Xn:Harmful;
75-27-4Relevant academic research and scientific papers
REACTIONS OF CARBENES WITH ANIONS
Suelzle, Detlev
, p. 2769 - 2770 (1987)
CHBrCl2, CHCl2I and CHBr2I are prepared by a simple method based on the reaction of dichloro or dibromocarbene with the corresponding alkali metal halogenides under phase transfer conditions.
PROCESS FOR PREPARING BROMOTRICHLOROMETHANE
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Page/Page column 6-7, (2018/10/19)
The present invention relates to a process for preparing bromotrichloromethane comprising a) providing bromine in chloroform; and b) radiation of the resulting solution with light in the range of 350 to 550 nm, wherein said solution of bromine in chloroform is not radiated with radiation of a wavelength below 350nm.
Effects of bromide on the formation of THMs and HAAs
Chang,Lin,Chiang
, p. 1029 - 1034 (2007/10/03)
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.
Transient puffs of trace organic emissions from a batch-fed waste propellant incinerator
Hart, John R.
, p. 559 - 569 (2007/10/03)
Emissions data have been obtained from a waste propellant incinerator. The incinerator is a dual fixed hearth, controlled air incinerator equipped with acid gas and particulate scrubbing. Puffing has been evident in this waste propellant incinerator by spikes in the CO concentration. Transient puffs of organics may travel down the combustion chambers and lead to stack emissions. The major conclusions from this study are that (1) transient puffs are formed due to the semi-batch feed nature of the combustion process (causing a local oxygen deficiency) and high water content of the desensitized propellant; (2) in batch-fed combustors, puffs can contribute to most of the organic emissions (which are relatively low) measured with US EPA sampling and analytical methods; (3) it is estimated that batch-fed combustion contributes up to 7-18 times more emissions than steady-state combustion will generate; (4) by applying dispersion analyses to determine the amount of oxygen deficiency in the flame zone, the combustion zone concentration of CO during batch-fed operation could be as high as 160,000 ppm, compared to a measured peak stack concentration of 1200 ppm CO; and (5) an organic sample is collected and averaged over at least a 2-h period that smooths out the transient peaks of organics emissions during batch-fed operation. For emissions that are associated with long-term potential health impacts, this is an appropriate sampling method. However, if a compound has a short-term potential health impact, it may be important to measure the time-resolved emissions of the compound.
Modelling the formation of brominated trihalomethanes in chlorinated drinking waters
Nokes,Fenton,Randall
, p. 3557 - 3568 (2007/10/03)
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.
Brominated-trihalomethane formation from phenolic derivatives as a model of humic materials by the reaction with hypochlorite and hypobromite ions
Ichihashi, Keiko,Teranishi, Kiyoshi,Ichimura, Akio
, p. 957 - 958 (2007/10/03)
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.
Brominated trihalomethane formation in halogenation of humic acid in the coexistence of hypochlorite and hypobromite ions
Ichihashi, Keiko,Teranishi, Kiyoshi,Ichimura, Akio
, p. 477 - 483 (2007/10/03)
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.
Kinetics of the R + Cl2 (R = CH2Cl, CHBrCl, CCl3 and CH3CCl2) reactions. An ab initio study of the transition states
Seetula, Jorma A.
, p. 3561 - 3567 (2007/10/03)
The kinetics of the reactions of CH2Cl, CHBrCl, CCl3 and CH3CCl2 radicals with molecular chlorine were investigated in a heatable tubular reactor coupled to a photoionization mass spectrometer. The reactions were studied under pseudo-first-order conditions. The radicals were photogenerated at 248 nm. The pressure-independent rate constants determined were fitted to the following Kooij and Arrhenius expressions (units in cm3 molecule-1 s-1): k-(CH2Cl) = 7.56 × 10-17(T)1.45 exp(-350 J mol-1/RT), k(CHBrCl) = 5.83 × 10-20(T)2.3 exp(-300 J mol-1/RT), k(CCl3) = (8.4 ± 2.9) × 10-13 exp[-(25 ± 9) kJ mol-1/RT] and k(CH3CCl2) = 1.10 × 10-26(T)4.3 exp(+15000 J mol-1/RT). The Arrhenius rate expression for the Cl + CCl4 reaction was determined to be k(Cl + CCl4) = (3.9 ± 3.2) × 10-13 exp[-(71 ± 9) kJ mol-1/RT] using the kinetics measured and the thermochemistry of the CCl3 radical. Errors for the Kooij expressions were estimated to be 25% overall, and for the Arrhenius expressions they were calculated to be 1σ + Student's t values. The transition states of the measured R + Cl2 and four other similar reactions were localized and fully optimized at the MP2/6-31G(d,p) level of theory by ab initio methods. The energetics of the reactions were considered by determining thermochemical and activation parameters of the reactions. The reactivity differences of the radicals studied were explained by a free-energy correlation using an electronegativity difference scale.
Chemistry of the biosynthesis of halogenated methanes: C1-organohalogens as pre-industrial chemical stressors in the environment?
Urhahn, Thorsten,Ballschmiter, Karlheinz
, p. 1017 - 1032 (2007/10/03)
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.
Facile halogen exchange reactions: Chloroform with bromoform and carbon tetrachloride with carbon tetrabromide
Orvik, Jon A.
, p. 4933 - 4936 (2007/10/03)
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.
