Chlorine‐photosensitized oxidations of chloroethanes and chloroethylenes in the gas phase

Leblond, Bertrand; Exsteen-Meyers, L.; Franklin, James A.; Huybrechts, G.; Olbregts, Jean

doi:10.1002/kin.550030108

Cited by 20 publications

(12 citation statements)

References 25 publications

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“…The further decomposition of CClO' is a potential source 0, + *cc1,cc1(0) -'oocc1,cc1(o) of the observed carbon monoxide CClO' -c1+ co (15) The experiments in which the yield of the DCAC increased with decreasing reactor radius are a result of the competition between TCE and DCAC for reactive species on or near the surface. With the larger reactors, bulk diffusion limits the access of the TCE to the area near the surface and the DCAC can more effectively compete for reactive species.…”

Section: Discussionmentioning

confidence: 99%

Direct mass spectrometric studies of the destruction of hazardous wastes. 2. Gas-phase photocatalytic oxidation of trichloroethylene over titanium oxide: products and mechanisms

Nimlos¹,

Jacoby²,

Blake³

et al. 1993

Environ. Sci. Technol.

212

156

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The gas-phase photocatalytic oxidation of trichloroethylene (TCE) over titanium dioxide was investigated as a potential method for destroying this common pollutant. The results from this study agree with earlier studies in that high levels of destruction of TCE were achieved. Accompanying these high rates of destruction were high quantum yields (approaching unity). However, directsampling mass spectrometry and gas-phase Fourier transform infrared (FTIR) spectroscopy revealed that there are significant quantities of byproducts produced [phosgene, dichloroacetyl chloride (DCAC), carbon monoxide, molecular chlorine]. The DCAC has been rationalized on the basis of a chemical reaction mechanism in which the TCE molecules are oxidized in a chain reaction involving C1 atoms. This mechanism appears to be validated by tests with other chlorinated ethylenes (perchloroethylene, dichloroethylenes). Phosgene may arise at least partially from the photocatalytic oxidation of DCAC, and molecular chlorine may result from the recombination of chlorine atoms. The results of this study are discussed relative to aqueous-phase photocatalytic oxidation of TCE where chlorinated intermediates have been observed.

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Section: Discussionmentioning

confidence: 99%

Direct mass spectrometric studies of the destruction of hazardous wastes. 2. Gas-phase photocatalytic oxidation of trichloroethylene over titanium oxide: products and mechanisms

Nimlos¹,

Jacoby²,

Blake³

et al. 1993

Environ. Sci. Technol.

212

156

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“…In all three of these cases, it can be seen that the branching ratios between CC, CCl, and where possible, CH bond scission are a reasonable reflection of the thermochemistry. That is, in all cases, the most favored unimolecular process is the most exothermic pathway, although it should be appreciated that the uncertainties in the values of Δ r H ° are large since the values of Δ f H ° for the chlorinated ethoxy radicals are only estimates based on group additivity rules …”

Section: CL Atom Initiated Oxidation Of H2cccl2 Clhcchcl and Clhcc...mentioning

confidence: 99%

“…In the case of the oxidation of C 2 Cl 4 , it seemed reasonable to suppose that this species might be involved in this additional reaction and one possible step that would influence the yields of products in the manner that is observed is This reaction is thermodynamically allowed, being exothermic by −128 kJ mol -1 , and, if it were fast enough to compete with the unimolecular decompositions R5d and R6d, its occurrence would explain why higher initial concentrations of C 2 Cl 4 result in higher yields of CCl 3 COCl and decreased yields of COCl 2 . The reaction is also exothermic, although reaction to produce C 2 Cl 5 + COCl 2 is possible.…”

Section: CL Atom Initiated Oxidation Of Cl2cccl2 and Cl3cccl2h: Dis...mentioning

confidence: 99%

Chlorine Atom Initiated Oxidation of Chlorinated Ethenes: Results for 1,1-Dichloroethene (H₂CCCl₂), 1,2-Dichloroethene (HClCCClH), Trichloroethene (HClCCCl₂), and Tetrachloroethene (Cl₂CCCl₂)

Hasson

Smith

1999

J. Phys. Chem. A

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Experiments have been carried out on the oxidation of the four chlorinated ethenes H2CCCl2, HClCCClH, HClCCCl2, and Cl2CCCl2. Reaction was initiated by continuous photolysis of Cl2, and product yields were measured using Fourier transform infrared (FTIR) spectroscopy. In all cases, experiments were performed at different concentrations of the chlorinated ethenes (down to 3 × 1013 molecule cm-3), Cl2 and O2. In the cases of H2CCCl2 and HClCCCl2, the product yields were invariant with these changes, consistent with them being determined by competitive unimolecular dissociations of the chlorinated alkoxy radical; that is, H2ClCCCl2O (HCl2CCCl2O) (+M) → H2ClCCOCl (HCl2CCOCl) + Cl (+M) and H2ClCCCl2O (HCl2CCCl2O) (+M) → COCl2 + CH2Cl (CHCl2) (+M), and the subsequent formation of HCOCl and/or COCl2 from CH2Cl and CHCl2. In the case of HCl2CCHClO formed from HClCCClH, H atom abstraction by O2 is competitive with CCl and CC bond cleavage, so the yields depended on the concentration of O2. With C2Cl4, the only products observed were CCl3COCl and COCl2, consistent with competitive dissociations of perchloroethyl radicals: CCl3CCl2O (+M) → CCl3COCl + Cl (+M); CCl3CCl2O (+M) → COCl2 + CCl3 (+M). However, the relative yields of CCl3COCl and COCl2 were found to depend on the initial concentration of C2Cl4 which is incompatible with the simple, and generally accepted, mechanism. To investigate this unexpected result further, experiments were performed on pentachloroethane (C2Cl5H). Again, the product yields depended on the initial concentration of the chlorinated compound. In addition, product yields from C2Cl4 were measured using two different rates of photolysis of Cl2, at three temperatures, 298, 353, and 393 K, and in the presence of added NO and added HCl. Although the experimental results could be modeled when bimolecular reactions of perchlorinated methoxy and ethoxy radicals with C2Cl4 and HCl were included in the reaction mechanisms, the values of the rate constants which were needed seem unrealistically large if the currently accepted rate for the unimolecular decomposition of CCl3CCl2O is correct. This observation on C2Cl4 is important since it casts doubt on the current view of the oxidative chemistry of this compound, which is released in significant amounts into the atmosphere.

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“…On the other hand, C2H4 does not oxidize through a long chain, and the details of the oxidation are quite different. Bertrand et al 14 reported that the chlorine-atom initiated oxidation has a chain length less than 2 at room temperature. The reaction of 0(3P) with C2H4 has been extensively examined.…”

Section: Introductionmentioning

confidence: 99%

Oxidation of chloroethylene

Sanhueza¹,

Heicklen²

1975

J. Phys. Chem.

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Chlorine‐photosensitized oxidations of chloroethanes and chloroethylenes in the gas phase

Cited by 20 publications

References 25 publications

Direct mass spectrometric studies of the destruction of hazardous wastes. 2. Gas-phase photocatalytic oxidation of trichloroethylene over titanium oxide: products and mechanisms

Direct mass spectrometric studies of the destruction of hazardous wastes. 2. Gas-phase photocatalytic oxidation of trichloroethylene over titanium oxide: products and mechanisms

Chlorine Atom Initiated Oxidation of Chlorinated Ethenes: Results for 1,1-Dichloroethene (H₂CCCl₂), 1,2-Dichloroethene (HClCCClH), Trichloroethene (HClCCCl₂), and Tetrachloroethene (Cl₂CCCl₂)

Oxidation of chloroethylene

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Chlorine‐photosensitized oxidations of chloroethanes and chloroethylenes in the gas phase

Cited by 20 publications

References 25 publications

Direct mass spectrometric studies of the destruction of hazardous wastes. 2. Gas-phase photocatalytic oxidation of trichloroethylene over titanium oxide: products and mechanisms

Direct mass spectrometric studies of the destruction of hazardous wastes. 2. Gas-phase photocatalytic oxidation of trichloroethylene over titanium oxide: products and mechanisms

Chlorine Atom Initiated Oxidation of Chlorinated Ethenes: Results for 1,1-Dichloroethene (H2CCCl2), 1,2-Dichloroethene (HClCCClH), Trichloroethene (HClCCCl2), and Tetrachloroethene (Cl2CCCl2)

Oxidation of chloroethylene

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Chlorine Atom Initiated Oxidation of Chlorinated Ethenes: Results for 1,1-Dichloroethene (H₂CCCl₂), 1,2-Dichloroethene (HClCCClH), Trichloroethene (HClCCCl₂), and Tetrachloroethene (Cl₂CCCl₂)