction (Φr) has been found to vary with the concentration of 1.A charge-transfer intermediate formed from the triplet excited state of 1 is proposed to explain the observations. Φr increases with added NaBH4 and 1/Φr varies directly with the inverse of the concentration of the electron-transfer reagent.The regiochemistry deuterium isotope effects, tracer studies, and quenching analyses are consistent with an electron-transfer process.
- Freeman, Peter K.,Ramnath, N.
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p. 148 - 152
(2007/10/02)
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- Photo-Rearrangement of Polychlorobenzenes meta-Migration of Chlorine Atom
-
Several polychlorobenzenes were irradiated by ultraviolet light (254 nm) in acetonitrile and the products were determined by gas chromatography.In addition to the abstraction of hydrogen atom from the solvent, photo-isomerization was shown to proceed giving isomeric polychlorobenzenes one of which chlorine atoms migrated to meta to the original position.The meta-rearrangement was rationalized by an MNDO calculation on o-chlorophenyl free radical.
- Morisaki, Kenji,Miura, Yasuki,Abe, Kazuhisa,Hirota, Minoru,Nakada, Masahiro
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p. 1589 - 1592
(2007/10/02)
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- The Photochemistry of Polyhaloarenes. 5. Fragmentation Pathways in Polychlorobenzene Radical Anions
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Negative chemical ionization mass spectroscopy of polychlorobenzenes reveals that parent radical anion undergoes fission by two pathways--(a) cleavage to aryl radical plus Cl- (kCl-) and (b) fission to aryl carbanion plus chlorine atom (kCl*)--and that there is a Hammett relationship between log(kCl*/kCl-) and Σ?.The dependence of the reciprocal of the quantum yield for photochemical dechlorination of trichlorobenzenes through pentachlorobenzene upon the reciprocal of the concentration of the electron donor, triethylamine, was analyzed in order to establish the optimum concentration for radical anion formation.The regiochemistries for the photodechlorination of trichlorobenzenes through pentachlorobenzene in the presence of triethylamine, with and without acetophenone sensitizer, were determined and found to be very similar and quite different from those observed for the direct photolysis in the absence of triethylamine for the comparison cases of 1,2,3,5-tetrachloro- and pentachlorobenzene.The regiochemistry of the fragmentation of polychlorobenzene radical anion to aryl radical plus chloride ion is rationalized in terms of a bent transition state.
- Freeman, Peter K.,Srinivasa, Ramanujan,Campbell, J.-A.,Deinzer, Max L.
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p. 5531 - 5536
(2007/10/02)
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- Reaction of Aryl Grignard Reagents with Hexahalobenzenes: Novel Arenes via a Multiple Aryne Sequence
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New methodology for forming four to six new carbon-carbon bonds to an existing benzene ring in a "one-pot" reaction is described.Reaction of hexabromobenzene (7) or 1,2,4,5-tetrabromo-3,6-dichlorobenzene with excess arylmagnesium bromide in THF gives, after aqueous quench, 1,2,4,5-tetraarylbenzenes in good yield (Table I).The actual product is the corresponding di-Grignard 29, formed from a tetrahalo di-Grignard (24, 31) through a sequence of organometallic aryne intermediates (Scheme II).
- Harada, Katsumasa,Hart, Harold,Du, Chi-Jen Frank
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p. 5524 - 5528
(2007/10/02)
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- Thermally Induced Degradation of 2,3,5,6-Tetrachloroterephthalylidenebis(o-aminoaniline)
-
The bis(Schiff base) 1, 2,3,5,6-tetrachloroterephthalylidenebis(o-aminoaniline), obtained by low-temperature solution condensation of o-phenylenediamine with 2,3,5,6-tetrachloroterephthalaldehyde, suffers fragmentation at 100 degC in dipolar aprotic solvent media under strictly anaerobic conditions, giving benzimidazole (3) and 1,2,4,5-tetrachlorobenzene (4).The same fragmentation of 1, although accompanied by side reactions, is observed in refluxing ethanol or toluene.The reaction involves fission of the C-C bonds connecting the central tetrachlorophenylene segment with the outer two substituent groups and probably proceeds via the ring-tautomeric bis(imidazoline) form of 1.Neither the bis(benzimidazole) 2, 1,4-bis(benzimidazol-2-yl)-2,3,5,6-tetrachlorobenzene, in which the outer two substituent groups already exist in the aromatized state, nor the bis(Schiff base) 6, terephthalylidenebis(o-aminoaniline), lacking the four bulky chloro groups at the center unit, undergo such C-C bond cleavage under the conditions indicated.These findings show that it is the combined effect of steric buttressing at the perchlorophenylene segment and imidazolation, i. e., aromatization, of the outer substituent groups which provides the driving force for the fragmentation observed.In a suitable oxidative environment, cyclodehydrogenation of the bis(Schiff base) 1 competes efficaciously enough with the degradative process to suppress the generation of the fragmentation products, and only the bis(benzimidazole) 2 is isolated.
- Leyden, Richard N.,Loonat, Mohamed S.,Neuse, Eberhard W.,Sher, Brian H.,Watkinson, Walter J.
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p. 727 - 731
(2007/10/02)
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- THE PREPARATION AND SOME REACTIONS OF 2,3,5,6-TETRACHLOROPHENYLMAGNESIUM CHLORIDE
-
The reaction of pentachlorobenzene with metallic magnesium in THF at 10-15 deg C gives after hydrolysis 1,2,4,5-tetrachlorobenzene (76percent) and pentachlorobenzene (8percent); after trimethylsilylation, 1,2,4,5-tetrachloro-3-(trimethylsilyl)benzene (74percent), pentachloro(trimethylsilyl)benzene (8percent) and 1,2,4,5-tetrachlorobenzene (6percent); after iodination, 1,2,4,5-tetrachloroiodobenzene (44percent), pentachloroiodobenzene (12percent) and 1,2,4,5-tetrachlorobenzene (9percent); and finally after carbonation, 2,3,5,6-tetrachlorobenzoic acid (58percent).These products indicate that in the Grignard reaction a mixture of largely 2,3,5,6-tetrachlorophenylmagnesium chloride and some pentachlorophenylmagnesium chloride is formed.The formation of pentachlorophenylmagnesium chloride is explained on the basis of metal-hydrogen exchange reaction between 2,3,5,6-tetrachlorophenylmagnesium chloride and the unreacted pentachlorobenzene.
- Rahman, M. T.
-
-
- Nucleophilic Displacement in Polyhalogenoaromatic Compounds. Part 11. Kinetics of Protiodeiodination of Iodoarenes in Dimethyl Sulphoxide-Methanol
-
The rates of methoxide-ion induced protiodeiodination of a number of polychloroiodobenzenes and their derivatives have been measured in dimethyl sulphoxide-methanol (9:1 v/v; 323.2 K).The true reagent under these conditions appears to be the dimethyl sulphoxide anion, and the rates of reaction in some cases appear to approach that expected of a diffusion controlled process.This corresponds to a major decrease in the efficacy of further activating substituents in the aromatic system, altough deactivating groups such as p-OMe still show large effects.Chlorine promotes protiodeiodination in the order of efficiency o-Cl > m-Cl > p-Cl; the trifluoromethyl group activates displacement in the order o-CF3 > p-CF3 > m-CF3, although with much less difference between isomeric sites. o-Nitro-groups promote protiodeiodination whereas the p-nitro-group encourages methoxydeiodination.No evidence of methoxydeiodination was found in attack of the polychloroiodobenzenes, although the rates of methoxydechlorination of the corresponding polychlorobenzenes suggest that in some cases this might occur.Evidence rejecting the possible SRN1 mechanism and supporting nucleophilic attack by a carbanionic species upon iodine is presented.
- Bolton, Roger,Moore, Clive,Sandall, John P.B.
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p. 1593 - 1598
(2007/10/02)
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- Participation of Oligochlorobenzenes in the Base-Catalyzed Halogen Dance
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The three trichlorobenzenes fail to participate in the base-catalyzed halogen dance even on treatment with the favorable base/solvent combination potassium tert-butoxide in hexamethylphosphoric triamide.However, 1,2,3,5- and 1,2,4,5-tetrachlorobenzenes undergo disproportionation to penta- and trichlorobenzenes as well as interconversion into each other.Pentachlorobenzene disproportionates to hexa- and tetrachlorobenzenes, but further reactions of C6Cl6 form pentachlorophenol.Substitution reactions to form aryl tert-butyl ethers are observed as side reactions and are believed to occur by the SNAr mechanism.The phenols produced in several reactions apparently result from E2 cleavage of these ethers.These observations are possibly relevant to the mechanism of formation of 2,3,7,8-tetrachlorodibenzo-p-dioxin from 1,2,4,5-tetrachlorobenzene.
- Mach, Martin H.,Bunnett, Joseph F.
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p. 4660 - 4666
(2007/10/02)
-