- The photoinduced reaction of 2-iodothiophene in solutions of n-heptane, dichloromethane and methanol
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The photoinduced reaction of 2-iodothiophene in n-heptane, dichloromethane and methanol was studied at room temperature from experiments carried out with degassed solutions. The photoproducts of the reaction were mainly thiophene and small amounts of iodine in all three solvents used. The concentration of 2-iodothiophene decreases throughout photolysis, following a first-order rate law and the pseudo-first-order rate constants were determined in the three solvents used. The photochemistry of the system was quantified determining the quantum yields of 2-iodothiophene consumption and thiophene formation in n-heptane solutions. The results show that under the experimental conditions of this research, products deriving only from the reaction of the thienyl radical were observed. To support the experimental results, calculations were performed of the ionization potential of the thienyl radical, electron affinity of the iodine atom and free energy of solvation of the corresponding iodide and carbocation in the different solvents used. Copyright
- Herrera,Nieto,Olleta,Lane
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experimental part
p. 398 - 406
(2011/11/06)
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- Determination, synthesis and survey of iodinated trihalomethanes in water treatment processes
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Trihalomethanes (THMs) are formed as a result of the interaction of free aqueous chlorine, used as a disinfectant in drinking water, with the organic matter in raw water. Although chlorinated, brominated and chlorobromotrihalomethanes are the most common disinfection by-products reported, iodinated trihalomethanes (ITHMs) can be formed when iodide is present in raw water. ITHMs have been usually associated with several medicinal or pharmaceutical taste and odor events in drinking water. For instance, the odor and taste threshold concentrations of iodoform are 0.02 and 5 μg/l, respectively. Different analytical techniques have been studied to identify these compounds but their quantitative determination has not been performed due to the lack of commercial standards. In this study ITHMs (CHCl2I, CHClI2, CHBr2I, CHBrI2 and CHBrClI) have been synthesized in order to evaluate headspace (HS), purge and trap (P&T), closed loop stripping analysis (CLSA) and liquid-liquid extraction (LLE) as analytical methods for determination. HS and LLE were followed by gas chromatography and electron capture detector (GC/ECD); whereas P&T and CLSA with gas chromatography and mass spectrometry (GC/MS). The most appropriate method, LLE/GC/ECD, was applied to evaluate the stability of ITHMs in water (ultrapure, raw and treated water) in order to confirm their presence in tap water. Ascorbic acid was the quenching reagent chosen to avoid free chlorine at the time of sample collection. Finally, samples from the different stages of the treatment plant in Barcelona (NE Spain) were analyzed. Only three (CHCl2I, CHBrClI and CHBr2I) of the six ITHMs were identified and determined, at average levels lower than 1μg/l, in sand filtered and ozonated waters. No ITHMs were identified in distribution system water. Trihalomethanes (THMs) are formed as a result of the interaction of free aqueous chlorine, used as a disinfectant in drinking water, with the organic matter in raw water. Although chlorinated, brominated and chlorobromotrihalomethanes are the most common disinfection by-products reported, iodinated trihalomethanes (ITHMs) can be formed when iodide is present in raw water. ITHMs have been usually associated with several medicinal or pharmaceutical taste and odor events in drinking water. For instance, the odor and taste threshold concentrations of iodoform are 0.02 and 5 μg/l, respectively. Different analytical techniques have been studied to identify these compounds but their quantitative determination has not been performed due to the lack of commercial standards. In this study ITHMs (CHCl2I, CHClI2, CHBr2I, CHBrI2 and CHBrClI) have been synthesized in order to evaluate headspace (HS), purge and trap (P and T), closed loop stripping analysis (CLSA) and liquid-liquid extraction (LLE) as analytical methods for determination. HS and LLE were followed by gas chromatography and electron capture detector (GC/ECD); whereas P and T and CLSA with gas chromatography and mass spectrometry (GC/MS). The most appropriate method, LLE/GC/ECD, was applied to evaluate the stability of ITHMs in water (ultrapure, raw and treated water) in order to confirm their presence in tap water. Ascorbic acid was the quenching reagent chosen to avoid free chlorine at the time of sample collection. Finally, samples from the different stages of the treatment plant in Barcelona (NE Spain) were analyzed. Only three (CHCl2I, CHBrClI and CHBr2I) of the six ITHMs were identified and determined, at average levels lower than 1μg/l, in sand filtered and ozonated waters. No ITHMs were identified in distribution system water. (C) 2000 Elsevier Science Ltd.
- Cancho, Beatriz,Ventura, Francesc,Galceran, Materesa,Diaz, Alfredo,Ricart, Susagna
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p. 3380 - 3390
(2007/10/03)
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- Direct Photolysis of 1-Halo-1-hexynes. Lack of Ionic Behavior
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Direct photolyses at >200 nm of 1-bromo- and 1-iodo-1-hexynes were performed in polar and nonpolar solvents.Only radical-derived products were obtained even in polar solvents, contrary to the previously reported ionic photochemical behavior of alkyl and vinyl halides.The results are discussed from an energy point of view; the ionization potential of the initially formed organic radical well accounts for the obvious difference in photobehavior between alkynyl and alkyl or vinyl halides.
- Inoue, Yoshihisa,Fukunaga, Takao,Hakushi, Tadao
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p. 1732 - 1737
(2007/10/02)
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