- Catalytic Dehalogenation of Highly Chlorinated Benzenes and Aroclors Using PdCl2(dppf) and NaBH4: Efficiency, Selectivity, and Base Support
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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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- Antagonism/agonism modulation to build novel antihypertensives selectively triggering I1-imidazoline receptor activation
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Pharmacological studies have suggested that I1-imidazoline receptors are involved in the regulation of cardiovascular function and that selective I1-agonists, devoid of the side effects associated with the common hypotensive α2
- Del Bello, Fabio,Bargelli, Valentina,Cifani, Carlo,Gratteri, Paola,Bazzicalupi, Carla,Diamanti, Eleonora,Giannella, Mario,Mammoli, Valerio,Matucci, Rosanna,Micioni Di Bonaventura, Maria Vittoria,Piergentili, Alessandro,Quaglia, Wilma,Pigini, Maria
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- Photoreductive dehalogenation of halogenated benzene derivatives using ZnS or CdS nanocrystallites as photocatalysts
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ZnS nanocrystallites (nc-ZnS) prepared in N,N-dimethylformamide (DMF) photocatalyze dehalogenation of halogenated benzenes to benzene as the final product from chlorinated benzenes and to difluorobenzenes from fluorinated benzenes in the presence of triethylamine (TEA) as an electron donor under UV light irradiation (λ > 300 nm). When CdS nanocrystallites (nc-CdS) are used as a photocatalyst (λ > 400 nm), halogenated benzenes are photoreductively dehalogenated, yielding trichlorobenzene from hexachlorobenzene and tetrafluorobenzene isomers from hexafluorobenzene as the final products. Photoformed electrons on nc-ZnS and nc-CdS have such negative reduction potentials that these electrons reduce polyhalogenated benzenes, leading to the successive dehalogenation. nc-ZnS exhibits higher photocatalytic activity than nc-CdS due to the more negative potential of the electrons on nc-ZnS than that on nc-CdS. The higher activities of nc-ZnS and nc-CdS compared to their bulk forms are explained as being due to their quantum size effects and the adsorptive interaction between the substrates and the nanosized photocatalysts. ZnS nanocrystallites (nc-ZnS) prepared in N,N-dimethylformamide (DMF) photocatalyze dehalogenation of halogenated benzenes to benzene as the final product from chlorinated benzenes and to difluorobenzenes from fluorinated benzenes in the presence of triethylamine (TEA) as an electron donor under UV light irradiation (λ>300 nm). When CdS nanocrystallites (nc-CdS) are used as a photocatalyst (λ>400 nm), halogenated benzenes are photoreductively dehalogenated, yielding trichlorobenzene from hexachlorobenzene and tetrafluorobenzene isomers from hexafluorobenzene as the final products. Photoformed electrons on nc-ZnS and nc-CdS have such negative reduction potentials that these electrons reduce polyhalogenated benzenes, leading to the successive dehalogenation. nc-ZnS exhibits higher photocatalytic activity than nc-CdS due to the more negative potential of the electrons on nc-ZnS than that on nc-CdS. The higher activities of nc-ZnS and nc-CdS compared to their bulk forms are explained as being due to their quantum size effects and the adsorptive interaction between the substrates and the nanosized photocatalysts.
- Yin, Hengbo,Wada, Yuji,Kitamura, Takayuki,Yanagida, Shozo
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- Dehalogenation of o-dihalogen substituted arenes and α,α′-dihalogen substituted o-xylenes with lanthanum metal
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It was found that lanthanum metal caused the dehalogenation of o-dihalogen substituted arenes and α,α′-dihalogen substituted o-xylenes to generate the corresponding benzynes and o-quinodimethanes. When o-dihalogen substituted arenes were allowed to react with lanthanum metal in the presence of dienes, the Diels-Alder products between benzyne and dienes were formed in moderate to good yields. Similarly, the Diels-Alder adducts of o-quinodimethane with dienophiles were obtained, in the reaction of α,α′-dibromo-o-xylenes with lanthanum metal in the presence of dienophiles.
- Nishiyama, Yutaka,Kawabata, Hiroshi,Nishino, Toshiki,Hashimoto, Kouji,Sonoda, Noboru
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Read Online
- Iron(iii)porphyrin electrocatalyzed enantioselective carbon-chloride bond cleavage of hexachlorocyclohexanes (HCHs): Combined experimental investigation and theoretical calculations
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Enantioselective electrocatalysis of α-, β-, γ- and δ-hexachlorocyclohexanes (HCHs) by tetrakis-pentafluorophenyl-Fe(iii)porphyrin is described. The first example of the combined use of electrochemical measurements and theoretical calculations to determine the mechanism of the enantioselective C-Cl bond cleavage of the electrocatalysis is reported. The electrochemical measurements demonstrate that the reactivity of the HCHs follows the order γ-HCH > α-HCH > δ-HCH > β-HCH. Steric considerations and a molecular orbital theory approach can be used to rationalize the enantioselective nature of the catalysis based on the ease of approach of each Cl atom to the central Fe(i) ion and a consideration of the nodes on the C-Cl bonds that weaken these bonds in a manner that results in bond cleavage and the formation of an Fe-Cl bond.
- Liang, Xu,Li, Minzhi,Mack, John,Lobb, Kevin,Zhu, Weihua
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p. 11470 - 11476
(2018/08/28)
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- PROCESS FOR THE PREPARATION OF ORGANIC HALIDES
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The present invention provides a halo-de-carboxylation process for the preparation of organic chlorides, organic bromides and mixtures thereof, from their corresponding carboxylic acids, using a chlorinating agent selected from trichloroisocyanuric acid (TCCA), dichloroisocyanuric acid (DCCA), or combination thereof, and a brominating agent.
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Paragraph 00146
(2017/08/01)
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- Dicamba preparation process
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The invention belongs to the technical field of herbicide dicamba preparation and relates to a dicamba preparation process. The dicamba preparation process includes steps: taking benzene as a raw material to generate 1,2,4-trichlorobenzene through directional chlorination, catalysis, re-chlorination and rectification; hydrolyzing the 1,2,4-trichlorobenzene to generate a mixture of 2,5-dichlorophenol and 2,4-dichlorophenol, and separating and purifying to obtain 2,5-dichlorophenol; using the 2,5-dichlorophenol to prepare 3,6-dichlorosalicylic acid; subjecting the 3,6-dichlorosalicylic acid to methylation, saponification, acidification and the like to obtain dicamba. By optimization of technical steps and parameters, the whole dicamba preparation process has advantages of simplicity, low cost, high yield, high selectivity, remarkable reduction of wastewater and increase of equipment utilization rate.
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Paragraph 0051; 0052; 0053
(2017/04/03)
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- A method for the synthesis of 2, 5 - dichlorophenol (by machine translation)
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The invention relates to a 2, 5?Dichiorophenol synthetic method, which belongs to the technical field of the synthesis of the key intermediate chamber. The invention is composed of a pure chlorization generated 1, 2, 4?Trichlorobenzene and santochlor is easy to separate, thereby avoiding the difficulties caused by the separating of the high production cost and low production efficiency; because the 1, 2, 4?Trichlorobenzene and to two chiorophenoxy can be obtained respectively 2, 5?Dichiorophenol, utilization rate of raw materials is high, thereby avoiding the waste of the by-product, so that the production cost is greatly reduced. In addition, the two paradichlorbenzene through two different method to obtain 2, 5?Dichiorophenol. The synthesis technique of this invention is simple, the production cost is low, the utilization rate of raw materials is high, and the craft there are few by-products, less generation of three wastes, is more suitable for large-scale industrial production. (by machine translation)
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- Substd. photoisomerization arom. compd. method
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Isomerizing substituted aromatic compounds (I), comprises carrying out isomerization in the presence of a salt melt, which contains a metal compound (II) and at least one metal compound (III). Isomerizing substituted aromatic compounds of formula (Ar1-R n) (I) or their mixtures, comprises carrying out isomerization in the presence of a salt melt, which contains a metal compound of formula ([M1][X1] m 1) (II) and at least one metal compound of formula ([M2][X2] m 2) (III). Ar1 : n-valent aryl radical; R : halo, alkyl, fluoroalkyl, aryl, alkyl-aryl or amino; M1 : Al, Ga, In, Cu, Fe, Co or Ni; X1, X2 : halo, preferably Cl or Br; M2, m2 : alkaline earth metal or alkali metal, where M2 is preferably Li, Na, or K; m1 : Al, Ga, In, Fe(III), Co, Ni or Cu(II); and n : >= 2, preferably 2.
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Paragraph 0064
(2017/01/02)
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- ORGANIC SEMICONDUCTOR
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The invention relates to novel compounds containing one or more units derived from 1,5-disubstituted-1,5-dihydro-[1,5]naphthyridine-2,6-dione, to methods for their preparation and educts or intermediates used therein, to mixtures and formulations containing them, to the use of the compounds, mixtures and formulations as organic semiconductors in organic electronic (OE) devices, especially in organic photovoltaic (OPV) devices and organic photodetectors (OPD), and to OE, OPV and OPD devices comprising these compounds, mixtures or formulations.
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Page/Page column
(2015/06/03)
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- Electroreductive dechlorination of α-hexachlorocyclohexane catalyzed by iron porphyrins in nonaqueous media
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Two iron porphyrins, (TPP)FeCl and (OEP)FeCl, where TPP and OEP are the dianions of tetraphenylporphyrin and octaethylporphyrin, respectively, were utilized as catalysts for the electroreductive dechlorination of α-hexachlorocyclohexane (α-HCH) which was monitored by electrochemistry, in situ UV-visible spectroelectrochemistry and controlled potential electrolysis in N,N′-dimethylformamide. GC-MS analysis of the α-HCH degradation products revealed the stepwise formation of pentachlorocyclohexene and tetrachlorocyclohexadiene as intermediates, prior to generation of the final dechlorination products which consisted of an isomeric mixture of trichlorobenzenes. Based on identification of the intermediates and final products in the reaction, an overall dechlorination mechanism of α-hexachlorocyclohexane is proposed.
- Zhu, Weihua,Ni, Cui,Liang, Lili,Li, Junwen,Li, Minzhi,Ou, Zhongping,Kadish, Karl M.
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p. 519 - 527
(2014/07/21)
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- Trichloroisocyanuric acid in 98% sulfuric acid: A superelectrophilic medium for chlorination of deactivated arenes
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Trichloroisocyanuric acid (TCCA) reacts with arenes and its reactivity is highly affected by the acid strength of the reaction medium. Deactivated arenes are efficiently chlorinated by TCCA in H2SO4. Our results, along with DFT calculations and 13C NMR spectrometry suggest the formation of a monoprotonated TCCA superelectrophile as the reactive species that can efficiently transfer electrophilic Cl+ to even very weak nucleophiles, such as m-dinitrobenzene.
- Mendo?a, Gabriela Fonseca,Senra, M?nica Rufino,Esteves, Pierre M.,De Mattos, Marcio C.S.
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experimental part
p. 176 - 181
(2012/04/04)
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- Cross-coupling of polychlorobenzenes with phenylboronic acid in the presence of [Pd]-imidazolium salts as catalytic systems
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The reactions of di-, tetra-, and hexachlorobenzenes with phenylboronic acid in the presence of [Pd]-imidazolium salt-base as catalytic systems afford cross-coupling products in moderate yields. The highest conversions are attained when imidazolium salts bearing bulky aromatic substituents are used and the reaction is carried out in the presence of alkali alkoxides containing H α atoms. Cross-coupling is accompanied by hydrodechlorination of aromatic C-Cl bonds.
- Burukin,Vasil'Ev,Merkulova,Chizhov,Mistryukov,Zlotin
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p. 1467 - 1469
(2008/09/18)
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- Novel catalysts for dechlorination of polychlorinated biphenyls (PCBs) and other chlorinated aromatics
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Diiron complexes of fluorene and fluorene* (1,2,3,4,5,6,7,8,9- nonamethylfluorene) have been found to be catalysts for the dechlorination of chlorinated aromatics, such as PCBs. The Royal Society of Chemistry.
- Fletcher, Andrew E. D.,Moss, James,Cowley, Andrew R.,O'Hare, Dermot
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p. 2971 - 2973
(2008/03/11)
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- PROCESS FOR HALOGENATION OF BENZENE AND BENZENE DERIVATIVES
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In a process of halogenation of benzene or benzene derivatives, di-substituted halobenzene derivatives having para-aromatic compounds or tri-substituted halobenzene derivatives having 1,2,4-substituted aromatic compounds are selectively produced. In halogenation of benzene or benzene derivatives, a fluorine-containing zeolite catalyst such as L-type zeolite, or a zeolite catalyst having the crystal size of at most 100 nm is used. The reaction is preferably effected in the presence of a solvent, and the solvent is preferably a halogenated compound.
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Page/Page column 22-23
(2008/06/13)
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- Formation and destruction of chlorinated pollutants during sewage sludge incineration
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The limitations facing land filling and recycling and the planned ban on sea disposal of sludge leads to the expectation that the role of sludge incineration will increase in the future. The expected increase in sludge incineration will also increase scrutiny of the main drawback to sewage sludge incineration-the formation of hazardous air pollutants (HAPs). Despite the extensive body of knowledge available on sewage sludge combustion, very few studies have been conducted on the formation of HAPs during sludge combustion. In this work, the interactions between sewage sludge pyrolysis products and sludge ash were investigated using a dual chamber flow reactor system and a horizontal laboratory scale reactor. The results of this study shows that sludge ash can catalyze oxidation and chlorination of organics. In the absence of HCl in the gas stream, sludge ash acts as an oxidizing catalyst, but in the presence of HCl, sludge ash acts as a chlorination catalyst producing high yields of organochloride compounds.
- Fullana, Andres,Conesa, Juan A.,Font, Rafael,Sidhu, Sukh
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p. 2953 - 2958
(2007/10/03)
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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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- Effects of FeS on the transformation kinetics of γ-hexachlorocyclohexane
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Distinctly different rates and pathways were observed for abiotic transformation of γ-hexachlorocyclohexane (γHCH) between homogeneous systems and systems containing FeS solid. The observed half-lives of γ-HCH decrease from about 1136 and 126 d in homogen
- Liu, Xiangmei,Peng, Ping'an,Fu, Jiamo,Huang, Weilin
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p. 1822 - 1828
(2007/10/03)
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- Electroreduction of polychlorobenzenes using either lead or copper electrodes
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Polychlorobenzenes can be reduced electrolytically to dichlorobenzenes by using either lead or copper as the electrodes in a MeOH/THF solution. Among the resultants of dichlorobenzenes, 1,4-dichlorobenzene is a major product that might be due to a low enthalpy of formation. A chlorine atom situated at the ortho position of another chlorine atom in the benzene ring is removed prior to others. However, the sequence of reactivities of the polychlorobenzenes for electroreducing by lead electrodes in this study is as follows: 1,2,3,4-C 6H2Cl4 > 1,3,5-C6H 3Cl3 > C6HCl5 - 1,2,4,5-C 6H2Cl4 > 1,2,3,5-C6H 2Cl4 - 1,2,3-C6H3Cl3 > 1,2,4-C6H3Cl3 > C6Cl 6.
- Lin, Shaw-Tao,Chao, Richard Yung-Ho,Lin, Sun-Che,Lin, Shu-Fan
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p. 539 - 544
(2007/10/03)
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- 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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- 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
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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
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- Radiolytic reduction of hexachlorobenzene in surfactant solutions: A steady-state and pulse radiolysis study
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Steady-state and pulse radiolysis experiments have been performed to gain insight into the mechanism of hexachlorobenzene (HCB) degradation in nonionic surfactant (Plurafac RA-40) solutions. This understanding is important for the environmental application of radiolysis to remediate soils contaminated with chlorinated aromatic compounds or to treat surfactant solution wastes from soil washing processes. Steady-state experiments showed that, after an applied dose of 50 kGy, reductive dechlorination of HCB to trichlorobenzene occurs under reducing conditions. Under oxidizing conditions at the same dose, reductive dechlorination proceeds more slowly to yield tetrachlorobenzene. Radiolytic experiments on the surfactant alone showed that the reaction rate constant between hydroxyl radicals and RA-40 (1.09 x 109 M-1 s-1) was nearly 2 orders of magnitude higher than that between hydrated electrons and RA-40 (2.0 x 107 M-1 s-1). Reaction kinetics analysis indicates efficient hydroxyl radical scavenging by surfactant molecules and the production of secondary surfactant radicals, which are reductive in nature. Thus, we observe HCB dechlorination in surfactant solutions even under strongly oxidizing conditions. Steady-state and pulse radiolysis experiments have been performed to gain insight into the mechanism of hexachlorobenzene (HCB) degradation in nonionic surfactant (Plurafac RA-40) solutions. This understanding is important for the environmental application of radiolysis to remediate soils contaminated with chlorinated aromatic compounds or to treat surfactant solution wastes from soil washing processes. Steady-state experiments showed that, after an applied dose of 50 kGy, reductive dechlorination of HCB to trichlorobenzene occurs under reducing conditions. Under oxidizing conditions at the same dose, reductive dechlorination proceeds more slowly to yield tetrachlorobenzene. Radiolytic experiments on the surfactant alone showed that the reaction rate constant between hydroxyl radicals and RA-40 (1.09 × 109 M-1 s-1) was nearly 2 orders of magnitude higher than that between hydrated electrons and RA-40 (2.0 × 107 M-1 s-1). Reaction kinetics analysis indicates efficient hydroxyl radical scavenging by surfactant molecules and the production of secondary surfactant radicals, which are reductive in nature. Thus, we observe HCB dechlorination in surfactant solutions even under strongly oxidizing conditions.
- Zacheis,Gray,Kamat
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p. 3401 - 3407
(2007/10/03)
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- Destruction of halogenated hydrocarbons with solvated electrons in the presence of water
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Model halogenated aromatic and aliphatic hydrocarbons and halogenated phenols were dehalogenated in seconds by solvated electrons generated from sodium in both anhydrous liquid ammonia and ammonia/water solutions. The minimum sodium required to completely dehalogenate these model compounds was determined by increasing the Na/substrate ratio until halogen loss was complete. Minimum sodium consumptions were determined in both anhydrous liquid ammonia and with a (5, 20, 50-fold molar excess of water per mole of halide). While more Na was consumed in the presence of water, these dehalogenations were still efficient when a 50-fold water excess was present. Dehalogenation is faster than competiting reactions with water. CCl4 and CH3CCl3 in the presence of a stoichiometric deficiency of sodium produced only CH4 and CH3CH3 and recovered CCl44 or CH3CCl3, respectively. No partially dechlorinated products were detected, indicating dechlorination was diffusion controlled. Na consumption per chlorine removed (as NaCl) was lower than that of Li, K or Ca and this advantage increased in the presence of water. Na consumption was lower using Na chunks instead of a thin Na mirror. Chloroaromatic compounds gave the parent aromatic hydrocarbon and aminated products in anhydrous ammonia but aminated products did not form when water was present. (C) 2000 Elsevier Science Ltd.
- Sun, Guang-Ri,He, Jin-Bao,Pittman Jr., Charles U.
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p. 907 - 916
(2007/10/03)
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- Electrocarboxylation of chlorinated aromatic compounds
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Chorinated benzenes (1, 4), biphenyls (6, 9), dibenzofurans (10, 15, 17, 18), 2-chlorodibenzo[1,4]dioxine (24) and 1-chloronaphthalene (26) as well as dibenzofuran (12) and naphthalene (27) themselves were transformed into carboxylic acids by galvanostatic electroreduction in the presence of carbon dioxide ("electrocarboxylation"). Dry DMF was used as solvent, zinc or stainless steel as cathode and magnesium as a sacrificial anode in an undivided cell. Hydrogenation of aromatic rings was not observed. However, reductive addition of two molecules of carbon dioxide to form dihydrodicarboxylic acids, e.g. 22 and 29, occurs in the dibenzofuran and naphthalene series.
- Golinske, Dirk,Voss, Juergen,Adiwidjaja, Gunadi
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p. 862 - 880
(2007/10/03)
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- Synergistic effect in bimetallic Ni-Al clusters. Application to efficient catalytic reductive dehalogenation of polychlorinated arenes
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Subnanometric Ni-Al clusters, in situ prepared by reduction of equimolar amounts of Ni(OAc)2 and Al(Acac)3 induced by alkoxide activated sodium hydride, exhibit a high catalytic activity for efficient reductive dehalogenation of aliphatic and aromatic halides and polychlorinated arenes. (C) 2000 Elsevier Science Ltd.
- Massicot, Fabien,Schneider, Rapha?l,Fort, Yves,Illy-Cherrey, Sandra,Tillement, Olivier
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p. 4765 - 4768
(2007/10/03)
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- Highly selective photochemical and thermal chlorination of benzene by Cl2 in NaZSM-5
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Loading of zeolite NaZSM-5 with benzene and chlorine from the gas phase at -100°C resulted in spontaneous reaction to form chlorobenzene and 1,4-dichlorobenzene as the sole products. Thermal reaction at elevated temperature (up to 0°C) accelerates the rates toward these products and yields, in addition, some 1,3-dichlorobenzene and a small (2 in the zeolite with green or blue light produced 1,2,4-trichlorobenzene as the only product at high conversion. Such selectivities of benzene chlorination by elemental chlorine are much higher than obtained currently by traditional methods. The sharp increase of the reaction rate in NaZSM-5 compared to that in homogeneous liquid or gas phase and the effect of electronic excitation by visible light are attributed to an enhanced electrophilic character of the chlorine molecule.
- Kirkby, Scott J.,Frei, Heinz
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p. 7106 - 7111
(2007/10/03)
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- Arenediazonium tetrachlorocuprates(ii). Modification of the meerwein and sandmeyer reactions
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In the copper-catalysed reactions of arenediazonium chlorides with unsaturated compounds arenediazonium tetrachlorocuprates(II) are formed as intermediates. A general method of preparation of these complexed diazonium salts is described. In polar solvents these salts undergo chlorinative dediazoniation to give chloroarenes in high yield. The reaction of an arenediazonium tetrachlorocuprate(II) with an activated alkene results in the same products as the Meerwein reaction. A radical cation mechanism for this reaction is proposed.
- Obushak, Mykola D.,Lyakhovych, Mykhaylo B.,Ganushchak, Mykola I.
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p. 9567 - 9570
(2007/10/03)
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- Methanesulfonylation of deactivated aromatics with superelectrophilic CH3so2F·3SbF5 and (CH3so2)2O-2CF3so 3H/B(O3SCF3)3 systems
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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)
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- Chemistry of superacids: 35. * NO2Cl-3MXN systems: Superelectrophilic aprotic nitrating agents for deactivated aromatics
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Superelectrophilic nitration of deactivated aromatics with NO2Cl-3MXn complexes in aprotic nonpolar solvents such as CH2Cl2 makes it possible to obtain the corresponding nitro derivatives in good to almost quantitative yields under mild conditions.
- Olah,Orlinkov,Ramaiah,Oxyzoglou,Prakash
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p. 924 - 927
(2007/10/03)
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- Hydrodehalogenation of Polyhalogenated Aromatics under Multiphase Conditions with H2 and Metal Catalyst: Kinetics and Selectivity
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Aryl halides have been catalytically hydrodehalogenated by bubbling H2 at atmospheric pressure into a biphasic system constituted by an organic solvent and an aqueous solution (aq., KOH 50percent), in the presence of a metal catalyst (Pd/C or Ranay-Ni) and a quaternary onium salt as a phase-transfer (PT) catalyst.Under such new conditions, the hydrodehalogenation of aromatic halides, even of sterically hindered ones, proceeds quickly at low temperatures (20-50 deg C) and affords the corresponding non-halogenated hydrocarbons in substantially quantitative yields.The addition of a quaternary onium salt to the multiphase system may induce remarkable effects both in the enhancement of the reduction rate and in the regio- and chemo-selectivity of the reaction.For instance, when Aliquat 336 (tricaprylmethylammonium chloride) is used, the isomeric chloroethylbenzenes react 50 times faster, para-dichlorobenzene is reduced slower than the ortho isomer, and halogenated aromatic ketones can be effectively dehalogenated, without any reduction of the carbonyl group.Under the same reaction conditions, the addition of an onium salt is required for the Raney-Ni catalyst to become effective as a hydrodehalogenation catalyst.
- Marques, Carlos Alberto,Selva, Maurizio,Tundo, Pietro
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p. 317 - 328
(2007/10/03)
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- Preparation of 1,2,4-Trichlorobenzene by Regioselective Chlorination of 1,2-Dichlorobenzene in the Presence of Catalytic Amounts of Zeolites
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1,2,4-Trichlorobenzene is synthesized in high yield by the chlorination of 1,2- and 1,4-dichlorobenzenes in the liquid phase using zeolites as catalysts and Cl2 gas as the chlorinating agent.
- Singh, Anand P.,Sharma, Sahida,Rojatkar, Supada R.
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p. 512 - 513
(2007/10/03)
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- Electrochemical reductive dehalogenation of chlorobenzenes
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Electrochemical dechlorination of 1,2,3,5-tetrachlorobenzene in methanol and chlorobenzene in dimethylsulfoxide with tetraalkylammonium salts as supporting electrolytes was carried out.The extent of dechlorination depends significantly on the electrode composition. - Key words: electrochemical dechlorination, cathodic materials, polychlorobenzenes.
- Plekhanov, V. P.,Tsyganok, A. I.,Kulikov, S. M.
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p. 1091 - 1095
(2007/10/02)
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- Titanium Catalyzed Reduction of Aromatic Halides by Sodium Borohydride
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The reduction of aryl halides by sodium borohydride is catalyzed by titanium complexes; di(cyclopentadienyl)titanium dichloride (titanocence dichloride) is highly effective.The reaction scope and mechanism are solvent dependent.In dimethylformamide (DMF), an adduct of DMF and sodium borohydride is formed which reduces simple aryl halides by a non-radical, likely nucleophilic route.Dimethylamino- substituted products are formed, as are simple dechlorinated species.In dimethylacetamide or in ethers, a radical-based reaction involving activated titanocene borohydride takes place, and only dechlorinated products result.
- Liu, Yumin,Schwartz, Jeffrey
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p. 4471 - 4482
(2007/10/02)
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- Dechlorination of chlorinated benzenes by an anaerobic microbial consortium that selectively mediates the thermodynamic most favorable reactions
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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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- DEHALOGENATION OF CHLOROBENZENES WITH SODIUM DIHYDRIDOBIS(2-METHOXYETHOXO)ALUMINATE
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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)
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- Nickel Complexes as Soluble Catalysts for Reductive Dehalogenation of Aromatic Halides
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Nickel(II) complexes 1 and 2 are soluble catalysts for reductive dehalogenation of aromatic bromides and polychlorobenzenes by sodium borohydride at 25-45 deg C in aqueous ethanol, aqueous acetonitrile, or ethanol-acetonitrile.Deuterium incorporation experiments, and rate retardation by added cumene, point to a radical-chain mechanism.Hydrazine can replace borohydride as a source of reducing power.Reactivity toward this reducing system increases with increasing halogen content of the substrate, a finding that parallels prior observations of dechlorination in natural sediments.
- Stiles Martin
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p. 5381 - 5385
(2007/10/02)
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- THIOCYANATO- AND CHLOROARYLATION OF ALLYL CHLORIDE AND BROMIDE
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We showed by the example of thiocyanato- and chloroarylation of allyl chloride and bromide that the shielding of the double bond of an olefin from the influence of electron-acceptor groups does not favor the reaction of anion-arylation. 2-Aryl-1-chloromethyl(bromomethyl)ethyl thiocyanates were synthesized by the reaction of aromatic aryldiazonium tetrafluoroborates with allyl chloride or bromide in the presence of thiocyanates or chlorides of alkali metals.
- Grishchuk, B. D.,Gorbovoi, P. M.,Ganushchak, N. I.,Brush, D. M.,Kudrik, E. Ya.
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p. 1156 - 1158
(2007/10/02)
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- Rate of Reaction of Phenyl Radicals with Oxygen in Solution and in the Gas Phase
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The rate constant for the title reaction, k1, is 3.8 X 109 M-1 s-1 in water at 298 K and is >/= 108 M-1 s-1 in the gas phase at 603 K.It is concluded that two reports that this reaction is very slow in the gas phase, k1 >/= 1.2 X 104 and ca.2.3 X 106 M-1 s-1, are in error.
- Sommeling, Paul M.,Mulder, Peter,Louw, Robert,Avila, David V.,Lusztyk, Janusz,Ingold, K. U.
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p. 8361 - 8364
(2007/10/02)
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- Facile Hydrodehalogenation with Hydrogen and Pd/C Catalyst under Multiphase Conditions
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A multiphase system consisting of a hydrocarbon solvent, a strong alkaline solution, and a quaternary onium salt, in the presence of a Pd/C catalyst with hydrogen at atmospheric pressure, allows the rapid and progressive displacement of the chlorine atoms from polyhalogenated benzenes.The onium salt in this case constitutes a third liquid phase in which the reaction takes place.At 50 deg C, 1,2,4,5-tetrachlorobenzene is reduced to benzene in 30 min using a Pd/Cl molar ratio of 1/130.Halogenated compounds are partitioned between the hydrocarbon solution and the liquid phase of the phase-transfer agent; rapid removal of HCl adsorbed on Pd/C is effected by neutralization with the alkaline solution.The enhancement of the reaction rate compared with the known methods might be attributed to the facile adsorption of H2 by the catalyst under the reaction conditions.Different reaction rates result in the reduction of the three isomeric chlorotoluenes, whether the reaction is carried out in the presence or absence of the onium salt.
- Marques, Carlos Alberto,Selva, Maurizio,Tundo, Pietro
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p. 5256 - 5260
(2007/10/02)
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- Hydrodehalogenation of Polychlorinated Aromatic Halides by Hypophosphite with Pd/C Catalyst under Multiphase Conditions
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Polyhalogenated benzenes in the presence of a Pd/C catalyst with sodium hypophosphite system consisting of a hydrocarbon solvent, concentrated aqueous alkali and a quaternary onium salt undergo reduction with rapid and progressive displacement of all their chlorine atoms.The onium salt, being insoluble in both the organic and the aqueous phases, coats, as a third liquid phase, the Pd/C catalyst.The strong alkaline medium and the phase-transfer agent are synergic.Operating at 50 deg C, 1,2,4,5-tetrachlorobenzene gives after 2.5 h a 99 percent yield of benzene.Enhancement of the reaction rate, compared with already known methods, has been attributed to the transfer of phosphite anion from the aqueous solution to the catalyst surface, to partition of halogenated compounds between the hydrocarbon solution and the liquid phase of the phase-tranfer agent and to the rapid removal of HCl adsorbed on Pd/C by the alkaline medium.The reaction is also effective with aryl bromides and deactivated p-methoxyaryl halides.
- Marques, Carlos Alberto,Selva, Maurizio,Tundo, Pietro
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p. 529 - 534
(2007/10/02)
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- Chlorination of Benzene with L-Zeolite Catalyst in the Presence of Oxygen and Various Solvents
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Benzene was chlorinated by using L type zeolite into p-dichlorobenzene (p-DCB) in a high yield in the presence of 1,2-dichloroethane (EDC) and oxygen.
- Nakamura, Tadashi,Shinoda, Kiyonori,Yasuda, Kensei
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p. 1881 - 1882
(2007/10/02)
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- Photolyses of Polychloro- and Polybromobenzenes. Novel Isomerization in Solvents Resisting against Hydrogen Abstraction
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Polychloro- and polybromobenzenes were photolyzed in acetonitrile and perfluorohexane.Photolyses of polychlorobenzenes in acetonitrile gave isomerized products in addition to dechlorinated products, which appeared exclusively in the photolyses in hexane and other solvents carrying hydrogen atoms active to hydrogen abstraction.The photolyses in perfluorohexane gave isomerized products to a lesser extent.The reaction in this solvent gave predominantly polyhalobiphenyls which are assumed to be produced through coupling.Without exception the isomerized products have the structure which can be expected to be formed via 1,3-migration of chlorine atom, though it is not sure at present whether it takes place actually.The isomerization was shown to proceed intramolecularly.Some evidence and theoretical rationalization in favor of the 1.3-chlorine migration mechanism are given.
- Hirota, Minoru,Nakada, Masahiro
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p. 2926 - 2933
(2007/10/02)
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- Photochemistry of Polyhaloarenes. 9. Characterization of the Radical Anion Intermediate in the Photodehalogenation of Polyhalobenzenes
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The product-determining intermediate in the photodehalogenation of polyhalobenzenes has been characterized by generating excimers and radical anions within a micellar core and by formation of corresponding radical anions by electron transfer from lithium p,p'-di-tert-butylbiphenyl radical anion (LiDBB).The photodechlorination of pentachlorobenzene (1; 254 nm, CH3CN) produces 1,2,3,5-tetrachloro- (2), 1,2,4,5-tetrachloro- (3), and 1,2,3,4-tetrachlorobenzene (4).The regiochemistry of this reaction is compared with that observed in the photodechlorination of 1 in a micellar solution of hexadecyltrimethylammonium bromide (CTAB) with occupancy numbers (n) principally /=2.Further comparisons with photodechlorination of 1 in a micellar CTAB solution (n 2) in the presence of triethylamine, as well as photodechlorination in CH3CN in the presence of triethylamine, were used to characterize unencumbered radical anions.The regiochemistries observed in photolytic dehalogenations of 1, 2, 1,2,4-trichlorobenzene, and pentafluorobenzene in the presence of triethylamine are in good agreement with those realized in the radical anion fragmentations induced by electron transfer from LiDBB.
- Freeman, P. K.,Ramnath, N.
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p. 3646 - 3651
(2007/10/02)
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- 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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- Magnetic susceptibilities of organic compounds: Part V - Influence of substituents on diamagnetic susceptibilities of disubstituted and trisubstituted benzenes
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The magnetic susceptibilities of a number of triads of isomeric disubstituted benzenes have been determined, choosing the compounds in such a way that the substituents are present in the following combinations: (i) two electron-releasing substituents, (ii) a halogeno and an electron-releasing substituent, (iii) a halogeno and an electron-attracting substituent, and (iv) two halogeno substituents.The data show that for types (i), (ii) and (iv), the ortho isomers have the highest magnetic susceptibilities, the susceptibilities decreasing in the order: ortho > meta > para; for type (iii), the meta-isomers have the highest susceptibilities, the susceptibilities decreasing in the order: meta > para > ortho.The diamagnetic susceptibilities of some isomeric trisubstituted benzenes have also been determined and the data reveal that the susceptibility is the highest where the crowding of substituents is the highest (1,2,3-isomer) and lowest where the substituents are staggered and least crowded (1,3,5-isomer).Another observation made in the case of trisubstituted benzene is the applicability of a principle of additivity of their diamagnetic susceptibilities.
- Baliah, V.,Jeyanthy, J. Judith Diana
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p. 472 - 476
(2007/10/02)
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