Xn:Harmful;
106-46-7Relevant articles and documents
Facile Hydrodehalogenation with Hydrogen and Pd/C Catalyst under Multiphase Conditions
Marques, Carlos Alberto,Selva, Maurizio,Tundo, Pietro
, p. 5256 - 5260 (1993)
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.
The Photochemistry of Polyhaloarenes. 5. Fragmentation Pathways in Polychlorobenzene Radical Anions
Freeman, Peter K.,Srinivasa, Ramanujan,Campbell, J.-A.,Deinzer, Max L.
, p. 5531 - 5536 (1986)
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.
Photolyses of Polychloro- and Polybromobenzenes. Novel Isomerization in Solvents Resisting against Hydrogen Abstraction
Hirota, Minoru,Nakada, Masahiro
, p. 2926 - 2933 (1992)
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.
Zeolite ZSM-5 and related materials as catalyst in benzene chlorination
Huizinga,Scholten,Wortel,van Bekkum
, p. 3809 - 3812 (1980)
ZSM-5 type zeolites and related high siliceous materials induce addition of chlorine to benzene yielding hexachlorocyclohexanes, whereas Y-type zeolites favour substitution to yield chlorobenzenes.
Photo-Rearrangement of Polychlorobenzenes meta-Migration of Chlorine Atom
Morisaki, Kenji,Miura, Yasuki,Abe, Kazuhisa,Hirota, Minoru,Nakada, Masahiro
, p. 1589 - 1592 (1987)
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.
Chlorination of Benzene with L-Zeolite Catalyst in the Presence of Oxygen and Various Solvents
Nakamura, Tadashi,Shinoda, Kiyonori,Yasuda, Kensei
, p. 1881 - 1882 (1992)
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.
Dechlorination of Polychlorobenzenes over Triiron Tetraoxide in the Presence of Hydrogen Donating Solvents
Hao, Cui Xiang,Nakada, Masahiro,Yamaguchi, Tatsuaki,Fukushi, Sachio,Hirota, Minoru
, p. 1707 - 1710 (1985)
Dechlorination of polychlorobenzenes over Fe3O4 was investigated by a pulse micro-reactor technique.Dechlorinations of various polychlorobenzenes in hexane and cyclohexane were carried out in the gas phase at the temperatures ranging from 498 to 623 K.In the presence of such hydrogen donating solvents, dechlorination was shown to proceed almost exclusively.The relative rates of dechlorination were measured by gas chromatography.It was found that the solvents used to dissolve polychlorobenzenes plays a role of a hydrogen donor in this reaction.The different rates among unequivalent chlorine atoms in a molecule were interpreted by the effect of steric acceleration caused by the neighboring chlorine atom(s).The reaction will probably proceed via hydrogenolytic cleavage of C-Cl bonds.
A Desirable Route to Heterodimers of 1,4-Dihalobenzenes and Anthracene and Their Photoproperties and Thermal Properties
Kimura, Masaru,Okamoto, Hideki,Kura, Hisatoshi,Okazaki, Ayumi,Nagayasu, Eiji,et al.
, p. 3908 - 3911 (1988)
Electronic oxidative bisdecarboxylation of photoadducts of 2,5-dihalo-1,2-dihydrophthalic anhydride and anthracene gave the corresponding energy-rich heterodimers 12 and 13.The quantum yields of the formation of the excited anthracene from 12 and 13 by the irradiation of 280-nm light were 0.65 and 0.25, respectively.We assumed that the heterodimers of 12 and 13 form biradicaloid intermediates during thermal retro cycloaddition and consumed their stored energy without any visible light.However, we observed emission light from 340 to 460 nm through a glass filter and the formation of anthracene using Nd-YAG laser IR light (1.06 μm) by the multiphoton absorption, when fine powders of 12 and 13 were used.
Dechlorination of lindane, dieldrin, tetrachloroethane, trichloroethene, and PVC in subcritical water
Kubatova, Alena,Lagadec, Arnaud J. M.,Hawthorne, Steven B.
, p. 1337 - 1343 (2002)
Pure water has been used to dechlorinate aliphatic organics without the need for catalysts or other additives. Dehydrohalogenation (loss of HCl with the formation of a double bond) occurred at temperatures as low as 105-200 °C for 1,1,2,2-tetrachloroethane, lindane (1,2,3,4,5,6-hexachlorocyclohexane, γ-isomer), and dieldrin (1,2,3,4,10,10-hexachloro-6,7-epoxy-1,4,4a,5,6,7,8,8a-octahydro-endo, exo-1,4:5,8-dimethanonaphthalene). Complete loss of the parent compounds was achieved in less than 1 h at 150, 200, and 300 °C for 1,1,2,2-tetrachloroethane, lindane, and dieldrin, respectively. The initial dechlorination of lindane had an activation energy of 84 kJ mol-1 with an Arrhenius pre-exponential factor of 1.5 x 106 s-1. Dehydrohalogenation of lindane formed trichlorobenzenes, followed by subsequent hydrolysis and hydride/chloride exchange to form chlorophenols, lower chlorobenzenes, and phenol as the major final product. Reaction of poly(vinyl chloride) at 300 °C for 1 h formed aromatic hydrocarbons ranging from benzene to anthracene and a char residue with a ca. 1:1 carbon-to-hydrogen ratio (mol/mol). The residue contained 1 wt % of chlorine compared to 57 wt % chlorine in the original polymer. All compounds tested yielded chloride ion as the major product (at higher temperatures), indicating that complete dechlorination of some aliphatic organochlorines may be feasible.
Nickel Complexes as Soluble Catalysts for Reductive Dehalogenation of Aromatic Halides
Stiles Martin
, p. 5381 - 5385 (1994)
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.
