- PHOTOSENSITIZED REACTION OF Hg(3P) ATOMS WITH THE DICHLOROETHENES IN KRYPTON MATRIX: TRIPLET SURFACE CHEMISTRY
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The reactions between Hg(3P) atoms with the there dichloroethenes in krypton matrix at 12 K have been studied.In the absence of Hg, matrix photolysis with wavelengths longer than 200 nm gives isomerization as well as, for cis-dichloroethene (c-DCE) and 1,1-dichloroethene (1,1-DCE) but not for trans-dichloroethene (t-DCE), HCl elimination to give ClH.C2HCl.In the presence of Hg atoms and with excitation in the range 246-257 nm, HCl elimination is substantially reduced and, for c-DCE and 1,1-DCE, new products appear.These products are identified as Cl2.C2H2 and chlorovinyl mercuric chlorides, the latter the net result of mercury insertion into a carbon-chloride bond.The insertion product from c-DCE is identified as trans-2-chlorovinyl mercuric chloride and that from 1,1-DCE is probably 1-chlorovinyl mercuric chloride.The results indicate that in the krypton matrix, Hg(3P)-initiated chemistry takes place on a triplet surface that is not accessed with higher energy, singlet excitation.Furthermore, the absence of Cl2 elimination or insertion chemistry for t-DCE indicates that the role of Hg(3P) is not merely energy transfer but, instead, one that opens reaction channels not observed without Hg(3P).
- Cartland, Harry E.,Pimentel, George C.
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- Factors influencing rates and products in the transformation of trichloroethylene by iron sulfide and iron metal
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Batch experiments were performed to assess (i) the influence of pH, solution amendments, and mineral aging on the rates and products of trichloroethylene (TCE) transformation by iron sulfide (FeS) and (ii) the influence of pretreatment of iron metal with NaHs on TCE transformation rates. The relative rates of FeS-mediated transformation of TCE to different products were quantified by branching ratios. Both pseudo-first-order rate constants and branching ratios for TCE transformation by FeS were significantly influenced by pH, possibly due to a decrease in the reduction potential of reactive surface species with increasing pH. Neither Mn2+, expected to adsorb to FeS surface S atoms, nor 2,2′-bipyridine, expected to adsorb to surface Fe atoms, significantly influenced rate constants or branching ratios. FeS that had been aged at 76 °C for 3 days was completely unreactive with respect to TCE over 6.5 months, yet this aged FeS transformed hexachloroethane to tetrachloroethylene with a rate constant only slightly lower than that for nonaged FeS. This finding suggests that the oxidation state of iron sulfide minerals in the environment will strongly influence the potential for intrinsic remediation of pollutants such as TCE. Treatment of iron metal with bisulfide significantly increased the pseudo-first-order rate constant for TCE transformation at pH 8.3. This effect was attributed to formation of a reactive FeS coating or precipitate on the iron surface.
- Butler, Elizabeth C.,Hayes, Kim F.
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- Corrinoid-mediated reduction of tetrachloroethene, trichloroethene, and trichlorofluoroethene in homogeneous aqueous solution: Reaction kinetics and reaction mechanisms
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It is shown that in homogeneous aqueous solution containing titanium(III) citrate or titanium(III)-NTA as bulk electron donor, cobalamin, cobinamide, and cobamide are effective electron transfer mediators for the reduction of tetrachloroethene (PCE), trichloroethene (TCE), and trichlorofluoroethene (TCFE). For a given chlorinated ethene, the reaction rate varied only slightly with pH and type of corrinoid present and was about 5 and 50 times faster for PCE as compared to TCFE and TCE, respectively. Evidence is presented that the first and rate-limiting step of the reduction of PCE, TCE, and TCFE by super-reduced corrinoids is a dissociative one- electron transfer yielding the corresponding vinyl radicals. Furthermore, the elimination of a chloride radical from the 1,1-dichlorovinyl radical yielding chloroacetylene and subsequently acetylene is proposed to account for the direct formation of acetylene out of TCE. Finally, it is demonstrated that at higher reduction potentials the corrinoid mediators may be blocked by the formation of addition products.
- Glod, Guy,Angst, Werner,Holliger, Christof,Schwarzenbach, Rene P.
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- Electroenzymatic reactions. Investigation of a reductive dehalogenase by means of electrogenerated redox cosubstrates
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As an illustration of how cyclic voltammetry can be used to unravel the mechanisms and kinetics of redox enzymes, the reductive dechlorination of trichloroethylene and tetrachloroethylene by a typical reductive dehalogenase, the tetrachloroethene reductive dehalogenase of Sulfurospirillum multivorans (formerly called Dehalospirillum multivorans), was investigated by means of several electrochemically generated cosubstrates. They comprised the monocation and the neutral form of methylviologen, the neutral form of benzylviologen, and cobaltocene. Cyclic voltammetry is used to produce the active form of the cosubstrate under controlled potential conditions. It shows large plateau-shaped catalytic responses, which are used to measure the kinetics of the enzymatic reaction as a function of the substrate and cosubstrate concentrations. The variation of the rate constant for the cosubstrate reaction with its standard potential shows the transition between two asymptotic behaviors, one in which the reaction is under diffusion control and the other in which it is under counter-diffusion control. Simple fitting of this plot allows an estimation of the standard potential of the electron acceptor center in the enzyme (E° = -0.57 V vs NHE).
- Diekert, Gabriele,Gugova, Denitsa,Limoges, Benoit,Robert, Marc,Saveant, Jean-Michel
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- FTIR Study of the Cl + C2H2 Reaction: Formation of cis- and trans-CHCl=CH Radicals
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FTIR spectroscopic studies of the photolysis (λ >/= 300 nm) of mixtures containing Cl2 and C2H2, cis-CHCl=CHCl, or trans-CHCl=CHCl were carried out in 700 Torr of N2 at 295 +/- 2 K.On the basis of the kinetic analysis of cis- and trans-CHCl=CHCl formed from C2H2, the branching ratio k1a/k1b has been determined to be 0.19 +/- 0.05.Cl + C2H2 (+M) -> cis=ClCH-CH (+M); Cl + C2H2 (+M) -> trans-ClCH=CH (+M).Implications of these results for our previously postulated mechanism of Cl atom initiated oxidation of C2H2 are discussed.
- Zhu, T.,Yarwood, G.,Chen, J.,Niki, H.
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- Highly efficient Mg(OH)Cl/SiO2 catalysts for selective dehydrochlorination of 1,1,2-trichloroethane
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A series of Mg catalysts supported on SiO2 were prepared by an incipient wetness impregnation method and tested for gas phase dehydrochlorination of 1,1,2-trichloroethane. It was found that these catalysts were very active and selective for the reaction. The catalytic performance depended on the Mg loading rather than the Mg precursors as the catalysts using Mg(NO3)2·6H2O and MgCl2·6H2O as the precursors showed the similar performance. A catalyst containing 10 wt.% of Mg showed the best performance with a steady state TCE conversion of 92% and cis-dichloroethene selectivity of 91%. Moreover, characterizations of the catalysts revealed the formation of Cl-containing Mg species on the surface during the reaction. The analyses of the compositions of the stable catalysts under working conditions indicated a Cl/Mg ratio of 1, suggesting that Mg(OH)Cl could be the active sites for the reaction.
- Tang, Cen,Jin, Yanxia,Lu, Jiqing,Li, Xiaonian,Xie, Guanqun,Luo, Mengfei
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- Pathways of chlorinated ethylene and chlorinated acetylene reaction with Zn(O)
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To successfully design treatment systems relying on reactions of chlorocarbons with zero-valent metals, information is needed concerning the kinetics and pathways through which transformations occur. In this study, pathways of chlorinated ethylene reaction with Zn(O) have been elucidated through batch experiments. Data for parent compound disappearance and product appearance were fit to pseudo-first-order rate expressions in order to develop a complete kinetic model. Results indicate that reductive β- elimination plays an important role, accounting for 15% of tetrachloroethylene (PCE), 30% of trichloroethylene (TCE), 85% of cis- dichloroethylene (cis-DCE), and 95% of trans-dichloroethylene (trans-DCE) reaction. The fraction of PCE, TCE, trans-DCE, and cis-DCE transformation that occurs via reductive elimination increases as the two-electron reduction potential (E2) for this reaction becomes more favorable relative to hydrogenolysis. In the case of PCE and TCE, reductive elimination gives rise to chlorinated acetylenes. Chloroacetylene and dichloroacetylene were synthesized and found to react rapidly with zinc, displaying products consistent' with both hydrogenolysis and reduction of the triple bond. Surface area-normalized rate constants (k(SA))for chlorinated ethylene disappearance correlate well with both one-electron (E1) and two-electron (E2) reduction potentials for the appropriate reactions. Correlation with E2 allows prediction of the distribution of reaction products as well as the rate of disappearance of the parent compound. To successfully design treatment systems relying on reactions of chlorocarbons with zero-valent metals, information is needed concerning the kinetics and pathways through which transformations occur. In this study, pathways of chlorinated ethylene reaction with Zn(0) have been elucidated through batch experiments. Data for parent compound disappearance and product appearance were fit to pseudo-first-order rate expressions in order to develop a complete kinetic model. Results indicate that reductive β-elimination plays an important role, accounting for 15% of tetrachloroethylene (PCE), 30% of trichloroethylene (TCE), 85% of cis-dichloroethylene (cis-DCE), and 95% of trans-dichloroethylene (trans-DCE) reaction. The fraction of PCE, TCE, trans-DCE, and cis-DCE transformation that occurs via reductive elimination increases as the two-electron reduction potential (E2) for this reaction becomes more favorable relative to hydrogenolysis. In the case of PCE and TCE, reductive elimination gives rise to chlorinated acetylenes. Chloroacetylene and dichloroacetylene were synthesized and found to react rapidly with zinc, displaying products consistent with both hydrogenolysis and reduction of the triple bond. Surface area-normalized rate constants (kSA) for chlorinated ethylene disappearance correlate well with both one-electron (E1) and two-electron (E2) reduction potentials for the appropriate reactions. Correlation with E2 allows prediction of the distribution of reaction products as well as the rate of disappearance of the parent compound.
- Arnold, William A.,Lynn Roberts
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- CO2 Laser-induced Decomposition of 1,2-Dichloro-1-fluoroethane
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CH2ClCHFCl was photolyzed with a TEA CO2 laser at 1033.5 cm-1.The infrared multiphoton dissociation mechanism of CH2ClCHFCl was investigated under various conditions: Sample gas pressure, additive gas presure, pulse number, pulse energy, and pulse duration.It is concluded that primary process of the IRMPD is direct eleimination of molecular HCl and HF, HCl elimination being predominant channel.Primary HCl elimination products cis-and trans-CHF=CHCl, and CH2=CFCl are formed at high vibrational levels, from which additional photon absorption occures in the secondary photolysis to give rise to CH=CCl, CH=CF, and CH2=CHF.All of the secondary products are concluded to be derived from mainly CH2=CFCl among the chlorofluoroethene isomers.CH2=CFCl decomposes via HF and HCl elimination channels together with the C-Cl bond repture channel. appears to be generated by the H atom abstraction reaction of C2H. radical, which may result from further decomposition of and/or .The neat IRMPD at higher pressures gives quite similar primary product distribution, but markedly different secondary product distribution from those in shock tube pyrolysis.
- Ogura, Hiroo,Yano, Takayuki
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- Isomeric Product Distributions from Solid-State Chain Reactions and Low-Temperature Microexplosions of Acetylene and Chlorine
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Free-radical chain reaction of acetylene and chlorine is initiated by pulsed ultraviolet photolysis of disordered solid films of these reagents at 10-60 K.The product (identified by FTIR spectroscopy) is a mixture of Z (cis) and E (trans) isomers of 1,2-dichloroethene.At 60 K in an equimolar mixture of reagents the photochemical quantum yield is 25 +/- 4; the isomeric product distribution is / = 10.2 +/- 1.5.At 10-30 K samples exhibit a sudden burst of reactivity (a microexplosion) after exposure to a cumulative laser fluence of 1-12 mJ/cm2 at 337 nm.The isomeric product distribution under these conditions is 2.9 +/- 0.4.The results demonstrate that reaction conditions during these microexplosions are characterized by high temperature and high mobility associated with transient liquefaction of the sample.
- Ovchinnikov, Mikhail A.,Wight, Charles A.
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- Pd-catalyzed TCE dechlorination in water: Effect of [H2](aq) and H2-utilizing competitive solutes on the TCE dechlorination rate and product distribution
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The aqueous-phase H2 concentration ([H2](aq)) and the presence of H2-utilizing competitive solutes affect trichloroethylene (TCE) dechlorination efficiency in Pd-based in-well treatment reactors. Batch kinetic studies in m
- Reinhard,Lowry
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- Abiotic reductive dechlorination of chlorinated ethylenes by iron-bearing soil minerals. 1. Pyrite and magnetite
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Abiotic reductive dechlorination of chlorinated ethylenes (tetrachloroethylene (PCE), trichloroethylene (TCE), cis- dichloroethylene (cis-DCE), and vinyl chloride (VC)) by pyrite and magnetite was characterized in a batch reactor system. Dechlorination kinetics was adequately described by a modified Langmuir-Hinshelwood model that includes the effect of a decreasing reductive capacity of soil mineral. The kinetic rate constant for the reductive dechlorination of target organics at reactive sites of soil minerals was in the range of 0.185 (±0.023) to 1.71 (±0.06) day-1. The calculated specific reductive capacity of soil minerals for target organics was in the range of 0.33 (±0.02) to 2.26 (±0.06) μM/g and sorption coefficient was in the range of 0.187 (±0.006) to 0.7 (±0.022) mM-1. Surface area-normalized pseudo-first-order initial rate constants for target organics by pyrite were found to be 23.5 to 40.3 times greater than those by magnetite. Target organics were mainly transformed to acetylene and small amount of chlorinated intermediates, which suggests that β-elimination was the main dechlorination pathway. The dechlorination of VC followed a hydrogenolysis pathway to produce ethylene and ethane. The addition of Fe(II) increased the dechlorination rate of cis-DCE and VC in magnetite suspension by nearly a factor of 10. The results obtained in this research provide basic knowledge to better predict the fate of chlorinated ethylenes and to understand the potential of abiotic processes in natural attenuation.
- Lee, Woojin,Batchelor, Bill
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- Cation-recognized photosensitization in E-Z isomerization of 1,2-dichloroethylene by crowned benzophenones
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Photosensitized isomerization of 1,2-dichloroethylene with 15- and 18-membered-ring crowned benzophenones (1a and 1b) as triplet sensitizers resulted in the cation-dependent increase in the Z/E isomer ratios up to ca. 10 by addition of alkali and alkaline earth metal ions in comparison with the metal-free reactions (Z/E = 1.5-2.1). The highest Z/E values were attained for 1a with Li+ (2.9) and Mg2+ (5.3), and for 1b with Na+ (8.2) and Ca2+ (9.8), respectively, among each family of alkali and alkaline earth metal ions. It was found that the cation recognized sensitization brought about the change of the inherent triplet energy ET as well as the ΦE/Φz ratio to raise the Z/E isomer ratio of 1,2-dichloroethylene. Copyright
- Kokubo, Ken,Kakimoto, Hidenobu,Oshima, Takumi
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- Determination of Arrhenius parameters for unimolecular reactions of chloroalkanes by IR laser pyrolysis
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A simple and reliable method is elaborated for accurate measurements of thermal rate constants of homogeneous gas phase unimolecular reactions.A pulse of CO2 laser radiation was used to multiphoton excite SiF4 sensitizer molecules and consequently produce temperatures in the range 1100-1400 K.Expansion of the heated gas column quenches pyrolysis reactions on a 10 μs time scale.There are no hot surfaces to induce chemistry.HCl elimination from C2H5Cl, Ea = 57.4 kcal/mol and log A(s-1) = 13.8, was used as an internal temperature standerd.For the molecular elimination CCL3CH3 -> HCl + CCl2CH2, Ea = 49.5 +/- 1.3 kcal/mol and log A(s-1) = 13.1 +/- 0.3, were determined.In these experiments the major decomposition products of CHCl2CH2Cl are HCl and cis- or trans-CHClCHCl with Ea = 58.5 +/-2, log A = 14.1 +/- 0.4 and Ea = 59.5 +/- 2, log A = 13.9 +/- 0.4, respectively.HCl elimination to give CCl2CH2 and C-Cl bond breaking to CHClCH2Cl radical have higher activation energies.The method is generally useful for kinetics at high temperature.
- Dai, Hai-Lung,Specht, Eliot,Berman, Michael R.,Moore, C. Bradley
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- Conductive magnetite nanoparticles accelerate the microbial reductive dechlorination of trichloroethene by promoting interspecies electron transfer processes
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Playing your part: Conductive magnetite nanoparticles accelerate the microbial reductive dechlorination of trichloroethene (TCE), an ubiquitous and toxic subsurface contaminant. The stimulatory effect most likely results from the nanoparticles promoting t
- Aulenta, Federico,Rossetti, Simona,Amalfitano, Stefano,Majone, Mauro,Tandoi, Valter
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- CO2 Laser-induced Decomposition of 1,1,2-Trichloroethane
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CH2ClCHCl2 was photolyzed with a focusing geometry using the P(24) line of the 10.6 μm CO2 band (940.6 cm-1).The final products of neat photolysis were cis- and trans-CHCl=CHCl, CH2=CCl2, CH2=CHCl, CHCCl, CHCH, and C4H2.The relative yield of CH2=CCl2 in particular was strongly dependent on CH2ClCHCl2 pressure and sensitive to the addition of H atom containing molecules.A series of diagnostic experiments shows that the dichloroethene isomers are formed by three different processes, i.e., infrared multiphoton decomposition, collision-induced decomposition, and radical chain reaction.Infrared multiphoton decomposition and collision-induced decomposition give rise to cis- and trans-CHCl=CHCl predominantly, while the radical chain reaction generates the dichloroethane isomers in comparable amounts at high reactant pressures, the most probable initiation step being the C-Cl bond-scission reaction of the parent molecule.Formation mechanisms for other minor products are also discussed.
- Ogura, Hiroo
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- Reductive dechlorination of cis-1,2-dichloroethene and vinyl chloride by Dehalococcoides ethenogenes
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cis-Dichloroethene (DCE) and vinyl chloride (VC) often accumulate in contaminated aquifers in which tetrachloroethene (PCE) or trichloroethene (TCE) undergo reductive dechlorination. Dehalococcoides ethenogenes strain 195 is the first isolate capable of dechlorinating chloroethenes past cis-DCE. Strain 195 could utilize commercially synthesized cis-DCE as an electron acceptor, but doses greater than 0.2 mmol/L were inhibitory, especially to PCE utilization. To test whether the cis-DCE itself was toxic, or whether the toxicity was due to impurities in the commercial preparation (97% nominal purity), we produced cis-DCE biologically from PCE using a Desulfitobacterium sp. culture. The biogenic cis-DCE was readily utilized at high concentrations by strain 195 indicating that cis-DCE was not intrinsically inhibitory. Analysis of the commercially synthesized cis-DCE by GC/mass spectrometry indicated the presence of approximately 0.4% mol/mol chloroform. Chloroform was found to be inhibitory to chloroethene utilization by strain 195 and at least partially accounts for the inhibitory activity of the synthetic cis-DCE. VC, a human carcinogen that accumulates to a large extent in cultures of strain 195, was not utilized as a growth substrate, and cultures inoculated into medium with VC required a growth substrate, such as PCE, for substantial VC dechlorination. However, high concentrations of PCE or TCE inhibited VC dechlorination. Use of a hexadecane phase to keep the aqueous PCE concentration low in cultures allowed simultaneous utilization of PCE and VC. At contaminated sites in which D. ethenogenes or similar organisms are present, biogenic cis-DCE should be readily dechlorinated, chloroform as a co-contaminant may be inhibitory, and concentrations of PCE and TCE, except perhaps those near the source zone, should allow substantial VC dechlorination. cis-Dichloroethene (DCE) and vinyl chloride (VC) often accumulate in contaminated aquifers in which tetrachloroethene (PCE) or trichloroethene (TCE) undergo reductive dechlorination. `Dehalococcoides ethenogenes' strain 195 is the first isolate capable of dechlorinating chloroethenes past cis-DCE. Strain 195 could utilize commercially synthesized cis-DCE as an electron acceptor, but doses greater than 0.2 mmol/L were inhibitory, especially to PCE utilization. To test whether the cis-DCE itself was toxic, or whether the toxicity was due to impurities in the commercial preparation (97% nominal purity), we produced cis-DCE biologically from PCE using a Desulfitobacterium sp. culture. The biogenic cis-DCE was readily utilized at high concentrations by strain 195 indicating that cis-DCE was not intrinsically inhibitory. Analysis of the commercially synthesized cis-DCE by GC/mass spectrometry indicated the presence of approximately 0.4% mol/mol chloroform. Chloroform was found to be inhibitory to chloroethene utilization by strain 195 and at least partially accounts for the inhibitory activity of the synthetic cis-DCE. VC, a human carcinogen that accumulates to a large extent in cultures of strain 195, was not utilized as a growth substrate, and cultures inoculated into medium with VC required a growth substrate, such as PCE, for substantial VC dechlorination. However, high concentrations of PCE or TCE inhibited VC dechlorination. Use of a hexadecane phase to keep the aqueous PCE concentration low in cultures allowed simultaneous utilization of PCE and VC. At contaminated sites in which `D. ethenogenes' or similar organisms are present, biogenic cis-DCE should be readily dechlorinated, chloroform as a co-contaminant may be inhibitory, and concentrations of PCE and TCE, except perhaps those near the source zone, should allow substantial VC dechlorination.
- Maymo-Gatell,Nijenhuis,Zinder
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- Rearrangement of alkylchlorocarbenes: 1,2-H shift in free carbene, carbene-olefin complex, and excited states of carbene precursors
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Photolysis of alkylchlorodiazirines (1) in the presence of olefins gives a cyclopropane (3) by addition of the generated carbene to the olefin and a vinyl chloride derivative (2) resulting from a 1,2-H shift rearrangement. This rearrangement may occur either in the carbene or in some excited state, precursor of the carbene (RIES mechanism), or in a 'carbene + olefin complex' on the way to the formation of 3 (COC mechanism). Results obtained by time-resolved photoacoustic calorimetry as well as by thermolysis and photolysis of ClCH2C(N2)Cl and CH3(CH2)2C(N2)Cl in the presence of tetramethylethylene clearly indicate that both the RIES and COC mechanisms play a role but with efficiencies which greatly depend on the nature of the diazirine. Reexamination of the results previously obtained with benzylchlorodiazirines indicates that, for this class of diazirines, the RIES mechanism is temperature dependent and has a very low efficiency at room temperature and below, whereas the nonlinearity of the plots [3]/[2] vs [olefin] is mainly due to the COC mechanism.
- Bonneau, Roland,Liu, Michael T. H.,Kim, Kyu Chul,Goodman, Joshua L.
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- Reductive Dechlorination of Tetrachloroethylene and Trichlproethylene Catalyzed by Vitamin B12 in Homogeneous and Heterogeneous Systems
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The reduction of tetrachloroethylene (PCE) and trichloroethylene (TCE) catalyzed by vitamin B12 was examined in homogeneous and heterogeneous (B12 bound to agarose) batch systems using titanium(III) citrate as the bulk reductant. The solution and surface-mediated reaction rates at similar B12 loadings were comparable, indicating that binding vitamin B12 to a surface did not lower catalytic activity. No loss in PCE reducing activity was observed with repeated usage of surface-bound vitamin B12. Carbon mass recoveries were 81-84% for PCE reduction and 89% for TCE reduction, relative to controls. In addition to sequential hydrogenolysis, a second competing reaction mechanism for the reduction of PCE and TCE by B12, reductive β-elimination, is proposed to account for the observation of acetylene as a significant reaction intermediate. Reductive β-elimination should be considered as a potential pathway in other reactive systems involving the reduction of vicinal polyhaloethenes. Surface-bound catalysts such as vitamin B12 may have utility in the engineered degradation of aqueous phase chlorinated ethenes.
- Burris, David R.,Delcomyn, Carrie A.,Smith, Mark H.,Lynn Roberts
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- Kinetics and inhibition of reductive dechlorination of chlorinated ethylenes by two different mixed cultures
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Kinetic studies with two different anaerobic mixed cultures (the PM and the EV cultures) were conducted to evaluate inhibition between chlorinated ethylenes. The more chlorinated ethylenes inhibited the reductive dechlorination of the less chlorinated ethylenes, while the less chlorinated ethylenes weakly inhibited the dechlorination of the more chlorinated ethylenes. Tetrachloroethylene (PCE) inhibited reductive trichloroethylene (TCE) dechlorination but not cis-dichloroethylene (c-DCE) dechlorination, while TCE strongly inhibited c-DCE and VC dechlorination. c-DCE also inhibited vinyl chloride (VC) transformation to ethylene (ETH). When a competitive inhibition model was applied, the inhibition constant (KI) for the more chlorinated ethylene was comparable to its respective Michaelis-Menten half-velocity coefficient, KS. Model simulations using independently derived kinetic parameters matched the experimental results well. k max and KS values required for model simulations of anaerobic dechlorination reactions were obtained using a multiple equilibration method conducted in a single reactor. The method provided precise kinetic values for each step of the dechlorination process. The greatest difference in kinetic parameters was for the VC transformation step. VC was transformed more slowly by the PM culture (kmax and KS values of 2.4 ± 0.4 μmol/mg of protein/day and 602 ± 7 μM, respectively) compared to the EV culture (8.1 ± 0.9 μmol/mg of protein/day and 62.6 ± 2.4 μM). Experimental results and model simulations both illustrate how low KS values corresponded to efficient reductive dechlorination for the more highly chlorinated ethylenes but caused strong inhibition of the transformation of the less chlorinated products. Thus, obtaining accurate K S values is important for modeling both transformation rates of parent compounds and their inhibition on daughter product transformation.
- Yu, Seungho,Dolan, Mark E.,Semprini, Lewis
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- Isotopic fractionation during reductive dechlorination of trichloroethene by zero-valent iron: Influence of surface treatment
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During reductive dechlorination of trichloroethene (TCE) by zero-valent iron, stable carbon isotopic values of residual TCE fractionate significantly and can be described by a Rayleigh model. This study investigated the effect of observed reaction rate, surface oxidation and iron type on isotopic fractionation of TCE during reductive dechlorination. Variation of observed reaction rate did not produce significant differences in isotopic fractionation in degradation experiments. However, a small influence on isotopic fractionation was observed for experiments using acid-cleaned electrolytic iron versus experiments using autoclaved electrolytic iron, acid-cleaned Peerless cast iron or autoclaved Peerless cast iron. A consistent isotopic enrichment factor of ε = -16.7‰ was determined for all experiments using cast iron, and for the experiments with autoclaved electrolytic iron. Column experiments using 100% cast iron and a 28% cast iron/72% aquifer matrix mixture also resulted in an enrichment factor of -16.9‰. The consistency in enrichment factors between batch and column systems suggests that isotopic trends observed in batch systems may be extrapolated to flowing systems such as field sites. The fact that significant isotopic fractionation was observed in all experiments implies that isotopic analysis can provide a direct qualitative indication of whether or not reductive dechlorination of TCE by Fe0 is occurring. This evidence may be useful in answering questions which arise at field sites, such as determining whether TCE observed down-gradient of an iron wall remediation scheme is the result of incomplete degradation within the wall, or of the dissolved TCE plume bypassing the wall.
- Slater,Sherwood Lollar,Allen King,O'Hannesin
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- Effects of alcohols, anionic and nonionic surfactants on the reduction of PCE and TCE by zero-valent iron
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The effects of surfactants, sodium dodecyl sulfate (SDS) and Triton X-a00 (TX), and alcohols (methanol, ethanol, and propanol) on the dehalogenation of TCE and PCE by zero-valent iron were examined. Surface concentrations of PCE and TCE on the iron were dependent on aqueous surfactant concentrations. At concentrations above the CMC, sorbed halocarbon concentrations declined and concentrations associated with solution phase micelles increased. The anionic surfactant SDS ([SDS]a mixed effect on reactivity, increasing the PCE reduction rate, but not affecting TCE removal. Production of TCE from PCE increased in the presence of TX. Similar experiments showed that methanol, ethanol, and propanol inhibited reduction of TCE and PCE by metallic iron. Zero-valent iron may be useful in recycling soil washing effluents contaminated with TCE and PCE. Copyright
- Loraine, Gregory A
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- Shelf-Stable (E)- A nd (Z)-Vinyl-λ3-chlorane: A Stereospecific Hyper-vinylating Agent
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We report the first stereoselective synthesis of stable (E)- A nd (Z)-β-chlorovinyl-λ3-chlorane via direct mesitylation of 1,2-dichloroethylene with mesityldiazonium tetrakis(pentafluorophenyl)borate under mild reaction conditions. The structure of the (E)-vinyl-λ3-chlorane was established by single-crystal X-ray analysis. Because of the enormously high leaving group ability of the aryl-λ3-chloranyl group, vinyl-λ3-chloranes undergo not only SNVσ-type reaction with extremely weak nucleophiles such as perfluoroalkanesulfonate, iodobenzene, and aromatic hydrocarbons but also coupling with phenylcopper(I) species.
- Kanazawa, Junichiro,Miyamoto, Kazunori,Takagi, Taisei,Uchiyama, Masanobu,Watanabe, Yuichiro
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- Reductive Dechlorination of Tetrachloroethylene by a Chlorobenzoate-Enriched Biofilm Reactor
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This study evaluates the potential and technical feasibility of treating chloroaliphatics, common groundwater contaminants, using a specialized microbial consortium under fixed-film conditions. The reactor was developed using 3-chlorobenzoate (3-CB) as a substrate under anaerobic conditions and the enrichment that harbored an unusual dechlorinator, Desulfomonile tiedjei DCB-1. The dechlorination rate of both PCE and 3-CB increased with increasing flow rates up to 50 mL/h. The maximum observed dechlorination rates of PCE and 3-CB fed at 6.0 and 1000 μM were 2.0 and 414 μmol L h-1, respectively. This corresponds to a PCE consumption rate of 3.7 nmol h-1 (mg of protein)-1 -1 day-1>. The rate of PCE dechlorination increased from 2.0 to 10.3 μmol L-1 h-1 when the influent PCE was increased from 6.0 to 120 μM, respectively; however, concentrations of 60 μM and above damaged reactor performance. PCE was mainly converted to TCE and cis- and trans-DCE at all the tested flow rates. Vinyl chloride (VC) was never detected, thus suggesting dechlorination of PCE to non-chlorinated products. Although the PCE dechlorination activity of the biofilm was dependent on 3-CB, the activity could be sustained for 4-5 days on cheaper substrates such as acetate or benzoate after a 1-day pulse feeding of 3-CB. In addition to PCE dechlorination, the biofilm also dechlorinated other compounds such as chloroform (CF) and 1,1,2-trichloroethane (1,1,2-TCA). The present study is important, since D. tiedjei was previousely shown to dechlorinate many other chloroaromatic and aliphatic compounds.
- Fathepure, Babu Z.,Tiedje, James M.
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- Kinetics of the Tansformation of Trichloroethylene and Tetrachloroethylene by Iron Sulfide
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The transformation of trichloroethylene (TCE), tetrachloroethylene (PCE), and 1,1-dichloroethylene (1,1-DCE) by 10 g/L (0.5 m2/L) FeS in aqueous solution at pH 8.3 was studied in batch experiments. TCE and PCE were transformed by FeS with pseudo-first-order rate constants, corrected for partitioning to the sample headspace, of (1.49 +/- 0.14) E-3 h-1 (TCE) and (5.7 +/- 1.0) E-4 h-1 (PGE). A 17 percent decrease in the concentration of 1,1-DCE was observed over 120 days; however, no reaction products were detected. TCE and PCE transformation data were fit to a rate law assuming transformation of TCE via parallel reaction pathways to acetylene and cis-1,2-dichloroethylene (cis-DCE) and transformation of PCE via parallel reaction pathways to acetylene and TCE. Acetylene was the major reaction product for both TCE and PCE. Determination of rate constants for each reaction pathway indicated that TGE was transformed to acetylene 11.8 +/- 1.1 times faster than to cis-DCE and that PCE was transformed to acetylene 8.2 +/-1.8 times faster than to TCE. Additional minor reaction products were vinyl chloride (VC) for TCE and cis-DCE for PCE. Detection of acetylene as the major product of both TCE and PCE transformation by FeS contrasts with the sequential hydrogenolysis products typically observed in the microbial transformation of these compounds, making acetylene a potential indicator of abiotic transformation of TCE and PCE by FeS in natural systems.
- Bulter, Elizabeth C.,Hayes, Kim F.
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- Effect of temperature, pH and electron donor on the microbial reductive dechlorination of chloroalkenes
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In order to elucidate the effect of environmental conditions such as pH, temperature, and electron donor on the microbial reductive dechlorination of tetrachloroethylene and its transformation products, batch, acetate-fed methanogenic cultures were developed from a field contaminated soil and incubated within a pH range of 4 to 9.5 and a temperature range of 5 to 45°C. Optimum conditions for reductive dechlorination were achieved at pH and temperature values of around 7 and 35°C, respectively. Methane production was more affected by pH and temperature than was the rate of dechlorination. Increased levels of electron donor (acetate) resulted in faster rates of both methanogenesis and reductive dechlorination. The effect of pH and temperature on the dechlorination rate and methane production were simulated by using previously established relationships pertaining to the activation and deactivation of enzymatic processes.
- Zhuang,Pavlostathis
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- Preparation and reactivity of vitaminB12-TiO2 hybrid catalyst immobilized on a glass plate
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The vitaminB12-TiO2 hybrid catalyst was effectively immobilized on a glass plate, and the immobilized catalyst shows an efficient reactivity for various molecular transformations, such as the 1,2-migration of a phenyl group and dechlorination of perchloroethylene during irradiation by UV light.
- Shimakoshi, Hisashi,Abiru, Makoto,Kuroiwa, Keita,Kimizuka, Nobuo,Watanabe, Midori,Hisaeda, Yoshio
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- Composition For the Vapor Phase Dehydrohalogenation of 1,1,2-Trihaloethane To 1,1-Dihaloethylene and Methods For Preparing and Using Such Composition
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Described are compositions adapted to catalyze the vapor phase dehydrohalogenation of 1,1,2-trihaloethane to 1,1-dihaloethylene, e.g., 1,1,2-trichloroethane to vinylidene chloride. These materials include activated carbon and at least one benzimidazole-containing material defined herein as including benzimidazole, a derivative thereof, a salt thereof or mixtures thereof. Also described are methods for producing and using these catalytic compositions.
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Page/Page column 7
(2008/12/07)
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- COMPOSITION FOR THE VAPOR PHASE DEHYDROHALOGENATION OF 1,1,2-TRIHALOETHANE TO 1,1-DIHALOETHYLENE AND METHODS FOR PREPARING AND USING SUCH COMPOSITIONS
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Described are compositions adapted to catalyze the vapor phase dehydrohalogenation of 1,1,2-trihaloethane to 1,1-dihaloethylene, e.g., 1,1,2-trichloroethane to vinylidene chloride. These materials include activated carbon and at least one benzimidazole-containing material defined herein as including benzimidazole, a derivative thereof, a salt thereof or mixtures thereof. Also described are methods for producing and using these catalytic compositions.
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Page/Page column 16-27; 31-32
(2010/11/25)
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- Kinetics of the transformation of halogenated aliphatic compounds by iron sulfide
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The transformation of nine halogenated aliphatic compounds, i.e., pentachloroethane (PCA), 1,1,2,2- and 1,1,1,2-tetrachloroethanes (1122-TeCA and 1112-TeCA), 1,1,1- and 1,1,2-trichloroethanes (111-TCA and 112-TCA), 1,1- and 1,2-dichloroethanes (11-DCA and 12-DCA), carbon tetrachloride (CT), and tribromomethane (TBM), by 10 g/L FeS at pH 8.3 was investigated in batch experiments. 11-DCA, 12-DCA, and 112-TCA showed no significant transformation by FeS over ~ 120 days, but the other compounds were transformed with half-lives of hours to days. PCA and 1122-TeCA underwent dehydrohalogenation faster than FeS-mediated reductive dehalogenation reactions. The remaining compounds for which considerable transformation was observed underwent FeS-mediated reactions more rapidly than hydrolysis or dehydrohalogenation. For 1112-TeCA, the dihaloelimination product, i.e., 1,1-dichlroethylene, was the only reaction product observed. For 111-TCA, CT, and TBM, hydrogenolysis products were the only products detected, even though their mass recoveries were significantly 100%. Two simple log-linear correlations between rate constants and either one-electron reduction potentials or homolytic bond dissociation enthalpies were developed, with determination coefficients of 0.48 and 0.82, respectively. These results were consistent with a rate-limiting step involving homolytic bond dissociation. However, neither correlation precisely characterized the reactivity of all the compounds, indicating distinctions among the mechanisms for reductive dehalogenation of the compounds by FeS or the influence of additional molecular or thermodynamic parameters on rate constants.
- Hayes,Butler
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p. 422 - 429
(2007/10/03)
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- A Method for the Rapid Dechlorination of Low Molecular Weight Chlorinated Hydrocarbons in Water
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1,1,2-Trichloroethylene (TCE), 1,1-dichloroethylene, cis and trans-1,2-dichloroethylene and tetrachloroethylene (PCE), at concentrations of 20 ppm in aqueous solutions were rapidly hydrodechlorinated to ethane (in a few minutes), on the surface of palladized iron in batch experiments that were performed in closed vials. No intermediate reaction products such as 1,1-dichloroethylene, 1,2-dichloroethylenes and vinyl chloride were detected at concentrations > 1 ppm either in the headspace or in solution. The chloromethanes, CCl4, CHCl3 and CH2Cl2 were also dechlorinated to methane on palladized iron; the CCl4 was dechlorinated in a few minutes, the CHCl3, in less than an hour and the CH2Cl2, in 4-5 h. These results indicate that an above-ground treatment method can be designed for the treatment of groundwater contaminated with low molecular weight chlorinated hydrocarbons.
- Muftikian, Rosy,Fernando, Quintus,Korte, Nic
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p. 2434 - 2439
(2007/10/03)
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- Xenon Matrix Photochemistry of 1,1-Dichloroethene: Matrix-Dependent Surface Crossing and Hydrogen-Bonding Geometries
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The photoproducts of 1,1-dichloroethene (DCE) in Xe matrix at 12 K differ from those observed in Kr.With 239-nm photolysis, chlorine is eliminated from 1,1-DCE in solid Xe, but not in Kr, although HCl elimination and DCE isomerization occur in both matrices.Just as in the 1,2-dichloroethenes, Cl2 elimination proceeds in the heavy Xe matrix via spin-orbit-enhanced intersystem crossing to a triplet reaction surface.At higher photolysis energies, a novel product appears in Xe and is identified with the aid of isotopic substitution as a second HCl*C2HCl isomer, ?-hydrogen-bonded through the acetylenic proton.The product dependence on wavelength, parent, and matrix indicates that it is formed through a triplet-surface process under geometric constraints specific to the 1,1 isomer.Loss of Cl from a dissociative triplett state to form an excited chlorovinyl radical, with further cage reaction of the energetic fragments, is postulated.
- Laursen, Sandra L.,Pimentel, George C.
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p. 8175 - 8182
(2007/10/02)
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- Matrix-Induced Intersystem Crossing in the Photochemistry of the 1,2-Dichloroethenes
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The photoproducts of the 1,2-dichloroethenes (DCE) in xenon matrix at 12 K differ from those observed in krypton matrix.In xenon, photolysis at 237 nm of both cis- and trans-dichloroethene results in elimination of both Cl2 and HCl as well as isomerization, whereas only HCl elimination and isomerization are observed in krypton.Longer wavelength irradiation has no effect on either DCE in Kr but produces small, distinct amounts of products in Xe.The results indicate that in xenon, chemistry is occuring through a triplet state as well as from the directly excited singlet state.Enchanced spin-orbit coupling in the heavy-atom environment facilitates intersystem crossing from the initial singlet to a triplet surface, as well as, no doubt enhanced absorption directly into the triplet state.These effects provide access to the normally spin-forbidden chlorine elimination channel.The appearance of products in Xe at the lower photon energies is ascribed to direct T1 0 absorption, assisted by the external heavy atom.
- Laursen, Sandra L.,Pimentel, George C.
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p. 2328 - 2333
(2007/10/02)
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- The gas-phase thermolyses of di-, tri- and tetrachloroethene in hydrogen between 828 and 1050 K
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The thermolyses in hydrogen of 3-6 vol. percent of 1,1-dichloroethene, (E)-1,2-dichloroethene, trichloroethene and tetrachloroethene have been examined in a tubular flow reactor at atmospheric pressure between 828 and 1068 K.Major products are HCl, lower chlorinated ethenes, ethyne, ethene, ethane and methane.Chlorinated benzenes, major products in the straight pyrolysis of these compounds, are formed in only small amounts, the reasons for which are discussed.Dechlorination occurs in part via a chain mechanism involving H-atom addition and ipso substitution of Cl.A second route, molecular elimination of HCl, also occurs but appears to become less important for the more chlorinated substrates.At 880 K, addition of a H atom to the monochloro-substituted carbon of C2HCl3 takes place ca. 8 x more rapidly than it does to the dichloro site.The hydrogen-atom concentration is somewhat greater than that calculated from equilibrum dissociation of H2 and varies by a factor of ca. 4 for the various substrates.Differences in hydrogen-atom concentration are larger at lower temperatures, apparently due to the presence of relatively unreactive radicals in some systems, which lead to increased chain termination.
- Manion, Jeffrey A.,Louw, Robert
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p. 235 - 241
(2007/10/02)
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- ALKYNE-COBALT COMPLEXES AS PROSTAGLANDIN SYNTHONS. IV. A POSSIBLE APPROACH VIA 2-PHENYLTHIOCYCLOPENT-2-ENONE.
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The effectiveness of (phenylthioethyne)hexacarbonyldicobalt as a precursor of mono, di- and tricyclic 2-phenylthiocyclopent-2-en-1-ones is demonstrated.These ketones are shown to undergo the expected 1,4-additions of mixed cuprate reagents, but further elaboration of the products to prostaglandin analogues was not pursued when models of the required alkylation reactions were found to proceed very poorly.
- Daalman, Lachlan,Newton, Roger F.,Pauson, Peter L.,Wadsworth, Alan
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p. 3150 - 3164
(2007/10/02)
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- Photoassisted Isomerisation of Olefins by Platinum Complexes
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Photoassisted isomerisation of carbon-carbon double bonds has been affected for the first time in the presence of platinum complexes; pent-2-ene, hex-2-ene, and 1,2-dichloroethene can be cis-trans interconverted with high efficiency.
- Courtot, Pierre,Pichon, Roger,Salauen, Jean-Yves
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p. 542 - 543
(2007/10/02)
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- Formation of Disubstituted Chloro-olefins by Treatment of Substituted 1,2-Dichloroethylenes with Hydrocarbons in the Vapour Phase
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Disubstituted chloro-olefins RCH=CR1Cl together with hydrogen chloride have been formed by treatment of substituted 1,2-dichloroethylenes with hydrocarbons in the gas phase in a flow system at 500 to 600 deg C.Some stereoselectivity towards formation of the Z isomers was observed.The results are interpreted in terms of a free-radical chain mechanism.
- Milner, David J.
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p. 3241 - 3255
(2007/10/02)
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