- 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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- Formation of acetylenic acetals by ring opening of 1,1,2-trihalocyclopropanes under phase-transfer conditions
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A number of substituted 1,1-dibromo- and 1,1-dichlorocyclopropanes with an additional chlorine or bromine atom attached to C-2 were synthesized in reasonabk to good yields by dihalocarbene addition to the corresponding alkenes under phase-transfer conditions. When the trihalides were treated with 50% aqueous sodium hydroxide in the presence of ethanol. triethylbenzylammonium chloride and dichloromethane. most of the compounds underwent ring opening and afforded mixtures of acetylenic acetals, usually in good yields. The reaction most likely involves cyclopropene intermediates, which in some cases also rearrange to a minor extent to the corresponding vinylcarbenes and afford α,β-unsaturated aldehydes. Acta Chemica Scandinavica 1996.
- Sydnes, Leiv K.,Bakstad, Einar
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p. 446 - 453
(2007/10/03)
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- Fluoride anion catalyzed halogen dance in polyhalomethanes
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Tetrabutylammonium fluoride catalyzes the exchange of halogens between tetrahalomethanes.The presence of small amounts of haloform is suspected to be a necessary co-catalyst.Key Words: tetrabutyl ammonium fluoride; tetrahalomethanes; halogen exchange in.
- Sasson, Y.,Kitson, F.,Webster, O, W.
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p. 599 - 600
(2007/10/02)
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- Synthesis of gem-Difluorocyclopropanes in a Phase-transfer Catalysed System
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Reaction of CH2Br2 with CBr2F2 and alkenes 1a-e in the presence of 60percent aqueous KOH and tetrabutylammonium hydrogensulphate as a catalyst affords gem-difluorocyclopropanes 2a-e.
- Balcerzak, Pawel,Fedorynski, Michal,Jonczyk, Andrzej
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p. 826 - 827
(2007/10/02)
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- Bromine Atom Complexes with Bromoalkanes. Their Formation in the Pulse Radiolysis of Di-, Tri-, and Tetrabromomethane and Their Reactivity with Organic Reductants
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Bromine atoms were produced in the pulse radiolysis of neat dibromomethane (DBM) and bromoform and of cyclohexane solutions containing DBM, bromoform, carbon tetrabromide, or ethyl bromide.The Br atoms form complexes with dimethyl sulfoxide (λmax 425 nm), with aromatic compounds, and with oxygen-containing compounds.In the absence of other complexing agents, since Br atoms do not abstract H from the solvents rapidly, they form complexes with their parent bromo compounds.The absorption maxima of these complexes are at 365 nm for C2H5Br*Br, 390 nm for CH2Br2*Br, 425 nm for CHBr3*Br, and 480 nm for CBr4*Br.The stability of RBr*Br appears to increase with the number of Br atoms in the molecule.These complexes act as oxidants towards p-methoxyphenol, 1,3,5-trimethoxybenzene, triphenylamine, and N,N,N',N'-tetramethyl-p-phenylenediamine.The cate constants for the oxidations were about 1E10 M-1 s-1 with CH2Br2*Br but only of the order of 1E8 - 1E9 M-1 s-1 with CBr4*Br.The initial products of the oxidation are the ion pairs between the radical cation of the organic substrate and the Br- ion.In the case of p-methoxyphenol the initial ion pair releases HBr under neutral or basic conditions to form the neutral p-methoxyphenoxyl radical.The Br atom complexes are also capable of abstracting H from weak C-H bonds.The benzylic and allylic hydrogens in hexamethylbenzene and cyclohexene are abstracted with rate constants near 1E9 by CH2Br2*Br and near 1E7 M-1 s-1 by CBr4*Br.The behavior of Br atoms is compared with that of Cl and I atoms.
- Shoute, Lian C. T.,Neta, P.
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p. 2447 - 2453
(2007/10/02)
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