67-66-3

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Teeple

, p. 536 (1904)

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Gas-phase photooxidation of trichloroethylene on TiO2 and ZnO: Influence of trichloroethylene pressure, oxygen pressure, and the photocatalyst surface on the product distribution

Driessen,Goodman,Miller,Zaharias,Grassian

, p. 549 - 556 (1998)

Transmission Fourier transform infrared spectroscopy has been used to identify gas-phase and surface-bound products and intermediates formed during the gas-phase photooxidation of trichloroethylene (TCE) on TiO2 and ZnO. Several factors are found to influence the gas-phase product distribution for this reaction. On clean TiO2 and ZnO surfaces and at high TCE and O2 pressures, gas-phase CO, CO2, COCl2, CCl2HCOCl, CHCl3, C2HCl5, and HCl are produced, whereas at low TCE and O2 pressures, TCE is converted to gas-phase CO and CO2 only. In addition to TCE and O2 pressure, the product distribution of the photooxidation of TCE is strongly dependent upon the coverage of adsorbed species on the surface of the photocatalyst. It is shown here that the complete oxidation of adsorbed TCE can occur on clean photocatalytic surfaces whereas only partial oxidation of adsorbed TCE occurs on adsorbate-covered surfaces. The role of adsorbed surface products in TCE photooxidation is discussed.

KINETICS OF THE GAS-PHASE PHOTOCHLORINATION OF DICHLOROMETHANE IN A TUBULAR PHOTOREACTOR.

Sugawara,Suzuki,Ohashi

, p. 854 - 859 (1980)

The kinetics were studied with due consideration taken of the radial variation in light intensity across the reactor and with the proper selection of kinetic equations, including the recombination of dichloromethyl radicals as the dominant termination step. The dependence of the absorbed radiant energy on the chlorine concentration was well simulated by the use of the radial-light and line-source model. The predominance of the observed production rate of hydrogen chloride over that of chloroform was also reproduced well by the appropriately selected kinetic expressions, without any use of the long-chain approximation. This work is pertinent to photochemical reactor design.

Patinkin,Lieber

, p. 2778 (1950)

Mechanistic studies of the photocatalytic oxidation of trichloroethylene with visible-light-driven N-doped TiO2 photocatalysts

Joung, Soon-Kil,Amemiya, Takashi,Murabayashi, Masayuki,Itoh, Kiminori

, p. 5526 - 5534 (2006)

Visible-light-driven TiO2 photocatalysts doped with nitrogen have been prepared as powders and thin films in a cylindrical tubular furnace under a stream of ammonia gas. The photocatalysts thus obtained were found to have a band-gap energy of 2.95 eV. Electron spin resonance (ESR) under irradiation with visible light (λ ≥ 430 nm) afforded the increase in intensity in the visible-light region. The concentration of trapped holes was about fourfold higher than that of trapped electrons. Nitrogendoped TiO 2 has been used to investigate mechanistically the photocatalytic oxidation of trichloroethylene (TCE) under irradiation with visible light (λ ≥ 420 nm). Cl and O radicals, which contribute significantly to the generation of dichloroacetyl chloride (DCAC) in the photocatalytic oxidation of TCE under UV irradiation, were found to be deactivated under irradiation with visible light. As the main by-product. only phosgene was detected in the photocatalytic oxidation of TCE under irradiation with visible light. Thus, the reaction mechanism of TCE photooxidation under irradiation with visible light clearly differs markedly from that under UV irradiation. Based on the results of the present study, we propose a new reaction mechanism and adsorbed species for the photocatalytic oxidation of TCE under irradiation with visible light. The energy band for TiO2 by doping with nitrogen may involve an isolated band above the valence band.

Electrochemical investigation of the rate-limiting mechanisms for trichlomethylene and carbon tetrachloride reduction at iron surfaces

Li, Tie,Farrell, James

, p. 3560 - 3565 (2001)

The mechanisms involved in reductive dechlorination of carbon tetrachloride (CT) and trichloroethylene (TCE) at iron surfaces were studied to determine if their reaction rates were limited by rates of electron transfer. Chronoamperometry and chronopotentiometry analyses were used to determine the kinetics of CT and TCE reduction by a rotating disk electrode in solutions of constant halocarbon concentration. Rate constants for CT and TCE dechlorination were measured as a function of the electrode potential over a temperature range from 2 to 42 °C. Changes in dechlorination rate constants with electrode potential were used to determine the apparent electron-transfer coefficients at each temperature. The transfer coefficient for CT dechlorination was 0.22 ± 0.02 and was independent of temperature. The temperature independence of the CT transfer coefficient is consistent with a rate-limiting mechanism involving an outer-sphere electron-transfer step. Conversely, the transfer coefficient for TCE was temperature dependent and ranged from 0.06 ± 0.01 at 2 °C to 0.21 ± 0.02 at 42 °C. The temperature-dependent TCE transfer coefficient indicated that its reduction rate was limited by chemical dependent factors and not exclusively by the rate of electron transfer. In accord with a rate-limiting mechanism involving an electron-transfer step, the apparent activation energy (Ea) for CT reduction decreased with decreasing electrode potential and ranged from 33.0 ± 1.6 to 47.8 ± 2.0 kJ/mol. In contrast, the E, for TCE reduction did not decline with decreasing electrode potential and ranged from 29.4 ± 3.4 to 40.3 ± 3.9. The absence of a potential dependence for the TCE Ea supports the conclusion that its reaction rate was not limited by an electron-transfer step. The small potential dependence of TCE reaction rates can be explained by a reaction mechanism in which TCE reacts with atomic hydrogen produced from reduction of water.

Stimulatory effect of anesthetics on dechlorination of carbon tetrachloride in guinea-pig liver microsomes

Fujii, Kohyu

, p. 147 - 153 (1996)

Effects of the anesthetics isoflurane, enflurane, halothane and sevoflurane on the dechlorination of carbon tetrachloride to produce chloroform were investigated using guinea pig liver microsomes. Under anaerobic conditions, chloroform is produced from carbon tetrachloride by the microsomes in the presence of NADPH, and chloroform production from 86 μM carbon tetrachloride was enhanced to 146%, 133%, 123% and 115% by the addition of isoflurane, enflurane, halothane and sevoflurane, respectively. The half-life of oxidized cytochrome P450 which remained during the reduction by the addition of NADPH was shortened to 51%, 54%, 60% and 80% by isoflurane, enflurane, halothane and sevoflurane, respectively, without alteration of NADPH-cytochrome c reductase activity. These anesthetics hastened the onset of the 445 nm absorption band formation which was shown by microsomes with carbon tetrachloride in the presence of NADPH under anaerobic conditions. These results indicate that the anesthetics isoflurane, enflurane, sevoflurane and halothane stimulate the reduction of cytochrome P450 results in the acceleration of the carbon tetrachloride dechlorination. These results may have implications for other type II drugs that are administered during anesthesia.

Carbon tetrachloride transformation in a model iron-reducing culture: Relative kinetics of biotic and abiotic reactions

Adriaens,Bouwer,McCormick

, p. 403 - 410 (2002)

CCl4 (CT) is one of the most frequently encountered chlorinated solvent pollutants in groundwater. Contributions of biotic (cell-mediated) and abiotic (mineral-mediated) reactions CT transformation were investigated in a model iron-reducing system that utilized hydrous ferric oxide (HFO) as the electron acceptor, acetate as the substrate, and Geobacter metallireducens as a representative dissimilative iron-reducing bacteria. The mineral-mediated (abiotic) reaction was estimated to be 60-260-fold faster than the biotic reaction throughout the incubation period. A second member of the dissimilative iron-reducing bacteria, G. metallireducens, could biotically transform CT. However, in the presence of HFO, G. metallireducens drove CT transformation primarily through the formation of reactive mineral surfaces. This did not diminish the role that DIRB play even though it suggested that biologically mineral surfaces may be the principal agents of reductive transformation in iron-reducing environments. The results indicated that an alternative approach to stimulate reductive transformation of pollutants in iron-reducing environments might be to improve the formation of reactive biogenic minerals in situ. Other FeII species have been identified in iron-reducing environments that are also reactive with chlorinated solvents including the ferrous sulfides, green rusts, and sorbed FeII. It could also be possible to couple microbial iron reduction to reactive barrier design to exploit the ability of such bacteria to reactivate passivated metal surfaces.

Micellar Effects on the Base-Catalyzed Oxidative Cleavage of a Carbon-Carbon Bond in 1,1-Bis(p-chlorophenyl)-2,2,2-trichloroethanol

Nome, Faruk,Schwingel, Erineu W.,Ionescu, Lavinel G.

, p. 705 - 710 (1980)

The base-catalyzed oxidative cleavage of 1,1-bis(p-chlorophenyl)-2,2,2-trichloroethanol (Dicofol) results in the formation of chloroform and 4,4'-dichlorobenzophenone.The reaction was studied in the presence of hexadecyltrimethylammonium bromide (CTAB) and hexadecyldimethyl(2-hydroxyethyl)ammonium bromide (CHEDAB), and catalytic factors of 200- and 345-fold, respectively, were obtained.The experimental results are rationalized in terms of an increase of the concentration of the reagents in the micellar phase.Sodium dodecyl sulfate (NaLS) inhibits the reaction, and dodecylcarnitine chloride (LCC) essentially does not alter the rate.The catalysis by cationic surfactants (CTAB, CHEDAB) is inhibited by added salts.The effectiveness of the salts in decreasing the rate constant is NaCl (excit.) = 27.7 kcal/mol, ΔG(excit.) = 19.8 kcal/mol, ΔS(excit.) = 25.9 eu) and for 1.0E-1 M CTAB (ΔH(excit.) = 26.7 kcal/mol, ΔG(excit.) = 20.8 kcal/mol, ΔS(excit.) = 19.6 eu) indicate that the rate decrease observed at high surfactant concentration is due to an entropic contribution to the free-energy term.

Formation of halocarbons in the methane-alkaline halide crystal system under UV radiation

Prilepsky,Povarov,Bredelev,Isidorov

, p. 1910 - 1913 (1998)

The possibility of formation of halomethanes upon the photostimulated reaction of halogen-containing minerals with methane was shown. The dynamics of accumulation of chloromethane, dichloromethane, and chloroform in model systems CH4-NaCl, CH4-sylvinite, and CH4-halite was studied experimentally. The kinetic parameters for the formation of methyl chloride were determined.

Mechanisms and Products of Surface-Mediated Reductive Dehalogenation of Carbon Tetrachloride by Fe(II) on Goethite

Elsner, Martin,Haderlein, Stefan B.,Kellerhals, Thomas,Luzi, Samuel,Zwank, Luc,Angst, Werner,Schwarzenbach, Rene P.

, p. 2058 - 2066 (2004)

Aliphatic chlorinated hydrocarbons, including CCl4, are widespread groundwater contaminants. Mechanisms and product formation of CCl4 reduction by Fe(II) sorbed to goethite, which may lead to completely dehalogenated products or to form chloroform, a toxic product that is fairly persistent under anoxic conditions, were studied. A simultaneous transfer of two electrons and cleavage of two C-Cl bonds of CCl4 would completely circumvent chloroform production. Product formation pathways did not primarily depend on the competition between an initial one- and two-electron transfer, but on the presence of different radical scavengers and the properties of the mineral surface with respect to stabilization of reaction intermediates. Specific adsorption of major anions or pH effects could modify the capability of the goethite surface to stabilize short-lived radical intermediates.

Effects of polydiallyldimethyl ammonium chloride coagulant on formation of chlorinated by products in drinking water

Chang,Chiang,Chao,Liang

, p. 1333 - 1346 (1999)

The objectives of this research work was to evaluate the reduction of THM precursors by cationic p-DADMAC and determine the correlations between the chlorine demand and trihalomethane formation in the presence of electrolyte solutions and ambient light. The chlorine demand was found to be significantly reduced provided that the H2SO4 electrolyte was fed to the sample solutions. The amount of CHCl3 formation was also decreased when the Na2SO4 electrolyte was introduced in spite of the levels of light intensity. The p-DADMAC can not only effectively remove the turbidity but also reduce the formation of CHCl3. The optimum dosage of p-DADMAC for reducing the turbidity, TOC and CHCl3 in the humic acid and source water samples was determined and depended upon the nature of organics. The objectives of this research work was to evaluate the reduction of THM precursors by cationic p-DADMAC and determine the correlations between the chlorine demand and trihalomethane formation in the presence of electrolyte solutions and ambient light. The chlorine demand was found to be significantly reduced provided that the H2SO4 electrolyte was fed to the sample solutions. The amount of CHCl3 formation was also decreased when the Na2SO4 electrolyte was introduced in spite of the levels of light intensity. The p-DADMAC can not only effectively remove the turbidity but also reduce the formation of CHCl3. The optimum dosage of p-DADMAC for reducing the turbidity, TOC and CHCl3 in the humic acid and source water samples was determined and depended upon the nature of organics.

PROTON-TRANSFER MECHANISM IN THE DECARBOXYLATION OF AMMONIUM TRICHLOROACETATE IN ACETONITRILE

Pawlak, Zenon,Fox, Malcolm F.,Tusk, Maria,Kuna, Stevan

, p. 1987 - 1994 (1983)

The rate constants, k, for the decomposition of ammonium trichloroacetate in acetonitrile were determined at 298 K where B is an N-base.The first-order decarboxylation of trichloroacetic acid in the presence of N-bases is strongly deopendent upon proton transfer in complexes.Discussion of the rate constants, k, obtained shows 3 types of complexes in the proton-transfer mechanism, i.e. a symmetrically positioned proton, and without proton transfer for 2 cases: .The sigmoidal curve of rate constants, -log k, plotted against (pKa)AN describes the location of the proton in the hydrogen bridge.The behaviour of (CCl3COOHR)(1-) complexes has many similarities to the molecular complexes, CCl3COOHB, discussed above.Implications of these results for carboxylate additives in overbased lubricating oils are discussed.

The role of hydrogen atoms in CIDNP effects in the reaction of diisobutylaluminum hydride with CCl4

Sadykov,Teregulov

, p. 2040 - 2042 (1998)

Integral polarization of chloroform, methylene dichloride, and pentachloroethane was observed in the 1H NMR spectra during the exothermal reaction of a 1 M solution of Bui2AlH in 1,4-dioxane with CCl4. CIDNP was shown to appear in the diffusion radical pair of the hydrogen atom and trichloromethyl radical.

Fachinetti, G.,Floriani, G.

, (1972)

A study of the Atherton-Todd reaction mechanism

Troev,Kirilov,Roundhill

, p. 1284 - 1285 (1990)

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Chlorination of phenols: Kinetics and formation of chloroform

Gallard, Herve,von Gunten, Urs

, p. 884 - 890 (2002)

The kinetics of chlorination of several phenolic compounds and the corresponding formation of chloroform were investigated at room temperature. For the chlorination of phenolic compounds, second-order in the phenolic compound. The rate constants of the reactions of HOCl with phenol and phenolate anion and the rate constant of the acid-catalyzed reaction were determined in the pH range 1-11. The second-order rate constants for the reaction HOCl + phenol varied between 0.02 and 0.52 M-1 s-1, for the reaction HOCl and phenolate between 8.46 × 101 and 2.71 × 104 M-1 s-1. The rate constant for the acid-catalyzed reaction varied between 0.37 M-2 s-1 to 6.4 × 103 M-2 s-1. Hammett-type correlations were obtained for the reaction for the reaction of HOCl with phenolate (log(k) = 4.15-3.00 × ∑σ). The formation of chloroform could be interpreted with a second-order model, first-order in chlorine, and first-order in chloroform precursors. The corresponding rate constants varied between k > 100 M-1 s-1 for resorcinol to 0.026 M-1 s-1 to p-nitrophenol at pH 8.0. It was found that the rate-limiting step of chloroform formation is the chlorination of the chlorinated ketones. Yields of chloroform formation depend on the type and position of the substituents and varied between 2 and 95% based on the concentration of the phenol.

Anschuetz

, p. 3512 (1892)

Chang et al.

, p. 2070 (1971)

Reductive dehalogenation of chlorinated methanes by iron metal

Matheson,Tratnyek

, p. 2045 - 2053 (1994)

Reduction of chlorinated solvents by fine-grained iron metal was studied in well-mixed anaerobic batch systems in order to help assess the utility of this reaction in remediation of contaminated groundwater. Iron sequentially dehalogenates carbon tetrachloride via chloroform to methylene chloride. The initial rate of each reaction step was pseudo-first-order in substrate and became substantially slower with each dehalogenation step. Thus, carbon tetrachloride degradation typically occurred in several hours, but no significant reduction of methylene chloride was observed over 1 month. Trichloroethene (TCE) was also dechlorinated by iron, although more slowly than carbon tetrachloride. Increasing the clean surface area of iron greatly increased the rate of carbon tetrachloride dehalogenation, whereas increasing pH decreased the reduction rate slightly. The reduction of chlorinated methanes in batch model systems appears to be coupled with oxidative dissolution (corrosion) of the iron through a largely diffusion-limited surface reaction.

Kinetics of Radiation-Induced Hydrogen Abstraction by CCl3 Radicals in the Liquid Phase. Secondary Alcohols

Feilman, Liviu,Alfassi, Zeev B.

, p. 3060 - 3063 (1981)

The dependence of the yield of products in the γ-radiation-induced free-radical reactions in carbon tetrachloride solutions of secondary alcohols on the alcohol concentration and the temperature was studied in the range of 0.05-0.6 M and 30-150 deg C.The rate constant for the reaction CCl3 + R1R2COH -> CHCl3 + R1R2COH (k1) was found as logk1 (M-1 s-1) = 8.63-9.1, where Τ = 2.303RT kcal mol-1.The activation energy is 1.8 +/- 0.3 kcal mol-1 lower than for secondary hydrogens in alkanes and about the same as for the tertiary hydrogens in 2,3-dimethylbutane.

Synthesis of Decorated Carbon Structures with Encapsulated Components by Low-Voltage Electric Discharge Treatment

Bodrikov, I. V.,Pryakhina, V. I.,Titov, D. Yu.,Titov, E. Yu.,Vorotyntsev, A. V.

, p. 60 - 69 (2022/03/17)

Abstract: Polycondensation of complexes of chloromethanes with triphenylphosphine by the action of low-voltage electric discharges in the liquid phase gives nanosized solid products. The elemental composition involving the generation of element distribution maps (scanning electron microscopy–energy dispersive X?ray spectroscopy mapping) and the component composition (by direct evolved gas analysis–mass spectrometry) of the solid products have been studied. The elemental and component compositions of the result-ing structures vary widely depending on the chlorine content in the substrate and on the amount of triphenylphosphine taken. Thermal desorption analysis revealed abnormal behavior of HCl and benzene present in the solid products. In thermal desorption spectra, these components appear at an uncharacteristically high temperature. The observed anomaly in the behavior of HCl is due to HCl binding into a complex of the solid anion HCI-2 with triphenyl(chloromethyl)phosphonium chloride, which requires a relatively high temperature (up to 800 K) to decompose. The abnormal behavior of benzene is associated with its encapsulated state in nanostructures. The appearance of benzene begins at 650 K and continues up to temperatures above 1300?K.

PRODUCTION OF CARBON TETRACHLORIDE FROM NATURAL GAS

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Paragraph 0058, (2020/07/07)

The present invention provides processes to prepare carbon tetrachloride by the chlorination of natural gas in the presence of a diluent.

Control of methane chlorination with molecular chlorine gas using zeolite catalysts: Effects of Si/Al ratio and framework type

Kwon, Seungdon,Chae, Ho-Jeong,Na, Kyungsu

, p. 111 - 117 (2020/01/31)

CH4 chlorination with Cl2 gas is used for the production of chlorinated products via C–H bond activation in CH4. Due to the high reactivity of Cl2, this reaction can occur spontaneously under UV irradiation or with mild thermal energy even in the absence of a catalyst via a free radical-mediated chain reaction mechanism that undesirably causes excessive chlorination of the CH4 and is thus non-selective. In this work, CH4 chlorination is investigated using HY and MFI zeolites with various Si/Al ratios, by which the reaction is catalytically controlled for selective production of the mono-chlorinated product (CH3Cl). Depending on the framework type, Si/Al ratio of the zeolites, and reaction conditions, different degrees of CH4 conversion, CH3Cl selectivity, and hence CH3Cl yield were achieved, by which systematic relationships between the catalyst properties and performance were discovered. A high aluminum content facilitated the production of CH3Cl with up to ～20 % yield at a high gas hourly space velocity of 2400 cm3gcat?1 h?1 with a CH4/Cl2 ratio of 1 at 350 °C. HY zeolites generally furnished a slightly higher CH3Cl yield than MFI zeolites, which can be attributed to the larger micropores of the HY zeolites that support facile molecular diffusion. With various flow rates and ratios of CH4 and Cl2, the CH4 conversion and CH3Cl selectivity changed simultaneously, with a trade-off relationship. Unfortunately, all zeolite catalysts suffered from framework dealumination due to the HCl produced during the reaction, but it was less pronounced for the zeolites having a low aluminum content. The results shed light on the detailed roles of zeolites as solid-acid catalysts in enhancing CH3Cl production during electrophilic CH4 chlorination.