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67-66-3Relevant articles and documents
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 R + HBr ? RH + Br (R = CH2Br, CHBrCl or CCl3) equilibrium. Thermochemistry of the CH2Br and CHBrCl radicals
Seetula, Jorma A.
, p. 849 - 855 (2003)
The kinetics of the reaction of the CH2Br, CHBrCl or CCl3 radicals, R, with HBr have been investigated separately in a heatable tubular reactor coupled to a photoionization mass spectrometer. The CH2Br (or CHBrCl or CCl3) radical was produced homogeneously in the reactor by a pulsed 248 nm exciplex laser photolysis of CH2Br2 (or CHBr2Cl or CBrCl3). The decay of R was monitored as a function of HBr concentration under pseudo-first-order conditions to determine the rate constants as a function of temperature. The reactions were studied separately over a wide ranges of temperatures and in these temperature ranges the rate constants determined were fitted to an Arrhenius expression (error limits stated are 1σ + Student's t values, units in cm3 molecule-1 s-1): k(CH2Br + HBr) = (7.5 ± 0.9) × 10-13 exp[- (2.53 ± 0.13) kJ mol-1/RT], k(CHBrCl + HBr) = (4.9 ± 1.1) × 10-13 exp[-(8.2 ± 0.3) kJ mol-1/RT] and k(CCl3 + HBr) -15 at 787 K. The kinetics of the reverse reactions, Br + R′H → HBr + R′ (R′ = CH2Br or CHBrCl), were taken from the literature and also calculated by ab initio methods at the MP2(fc)/6-31G(d,p)//MP2(fc)/6-31G(d,p) level of theory in conjunction with the thermodynamic transition state theory to calculate the entropy and the enthalpy of formation values of the radicals studied. The thermodynamic values were obtained at 298 K using a second-law method. The results for entropy values are as follows (units in J K-1 mol-1): 263 ± 7 (CH2Br) and 294 ± 6 (CHBrCl). The results for enthalpy of formation values at 298 K are (in kJ mol-1): 171.1 ± 2.7 (CH2Br) and 143 ± 6 (CHBrCl). The C-H bond strength of analogous halomethanes are (in kJ mol-1): 427.2 ± 2.4 (CH3Br) and 406.0 ± 2.4 (CH2BrCl). Thermodynamic properties of the CH2Br radical were calculated by statistical thermodynamic methods over the temperature range 100-1500 K.
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.
Investigation of the behaviour of haloketones in water samples
Nikolaou, Anastasia D.,Lekkas, Themistokles D.,Kostopoulou, Maria N.,Golfinopoulos, Spyros K.
, p. 907 - 912 (2001)
The behaviour of the haloketones (HKs) 1,1-Dichloropropanone (1,1-DCP), 1,1,1-Trichloropropanone (1,1,1-TCP) and 1,3-Dichloropropanone (1,3-DCP) in ultrapure water solutions and in fortified drinking water samples was invest/gated. Their concentrations were determined at regular time intervals by the use of a gas chromatography-electron capture detector (GC-ECD) method. Two different temperatures were studied. The results have shown that HKs decompose both in ultrapure water solutions and in drinking water samples. The decomposition rates are higher in the drinking water samples, especially at higher temperature. 1,1,1-TCP is the compound which decomposes fastest followed by 1,3-DCP and 1,1-DCP. Chloroform was formed both in the ultrapure water solutions and in the drinking water samples, probably due to the decomposition of 1,1,1-TCP. In the drinking water samples, formation of chloral hydrate was also observed.
The formation and control of disinfection by-products using chlorine dioxide
Chang, Chen-Yu,Hsieh, Yung-Hsu,Shih, I-Chen,Hsu, Shen-Sheng,Wang, Kuo-Hua
, p. 1181 - 1186 (2000)
In this study, chlorine dioxide (ClO2) was used as an alternative disinfectant with vanillic acid, p-hydroxybenzoic acid, and humic acid as the organic precursors in a natural aquatic environment. The primary disinfection by-products (DBPs) formed were trihalomethanes (THMs) and haloacetic acids (HAAs). Under neutral conditions (pH = 7) for vanillic acid, more total haloacetic acids (THAAs) than total trihalomethanes (TTHMs) were found, with a substantial increase during the later stages of the reaction. In the case of p-hydroxybenzoic acid, the amount of THAAs produced was minimal. Raising the concentration of ClO2 was not favorable for the control of THAAs in low concentrations of vanillic acid. ClO2 could reduce the total amount of TTHMs and THAAs for higher concentration of vanillic acid. It was found that the humic acid treatment dosage was not significant. Under alkaline conditions (pH = 9), the control of TTHMs and THAAs for the treatment of vanillic acid was better and more economical, however, an appreciable amount of inorganic by-products were observed. Under the same alkaline condition, the control of THAA for the treatment of p-hydroxybenzoic acid was not beneficial and for the treatment of humic acid was not significant. (C) 2000 Elsevier Science Ltd.
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.
Isoflurane enhances dechlorination of carbon tetrachloride in guinea-pig liver microsomes
Fujii, Kohyu,Rahman, Md. Mustafizur,Yuge, Osafumi
, p. 249 - 253 (1996)
Effect of isoflurane on the dechlorination of carbon tetrachloride to chloroform was investigated in the guinea-pip liver microsomes. Under anaerobic conditions, chloroform is produced from carbon tetrachloride through the microsomes in the presence of NADPH, and such production of chloroform was increased by the addition of isoflurane. The K(m) for the production of chloroform from carbon tetrachloride was decreased to 86% by isoflurane compared with the control; however the maximum velocity of chloroform production was also decreased to 50%. The formation of the 445 nm band in the mixture of reduced cytochrome P-450 and carbon tetrachloride, and cytochrome P-450 reduction by NADPH were both accelerated by isoflurane, without alteration of NADPH-cytochrome c reductase activity. These results indicate that trichloromethyl radical, an intermediate product of carbon tetrachloride, easily combines to the haeme part of cytochrome P-450, whereas the protein part combines to isoflurane after being reduced by NADPH, which results in acceleration of carbon tetrachloride dechlorination under a lower concentration of carbon tetrachloride. These results may have implications for other drugs that are administered during isoflurane anaesthesia.
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.
Formation of chloroform by aqueous chlorination of organic compounds
Chaidou,Georgakilas,Stalikas,Saraci,Lahaniatis
, p. 587 - 594 (1999)
Thirty organic compounds were selected to investigate their chloroform formation characteristics during chlorination with sodium hypochlorite at pH-values 7.0 and 8.0. These experiments were conducted under conditions similar to those applied on the chlorination of raw water. The results indicated that the chloroform concentrations occurred by the all tested compounds was in the ppm range. The maximum levels of chloroform (11-13 mg/l) were determined during the reaction of resorcinol and phloroglucinol at pH-value 8.0.
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.