- Brominated-trihalomethane formation from phenolic derivatives as a model of humic materials by the reaction with hypochlorite and hypobromite ions
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Among the 21 phenolic derivatives tested for the model system of the disinfection process in the natural water containing humic acid, 2-hydroxytoluene and 2,6-dihydroxybenzoic acid produced high yields of CHBr3 under the co-existence of NaOCl and NaOBr. In the study of distribution of THMs produced, the amount of CHBr3 increased with the relative concentration of NaOCl added to NaOBr. These results were similar to the case of halogenation of the humic acid under the co-existence of NaOCl and NaOBr.
- Ichihashi, Keiko,Teranishi, Kiyoshi,Ichimura, Akio
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- Fe3O4-Catalyzed Halogen-Exchange Reactions of Polyhalomethanes
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Triiron tetraoxide pretreated by polyhalomethane was shown to catalyze the halogen-exchange reaction of polyhalomethanes CHlBrmCln (l=1 or 2).The exchange proceeds consecutively giving, for example, CHBrCl2, CHBr2Cl, and C
- Nakada, Masahiro,Tokumoto, Sei-ichi,Hirota, Minoru
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- Chemistry of the biosynthesis of halogenated methanes: C1-organohalogens as pre-industrial chemical stressors in the environment?
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We have chemical evidence that in the biosynthesis of the halomethanes C1H(4-n),X(n) (n = 1-4) three different pathways of biogenic formation have to be distinguished. The formation of methyl chloride, methyl bromide, and methyl iodide, respectively, has to be considered as a methylation of the respective halide ions. The dihalo- and trihalomethanes are formed via the haloform and/or via the sulfo-haloform reaction. The possible formation of tetrahalomethanes may involve a radical mechanism. Methionine methyl sulfonium chloride used as substrate in the incubation together with chloroperoxidase (CPO) and H2O2 gave high yields of monohalomethanes only. We were able to show that next to the CPO/H2O2 driven haloform reaction of carbonyl activated methyl groups also methyl-sulphur compounds - e.g. dimethylsulfoxide, dimethylsulfone, and the sulphur amino acid methionine - can act as precursors for the biosynthesis of di- and trihalogenated methanes. Moreover, there is some but not yet very conclusive evidence for an enzymatic production of tetrahalogenated methanes. In our experiments with chloroperoxidase involving amino acids and complex natural peptide based substrates, dihalogenated acetonitriles and several other volatile halogenated but yet unidentified compounds were formed. On the basis of these experiments we like to suggest that biosynthesis of halogenated nitriles occurs in general and therefore a natural atmospheric background should exist for halogenated acetonitriles and halogenated acetaldehydes, respectively.
- Urhahn, Thorsten,Ballschmiter, Karlheinz
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- Brominated trihalomethane formation in halogenation of humic acid in the coexistence of hypochlorite and hypobromite ions
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Brominated trihalomethanes (Br-THMs) such as CHCl2Br, CHClBr2, and CHBr3 are produced by the reaction of hypobromite with humic acid in the presence of hypochlorite. In the presence of excess NaOCl, addition of NaOBr enhanced the formation of Br-THMs but reduced the formation of CHCl3. The product distribution of THMs was affected by the ratio of [NaOBr]/[NaOCl] and was independent of pH and reaction time. In the presence of excess NaOBr, the yield of CHBr3 only increased linearly with the NaOCl concentration added. However, the other three THMs were hardly produced even though NaOCl concentration was increased up to 0.5 of the [NaOCl]/[NaOBr] molar ratio. Our results suggest that in the process of THM formation, hypochlorite ion reacts effectively with humic acid in the oxidation reaction and hypobromous acid plays a predominant role in the electrophilic substitution when both of hypohalites are present. Brominated trihalomethanes (Br-THMs) such as CHCl2Br, CHClBr2, and CHBr3 are produced by the reaction of hypobromite with humic acid in the presence of hypochlorite. In the presence of excess NaOCl, addition of NaOBr enhanced the formation of Br-THMs but reduced the formation of CHCl3. The product distribution of THMs was affected by the ratio of [NaOBr]/[NaOCl] and was independent of pH and reaction time. In the presence of excess NaOBr, the yield of CHBr3 only increased linearly with the NaOCl concentration added. However, the other three THMs were hardly-produced even though NaOCl concentration was increased up to 0.5 of the [NaOCl]/[NaOBr] molar ratio. Our results suggest that in the process of THM formation, hypochlorite ion reacts effectively with humic acid in the oxidation reaction and hypobromous acid plays a predominant role in the electrophilic substitution when both of hypohalites are present.
- Ichihashi, Keiko,Teranishi, Kiyoshi,Ichimura, Akio
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- Effects of bromide on the formation of THMs and HAAs
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The role of bromide in the formation and speciation of disinfection by-products (DBPs) during chlorination was investigated. The molar ratio of applied chlorine to bromide is an important factor in the formation and speciation of trihalomethanes (THMs) and halogenacetic acids (HAAs). A good relationship exists between the molar fractions of THMs and the bromide incorporation factor. The halogen substitution ability of HOBr and HOCl during the formation of THMs and HAAs can be determined based on probability theory. The formation of HAAs, and their respective concentrations, can also be estimated through use of the developed model.
- Chang,Lin,Chiang
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- Facile halogen exchange reactions: Chloroform with bromoform and carbon tetrachloride with carbon tetrabromide
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Both of the title systems undergo rapid halogen exchange (half-life ca. 1-2 min) in N-methylpyrolidinone with catalytic sodium hydroxide at room temperature. Yet they differ markedly in response to added p-dinitrobenzene. The rate of the haloform exchange is unaffected, whereas the rate of the carbon tetrahalide exchange is severely retarded. The known base-induced halogen exchange reaction between chloroform and bromoform is shown not to proceed through a reversible carbene intermediate as claimed in the literature. It appears to be best described in terms of the so-called RARP mechanism (radical anion-radical pair). The mechanism proposed for the rapid exchange between carbon tetrachloride and carbon tetrabromide is initial electron transfer, halide ion loss, and ensuing radical chain scrambling of halogen atoms. The acronym RARC, standing for radical anion-radical chain, is proposed.
- Orvik, Jon A.
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- Modelling the formation of brominated trihalomethanes in chlorinated drinking waters
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The chlorination of water containing bromide and natural organic matter (NOM) leads to the formation of brominated trihalomethanes (THMs). The extent of brominated THM formation depends, inter alia, on the bromide:chlorine concentration ratio ([Br-]:[chlorine]). A reaction scheme is proposed from which a simple kinetic model is developed that mathematically relates the extent of bromination, and the relative abundances of the four THMs, to the [Br-]:[chlorine] ratio. In the scheme, the trihalogenated precursors to THMs are formed by three steps each of which substitutes either bromine or chlorine into an activated carbon site in the NOM. This leads to six pairs of competing bromination:chlorination reactions, whose rate constant ratios (k(b):k(c)) have been estimated by using the model to fit THM data obtained from the chlorination of 17 waters from New Zealand. The individual k(b):k(c) ratios range from 4 to 15. From a plot of the ratio of total bromine to total chlorine present in the THMs as a function of the [Br-]:[chlorine] ratio, an apparent overall k(b):k(c) ratio of 9.1 is obtained. Using USEPA cancer potency factors, the model is used to predict the relative cancer risk associated with THMs as a function of the [Br-]:[chlorine] ratio. This risk increases steeply to a peak at a [Br-]:[chlorine] ratio of approximately 0.15, then gradually decreases to the value associated with bromoform alone. The risk associated with THMs may vary considerably through changes in the [Br-]:[chlorine] ratio as the result of natural variation in the [Br-], or through poor control of chlorine dosing.
- Nokes,Fenton,Randall
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- MANUFACTURE OF DICHLOROPROPANOL
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Manufacture of dichloropropanol Process for manufacturing dichloropropa nol wherein a glycerol-based product comprising at least one diol containi ng at least 3 carbon atoms other than 1,2- propanediol, is reacted with a chlorinati ng agent, and of products derived from dichloropropanol such as ep ichlorohydrin and epoxy resins. No figure.
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Page/Page column 19-21
(2009/03/07)
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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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- Specific Catalyst Effects on Halogen-Exchange Processes with Mixed Dihalogenocarbenes
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An improved preparation of chlorodiiodomethane and dibromochloromethane by phase-transfer catalysis is described.Bromochlorocarbene is generated from HCBr2Cl highly selectively (>=97percent) only if tetramethylammonium chloride, dibenzo-18-crown-6, its 3,3',5,5'-tetra-tert-butyl derivative, or 3',5'-di-tert-butylbenzo-15-crown-5 are catalysts.Other investigated catalysts promote extensive halide exchange whereby olefin adducts of dibromo- and dichlorocarbene are formed additionally.
- Dehmlow, Eckehard V.,Stuetten, Joerg
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p. 187 - 190
(2007/10/02)
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- Catalytic Halide Exchange in Hydrocarbons Promoted by Aluminas Coated with Phosphonium Salts
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Passing a mixture of two different alkyl halides, in the gas phase, through a column filled with alumina and a phosphonium salt, gives halide-exchange products which are collected at the outlet by condensation; the process is catalytic and allows transformations to be carried out in a continuous flow process.
- Angeletti, Enrico,Tundo, Pietro,Venturello, Paolo
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p. 1127 - 1128
(2007/10/02)
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