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Focuses on the formation of a reaction complex from a van der Waals dimer precursor, HBr.I[sub 2], monitored with time resolution using standard pump-probe spectroscopy. Initiation of the reaction in an attractive region of an excited electronic state with insufficient energy to fragment; Detection of an isotope effect; Temporal discrepancies in risetimes.

The quasiclassical trajectory (QCT) method was used to study the dynamics of the OH(X 2Π) and OD(X 2Π)+HBr chemical reactions on an empirical potential energy surface (PES). The main emphasis in the calculation was the vibrational energy distributions of H2O (and HDO) and the magnitude and temperature dependence of the rate constant. However, this PES also serves as a generic model for the dynamics of direct H atom abstraction by OH radicals. Since this PES has no formal potential energy barrier, variational transition-state theory was used to obtain rate constants for comparison with the QCT calculations and experimental results. The parameters of the potential energy surface were adjusted to obtain better agreement with the experimentally measured fraction of H2O vibrational energy, 〈fV(H2O)〉=0.6, without significantly changing the entrance channel. No isotope effect for the partition of energy to H2O vs HOD was found. Analysis of the trajectories indicates that the reactant OH(OD) bond is a spectator, until the system begins to traverse the exit channel, i.e., until H2O(HDO) starts to retreat from Br. The calculated average energy in the bending mode of H2O or HDO was lower than the experimental value, and the PES could not be adjusted in its present form to give a significantly larger fraction of energy to the bending mode. A nonlinear 1:2 resonance between the OH local mode and the bending mode was found to be the main mechanism leading to bending mode excitation for this PES. The QCT rate constant is larger than the value calculated by quantum methods or variational transition-state theory. This difference may arise from the absence of a zero point energy constraint in the QCT calculation. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Quantum scattering calculations are reported for the reactions OH+HCl→H2O+Cl and OH+HBr→H2O+Br. The rotating bond approximation is used. This involves the explicit treatment of the bending vibration and local OH stretching vibration in H2O together with the vibration of HX (X=Cl,Br) and rotation of OH. Simple potential energy surfaces for the reactions are used which contain an accurate potential for H2O. The transition state of the potential for the OH+HCl reaction agrees quite well with ab initio data. The most likely product vibrational state of H2O is the ground state for the OH(j=0)+HCl reaction, and the combination band that has one quantum of energy in the H2O bending mode and one quantum in the local OH stretching mode of H2O for the OH(j=0)+HBr reaction. The reaction cross sections are found to depend on (2j+1)-1, where j is the initial rotational quantum number of OH. This results in a T-1/2 dependence in the rate constant for the OH+HBr reaction at low temperatures, in agreement with experiment. [ABSTRACT FROM AUTHOR]

The rate constants for the reactions of H+Br2 and D+Br2 were measured by employing a pulse radiolysis–resonance absorption technique. The rate constants could be expressed by the following Arrhenius equations between 214 and 295 K: k(H+Br2) =6.7×10-10 exp(-680/T), k(D+Br2)=6.0×10-10 exp(-720/T), in units of cm3 s-1. Sudden transition state theoretical calculations were performed on the basis of modified LEPS surfaces. The calculated results were compared with the experimental ones. [ABSTRACT FROM AUTHOR]

Time resolved resonance fluorescence detection of O(3P) and H(2S) has been employed in conjunction with pulsed laser photolysis of O3/HX/He mixtures to determine absolute rate coefficients and product yields for reactions of O(1D) with HCl(1) and HBr(2) at 297 K. Total rate coefficients for O(1D) removal are found to be, in units of 10-10 cm3 molecule-1 s-1, k1=1.50±0.18 and k2=1.48±0.16, where the quoted errors are 2σ and represent precision only. The absolute accuracy of these rate coefficients is estimated to be ±20%. Formation of O(3P)+HX is found to account for 9%±5% of the overall rate of reaction (1) and 20%±7% of the overall rate of reaction (2). Formation of H(2S)+XO is found to account for 24%±5% of the overall rate of reaction (1) but <4.5% of the overall rate of reaction (2). By difference, the OH+X(2P) channel accounts for 67%±10% of the overall rate of reaction (1) and 80%±12% of the overall rate of reaction (2). [ABSTRACT FROM AUTHOR]

An efficient approach for α-bromination of aryl alkyl ketones, utilizing a system consisting of aqueous hydrobromic acid as bromine source, sodium nitrite–KI as catalyst, and air as terminal oxidant, has been developed. The method offers advantages of selective monobromination, mild reaction conditions, broad substrate scope, and good yield. The use of air as the terminal oxidant makes the reaction very attractive from both economical and environmental viewpoints. [ABSTRACT FROM AUTHOR]

We report rovibrationally selected differential cross sections (DCSs) of the benchmark reaction H + D2 → HD(v′ = 3, j′ = 4-10) + D at a collision energy of 3.26 eV, which exceeds the conical intersection of the H3 potential energy surface at 2.74 eV. We use the PHOTOLOC technique in which a fluorine excimer laser at 157.64 nm photodissociates hydrogen bromide (HBr) molecules to generate fast H atoms and the HD product is detected in a state-specific manner by resonance-enhanced multiphoton ionization. Fully converged quantum wave packet calculations were performed for this reaction at this high collision energy without inclusion of the geometric phase (GP) effect, which takes into account coupling to the first excited state of the H3 potential energy surface. Multimodal structures can be observed in most of the DCSs up to j′ = 10, which is predicted by theory and also well-reproduced by experiment. The theoretically calculated DCSs are in good overall agreement with the experimental measurements, which indicates that the GP effect is not large enough that its existence can be verified experimentally at this collision energy. [ABSTRACT FROM AUTHOR]

An efficient one-pot procedure for the synthesis of propargyl alcohol derivatives from allyl alcohol derivatives has been developed. The key to this transformation from a C-C double bond to a C-C triple bond is that hydrogen bromide elimination from 1,2-dibromoalkanes that contain a neighboring oxygen functional group is promoted by the inductive electron-withdrawing effect of the oxygen functional group. In the one-pot reaction, tetrabutylammonium hydroxide was the best base, and the addition of molecular sieves 13X also promoted the reaction. [ABSTRACT FROM AUTHOR]

Wereport reaction cross sections, energy disposal, and rate constantsfor the OH + HBr → Br + H2O and OH + DBr →Br + HDO reactions from quasiclassical trajectory calculations usingan ab initio potential energy surface [de Oliveira-Filho, A. G. S.; Ornellas, F. R.; Bowman, J. M.J. Phys. Chem. Lett.2014, 5, 706−712]. Comparison with available experiments are made and generally showgood agreement. [ABSTRACT FROM AUTHOR]

1,1-Dihydroperoxides were converted into 1,2,4,5-tetraoxanes through condensation with the corresponding ketones in 36-91% yields using phosphomolybdic acid as the catalyst and anhydrous MgSO4 as the water scavenger. [ABSTRACT FROM AUTHOR]

2-Phenacyl-1 H-benzimidazoles were prepared by the acylation of 2-methylbenzimidazole using aroyl chlorides with subsequent alcoholysis or aminolysis of the N,C,O-triacylation products obtained. Treatment of the 2-phenacyl-1 H-benzimidazoles with hydrobromic acid gave the corresponding salts. The structure of the products was supported by IR, H and C NMR, and HMBC spectroscopy as well as by quantum-chemical calculations. 2-Phenacyl-1 H-benzimidazoles in DMSO-d solution were found to display predominantly imino-enamino tautomerism, while their salts were found to display predominantly keto-enol tautomerism. [ABSTRACT FROM AUTHOR]

Abstract: Thermal degradation of mixture of tetrabromobisphenol A (TBBA) and metal oxide (ZnO, Fe2O3, La2O3, CaO and CuO) has been studied under inert atmosphere. The formation of hydrogen bromide and brominated organic compounds is observed for pyrolysis of TBBA. The addition of metal oxide gives rise to considerable suppression of HBr as well as brominated organic compounds. The suppression owes to the bromination of oxides. The influence of oxide on thermal degradation of TBBA is discussed with emphasis on the conversion of bromine. [Copyright &y& Elsevier]

Reaction of quinoline with HBr and CuBr2 generales a mixture of two compounds, (quinolinium)2CuBr4 . 2H2O (1) and (quinolinium)2CuBr4 (2) for which single-crystal X-ray structures have been solved. Compound 1 crystallizes in the monoclinic space group C2/c as layers of tetrabromocuprate ions which are separated by intervening layers of quinolinium ions. Compound 2 crystallizes in the triclinic space group P¯. Magnetic data analysis reveals that 1 behaves as a 2D-quantum Heisenberg antiferromagnet wilh 2J/kB = -6.17(3) K within the layers. High field magnetization data allow temperatures suggests Ihat TN must be less than 1.8 K for 1, yielding a figure of merit lkB TN/ 2J/ < 0.29, which indicates excellent isolation between the layers. Magnetic exchange in compound 2 was much weaker and was fit to a linear chain antiferromagnet with 2511k8 = —1.59(3) K. [ABSTRACT FROM AUTHOR]

Our prior research indicates that hydrogen bromide (HBr) evolved during thermal decomposition of tetrabromobisphenol A (TBBPA) can be utilized as a reagent for selective bromination and evaporation of zinc oxide. The present work investigated dependency of the bromination reaction on time at selected temperatures using a laboratory-scale furnace. The formed solid, condensed, and gaseous products were analyzed by X-ray diffraction analysis, electron probe microanalysis, inductively coupled plasma analysis, ion chromatography, and gas chromatography coupled with mass spectrometry. Results indicate that the bromination rate is strongly dependent on heating time. This dependency is a direct consequence of progress in the decomposition of TBBPA, which provides inorganic bromine suitable for the reaction. The bromination rate increases with time until the bromine source is depleted. The process is shorter at higher applied temperatures and appears instantaneous at 310 °C and above. However, the maximum bromination yield is independent of the applied conditions and ranges from 64 to 70%. Additionally, the influence of oxidizing conditions on the bromination reaction and the effect of ZnO on decomposition of TBBPA were investigated in this study. [ABSTRACT FROM AUTHOR]

Abstract: In this study, we carried out an investigation of the etching characteristics (etch rate, selectivity to Si) of ZrO2 thin films in the HBr/SF6 high density plasma (HDP) system. The maximum etch rate of 54.8 nm/min for ZrO2 thin films was obtained at HBr(25%)/SF6(75%) gas mixing ratio. At the same time, the etch rate was measured as function of the etching parameters such as HDP source power, bias power, and chamber pressure. The X-ray photoelectron spectroscopy analysis showed an efficient destruction of the oxide bonds by the ion bombardment as well as showed an accumulation of low volatile reaction products on the etched surface. Based on these data, the ion-assisted chemical reaction was proposed as the main etch mechanism for the SF6-containing plasmas. [Copyright &y& Elsevier]

The synthesis and reactivity of the thiophyne and furyne clusters [Ru3(CO)7(μ-dppm)(μ3-η2-C4H2E){μ-P(C4H3E)2}(μ-H)] (E = S, O) is reported. Addition of P(C4H3E)3to [Ru3(CO)10(μ-dppm)] (1) at room temperature in the presence of Me3NO gives simple substitution products [Ru3(CO)9(μ-dppm){P(C4H3E)3}] (E = S, 2; E = O, 3). Mild thermolysis in the presence of further Me3NO affords the thiophyne and furyne complexes [Ru3(CO)7(μ-dppm)(μ3-η2-C4H2E){μ-P(C4H3E)2}(μ-H)] (E = S, 4; E = O, 6) resulting from both carbon-hydrogen and carbon-phosphorus bond activation. In each the C4H2E (E = S, O) ligand donates 4-electrons to the cluster and the rings are tilted with respect to the μ-dppm and the phosphido-bridged open triruthenium unit. Heating 4at 80 °C leads to the formation of the ring-opened cluster [Ru3(CO)5(μ-CO)(μ-dppm)(μ3-η3-SC4H3){μ-P(C4H3S)2}] (5) resulting from carbon-sulfur bond scission and carbon-hydrogen bond formation and containing a ring-opened μ3-η3-1-thia-1,3-butadiene ligand. In contrast, a similar thermolysis of 3affords the phosphinidene cluster [Ru3(CO)7(μ-dppm)(μ3-η2-C4H2O){μ3-P(C4H3O)}] (7) resulting from a second phosphorus-carbon bond cleavage and (presumably) elimination of furan. Treatment of 4and 6with PPh3affords the simple phosphine-substituted products [Ru3(CO)6(PPh3)(μ-dppm)(μ3-η2-C4H2E){μ-P(C4H3E)2}(μ-H)] (E = S, 8; E = O, 9). Both thiophyne and furyne clusters 4and 6readily react with hydrogen bromide to give [Ru3(CO)6Br(μ-Br)(μ-dppm)(μ3-η2-η1-C4H2E){μ-P(C4H3E)2}(μ-H)] (E = S, 10; E = O, 11) containing both terminal and bridging bromides. Here the alkynes bind in a highly unsymmetrical manner with one carbon acting as a bridging alkylidene and the second as a terminally bonded Fisher carbene. As far as we are aware, this binding mode has only previously been noted in ynamine complexes or those with metals in different oxidation states. The crystal structures of seven of these new triruthenium clusters have been carried out, allowing a detailed analysis of the relative orientations of coordinated ligands. [ABSTRACT FROM AUTHOR]

Abstract: Time-dependent wave packet calculations have been performed for the O(1D)+HBr→BrO+H and O(1D)+HBr→OH+Br reactions. The state-to-state and state-to-all reaction probabilities for total angular momentum J =0 have been calculated. The probabilities for J >0 have been estimated from the J =0 results by using J-shifting approximation based on a capture model. Then, the integral cross-sections and thermal rate constants have been calculated. The calculations show that the initial state-selected reaction probabilities are dominated by resonance structures. The reaction cross-section also manifests resonances and is a decreasing function of the translational energy and the thermal rate constants are not sensitive to the temperature. [Copyright &y& Elsevier]

General purpose poly(styrene) is a large volume commodity polymer widely used in a range of applications. For many of these the presence of an additive to impart some flammability resistance is required. Most commonly, brominated aromatics are used for this purpose. As the polymer undergoes combustion these compounds decompose to generate bromine atoms and/or hydrogen bromide which escape to the gas phase and trap flame propagating radicals. While these species are effective in inhibiting flame propagation they present the opportunity for loss of halogen to the atmosphere. For this reason, the use of these compounds is being limited in some parts of the world. Phosphorus compounds, on the other had, impart a flame retarding influence by promoting char formation at the surface of the burning polymer. This prevents heat feedback to the polymer and consequent pyrolysis to generate fuel fragments. The combination of both bromine and phosphorus present in a single compound might generate a superior flame-retarding additive in that both modes of retardancy might be promoted simultaneously. Should this be the case smaller amounts of additive might be necessary to achieve a satisfactory level of flame retardancy. A series of such additives, brominated aryl phosphates, has been synthesized and fully characterized spectroscopically. Blends of these additives, at various levels, with poly(styrene) have been examined by DSC, TG and in the UL-94 flame test. The flammability of the polymer is dramatically diminished by the presence of the additive. [ABSTRACT FROM AUTHOR]

The homocoupling of bromide compounds was successfully performed in one pot by a combination of metallic magnesium and a catalytic amount of iron salts. The binary catalytic system differentiates itself from other homocoupling reactions catalyzed by iron salts in that it requires neither the in situ preparation of Grignard reagent nor the addition of a 1,2-dihalogen compound as an oxidant. Various aromatic and alkyl bromides underwent the homocoupling smoothly affording the corresponding symmetrical hydrocarbon compounds in moderate to excellent yields. [ABSTRACT FROM AUTHOR]

The article focuses on the study which discusses the behavior of 2-{(E)-2-[furan-(thiophen)-2-yl]ethenyl}-1,3-benzothiazoles in reactions with strong electrophiles. Topics include the impact of the thiazole ring on the furan or thiophene ring reactivity, the addition of bromine to the exocyclic double bond in the presence of subsequent elimination of hydrogen bromide, and the procedure used for the synthesis of the said compounds.

Abstract: Gallium indium zinc oxide (GIZO) thin films patterned with a photoresist (PR) were dry etched using inductively coupled plasma (ICP) of HBr/Ar gas. The etch rate of the GIZO films and the etch selectivity of GIZO/PR decreased gradually as HBr gas was added to Ar. In addition, the etch rate increased with increasing ICP power and dc-bias voltage to the substrate. However, the etch rate was decreased with increasing gas pressure. X-ray photoelectron spectroscopy and atomic force microscopy revealed Br compounds on the film surface during the etching process. It can be concluded that the high density plasma etching of GIZO films using HBr/Ar gas follows a sputtering etching mechanism with the assistance of a chemical reaction on the films. [ABSTRACT FROM AUTHOR]