Bromine Molecules Research Articles

Nearly Complete Oxidation of Au° in Hydrophobized Nanoparticles to Au3+ Ions by N-Bromosuccinimide

Au° atoms in hydrophobized gold nanoparticles were oxidized to Au3+ ions, nearly quantitatively, simply by treatment with N-bromosuccinimide and sonication. 1H NMR results indicate that the octadecylamine molecules are detached from the Au° surface by NBS. The bromine molecules released by NBS are suggested to be the species responsible for the oxidation of Au° to Au3+, which is supported by the observation that addition of molecular bromine also leads to similar results. A gratifying feature is that the Au3+ ions could be subsequently reduced back to Au nanoparticles.

Barrier-discharge excilamp on a mixture of krypton and molecular bromine and chlorine

Spectral and energy characteristics of a barrier-discharge excilamp on a mixture of krypton with bromine and chlorine molecules that emits in the range 200–300 nm are presented. The radiation spectrum contains the bands of the B → X transitions of the KrCl* (222 nm) and KrBr* (207 nm) molecules and the band of the D′ → A′ transition of the Br*2 molecule (291 nm). It is demonstrated that the bromine content must be higher than the chlorine content in the triple (Kr−Cl2−Br2) mixtures that are optimal with respect to the radiant power. A radiant power of 0.7 W and an efficiency of 3% are realized. A multiband barrier-discharge excilamp based on the triple mixture exhibits a potentially long lifetime.

Global Inorganic Source of Atmospheric Bromine

A few bromine molecules per trillion (ppt) causes the complete destruction of ozone in the lower troposphere during polar spring and about half of the losses associated with the "ozone hole" in the stratosphere. Recent field and aerial measurements of the proxy BrO in the free troposphere suggest an even more pervasive global role for bromine. Models, which quantify ozone trends by assuming atmospheric inorganic bromine (Bry) stems exclusively from long-lived bromoalkane gases, significantly underpredict BrO measurements. This discrepancy effectively implies a ubiquitous tropospheric background level of approximately 4 ppt Bry of unknown origin. Here, we report that I- efficiently catalyzes the oxidation of Br- and Cl- in aqueous nanodroplets exposed to ozone, the everpresent atmospheric oxidizer, under conditions resembling those encountered in marine aerosols. Br- and Cl-, which are rather unreactive toward O3 and were previously deemed unlikely direct precursors of atmospheric halogens, are readily converted into IBr2- and ICl2- en route to Br2(g) and Cl2(g) in the presence of I-. Fine sea salt aerosol particles, which are predictably and demonstrably enriched in I- and Br-, are thus expected to globally release photoactive halogen compounds into the atmosphere, even in the absence of sunlight.

A theoretical and experimental study of the double photoionisation of molecular bromine and a new double ionisation mechanism

Complete double photoionisation spectra of Br 2 have been measured at 30.4, 37.9 and 40.7 nm. The spectra are compared with high level relativistic calculations of the state energies and potential energy surfaces of Br 2 2 + carried out within a four-component relativistic framework. Excellent agreement is obtained between experimental and theoretical relative state energies which allows for an assignment of the main part of the spectrum. Spectroscopic constants and tunnelling lifetimes have been determined for quasi-bound states. From the experimentally determined electron distributions we deduce that a new form of dissociative autoionisation plays a major role in double photoionisation of bromine and other molecules where certain atomic ions are major fragmentation products.

Density functional study on the bromination of heteroelement-substituted acetylenes

The reactions of heteroelement-containing alkynes H3SiC≡CH and R3MC≡CPh [R3M = H3Si, Et3Si, Et3Ge, (MeO)3Si, (EtO)3Ge, N(CH2CH2O)3Si, N(CH2CH2O)3Ge, Bu3Sn] with one and two bromine molecules were studied in terms of the density functional theory. Transition states along reaction channels leading to products of both addition at the triple bond (cis- and trans-dibromoalkenes and 1,1-dibromoalkenes) and cleavage of the M-C≡ bond were localized.

Formation of polybromine anions and concurrent heavy hole doping in carbon nanotubes

Using density-functional theory calculations, we investigate the atomic and electronic structure of the bromine species encapsulated in carbon nanotubes. We find that the odd-membered molecular structures (Br3 and Br5) are energetically favored than the common Br2 molecule. The transformation from bromine molecules (Br2) into Br3 or Br5 is found to be almost barrierless. A strong electron transfer from the nanotube to the adsorbates, which has been doubtful in previous studies, is accompanied by the formation of such odd-membered polybromine anions. We suggest that the tip-opened carbon nanotube samples can be heavily hole-doped after exposure to Br2 gas.

Competing kinetic pathways in the bromine addition to allylic ethers in 1,2‐dichloroethane: Opposite temperature effects

AbstractThe kinetics of the electrophilic bromination of three allylic ethers in a nonprotic solvent, 1,2‐dichloroethane, has been investigated. Two of them followed a prevalent second‐order pathway, while the third one exhibited a classical, clean third order. The second‐order pathway in the first two olefins is attributed to electrophilic assistance of the ethereal oxygen to the attacking bromine molecule. In the molecular bromination of 2,4‐cis‐dimethyl‐8‐oxabicyclo[3.2.1]‐6‐octen‐3‐cis‐ol, opposite temperature dependences were found for the two different kinetic pathways. An exoergonic process for the second‐order reaction was explained by the lesser stability of the bromiranium–bromide ionic intermediate, compared to the bromiranium–tribromide in the third‐order profile. © 2007 Wiley Periodicals, Inc. 39: 197–203, 2007

Microstructure analysis of brominated styrene–butadiene rubber

AbstractThe bromine addition to the SBR double bonds in chloroform at 0°C has been investigated by FTIR, 1H NMR and DSC techniques. In this case, bromine molecules react exclusively with the polydiene double bonds and the polystyrene units are unaffected. The bromine reacts preferentially with 1,4‐trans double bonds of the polybutadiene segment of SBR. At low bromination level (below 15%) the bromine reacts mainly with the 1,4‐trans double bonds of SBR, while at higher bromination level (up to 30%) the bromine shows the most reactivity toward the vinylic double bond. Above 30%, the addition reaction occurs on 1,4‐trans double bonds. The microstructure of modified and unmodified styrene–butadiene copolymers were fully characterized by 1H NMR technique. Expanded regions have been utilized to resolve the complex 1H NMR spectrum and establish the compositional and configurational sequences of styrene–butadiene copolymers. POLYM. ENG. SCI., 47:87–94, 2007. © 2007 Society of Plastics Engineers

Spectroscopic Signatures of Halogens in Clathrate Hydrate Cages. 1. Bromine

We report the first UV-vis spectroscopic study of bromine molecules confined in clathrate hydrate cages. Bromine in its natural hydrate occupies 51262 and 51263 lattice cavities. Bromine also can be encapsulated into the larger 51264 cages of a type II hydrate formed mainly from tetrahydrofuran or dichloromethane and water. The visible spectra of the enclathrated halogen molecule retain the spectral envelope of the gas-phase spectra while shifting to the blue. In contrast, spectra of bromine in liquid water or amorphous ice are broadened and significantly more blue-shifted. The absorption bands shift by about 360 cm-1 for bromine in large 51264 cages of type II clathrate, by about 900 cm-1 for bromine in a combination of 51262 and 51263 cages of pure bromine hydrate, and by more than 1700 cm-1 for bromine in liquid water or amorphous ice. The dramatic shift and broadening in water and ice is due to the strong interaction of the water lone-pair orbitals with the halogen sigma* orbital. In the clathrate hydrates, the oxygen lone-pair orbitals are all involved in the hydrogen-bonded water lattice and are thus unavailable to interact with the halogen guest molecule. The blue shifts observed in the clathrate hydrate cages are related to the spatial constraints on the halogen excited states by the cage walls.

A glow-discharge-pumped broadband short-wavelength lamp

A broadband ultraviolet-vacuum-ultraviolet lamp, which emits at wavelengths of 150–300 nm, and its output characteristics are described. The lamp is excited by a longitudinal glow discharge, which is initiated in a quartz tube with an inner diameter of 1.4 cm and an interelectrode distance of 10 cm. The tube is filled with a He/Br2 working mixture at a total pressure of 0.2–1.0 kPa. The lamp emission spectrum consists of a 163.3-nm spectral line of bromine atoms and continuum in the spectral region 165–300 nm. A continuum is formed as a result of an overlap of broad emission bands of bromine molecules. The total emission power of the lamp reaches 4–5 W at an electric power of up to 60 W. The lamp’s efficiency is 5–10%, and its service life in the gas-static mode is 300–400 h.

Theoretical DFT Study on the Interaction of NO and Br2 with the Pt(111) Surface.

Density functional calculations were performed at the B3LYP level using combined basis sets for the NO and bromine interactions with the Pt(111) surface mimicked by the two-layer Pt10 cluster model. It explains well an attractive bonding interaction not only for bromine and Pt(111) but also for all three adsorption modes of NO on the Pt(111) surface. In accordance with the experimental observations, the calculations predict that the first peak in the IR spectra appears at around 1515 cm(-)(1) at the initial stage of low NO coverage, while it would shift to 1707 cm(-)(1) at high NO coverage. The bonding of NO on the 3-fold hollow fcc and hcp sites of Pt(111) proceeds via predominant back-donation interactions, while for the on-top adsorption, both the donation and back-donation interactions become equally important. Energetic criteria show also that the STM tip (made from Pt and Ir alloys) immersed into a bromine solution may contain only dissociated bromine atoms that bind strongly with the surface Pt atoms. As a result, the νBrBr stretching vibration mode for the bromine molecule may not be seen in the IR spectra because of its dissociation into adsorbed atoms. This leads to an appearance of a blue shifted band centered at ca. 202 cm(-)(1).

Emission characteristics of a high-power glow discharge plasma in a mixture of inert gases with bromine and iodine vapor

The results of an investigation of the UV radiation from the plasma of a dc glow discharge in mixtures of inert gases with bromine and iodine molecules are presented. The current-voltage and spectral characteristics of a longitudinal glow discharge with a power of 10–250 W are studied. The power and the efficiency of the total UV radiation of the plasma, as well as the power of radiation at the spectral line of the iodine atom at 206.2 nm, are optimized as functions of the power deposited into the plasma and the composition of the gas mixture. In active media based on Kr-Br2 mixtures, the molecular emission of the plasma was represented by bands at 207 (KrBr(B-X)) and 289 nm (Br 2 * ), while, in He-Xe-I2 mixtures, it was represented by bands at 253 (XeI(B-X)) and 342 nm (I2).

A DFT Investigation of Alkyne Bromination Reactions

[Structure: see text]. A DFT calculation study of the addition reaction between molecular bromine and the number of symmetrical or unsymmetrical substituted alkynes 1 (R-CC-R'), where R = R' = H (1a), Me (1b), t-Bu (1c), or Ph (1d), or R = H and R' = Me (1e), t-Bu (1f), or Ph (1g), was performed. Two possible reactions were checked: (a) the reactions suitable for the gas-phase interactions, which start from a 1:1 Br2-alkyne pi-complex and do not enter into a 2:1 Br2-alkyne pi-complex; and (b) the processes passing through a 2:1 Br2-alkyne pi-complex, which look more realistic for the reactions in solutions. The structures of the starting reactants and the final products as well as the possible stable intermediates have been optimized. The transition states of the predicted process have been found. Both trans- and cis-dibromoalkenes (2 and 3) may ensue without the formation of ionic intermediates from a pi-complex of two bromine molecules with the alkyne (solution reactions). The geometry around the double bond forming in dibromoalkenes strongly depends on the nature of the substituents at the triple bond. The "cluster model" was also used for the prediction of solvent influence on the value of the activation barrier of the but-2-yne (1b) bromination reaction.

Search for Stratospheric Bromine Reservoir Species: Theoretical Study of the Photostability of Mono-, Tri-, and Pentacoordinated Bromine Compounds

Previous work has shown that pentacoordinated bromine compounds have their lowest excited electronic states shifted to the blue relative to monocoordinated bromine molecules, and that this shift may be large enough to render them photostable in the lower stratosphere. Our earlier work has also shown that certain pentacoordinated bromine compounds are thermodynamically stable relative to their mono- or tricoordinated isomers, suggesting that if a bromine stratospheric reservoir species exists, it may be a pentacoordinated compound. In this study we have examined the singlet and triplet excited electronic states of several bromine compounds, using time dependent density functional theory, to assess their photostability under stratospheric conditions and in order to elucidate the nature of lowest excited states in mono-, tri-, and pentacoordinated bromine molecules. The triplet states have been included due to the strong spin-orbit mixing in bromine. We have found several pentacoordinated bromine/oxygen compounds that could be photostable in the lower stratosphere, but we have also found that monovalent bromine compounds where the bromine atom is bonded to an atom with no lone-pair p-electrons is far and away the most photostable. Attachment/detachment electron density plots have been useful in ascertaining the nature of the excited electronic states and their likely path to photodissociation.

Metallization of the semiconducting carbon nanotube by encapsulated bromine molecules

We use ab initio density-functional calculations to investigate the electronic structure of the bromine-adsorbed carbon nanotubes. When a Br 2 molecule is inside the (10,0) carbon nanotube, a trace of electron charge transfers from the nanotube to the Br 2 adsorbate, resulting in an increased Br–Br bond length. When the supercell contains two Br 2 molecules, total energy calculations reveal the formation of a linear chain of bromine atoms inside the carbon nanotube. Electron transfer from the nanotube to the atomic chains of the bromine adsorbates is much enhanced even in large-diameter nanotubes. We suggest that an exposure of the tip-opened carbon nanotube samples to a modest Br 2 partial pressure could result in a strong hole-doping of the nanotube, which makes the semiconducting nanotubes nearly metallic.

Band gap sensitivity of bromine adsorption at carbon nanotubes

We report results of our first-principles investigation on the energetics and electronic structures of bromine-adsorbed carbon nanotubes. While the bromine molecule binds preferentially to the outer wall of metallic nanotubes, the binding energy of adsorbed atomic bromines are found to depend on the radius as well as the energy gap. A recent experiment on the nanotube separation using bromines is discussed based on our computational data. The formation of strong C–Br chemical bonds at the zigzag edge of graphite demonstrates a close relationship between the density of states at the Fermi level and the binding strength.

Synthesis of four isomers of parinaric acid

A simple and reliable method for synthesizing four isomers of parinaric acid from α-linolenic acid (ALA) in high yields is described. The methylene-interrupted, cis triene system (1,4,7-octatriene) of ALA and common to other naturally occurring polyunsaturated fatty acids was transformed to a conjugated tetraene system (1,3,5,7-octatetraene). The synthesis involves bromination of ALA using 0.l M Br 2 in a saturated solution of NaBr in methanol, esterification of the fatty acid dibromides, double dehydrobromination by 1,8-diazabicyclo[5.4.0]undec-7-ene and saponification of the conjugated esters to a mixture of free conjugated acids. Addition of one molecule of bromine to the 12,13-double bond of ALA and subsequent dehydrobromination produces α-parinaric acid (9Z,11E,13E,15Z-octadecatetraenoic acid); addition of Br 2 to the 9,10-double bond or 15,16-double bond and then dehydrobromination and rearrangement yields 9E,11E,13E,15Z-octadecatetraenoic or 9E,11E,13E,15Z-octadecatetraenoic acids, respectively. The mixture of parinaric acid isomers is obtained in 65% yield, and the isomers can be purified by preparative HPLC; alternatively, the isomers can be converted by base catalyzed cis–trans isomerization (or by treatment with I 2) to exclusively β-parinaric acid (9E,11E,13E,15E-octadecatetraenoic acid). The various parinaric acid isomers were characterized by 1 H NMR, 13 C NMR, UV, GLC, HPLC and mass spectrometry.

Reaction of Some Dibromomethyl‐Substituted Cyclohexadienones with Molecular Bromine.

AbstractFor Abstract see ChemInform Abstract in Full Text.

The first example of bromination of aromatic compounds with unprecedented atom economy using molecular bromine

Bromination of organic compounds is usually effected using equimolar ratios of bromine with the substrate. The generated HBr is used either in the preparation of value added brominated products or is disposed as waste, causing serious environmental problems. A catalyst for an inbuilt recycle of HBr by oxidation and subsequent bromination of the organic compounds has been designed and developed. The efficacy is demonstrated in the production of tetrabromobisphenol-A (TBBA) in an integrated approach of bromination coupled with oxybromination of bisphenol-A (BA), aimed at utilisation of both bromine atoms of the bromine molecule. Here 2.05 mol of bromine and 2.1 mol of H 2O 2 as an oxidant were used per mol of BA catalysed by tungstate-exchanged Mg-Al layered double hydroxide (LDH-WO 4) with unprecedented atom economy in a biphase system comprising dichloroethane and water under auto-reflux for the first time. This is quite impressive when compared with the currently used process, in which >4 mol of bromine per mol of BA is being used. The TBBA thus obtained allows in-process control of pollutants in the integrated process and conforms to all the 14 specifications that include American Public Health Administration (APHA) colour values and hydrolysable bromide, very important specifications for marketability. Effects of mole ratios of H 2O 2/BA and Br 2/BA, concentration of the catalyst, solvent and temperature on yields and quality of the product were studied in an effort to optimise the parameters. Environmental and economical factors of the process evolved are highlighted. The Mg-Al and Ni-Al-LDH-WO 4 catalysts used in the above process and their precursors were characterised by means of powder-XRD, TGA-DTA, FT-IR spectroscopy, scanning electron microscopy (SEM), and particle size distribution. The heterogeneity and reusability of the Mg-Al-LDH-WO 4 were well established. The catalyst displayed consistent activity and selectivity for four recycles.

Reaction of Some Dibromomethyl-Substituted Cyclohexadienones with Molecular Bromine

4-Dibromomethyl-4-methyl-2,5-cyclohexadienone and its 2- and 3-methyl-substituted derivatives react with an equimolar amount of molecular bromine in carbon tetrachloride, yielding vinyl bromination products at the α-position with respect to the carbonyl group. The reaction of 4-dibromomethyl-3,4-dimethyl-2,5-cyclohexadienone with a large excess of bromine, apart from the vinyl bromination product, gives the corresponding 3-bromomethyl and 3-dibromomethyl derivatives. 4-Dibromomethyl-2,4-dimethyl-2,5-cyclohexadienone takes up bromine molecule at the C 2 IC 3 double bond.