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Fixing the greenhouse gas CO2 through epoxide helps to mitigate worldwide ecological troubles. The applications of metal‐free and solvent‐free catalysts remain a challenge for CO2 catalytic conversion. In this work, an array of quaternary ammonium salts derived from polyethyleneimine with hydroxyl groups ([PEI‐GDMAB‐Cn]Br) were constructed by the reaction of branched PEI with a molecular weight of 10000 and glycidyl alkyl dimethylammonium bromide. A range of experiments were designed to demonstrate that [PEI‐GDMAB‐Cn]Br can be considered as a valid metal‐free and solvent‐free homogeneous catalyst for the CO2‐epoxide cycloaddition reaction. Among of [PEI‐GDMAB‐Cn]Br, [PEI‐GDMAB‐C18]Br catalyzed the model reaction of CO2 and epichlorohydrin under optimized reaction conditions (T=80 °C, 1.0 atm CO2, catalyst 1 mol%, ECH 15 mmol, 16 h) and the conversion achieved at 97.5 %. Moreover, the catalyst exhibited stable reusability and broad substrate applicability, which was used in the following cycle succinctly, because of self‐separated properties by temperature control. The [PEI‐GDMAB‐C18]Br catalyzed reaction process was detected as a pseudo‐first‐order reaction after kinetic studies and an Ea was calculated to be 50.65 kJ/mol. A combinatorial catalytic mechanism of hydrogen bonding and bromide ions is suggested to explain the remarkable catalytic performance of this bifunctional catalyst. [ABSTRACT FROM AUTHOR]

During the synthetic studies toward 5,6,7,3′,4′-monomethoxytetrahydroxyflavones, a concise pedalitin synthesis procedure was achieved. As previously reported, 6-hydroxy-2,3,4-trimethoxyacetophenone was prepared by Friedel–Crafts acylation of 1,4-dihydroxy-2,6-dimethoxybenzene with boron trifluoride diethyl etherate in acetic acid. When aldol condensation of 6-hydroxy-2,3,4-trimethoxyacetophenone 2b with vanillin was performed in basic conditions, it produced 2′-hydroxychalcone 3b, and, surprisingly, along with 3-hydroxyflavone 4 in a considerable amount. We propose that this oxidative cyclization is presumably due to the contribution of a quinone methide, likely to be subjected to aerobic oxidation. The chalcone was then subjected to oxidative cyclization with iodine in dimethyl sulfoxide to afford flavone 5 in good yield. To our delight, serial demethylation of the three methoxy groups at the 5-, 6-, and 3′-positions of 5 proceeded smoothly to produce pedalitin 1, under hydrogen bromide solution (30% in acetic acid). The crystal structures of 3-hydroxyflavone 4 and pedalitin tetraacetate 6 were unambiguously determined by X-ray crystallography. [ABSTRACT FROM AUTHOR]

The hydrohalogenation of olefins is one of the most straightforward methods to access alkyl halides. Despite safety hazards, using pure hydrogen halide gas remains the most atom economic way of performing hydrohalogenation reactions. In this work, we describe the solvent‐free hydro‐ and deuteriohalogenation of olefins using down to near‐stoichiometric amounts of hydrogen and deuterium halide gas. Two‐chamber reactors are employed as an enabling platform to access these reactive gases in a laboratory setting. Ex situ generation from inexpensive and readily available precursors provides on‐demand access to these gases (hydrogen chloride, deuterium chloride, hydrogen bromide, deuterium bromide, hydrogen iodide, and deuterium iodide) with precise stoichiometric control. Upon chemo‐ and regioselective conversion of the substrate, the halide products may be isolated without the need for any work‐up or purification steps making it a clean and labor‐, waste‐ and cost‐effective method. [ABSTRACT FROM AUTHOR]

Synthesis and characterization of poly(β-alanine-b-vinyl benzyl-g-vinyl chloride) [PBA-b-(PVB-g-PVC)] block-graft copolymer was done by reversible addition-fragmentation chain transfer polymerization and 'click' chemistry. For this, poly-β-alanine with a vinyl end group was synthesized by hydrogen transfer polymerization of acrylamide. Bromine-terminated poly-β-alanine (PBA-Br) was obtained by treating the synthesized poly-β-alanine with hydrogen bromide. Poly-β-alanine ethyl xanthate (macro-RAFT agent) was synthesized using PBA-Br and potassium ethyl xanthate. Poly(β-alanine-b-vinyl benzyl chloride) [poly(BA-b-VBC)] block copolymer was obtained by reversible addition-fragmentation chain transfer polymerization of macro-RAFT agent with vinyl benzyl chloride. Azido-terminated poly(β-alanine-b-vinyl benzyl chloride) [poly(BA-b-VBC)-N3] was synthesized by the reaction of poly(BA-b-VBC) with sodium azide. Alkyne-terminated polyvinyl chloride (PVC-propargyl) was obtained by treating polyvinyl chloride with propargyl alcohol. Finally, the synthesis of PBA-b-(PVB-g-PVC) block-graft copolymer was carried out by the 'click' chemistry method of poly(BA-b-VBC)-N3 and PVC-propargyl. The products were characterized by various spectroscopic and thermal methods. [ABSTRACT FROM AUTHOR]

The present study explores the renewable route to synthesize AA-type monomers for condensation polymerization, namely adipic and azelaic acid, from linoleic acid (LA) using a bromide-promoted transition metal catalyst. For this, liquid-phase catalytic oxidation of LA is carried out using a catalyst system involving the acetates of Cobalt(II) and Manganese(II) and hydrogen bromide in an acetic acid green solvent at temperature: 393–423 K and a pressure of 5.8–8.8 bar in the air. The oxidation products are confirmed by a gas chromatography-mass spectrometer and carbon dioxide analyzer. At the early stage of LA oxidation (i.e.,<5.0 h), the identified major products are malonic acid, azelaic acid, and adipic acid, whereas malonic acid decomposes to carbon dioxide after increasing oxidation time. The influence of process variables, i.e., (i) the loading of LA, bromide, Cobalt(II), and Manganese(II), (ii) temperature, and (iii) pressure on LA conversion and yield of adipic acid and azelaic acid have also been carried out, and the loading of catalyst, pressure, and temperature plays a vital role on the LA conversion and product yields. The temperature-dependent kinetic parameters are also determined, and the rate-controlling step for LA oxidation is analyzed and further extended by evaluating the Hatta number and enhancement factor. The lower values of the Hatta numbers and enhancement factors suggest that the oxidation using air is controlled by the diffusion of oxygen and reaction in the film, and adequate gas-liquid mixing will improve the rate of LA oxidation. [Display omitted] • Synthesis of renewable AA-type monomers from polyunsaturated fatty acid is developed. • Linoleic acid is oxidized with air to adipic and azelaic acid using a green solvent. • Linoleic acid oxidation path, rate-determining step, and kinetics are established. • Oxygen diffusion and reaction in the film control linoleic acid oxidation simultaneously. [ABSTRACT FROM AUTHOR]

[Display omitted] Hydrogen bromide (HBr) could substantially improve the quality of cesium lead bromide perovskite (CsPbBr 3) nanocrystals (NCs) and greatly enhance their optoelectronic performance. However, clarifying the role of HBr in the growth of CsPbBr 3 NCs has been a substantial challenge thus far. Herein, we design an in situ cryogenic photoluminescence system using liquid nitrogen to unravel the role played by HBr in the growth of CsPbBr 3 NCs. Compared with no HBr (∼40 s), HBr improves the nucleation rate of CsPbBr 3 NCs about two times (∼20 s), and its emission peak also exhibits a redshift of ∼30 nm. Thus, we conclude that HBr accelerates the nucleation rate of CsPbBr 3 NCs and extends their growth stage, affording the generation of large grains. Perovskite light-emitting diodes based on CsPbBr 3 NCs with added HBr also exhibit an outstanding performance. These outcomes provide new insights into the role of HBr in CsPbBr 3 NCs and help prepare high-quality CsPbBr 3 NCs for use in the fabrication of efficient CsPbBr 3 NC-based optoelectronic devices. [ABSTRACT FROM AUTHOR]

We investigated the photodissociation dynamics of vibrationally excited HBr molecules and clusters. The species were generated in a molecular beam and excited with an IR laser to a υ = 1 vibrational state. A subsequent ultraviolet (UV)-pulse with 243 nm radiation photolysed the molecules to yield H-fragments, which were resonantly ionized by the same UV-pulse (2 + 1 REMPI) and detected in a velocity map imaging (VMI) experiment. We performed action spectroscopy to distinguish between two expansion regimes: (i) expansion leading to isolated HBr molecules and (ii) generation of large (HBr)n clusters. Photodissociation of isolated HBr (υ = 1) molecules in particular J ro-vibrational states yielded faster H-fragments (by approximately 0.3 eV) with respect to the photodissociation of the ground state HBr (υ = 0). On the contrary, the IR excitation of molecules in (HBr)n clusters enhanced the yield of the H-fragments UV-photodissociated from the ground-state HBr (υ = 0) molecules. Our findings showthat these molecules are photodissociated within clusters, and they are not free molecules evaporated from clusters after the IR excitation. Nanosecond IR-UV pump-probe experiments show that the IR-excitation enhances the H-fragment UV-photodissociation yield up to ~100 ns after the IR excitation. After these long IR-UV delays, excitation of HBr molecules in clusters does not originate from the IR-excitation but from the UV-photodissociation and subsequent caging of HBr molecules in υ > 0 states.We show that even after ~100 ns the IR-excited larger (HBr)n clusters do not decay to individual molecules, and the excitation is still present in some form within these clusters enhancing their UV-photodissociation. [ABSTRACT FROM AUTHOR]

The effects of fuel moisture content (FMC) on emissions under both flaming and smoldering combustion conditions were studied for two different vegetative fuels, Douglas fir and lodgepole pine. A custom linear tube-heater apparatus was developed to produce steady-state emissions for two extreme FMC, recently live (FMC ∼ 50%) and fully dead and dry (FMC ∼ 3%). The concentrations of particulate matter and gaseous species measured using a TSI DustTrak and Fourier transform infrared spectroscopy (FTIR), respectively, showed a significant relationship with FMC for both flaming and smoldering combustion conditions. As expected, smoldering combustion showed larger production of CO, particulate matter, and unburned hydrocarbons when compared to flaming combustion. Unburnt hydrocarbons with higher emission factors produced during smoldering are CH 4 , C 2 H 2 , C 2 H 6 , C 4 H 10 , C 4 H 8 , C 2 H 4 , C 3 H 6 , CH 2 O 2 , C 3 H 4 O, CH 2 O, and CH 3 OH. This work also identified butane (C 4 H 10) and hydrogen bromide (HBr) as gaseous species, which have not been commonly reported in literature. Acrolein (C 3 H 4 O) was also identified during combustion and it has previously reported only by ion detection method. These emissions were further investigated by performing a carbon balance of the carbon in the fuel vs. emitted carbon, and these were compared to literature values. Flaming-mode emission factors significantly correlated with FMC, while FMC had little influence on emission factors for smoldering combustion, when considering the dry mass of the burned fuel. These variations were not the same for each fuel species, suggesting that the type of fuel plays an important role in burning behavior and emissions, possibly due to the chemical makeup of moist and recently live fuels. The results were discussed and compared with previous measurements, where good agreement was observed. This study provides an important emissions dataset for modeling emissions from common wildland fuels under varying FMC and combustion conditions. Novelty and significance This research investigates the impact of fuel moisture content (FMC) on emissions during flaming and smoldering combustion of Douglas fir and lodgepole pine. A unique linear tube-heater apparatus was developed to maintain steady-state emissions for extreme FMC levels of recently live (FMC 50%) and fully dead/dry (FMC 3%). The study reveals a noteworthy correlation between FMC and concentrations of particulate matter and gaseous species. This finding provides valuable insights into combustion behavior. It also identifies butane (C 4 H 10), acrolein (C 3 H 4 O), and hydrogen bromide (HBr), not commonly reported in literature. Additionally, the study highlights the varying influence of FMC on emission factors for flaming and smoldering combustion, indicating the pivotal role of fuel type in emissions. The dataset obtained serves as a valuable resource for modeling emissions from wildland fuels under diverse FMC and combustion conditions, advancing our understanding of fire behavior and environmental impacts. [ABSTRACT FROM AUTHOR]

The reaction of OH radicals with HBr plays a key role in atmospheric chemistry as the reaction, OH + HBr → Br + H2O, produces Br atoms that destroy ozone. The experimental measurements of the kinetic isotope effect of k(OH + HBr)/k(OH + DBr) found that the kinetic isotope effects are temperature-independent. However, previous quasi-classical trajectory calculations on an accurate ab initio potential energy surface showed that the kinetic isotope effect is temperature-dependent. By contrast, the present full-dimensional time-dependent quantum dynamics calculations on the same potential energy surface find that the kinetic isotope effect is temperature-independent, agreeing well with the experimental studies both qualitatively and quantitatively. Furthermore, the rate constants from both quantum dynamics and quasi-classical trajectory calculations have a peak at around 15 K whereas the experimental data are not available in this low temperature range. The good agreement of the temperature-dependence of kinetic isotope effects between the present quantum dynamics calculations and the experimental measurements indicates that the kinetic isotope effect of k(OH + HBr)/k(OH + DBr) should be temperature-independent and the peak of the rate constants from the theoretical calculations call for experimental measurements at a very low temperature range. [ABSTRACT FROM AUTHOR]

A series of novel 1-{8-[(het)arylmethoxy]-2-(trifluoromethyl)imidazo[1,2-a]pyrazin-6-yl}ethan-1-amine derivatives 11a–11h were synthesized by the O-alkylation of 1-[8-chloro-2-(trifluoromethyl)imidazo[1,2-a]pyrazin-6-yl]ethan-1-amine (9) with (het)arylmethyl alcohols 10a–10h in the presence of potassium carbonate. The reaction of commercially available ethyl 2-amino-2-sulfanylideneacetate (1) with triethyloxo-nium hexafluorophosphate(V) gave ethyl 2-(ethylsulfanyl)-2-iminoacetate (2) which was reacted with 3-amino-1,1,1-trifluoropropan-2-one hydrochloride to afford ethyl 4-(trifluoromethyl)-1H-imidazole-2-carboxylate (3). Treatment of Boc-protected alanine (4) with ethyl chloroformate and diazomethane produced tert-butyl N-(4-di-azo-3-oxobutan-2-yl)carbamate (5) which was converted to tert-butyl N-(4-bromo-3-oxobutan-2-yl)carbamate (6) via reaction with 48% hydrogen bromide. Compound 3 was reacted with 6 to give 1-{3-[(tert-butoxy-carbonyl)amino]-2-oxobutyl}-4-(trifluoromethyl)-1H-imidazole-2-carboxylic acid (7). Cyclization of the latter with ammonium hydrogen carbonate gave tert-butyl N-{1-[8-oxo-2-(trifluoromethyl)-7,8-dihydroimidazo-[1,2-a]pyrazin-6-yl]ethyl}carbamate (8), which was chlorinated with phosphoryl chloride to afford 9. All newly synthesized compounds were characterized by analytical spectral techniques like 1H NMR and LCMS, and their antibacterial activity was evaluated. [ABSTRACT FROM AUTHOR]

The bromination reaction of oligoetherdiol derived from allyl glycidyl ether by two procedures has been studied. It has been shown that one procedure provides monohydroxy conpounds and compounds containing no OH groups along with completely brominated oligoetherdiol. Their formation has been supposed to proceed via cyclodehydrobromination reaction due to elimination of one or two hydrogen bromide molecules from oligoetherdiol to form dioxane and dioxepane cyclic fragments. Conditions for complete bromination of oligodiol with retention of OH group functionality have been determined. [ABSTRACT FROM AUTHOR]

Introduced free radical scavengers and decreased gas crossover have a significant impact on a proton exchange membrane's (PEM's) chemical stability and performance. A novel PEM containing expanded polytetrafluoroethylene (ePTFE) functionalized with free radical scavengers and hydrophilic groups was designed and fabricated to enhance the PEM's electrochemical performance and chemical stability. ePTFE with unsaturated bonds was prepared by a chemical modification reaction using benzoin and potassium tert-butoxide; hydrogen bromide acted as a halogenating agent, and 3-mercapto-1,2,4-triazole worked as a free radical scavenger grafted onto the ePTFE molecular chains. The ePTFE was functionalized by hydrophilic groups, and radical scavenger groups led to perfluorosulfonic acid (PFSA) ionomers that had better compatibility with the modified ePTFE. The prepared membrane's gas permeability, proton conductivity, and electrochemical performance were thereby significantly improved. In addition, the generated free radicals were quickly eliminated by the free radical scavenger groups, thus enhancing the PEM's chemical stability. The microstructure, morphology, and performance of the PEM at various degradation levels were systematically evaluated. This work reveals that expanded polytetrafluoroethylene functionalized with free radical scavengers and hydrophilic groups not only reduced the hydrogen peroxide and active free radicals generated but also effectively eliminated the free radicals, thereby mitigating chemical degradation of the PEM. This paper provides a promising way to improve the proton conductivity and chemical stability of PEMs, offering excellent application potential for boosting fuel cell lifetime and performance. • The ePTFE membrane with hydrophilicity and radical scavenger groups were prepared. • The compatibility of ePTFE membrane with PFSA ionomer is improved. • The prepared PEM have less defect and possess better performance. • The chemical stability of PEM is significantly improved. [ABSTRACT FROM AUTHOR]

Vanadate‐dependent chloroperoxidase from Curvularia inaequalis catalyzes 5‐endo‐trig bromocyclizations of α‐allenols to produce valuable halofunctionalized furans as versatile synthetic building blocks. In contrast to other haloperoxidases, also the more challenging 5‐exo‐trig halocyclizations of γ‐allenols succeed with this system even though the scope still remains more narrow. Benefitting from the vanadate chloroperoxidase's high resiliency towards oxidative conditions, cyclization‐inducing reactive hypohalite species are generated in situ from bromide salts and hydrogen peroxide. Crucial requirements for high conversions are aqueous biphasic emulsions as reaction media, stabilized by either cationic or non‐ionic surfactants. [ABSTRACT FROM AUTHOR]

Numerous approaches to receptor fabrication have been introduced for supramolecular anion recognition, not only for academic purposes but also for their substantial application in environmental and biological fields. We highlight halide (X = Cl−/Br−) coordination-triggered self-assembly formation using two dipodal receptors, L1 and L2. This approach involves several non-covalent interactions, such as N–Hurea⋯X, C–Hphenyl⋯X, and C–Hn-TBA⋯X. Structural aspects of the anion-coordinated supramolecular architectures of L1 and L2 (1a, 1b, 2a, 2b) revealed 2 : 1 anion-receptor assembly formation in almost identical fashion, possessing different coordination numbers. Receptor L1 is composed of cyclohexane-urea motifs, whereas L2 comprised a piperazine-urea scaffold connected via a propyl spacer, which might be the backbone of the contrasting coordination number of the isostructural anionic ensembles. Solution-state 1H-NMR and photoluminescence studies corroborated the efficient encapsulation of chloride/bromide via hydrogen bonding interactions. FESEM studies depicted the variations in morphologies in the anion-recognition-triggered self-assembly of the receptors. [ABSTRACT FROM AUTHOR]

The aug‐cc‐pVTZ‐J basis set family is extended to include the fourth‐row p‐block elements Ga, Ge, As, Se, and Br. We use the established approach outlined by Sauer and coworkers (J. Chem. Phys. 115, 1324 [2001], J. Chem. Phys. 133, 054308 [2010], J. Chem. Theory Comput. 7, 4070 [2011], and J. Chem. Theory Comput. 7, 4077 [2011]) where the completely uncontracted aug‐cc‐pVTZ basis set is saturated with tight s‐, p‐, d‐, and f‐functions to form the aug‐cc‐pVTZ‐Juc basis set for the tested elements. The saturation is carried out on the simplest hydrides possible for the tested elements GaH, GeH4, AsH3, H2Se, and HBr until an improvement is less than 0.01% for all s‐, p‐, and d‐functions added. f‐Functions are added to an improvement less than or equal to 1.0% due to the computational expense these functions add. The saturated aug‐cc‐pVTZ‐Juc (26s16p12d5f) is then recontracted using the molecular orbital coefficients from self‐consistent field calculations on the simple hydrides to improve computational efficiency. During contraction of the basis set, we observe that the linear hydrogen bromide molecule has a slower convergence than the other tested molecules which sets a limit on the accuracy obtained. All calculations with the contracted aug‐cc‐pVTZ‐J [17s10p7d5f] gives results that are within 1.0% of the uncontracted results at considerable computational savings. [ABSTRACT FROM AUTHOR]

The chemical characterization of volcanic gas emissions gives insights into the interior of volcanoes. Bromine species have been correlated with changes in the activity of a volcano. In order to exploit the volcanic bromine gases, we need to understand what happens to them after they are outgassed into the atmosphere. This study aims to shed light on the conversion of bromospecies after degassing. The method presented here allows for the specific analysis of gaseous hydrogen bromide (HBr) in volcanic environments. HBr is immobilized by reaction with 5,6-epoxy-5,6-dihydro-[1,10]-phenanthroline (EP), which acts as an inner coating inside of diffusion denuder tubes (in situ derivatization). The derivative is analyzed by high-performance liquid chromatography coupled to electrospray ionization mass spectrometry (HPLC-ESI-MS). The collection efficiency for HBr (99.5 %), the collection efficiency for HBr alongside HCl (98.1 %), and the relative standard deviation of comparable samples (8 %) have been investigated. The comparison of the new denuder-based method and Raschig tubes as alkaline traps resulted on average in a relative bias between both methods of 10 ± 6 %. The denuder sampling setup was applied in the plume of Masaya (Nicaragua) in 2016. HBr concentrations in the range between 0.44 and 1.97 ppb were measured with limits of detection and quantification below 0.1 and 0.3 ppb respectively. The relative contribution of HBr as a fraction of total bromine decreased from 75 ± 11 % at the Santiago crater (214 m distance to the volcanic emission source) to 36 ± 8 % on the Nindiri rim (740 m distance). A comparison between our data and the previously calculated HBr, based on the CAABA/MECCA box model, showed a slightly higher trend for the HBr fraction on average than expected from the model. Data gained from this new method can further refine model runs in the future. [ABSTRACT FROM AUTHOR]

FV520B stainless steel is an important material for compression turbine impellers. Its corrosion resistance at high temperatures is critical for the manufacturing and service reliability management of impellers. Therefore, this study investigated the electrochemical corrosion of FV520B stainless steel in an acetic acid solution bearing hydrogen bromine from 130 to 200 °C by potentiodynamic polarisation, electrochemical impedance and corrosion morphology observation. Active corrosion peaks were evident, and the corrosion current densities increased with the increase of the concentration of hydrogen bromine and temperature. However, the breakdown potential first shifted into noble value and then decreased with the further rise in temperature, where the maximum value was at 175 °C. EIS analysis and corrosion morphology revealed that the presence of pitting potential peak is possibly attributed to the competition between the attack of bromine ion and the growth of a surface oxide film under high-temperature water. [ABSTRACT FROM AUTHOR]

A continuous flow procedure for the synthesis of aziridines from alkenes based on the in situ generation and utilization of bromodimethylsulfonium bromide (BDMS) is presented. In this process, BDMS was generated from hydrogen bromide and dimethylsulfoxide in the presence of the olefin, ensuing the corresponding 1,2-bromodimethylsulfonium bromide addition product. The solution containing this intermediate was mixed with a primary amine in flow, resulting in a rapid aziridination in a fast 3-step telescoped process. Notably, the exothermic formation of BDMS could be readily controlled in flow mode at room temperature, rendering a safe and reliable process. The complete sequence only required 7 min of total residence time, and provided a variety of 2-aryl aziridines in synthetically useful yields. [ABSTRACT FROM AUTHOR]

Bromination of (diethoxyphosphorylmethyl)acetylfurans with dioxane dibromide in the mixture of chloroform and acetic acid in presence of traces of hydrogen bromide at room temperature proceeds selectively at the methyl group of ketone does not involving phosphonate group. Obtained bromoacetyl derivatives were used for alkylation of acetoacetic ester and cyclohexan-1,3-dione. Reaction of 1,4-diketone prepared from acetoacetic ester with hydrazine hydrate in ethanol at room temperature leads to formation of furylpyrazines due to aromatization of intermediate azines by means of air oxygen. [ABSTRACT FROM AUTHOR]

Oxidative rearrangement of indoles is an important transformation to yield 2-oxindoles and spirooxindoles, which are present in many pharmaceutical agents and bioactive natural products. Previous oxidation methods show either broad applicability or greenness but rarely achieve both. Reported is the discovery of Fenton chemistry-enabled green catalytic oxidative rearrangement of indoles, which has wide substrate scope (42 examples) and greenness (water as the only stoichiometric byproduct) at the same time. Detailed mechanistic studies revealed that the Fenton chemistry generated hydroxyl radicals that further oxidize bromide to reactive brominating species (RBS: bromine or hypobromous acid). This in situ generated RBS is the real catalyst for the oxidative rearrangement. Importantly, the RBS is generated under neutral conditions, which addresses a long-lasting problem of many haloperoxidase mimics that require a strong acid for the oxidation of bromide with hydrogen peroxide. It is expected that this new catalytic Fenton-halide system will find wide applications in organic synthesis. [ABSTRACT FROM AUTHOR]

The chemical characterization of volcanic gas emissions gives insights into the interior of volcanoes. Monitoring of BrO/SO2-ratios has recently been correlated with changes in the activity of a volcano. BrO and SO2 can both be measured autonomously and simultaneously with the same instruments from a safe distance, making their ratio potentially a strong monitoring tool. However, BrO is not a primary emitted volcanic volatile and there exist still uncertainties about the formation of BrO in volcanic plumes, mostly due to the lack of analytical approaches for the accurate speciation of certain key compounds. This study describes a new method for the determination of the BrO precursor, the gaseous hydrogen bromide (HBr), by quantitative collection in denuder samplers. Gas diffusion denuders use the difference in diffusion coefficients to separate gaseous from particle-phase compounds. Gaseous HBr molecules are immobilized with an organic coating at the inner walls of the denuder tubes when pumped through the denuders. Five different coatings using 1,2-epoxycyclooctane, trans-oxirane-2,3-dicarboxylic acid, 2,3-epoxy-3-phenylpropanoic acid, 9,10-epoxystearic acid, 5,6-epoxy-5,6-dihydro-[1,10]-phenanthroline (EP) were tested as denuder coatings. EP proved to be a suitable coating reagent, which at the same time, transfers the analyte into an appropriate derivate to be analyzed by high-performance liquid chromatography coupled to electrospray ionization mass spectrometry (in situ derivatization). Coating amount, breakthrough, matrix effects and the storage behavior have been characterized. No considerable cross-sensitivity with hydrogen chloride or other bromine species such as molecular bromine was observed. The comparison of HBr determination using EP-coated denuders and Raschig Tubes as alkaline traps in the laboratory showed a deviation of 2 ± 11 % for gaseous HBr between the two methods. This allows considering HBr determined by denuders as a fraction of total bromine determined by Raschig Tubes. Since other bromine species (e.g. elemental bromine, bromine oxides) are also collected and determined as bromide by Raschig Tubes, but exclusively HBr in EP-coated denuders, the method presented here allows more accurate speciation of gaseous bromine compounds and their application in volcanic plumes. The denuder sampling setup was applied with complementary denuder systems and alkaline traps in the plume of Masaya (Nicaragua) in 2016. HBr concentrations in the range between 0.44 and 2.27 ppb were measured with limits of detection and quantification below 0.1 and 0.3 ppb respectively at typical ground-based sampling conditions. The relative contribution of HBr as a fraction of total bromine decreased from 75 ± 11 % at Santiago rim (214 m distance to the volcanic emission source) to 36 ± 8 % on Nindiri rim (740 m distance). Our findings are in good agreement with previous estimations of the HBr conversion from the chemistry box model (CAABA/MECCA). [ABSTRACT FROM AUTHOR]

Bisphosphonium salt containing a 1,4-dihydroxynaphthyl-substituted moiety was synthesized in high yield by the reaction of 2-methyl-1,4-naphthoquinone with three equivalents of triphenylphosphine and hydrogen bromide. The structure of the synthesized bisphosphonium salt was determined by NMR spectroscopy and X-ray diffraction. [ABSTRACT FROM AUTHOR]

Peroxidasin is a heme peroxidase that oxidizes bromide to hypobromous acid (HOBr), a powerful oxidant that promotes the formation of the sulfilimine crosslink in collagen IV in basement membranes. We investigated whether HOBr released by peroxidasin leads to other oxidativemodifications of proteins, particularly bromination of tyrosine residues, in peroxidasinexpressing PFHR9 cells. Using stable isotope dilution LC-MS/MS, we detected the formation of 3-bromotyrosine, a specific biomarker of HOBr-mediated protein modification. The level of 3-bromotyrosine in extracellular matrix proteins from normally cultured cells was 1.1 mmol/mol tyrosine and decreased significantly in the presence of the peroxidasin inhibitor, phloroglucinol. A negligible amount of 3-bromotyrosine was detected in peroxidasin-knockout cells. 3-Bromotyrosine formed both during cell growth in culture and in the isolated decellularized extracellular matrix when embedded peroxidasin was supplied with hydrogen peroxide and bromide. The level of 3-bromotyrosine was significantly higher in extracellular matrix than intracellular proteins, although a low amount was detected intracellularly. 3-Bromotyrosine levels increased with higher bromide concentrations and decreased in the presence of physiological concentrations of thiocyanate and urate. However, these peroxidase substrates showedmoderate tominimal inhibition of collagen IVcrosslinking. Our findings provide evidence that peroxidasin promotes the formation of 3-bromotyrosine in proteins. They show that HOBr produced by peroxidasin is selective for, but not limited to, the crosslinking of collagen IV. Based on our findings, the use of 3-bromotyrosine as a specific biomarker of oxidative damage by HOBr warrants further investigation in clinical conditions linked to high peroxidasin expression. [ABSTRACT FROM AUTHOR]

Bromine and peroxidasin (an extracellular peroxidase) are essential for generating sulfilimine cross-links between a methionine and a hydroxylysine within collagen IV, a basement membrane protein. The sulfilimine cross-links increase the structural integrity of basement membranes. The formation of sulfilimine cross-links depends on the ability of peroxidasin to use bromide and hydrogen peroxide substrates to produce hypobromous acid (HOBr). Once a sulfilimine cross-link is created, bromide is released into the extracellular space and becomes available for reutilization. Whether the HOBr generated by peroxidasin is used very selectively for creating sulfilimine cross-links or whether it also causes oxidative damageto bystandermolecules (e.g., generating bromotyrosine residues in basement membrane proteins) is unclear. To examine this issue, we used nanoscale secondary ion mass spectrometry (NanoSIMS) imaging to define the distribution of bromine in mammalian tissues. We observed striking enrichment of bromine(79Br, 81Br) in basement membranesof normalhuman and mouse kidneys. Inperoxidasin knockout mice, bromine enrichment of basement membranes of kidneys was reduced by ∼85%. Proteomic studies revealed bromination of tyrosine-1485 in the NC1 domain of α2 collagen IV from kidneys of wild-type mice; the same tyrosine was brominated in collagen IV from human kidney. Bromination of tyrosine-1485 was reduced by >90% inkidneys of peroxidasinknockout mice. Thus, in addition to promoting sulfilimine cross-links in collagen IV, peroxidasin can also brominate a bystander tyrosine. Also, the fact that bromine enrichment is largely confined to basement membranes implies that peroxidasin activity is largely restricted to basement membranes in mammalian tissues. [ABSTRACT FROM AUTHOR]

2-Aminocyclododecan-1-ol and 6(3)-aminodecahydro-1,4-ethanonaphthalen-5(2)-ols (mixture of isomers) were synthesized in two steps via oxidative hydroxybromination of cyclododecene and 1,2,3,4,4a,5,6,8a(1,4,4a,5,6,7,8,8a)-octahydro-1,4-ethanonaphthalines with the system hydrogen peroxide–HBr. In the first step, oxidation of hydrogen bromide with hydrogen peroxide generated intermediate dioxidanium bromide which added to the C=C double bond of the unsaturated substrate to give the corresponding α-bromo alcohols. In the second step, substitution of the bromine atom by amino group in the presence of an alkali afforded α-amino alcohols. [ABSTRACT FROM AUTHOR]

An efficient procedure of continuous-flow microwave reactor, for oxidative bromination with HBr (hydrogen bromide) -DMSO (dimethyl sulphoxide) in large scale is described herein. The reaction is carried out in a metal-free manner, with the use of water as solvent under microwave irradiation conditions. The productivity of this continuous step attains 60 g/min under the optimal conditions, implying a theoretical productivity of 8.6 kg/day. The reaction mixture is screened by thermal insulation accelerometer to ensure the safe process of this reaction in these conditions. 4-Bromo-3-methylanisole is further reacted with formanilide in the presence of cuprous iodide (CuI) and potassium carbonate (K2CO3) to give 4-methoxy-2-methyldiphenylamine, a common intermediate in fine chemical industry such as dye and paper chemistry, in an isolated yield of 65.2%. with more than 200 g scale. [ABSTRACT FROM AUTHOR]

Using solid oxide membrane, this paper presents the theoretical modeling of the high temperature electrolysis of hydrogen bromide gas for hydrogen production. The electrolysis of hydrogen halides such as hydrogen bromide is an attractive process, which can be coupled to hybrid thermochemical cycles. The high temperature electrolyzer model developed in the present study includes concentration, ohmic, and activation losses. Exergy efficiency, as well as energy efficiency parameters, are used to express the thermodynamic performance of the electrolyzer. Moreover, a detailed parametric study is performed to observe the effects of various parameters such as current density and operating temperature on the overall system behavior. The results show that in order to produce 1 mol of hydrogen, 1.1 V of the applied potential is required, which is approximately 0.8 V less compared to high temperature steam electrolysis under same conditions (current density of 1000 A/m2 and temperature of 1073 K). Furthermore, it is found that with the use of the presented electrolyzer, one can achieve energy and exergy efficiencies of about 56.7% and 53.8%, respectively. The results presented in this study suggest that, by employing the proposed electrolyzer, two-step thermochemical cycle for hydrogen production may become more attractive especially for nuclear- and concentrated solar-to-hydrogen conversion applications. • High temperature electrolysis of hydrogen bromide gas is reported. • High temperature electrolyser model includes concentration, ohmic, and activation losses. • Performance assessment in terms of energy and exergy efficiencies is conducted. [ABSTRACT FROM AUTHOR]

A palladium‐catalyzed multicomponent reaction of propargylic amines, alkynyl bromides and cesium hydrogen carbonate to access oxazolidinones is reported. In contrast to previous reports, only a slight excess of cesium hydrogen carbonate is used as a surrogate of carbon dioxide. The reaction gives access to oxazolidinones bearing alkyl‐ and aryl polysubstituted enynes in good yield and very high E stereoselectivity. [ABSTRACT FROM AUTHOR]

The dynamic of charged particles in pulsed plasma is relatively well known since the 1990s. In contrast, works reporting on the impact of the plasma modulation frequency and duty cycle on the radicals' densities are scarce. In this work, we analyze the impact of these modulation parameters on the radicals' composition in Cl2 and HBr plasmas. The radicals' densities are measured by broad-band UV and vacuum-ultraviolet (VUV) absorption spectroscopy and modulated-beam mass spectrometry. We show that pulsing the rf power allows controlling the plasma chemistry and gives access to the plasma conditions that cannot be reached in continuous wave plasmas. In particular, we show that above 500 Hz, the pulsing frequency has no influence on the plasma chemistry, whereas in contrast the duty cycle is an excellent knob to control the fragmentation of the parent gas, thus the chemical reactivity of the discharge. At low duty cycle, a reduced gas fragmentation combined with a large ion flux leads to new etching conditions, compared to cw plasmas and the expected consequences on pulsed-etching processes are discussed. [ABSTRACT FROM AUTHOR]

We have implemented the velocity map imaging technique to study clustering in the pulsed supersonic expansions of hydrogen bromide in helium, argon, and xenon. The expansions are characterized by direct imaging of the beam velocity distributions. We have investigated the cluster generation by means of UV photodissociation and photoionization of HBr molecules. Two distinct features appear in the hydrogen atom photofragment images in the clustering regime: (i) photofragments with near zero kinetic energies and (ii) 'hot' photofragments originating from vibrationally excited HBr molecules. The origin of both features is attributed to the fragment caging by the cluster. We discuss the nature of the formed clusters based on the change of the photofragment images with the expansion parameters and on the photoionization mass spectra and conclude that single HBr molecule encompassed with rare gas 'snowball' is consistent with the experimental observations. [ABSTRACT FROM AUTHOR]

Ab initio calculations are performed to probe the hydrogen bonding, structural, and superconducting behaviors of HBr and HCl under high pressure. The calculated results show that the hydrogen bond symmetrization (Cmc21→Cmcm transition) of HBr and HCl occurs at 25 and 40 GPa, respectively, which can be attributed to the symmetry stretching A1 mode softening. After hydrogen bond symmetrization, a pressure-induced soft transverse acoustic phonon mode of Cmcm phase is identified and a unique metallic phase with monoclinic structure of P21/m (4 molecules/cell) for both compounds is revealed by ab initio phonon calculations. This phase preserves the symmetric hydrogen bond and is stable in the pressure range from 134 to 196 GPa for HBr and above 233 GPa for HCl, while HBr is predicted to decompose into Br2+H2 above 196 GPa. Perturbative linear-response calculations predict that the phase P21/m is a superconductor with Tc of 27–34 K for HBr at 160 GPa and 9–14 K for HCl at 280 GPa. [ABSTRACT FROM AUTHOR]

Relative state-to-state cross sections of OH molecules in the 2Π3/2, v=0, J=3/2, MJ=3/2, f state have been determined for transitions up to 2Π3/2, v=0, J=11/2, f and 2Π1/2, v=0, J=7/2, e states by collisions with HBr molecules (1Σ, v=0, J<4) at 750 cm-1 collision energy. In order to investigate features of the anisotropy of the OH–HBr potential energy surface, the steric asymmetries, which account for the effect of the OH orientation with respect to the collision partner, have been measured. A comparison with other systems previously studied shows strong similarities with the OH–HCl system. [ABSTRACT FROM AUTHOR]

Absolute optical oscillator strength density spectra for valence-shell excitations of HCl and HBr, as well as for Br-3d inner-shell excitations of HBr, have been determined by high-resolution electron-energy-loss-spectroscopy method in the dipole limit. Absolute optical oscillator strengths for the discrete transitions of HCl and HBr are reported and compared with the previous results determined by the photoabsorption method. [ABSTRACT FROM AUTHOR]

The temporal behavior of the photoinduced ion-pair formation process in the (HI)m(H2O)n (n=1–6 for m=1 and n=1–4 for m=2) cluster system has been studied via the coupling between the g 3Σ- Rydberg and V 1Σ+ valence states. Comparison of the time constants obtained to those measured in previous experiments for the analogous process in HBr-water clusters, along with a detailed analysis of the signal intensity as a function of laser-pulse power, provides new insight into and confirmation of the previously proposed ion-pair formation mechanism. [ABSTRACT FROM AUTHOR]

The rotational spectra of two isotopomers, C5H5N...H79Br and C5H5N...H81Br, of a complex formed by pyridine and hydrogen bromide were observed by using a pulsed-jet, Fourier-transform microwave spectrometer that incorporated a mixing nozzle. Rotational constants, centrifugal distortion constants, and nuclear quadrupole coupling constants for the 14N and Br nuclei were determined. The rotational constants indicate that the observed complex has a planar geometry of C2v symmetry, with the HBr subunit lying along the C2 axis of pyridine. These conclusions are in good agreement with those obtained earlier from infrared spectroscopy in cryogenic matrices and ab initio calculations. The distance r(N...H)=1.137(2) Å was obtained by fitting the rotational constants under the assumption of an unchanged pyridine geometry and with r(H–Br) fixed at the value obtained through an ab initio calculation. The nuclear quadrupole coupling constants were interpreted, with the aid of ab initio calculations for the complex, as well as hydrogen-bonded and ion-pair limiting models for the interaction of pyridine and HBr, to establish that the complex may be visualized in terms of a substantial contribution (>60%) of the ionic structure C5H5NH+...Br- to its valence-bond description. The intermolecular force constant kσ=57.8(16) N m-1 determined from the centrifugal distortion constants ΔJ of the two isotopomers is also consistent with a strongly bound complex involving partial proton transfer. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The orientation and alignment of the 2P3/2 and 2P1/2 Br photofragments from the photodissociation of HBr is measured at 193 nm in terms of aq(k)(p) parameters, using slice imaging. The A 1Π state is excited almost exclusively, and the measured aq(k)(p) parameters and the spin-orbit branching ratio show that the dissociation proceeds predominantly via nonadiabatic transitions to the a 3Π and 1 3Σ+ states. Conservation of angular momentum shows that the electrons of the nascent H atom cofragments (recoiling parallel to the photolysis polarization) are highly spin polarized: about 100% for the Br(2P1/2) channel, and 86% for the Br(2P3/2) channel. A similar analysis is demonstrated for the photodissociation of HCl. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A threshold-photoelectron-coincidence spectrum of HBr has been recorded in the 32.2–35.8 eV photon energy range, with a resolution of ∼0.01 eV, using a synchrotron radiation source. The X 3Σ- and a 1Δ2 states of the HBr2+ dication are clearly observed in the spectrum, while there is no clear evidence for the formation of the b 1Σ+ electronic state. For the first two states, the vibrational states v=0–3 have been resolved, while for the ground X 3Σ- state also spin–orbit splitting has been detected. The results appear in good agreement with previous experimental observations. A comparison with theoretical predictions indicates the role of “noncovalent” contributions to the interaction between the two atomic partners for the formation of metastable states. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The present study describes the characterization of energy and structure of HBr2+ in its low-lying electronic states, achieved through an extension of a new empirical method [Chem. Phys. Lett. 379, 139 (2003)] recently introduced to evaluate the interatomic interaction in the HX2+ (X=F,Cl,Br,I) molecular dications. The method is based on identification of the main components of the interaction and their evaluation through some simple correlation formulas. Potential energy curves, given in a simple, natural, and analytical form, made possible the calculations of some important properties, such as double-photoionization energy thresholds, vibrational spacing, average lifetime, and Franck–Condon factors. The predictions, compared with data available in the literature, are of great interest for the analysis and interpretation of some new experimental results. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Coaxial pulsed jet submillimeter spectra are reported for Ar:H[sup 79]Br and Ar:H[sup 81]Br transition frequencies measured with sub-kHz precision. This is confirmed by comparing combination frequency differences associated with ΔF=+/-1 hyperfine components in the rovibrational transitions of the low frequency Σ bending mode with corresponding sum frequencies of the rotational transitions in the ground state precisely measured with a pulsed-nozzle FT microwave spectrometer (1.5 kHz resolution, 200 Hz accuracy). Ground state molecular parameters evaluated using the submillimeter-wave and microwave techniques are demonstrated to have comparable accuracy. Furthermore, excited Σ state molecular constants for the isotopic band origins of Ar:H[sup 79]Br and Ar:H[sup 81]Br at 329 611.4284(10) and 329 225.6778(10) MHz are shown to be determined with equivalent accuracy. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The weakly bound cyclic trimer (H[sub 2]O)[sub 2]HBr was observed in supersonic expansion and its rotational spectrum was measured in the region 3.6–17.7 GHz by cavity Fourier-transform microwave spectroscopy. Rotational, centrifugal distortion constants, and inertial and principal hyperfine splitting constants were determined for seven isotopomers of (H[sub 2]O)[sub 2]HBr. In addition to the large bromine hyperfine splitting each rotational transition exhibits a fine vibrational splitting into four components, at relative intensities consistent with expectations from the G[sub 8] group classification of the vibration–rotation–tunneling motions in the trimer. The associated four low-lying states are either very close together or well below the inversion barriers, since the differences between their rotational constants are all below 0.02%. The experimental moments of inertia were used to determine r[sub s], r[sub 0], r[sub z], and r[sub m][sup (1L)] geometries, in all of which the heavy atom distances are considerably shorter than similar distances in H[sub 2]O–HBr and (H[sub 2]O)[sub 2]. An improved analysis of the measured electric dipole moment of (H[sub 2]O)[sub 2]HBr is reported, and all experimental results are confronted with predictions from ab initio calculations. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A comprehensive study of the proton vibrational dynamics in isolated (HX)[SUBm]·(M)[SUBn] (X = Cl, Br, and M = H[SUB2]O, D[SUB2]O, CH[SUB3]OH) cluster is presented. Mid-IR (1900- 3900 cm[SUP-1]) spectra are measured in pulsed, seeded slit nozzle expansions. A close similarity among the HCl and HBr systems is revealed and exploited for cluster assignment. Distinct absorptions by small HX and mixed HX-M clusters are superimposed on broadbands, partly due to electrolytically dissociated HX in larger mixed clusters. Assignments of bands corresponding to mixed dimers and trimers based on their X-H and O-H stretching fundamentals are provided. The broad Cl-H stretching band profile of the 1:2 complex is indicative of sub-picosecond intracluster vibrational energy redistribution. The assignments are compared to matrix isolation experiments, when available. Systematic quantum chemistry calculations are performed for HCl-water complexes with up to three molecules and their isotopomers. Hydrogen bond induced frequency shifts of Cl-H stretching vibrations are best described at the coupled-cluster [CCSD(T)] level of theory. Lower level correlated quantum-chemical calculations clearly overestimate Cl-H frequency shifts. The low abundance of mixed clusters in the size range close to electrolytic dissociation (n = 3-5) is discussed. [ABSTRACT FROM AUTHOR]

The ultrafast dynamics of HBr-water clusters have been investigated using pump-probe spectroscopy coupled with reflectron time-of-flight mass spectrometry. HBr clusters, mixed HBr-water clusters, and protonated water clusters are observed in the mass spectra. Dynamic studies reveal that when an HBr chromophore of a cluster with less than five solvent molecules is excited electronically, solvent reorganization occurs to form the solvent separated ion-pair [S. M. Hurley et al., Science 298, 202 (2002)]. The present paper focuses on the influence of clustering on the dynamics of the C and D states of HBr. In addition, further evidence is presented which confirms that complete dissolution of HBr requires five solvent molecules in the isolated species found in (complexes comprised of pure water or HBr/H[SUB2]O mixtures. [ABSTRACT FROM AUTHOR]

The ultraviolet photolysis of Ar–HBr(v=1) is studied through wave packet dynamics simulations, focusing on the fragmentation pathway Ar–HBr +hω→H+Ar–Br. Photolysis starts from two initial states of Ar–HBr(v=1) with a different angular shape, namely the ground and the first excited van der Waals (vdW) states, corresponding to the Ar–H–Br and Ar–Br–H isomers, respectively. It is found that the yield of Ar–Br radical products is substantially higher for the initial excited vdW state of the cluster, where H dissociation is less hindered. In addition, the yield of radical formation is much higher in the Ar–HBr(v=1) photolysis than that previously found in the Ar–HCl(v=0) case, even for the ground vdW state, where the initial angular distribution of both clusters is similar. Another unexpected difference is that Ar–HCl(v=0) photolysis exhibits strong manifestations of quantum interference, while these effects are much weaker in Ar–HBr(v=1). A lower probability of the first collision between the recoiling hydrogen and the Ar atom in the case of Ar–HBr(v=1), due to geometrical differences between its initial state and that of Ar–HCl(v=0), is suggested to explain the different photolysis behavior of both clusters. The implications of the present findings in the photolysis of other related precursor clusters are discussed. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Studies the ultraviolet photodissociation dynamics of hydrogen bromide (HBr). Bond dissociation energy of HBr; Spin-orbit branching fractions; Photofragment angular distributions; Interpretation of the experimental results in terms of dissociation on multiple potential energy surfaces.

Focuses on the ultraviolet photolysis of hydrogen bromide molecules and clusters at three different wavelengths. Measurement of the kinetic energy distribution of the hydrogen photofragment using a time-of-flight mass spectrometer; Emerging groups which can be classified according to their kinetic energy.

Liu et al. [Chin. J. Struct. Chem. (1996). 15, 371–373] reported the structure of 6‐hydroxy‐1,4‐diazepane di(hydrogen bromide), C5H12N2O·2HBr, which was interpreted in terms of neutral diazepane and HBr molecules. We found, however, ample evidence that the formation of an organic salt, consisting of a diammonium cation and two bromide anions, is more plausible. This interpretation is also in agreement with thermogravimetric analysis and with the observed solution behaviour. The crystal structure of 6‐hydroxy‐1,4‐diazepane‐1,4‐diium dibromide, C5H14N2O2+·2Br−, measured at 142 K, crystallized in the orthorhombic space group P212121. The structure displays O—H...Br and N—H...Br hydrogen bonding. Contact distances are given. A search in the Cambridge Structural Database for the singly‐bonded H—Br moiety revealed a total of 69 structures. The question, whether these structures really include HBr as neutral molecules or rather Br− anions and a protonated substrate such as an amine, is addressed. [ABSTRACT FROM AUTHOR]

Abstract Oxazoles and pyrazines are fundamental heterocycles that widely found in natural products or drugs. In this work, a selective strategy for oxazoles and pyrazines synthesis using α-bromo-1-phenylethanone and ammonium acetate as starting materials was reported. This methodology features mild reaction conditions, readily accessible starting materials and good chemoselectivity. Mechanistic study indicates that this reaction involves a by-product-promoted (BPP) process for the formation of oxazole, that is, the in-situ formed hydrogen bromide (HBr) during the reaction promotes the whole tandem process. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Examines the dynamics of photofragmentation of hydrogen bromide (HBr). Treatment within time-independent, time-dependent and semiclassical methods; Calculation of relative cross sections for formation of the two accessible fine-structure channels; Small photon wavelength values.

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.