Number Of Bromine Atoms Research Articles

Photochemical degradation of six polybrominated diphenyl ether congeners under ultraviolet irradiation in hexane

The photodegradation of six individual PBDE congeners (BDE-28, 47, 99, 100, 153, 183) in hexane was investigated under UV light in the sunlight region, employing a mercury lamp filtered with Pyrex glass. All photodegradation reactions followed the pseudo-first-order kinetics, with the half-lives ranging from 0.26 h for BDE-183 to 6.46 h for BDE-100. The photochemical reaction rates of PBDEs decreased with decreasing number of bromine substituents in the molecule, also in some cases were influenced by the PBDE substitution pattern. Principal photoproducts detected were less brominated PBDEs, and no PBDE-solvent adducts were found. Consecutive reductive debromination was confirmed as the main mechanism for the photodegradation of PBDEs in hexane. In general, debromination firstly occurred on the more substituted rings, when the numbers of bromine atoms on the two phenyl rings were unequal. For less brominated PBDEs, the photoreactivity of bromines at various positions of phenyl rings decreased in the order: ortho > para; while for higher brominated PBDEs, the difference became not significant.

On the use of computer assisted resolution of non-separable peaks in a congener specific polybrominated diphenyl ether capillary gas chromatographic analysis

The use of computer assisted deconvolution for chromatographically not separated peaks in the analysis of polybrominated diphenyl ethers (PBDEs) by capillary gas chromatography (CGC) was studied. Twenty-two not separated clusters containing 48 overlapped PBDEs were registered in the separation of a sample containing 122 PBDE congeners on a semipolar poly(8%-phenyl–92%-dimethyl)siloxane column. There were only two clusters in which overlapped PBDEs differ in the number of bromine atoms {PBDE 126(5Br) co-elutes with 154(6Br) and PBDE 105(5Br) co-elutes with 144(6Br)} and therefore their mass spectra could be successfully used for deconvolution purposes. In 22 other clusters 46 isomeric PBDEs with identical mass spectra overlapped and for their resolution a computer assisted deconvolution procedure using a commercial available program was used. A published procedure for the estimation of minimum number of peaks in a peak cluster for which the data found by deconvolution are reliable, has been adapted. Using this procedure, for eight overlapped PBDE full peak data (single peak retention times and peak areas) were extracted.

Predicting the Gas Chromatographic Relative Retention Time of Polybrominated Diphenyl Ethers by MEDV-13 Descriptors

Polybrominated diphenyl ethers (PBDEs) have been used extensively over the past two decades as flame or fire retardants added into many products such as textiles, electronic equipment and insulation material. PBDEs are now ubiquitous environmental pollutants and have been detected in biotic and abiotic matrices that include fish, birds, sediments, air, marine mammals, and human plasma and milk. The purpose of the paper is to develop some models which can predict the gas chromatographic relative retention time of PBDEs on seven stationary phases. The molecular electronegativity distance vector based on 13 atomic types (MEDV-13) were employed to describe the structural changes of PBDEs. Using the variables selection and modeling based on the prediction (VSMP), some four-variable linear equations from 80 PBDEs in the training sets with the correlation coefficient (r2) >0.98 and the root mean square errors of estimation <0.029 (except for CP-Sil19) were established. The standard regression coefficient indicated that MEDV descriptor x91 (interaction between the substructure –Br and –Br) was the most important descriptor to affect the RRT values of PBDEs. At the same time, it was found that the number of the ortho-substituent bromines and the number of bromine atoms in PBDE molecule may improve the predictive quality.

Synthesis of oligo-6-bromo-6-deoxy-β-cyclodextrins

Two methods of synthesis of oligo-6-bromo-6-deoxy-β-cyclodextrins, with use of the Vilsmeier-Haack reagent and via tosyl derivatives of β-cyclodextrin, were compared. The second method holds more promise, since it allows a desired number of bromine atoms to be introduced into the β-cyclodextrin molecule instead of hydroxy groups. A correlation between the decomposition onset points of oligo-6-bromo-6-deoxy-β-cyclodextrins and the number of bromine substituents in them was revealed.

A Mass Spectral Chlorine Rule for Use in Structure Determinations in Sophomore Organic Chemistry

The number of chlorine atoms, n, is stoichiometrically related to the ratio of peak intensities of the lowest-mass-to-highest-mass molecular ions in ideal molecular-ion clusters displayed in the mass spectra of Br- and Cl-containing compounds. Intensity ratios for these peaks are independent of the number of bromine atoms and equal the nth power of 3. For ratios of 1, 3, 9, 27, and 81, the values of n are 0, 1, 2, 3, and 4, respectively. When real clusters are peak-normalized, n can be found by cluster analysis of compounds containing C, H, O, N, Br, and Cl. Given a cluster, students can find the number of chlorine atoms in these compounds directly from the normalized intensity of M, the lowest-mass molecular ion, and can find the number of bromine atoms from the number of peaks in the cluster. The chlorine rule provides a new tool for use in organic structure determination. A discovery exercise for the chlorine rule and the names of 69 compounds, the spectra of 68 of which have been successfully analyzed...

Matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry analysis of atom transfer radical polymerization macroinitiators derived from poly(3‐ethyl‐3‐hydroxymethyloxetane)

AbstractThe matrix‐assisted laser desorption/ionization time‐of‐flight analysis of macroinitiators for atom transfer radical polymerization prepared by the functionalization of a multihydroxyl, highly branched polyether, poly(3‐ethyl‐3‐hydroxymethyloxetane), allows the exact determination of the macroinitiator functionality, providing information on the number of bromine atoms in individual macromolecules, in contrast to NMR analysis, which gives average values. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 608–614, 2004

The photodissociation dynamics of dibromobenzenes and tribromobenzene in the gas phase studied with femtosecond pump–probe spectroscopy

The photodissociation dynamics of o-, m-, p-dibromobenzene and 1,3,5-tribromobenzene have been investigated in a molecular beam following excitation at 266 nm using ultrafast spectroscopy. In o- and m-dibromobenzene two dissociation pathways have been observed, whereas p-dibromobenzene and 1,3,5-tribromobenzene dissociates via one channel. The channel common for all the compounds has been assigned to predissociation from 1(π,π *) state to the repulsive 3( n,σ *) state. The rate of this process increases with the number of bromine atoms and with decreasing distance on the phenyl ring. The presence of two dissociation channels in o- and m-dibromobenzene is probably related to the lower symmetry of these molecules.

Optical characterization of bromo-alkoxyl-substituted copper phthalocyanine derivative thin films

A series of thin films of copper phthalocyanine derivatives with bromine and alkoxyl substituents [CuPc(OC 8H 17) 4Br m , m=0,1,2,4] were prepared on single-crystal silicon substrates by spin coating. The ellipsometric spectra of the films have been studied on a rotating analyzer–polarizer type of scanning ellipsometer. The optical, dielectric constants and absorption coefficients of the films in 500–800 nm wavelength region were obtained. The results show that the complex refractive index, dielectric constants and absorption coefficient of these thin films are influenced regularly by bromine substituent on conjugated macrocycle. It was found that there are approximately linear relationships between the resonance absorption wavelengths of the films and the average number of bromine atoms substituted on the phthalocyanine ring.

Using BAC for HAA removal PART 1: BATCH STUDY

The stability and biodegradation of haloacetic acids (HAAs) in the presence of bioactivity were evaluated using batch experiments; a separate experiment assessed the carbon adsorption capacities of HAAs. HAAs were significantly degraded in dechlorinated drinking water in the presence of suspended bacteria. Increasing the number of halogen atoms on an HAA decreased its biodegradation rate but increased its carbon adsorption capacity; increasing the number of bromine atoms on an HAA also increased its carbon adsorption capacity. Biologically active carbon effectively removed milligram‐per‐litre–level HAAs spiked in dechlorinated drinking water. This removal may be a result of the combination of carbon adsorption and biodegradation and can be described by a pseudo first‐order reaction model. The findings from this study are significant for sample preservation for HAA monitoring and could lead to the development of an innovative technology for HAA control in drinking water.

Vapor pressures of six brominated diphenyl ether congeners

Subcooled liquid vapor pressures (PLo) of six polybrominated diphenyl ether (PBDE) congeners containing three to seven bromine atoms were determined using the gas chromatograph retention time technique. Values ranged from 2.3 x 10(-7) to 1.45 x 10(-4) Pa at 25 degrees C. An increase in the number of bromine atoms tended to decrease PLo according to the correlation log PLo = -0.692 (bromine number)--1.76 (R2 = 0.953, p < 0.001). In addition, the first such data for individual PBDE congeners demonstrates that PLo would vary four orders of magnitude over environmentally relevant temperatures.

Non-planar porphyrins with mixed substituent pattern: bromination and formylation of ethyl-substituted tetraphenylporphyrins and tetraalkylporphyrins

A series of 5,10,15,20-tetraphenylporphyrins (TPPs) bearing different numbers and orientations of β-ethyl substituents have been used for studies on the functionalization of non-planar porphyrins. Attempts to monofunctionalize the diethyl-TPP via monobromination failed and resulted in the isolation of two different regioisomers. All ethyl-TPPs were easily converted into the perbrominated porphyrins bearing twelve peripheral substituents but with different numbers of β-bromo and -ethyl groups. These porphyrins are interesting precursors for further mixing of the substituent pattern and are novel push-pull porphyrins bearing electron donating and withdrawing groups in a defined pattern directly on the ring system. They have a similar degree of overall conformational distortion, however each with considerably altered electronic effects due to the different number of bromine atoms. In order to gain access to monofunctionalized derivatives, some of the ethyl-TPPs were converted into the monoformyl derivatives. In a similar manner, a number of 5,10,15,20-tetraalkylporphyrins were formylated, albeit in lower yields than the ethyl-TPPs. Several compounds were investigated in detail by single crystal X-ray crystallography and allowed a comparison of the influence of different substituent patterns on the conformation. The structural analyses include a comparison of different crystalline modifications for some compounds. Structural data for perbrominated ethyl-TPPs present the first examples of highly non-planar, dodecasubstituted porphyrins bearing two different types of β-substituents.

Substituent effect by chlorine and bromine atoms for carbon-13, silicon-29 and tin-119 NMR chemical shifts in tetramethyl compounds.

Carbon-13, silicon-29 and tin-119 chemical shifts were measured for chloro and bromo-substituted compounds [(CH3)nMX4-n; M=C, Si, Sn;n=0-4], and the behavior of the chemical shifts for carbon, silicon and tin atoms in those compounds were investigated. The 13C, 29Si and 119Sn chemical shifts of monochloro-substituted compounds were shifted to a lower field by 30-172 ppm in the order of 29Si, 13C and 119Sn, which could. be explained by an inductive effect. The 13C chemical shifts for chloro-substituted compounds were shifted to a lower field in order of mono, di, tri and tetrachloro substituents, however, the 119Sn chemical shifts in those compounds were shifted to higher fields with increasing number of chlorine atoms in a molecule. This is considered to be due to the effect of a steric compression between the substituted chlorine atoms. The 13C, 29Si and 119Sn chemical shifts of monobromo-substituted compounds were also shifted to a lower field by 27135 ppm in the same order as that of monochloro-substituted compounds. The 13C, 29Si and 119Sn chemical shifts for bromo-substituted compounds shifted largely toward a higher field with increasing number of bromine atoms in a molecule, which probably could be attributed to the heavy atom effect.

Synthesis of biologically active bromine derivatives of quercetin

The synthesis of a series of bromine derivatives of quercetin differing by the number of bromine atoms introduced is described. It has been shown that in the dynamics of the bromination process the deciding factors affecting the qualitative and quantitative compositions of the reaction products are the temperature regime and the ratio of the reactants. Thus, the use of equimolar amounts of the reactants in dioxane in the temperature interval from 20 to 25° C gives a monobromo derivative, while all other conditions give mixtures of bromo derivatives. The antiviral and antitumoral activities of the mono- and dibromo derivatives of quercetin have been studied.

Non-Metal Redox Kinetics: Oxidation of Bromide Ion by Nitrogen Trichloride

Bromide ion reacts with NC13 to generate NBrC12 with the rate expression d[NCl3]/dt = 12[Br-][NC13] (M s-' at 25.0 C, y = 0.50 M). The NBrC12 intermediate subsequently reacts with Brto give N2, Br2, and C1with the rate expression -d[NBrClz]/dt = (0.05 + 5.3[Br-])[NBrC12]. The overall stoichiometry from pH 3.2 to 6.5 corresponds to 2NC13 + 6BrN2 + 3Br2 + 6C1-. Rate constants for NCl3 reactions show extreme sensitivity to nucleophilic strength with so32> CN> I>> Br-. Aqueous absorption spectra are determined for NC13 with maxima at 336 nm ( E 190 M-' cm-I) and 220 nm ( E 5320 M-' cm-') and for NBrC12 with a maximum at 228 nm ( E 4800 M-' cm-I). Spectral bands for NCl3, NBrC12, NBr2C1, and NBr3 shift systematically with the number of bromine atoms from 220 to 256 nm. The rate constants for the reactions of NHCl2 with Br2, HOBr, and Brare much larger than that for the reaction of NCl3 with Br-.

X-ray crystallographic study of α-brominated diketo teraquinanes. Conformational effects of the number of halogens and their position on bond length and solit-state conformation

Halogenative substitution of tetracyclo[7.2.10 4,110 6,10]dodecane-5,12-dione with copper(II) bromide or molecular bromine has provided synthetic entry to the monobromo, 1,4- and 1,6-dibromo, 1,4,6- tribromo, and 1,4,6,9-tetrabromo derivatives. X-ray structural analysis of the latter four compounds has shown bond lengths and bond angles not to be greatly affected by the number of bromine atoms or their relative position. On the other hand, conformational preferences are seen to vary appreciably with substitution pattern across the series.

Enhancement of electron affinity of benzocycloheptene-1,4,7-trione by substitution

To obtain new efficient electron acceptors, three bromine-substituted benzocycloheptene-1,4,7-triones, 14, 15, 16, and 7-dicyanomethylene-7H-benzocycloheptene-1,4-dione 36 have been synthesized. The electron affinities of the bromine-substituted quinones were found to be raised considerably as the number of bromine atoms increased compared with the parent trione 3. A linear correlation between E1redox and ELUMO(MNDO) has been shown. The dicyanomethylene substitution (36) of the tropone carbonyl of 3 caused an increase in the electron affinity by E1+ 0.2 V. To obtain an acceptor carrying electron-withdrawing substituents on C6 and C8 of 3, the 6,8-dimethoxycarbonyl derivative 18 was oxidized and gave a ring-contracted product 22 in fair yield. The formation is discussed in terms of electron distribution in the molecule of the expected product 19.

Photochemical degradation of brominated dibenzo-p-dioxins and -furans in organic solvents

The photolytic behavior of halogenated dibenzo-p-dioxins and -furans in the organic solvents methanol and n-hexane was investigated and the corresponding quantum-yields and first order decay rates are reported. The photolysis constants in n-hexane increase with increasing number of bromine atoms in the dibenzo-p-dioxin or dibenzofuran skeleton, e.g. from 4.5×10 −4 s −1 for the monobrominated to 7.7×10 −3 s −1 for the octabrominated dioxin, and from 4.0×10 −3 s −1 for the dibrominated to 8.3×10 −2 s −1 for the heptabrominated furan. Photolysis in methanol is nearly six times slower than in n-hexane. The bromine compounds react an order of magnitude faster than the chlorine analogues. The results were used to extrapolate the photochemical fate to lipohilic environmental surfaces.

Comparison of the effect of trihalomethanes on lipid metabolism in rat liver slice

The effect of a series of trihalomethanes, CHCl 3, CHBrCl 2, CHBr 2Cl, and CHBr 3, on in vitro lipid metabolism was compared using rat liver slices. The incorporation of 32Pi and [ 3H]glycerol into phospholipid of liver slices was inhibited in the presence of trihalomethanes. The inhibitory effect followed the number of bromine atoms in the trihalomethane molecule in the initial period of incubation. CHBr 3 markedly inhibited the incorporation of [ 3H]glycerol into triacylglycerol (TG); CHBr 2Cl was less effective and the other two trihalomethanes were without effect. The activities of glycerophosphate acyltransferase, phosphatidate phosphatase and diacylglycerol acyltransferase were changed by the exposure to trihalomethanes. The effects of CHBr 2Cl and CHBr 3 were much more severe as compared to those of CHBrCl 2 and CHCl 3. The change in the enzyme activities could explain the alteration in the incorporation of [ 3H]glycerol into TG.

The fluorescence quenching of 1,4-bis[2-(5-phenyl-oxazolyl)]-benzene by bromomethanes

The interaction between the ground and excited states of 1,4-bis[2-(5-phenyloxazolyl)]-benzene and bromomethanes such as CBr 4, CHBr 3 and CH 2Br 2 were investigated in benzene. Distinct complex formation was not observed either in the ground state or in the excited states. The excited singlet and triplet states are deactivated by these bromomethanes. The triplet yield is increased on the addition of CHBr 3 or CH 2Br 2, whereas it is decreased on the addition of CBr 4. The fluorescence quenching rate constants k q at 23 °C were determined to be 1.6 × 10 10 M −1 s −1, 3.6 × 10 8M −1s −1 and 2.4 × 10 7M −1s −1 for CBr 4, CHBr 3 and CH 2Br 2 respectively. The rate constants k ST′ of the enhanced intersystem crossing associated with the fluorescence quenching were evaluated from emission—absorption flash photolysis experiments as 3.0 × 10 8 M −1s −1, 1.9 × 10 8 M −1s −1 and 5.1 × 10 7 M −1s −1 for CBr 4, CHBr 3 and CH 2Br 2 respectively. k ST′ increases with increasing number of bromine atoms contained in the quencher, so that the enhanced intersystem crossing is due to the external heavy-atom effect of the quencher. The apparent triplet yield for the quenching system depends not only on k ST′ but also on the rates of the other non-radiative processes. This is the reason why the apparent triplet yield does not necessarily increase on fluorescence quenching by bromomethanes.

A study of reaction conditions for the reaction of polybromobenzyl bromides and other benzyl bromides with metallic mercury

1. The reactions of pentafluoro-, pentachloro-, polybromo-, nitro-, and p-methoxy-substituted benzyl bromides with metallic mercury, leading to the synthesis of benzyl mercury compounds, have been investigated. The ease of the reaction increases as the number of bromine atoms on the benzene ring increases. Optimum reaction conditions have been recommended; these involve use of DMF as solvent in the presence of Br− ion catalysts. 2. The oxidative addition reaction of Hg (into the C-Br bond) is accompanied in many cases by side products of radical origin (dibenzyls, toluenes, benzaldehydes). The smoothest reactions were encountered with polybromo- and polychlorobenzyl bromide substrates.