HBr/H2O2-mediated formation of C–S bond with thiosulfates

A novel, efficient, and green protocol to construct C–S bond has been developed via HBr/H₂O₂-mediated sulfenylation of styrenes and 4-hydroxycoumarins leading to unsymmetrical sulfides. Various unsymmetrical sulfides were prepared in one step with moderate to good yields using environmentally-friendly H₂O₂ as oxidant and HBr as catalyst. Based on the preliminary experimental results, a plausible reaction mechanism was proposed for HBr/H₂O₂-mediated formation of C–S bond with thiosulfates.     

Highly efficient and selective oxidation of secondary alcohols to ketones under organic solvent and transition metal free conditions

The aqueous HBr/H₂O₂ was found to be highly efficient and green catalytic system for the selective oxidation of the secondary alcohols to ketones in excellent yields under organic solvent free conditions. The results of the oxidation of the secondary alcohols with solid alternatives of the aqueous hydrogen peroxide like SPC or SPB are also described.     

An efficient transition metal-free aziridination of alkenes with Chloramine-T using aqueous H2O2/HBr

The combination of aqueous H₂O₂ and HBr was found to be an efficient transition metal-free green catalytic system for the aziridination of a variety of alkenes under very mild reaction conditions.     

Branching ratios for BrO production from reactions of O(1D) with HBr,CF3Br,CH3Br,CF2ClBr,and CF2HBr

Laser-flash photolysis of RBr/O₃/SF₆/He mixtures at 248 nm has been coupled with BrO detection by time-resolved UV absorption spectroscopy to measure BrO product yields from O(¹D) reactions with HBr, CF₃Br, CH₃Br, CF₂ClBr, and CF₂HBr at 298±3 K. The measured yields are: HBr, 0.20±0.04; CF₃Br, 0.49±0.07; CH₃Br, 0.44±0.05; CF₂ClBr, 0.31±0.06; and CF₂HBr, 0.39±0.07 (uncertainties are 2σ and include estimates of both random and systematic errors). The results are discussed in light of other available information or O(¹D)+RBr reactions. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 555–563, 1998     

Experimente und Modellrechnungen zum chemischen Transport von WO2 mit HgCl2 oder HgBr2

Experiments and Calculations on the Chemical Transport of WO₂ with HgCl₂ or HgBr₂ Transport experiments with WO₂ or WO₂ + W₁₈O₄₉ or W + WO₂ as starting phases show that HgCl₂ or HgBr₂ are suitable transport agents. When using HgBr₂ we observed (in customary silica ampoules) unusual high transport rates n′ > 1000 mg/h. Experimental and calculated results agree to a large extent if the presence of small amounts of H₂O from the quartz glass wall and the resulting gaseous particles (for example HCl or HBr) formed under equilibrium conditions as well as an influence of convection are taken into consideration.     

Thermochemistry of Lappaconitine Hydrobromide and Its Analogues

Isothermal calorimetry was applied to study the heats of dissolution of lappaconitine hydrobromide at varied dilution. The data obtained were used to calculate the standard enthalpy of dissolution of C₃₂H₄₄N₂O₈ · HBr in an infinitely diluted (standard) aqueous solution. The heats of combustion and melting of C₃₂H₄₄N₂O₈ · HBr were calculated using approximate methods. A combination of experimental and calculation techniques was used to find the standard heats of formation of lappaconitine hydrobromide and its 33 analogues.     

An efficient vanadium-catalyzed bromination reaction

An efficient catalytic oxidative bromination of arenes, alkenes, and alkynes in aqueous media was achieved under relatively mild conditions by using NH₄VO₃ catalyst combined with H₂O₂, HBr, and KBr. Dodecyltrimethylammonium bromide was found to serve as an efficient surfactant to facilitate the NH₄VO₃-catalyzed bromination in aqueous media.     

Simultaneous determination of In and In2O3 by cyclic voltammetry in the DC and the AC mode

Summary Cyclic voltammetry on solid phases using the carbon-paste electrode (CPE) has been applied to the In- In₂O₃ system. Electrochemical reactions can be recorded more sensitively, and interpretation of the complex processes is simpler with AC voltammetry.Additional electrochemical experiments concerning the condition of formation and the chemical stability of intermediates yielded a model of electrochemical reactions in connection with preliminary and consecutive chemical processes.It is possible to detect unambiguously In and In₂O₃ simultaneously in 1 N HBr, but not in 1 N HCl.

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Simultanbestimmung von In und In₂O₃ durch cyclische Voltammetrie (Gleich- und Wechselstrom)

Zusammenfassung Die cyclische Voltammetrie unter Verwendung der Kohlepasteelektrode wurde am System In- In₂O₃ angewandt. Durch den Einsatz der Wechselstrom-Voltammetrie können die elektrochemischen Reaktionen empfindlicher erfaßt und komplexe Prozesse klarer interpretiert werden.Ergänzende elektrochemische Experimente zur Aufklärung der Bildungsbedingungen und chemischen Stabilität von Zwischenprodukten ergeben ein Modell der elektrochemisch auswertbaren Reaktionen unter Berücksichtigung vor- und nachgelagerter chemischer Prozesse.Es ist in 1 N HBr, nicht aber in 1 N HCl, möglich, In und In₂O₃ eindeutig nebeneinander nachzuweisen.

     

Thermal degradation study of tetrabromobisphenol A under the presence metal oxide: Comparison of bromine fixation ability

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.     

Desilylation of t-butyldimethylsilyl ethers of hydroxyquinones

Desilylation of a series of hydrolytically stable hydroxyquinone t-butyldimethylsilyl ethers was achieved in high yields by the use of potassium fluoride in the presence of catalytic amounts of aqueous 48% hydrobromic acid (HBr), or basic aluminium oxide (Al₂O₃), and tetra-n-butylammonium fluoride (Bu₄NF) as cleaving agents. Copyright © 1998 John Wiley & Sons, Ltd.     

TEMPO-catalyzed oxidation of benzylic alcohols to aldehydes with the H2O2/HBr/ionic liquid [bmim]PF6 system

A selective oxidation of benzylic alcohols to the corresponding aldehydes in room temperature ionic liquid was achieved by using TEMPO/HBr/H₂O₂ system, and both ether-insoluble acetamido-TEMPO and ionic liquid [bmim]PF₆ can be successfully recovered and reused for the oxidation of the same (different) substrate.     

Europium Oxybromide Catalysts for Efficient Bromine Looping in Natural Gas Valorization

The industrialization of bromine‐mediated natural gas upgrading is contingent on the ability to fully recycle hydrogen bromide (HBr), which is the end form of the halogen after the activation and coupling of the alkanes. Europium oxybromide (EuOBr) is introduced as a unique catalytic material to close the bromine loop via HBr oxidation, permitting low‐temperature operation and long lifetimes with a stoichiometric feed (O₂:HBr=0.25)—conditions at which any catalyst reported to date severely deactivates because of excessive bromination. Besides, EuOBr exhibits unparalleled selectivity to methyl bromide in methane oxybromination, which is an alternative route for bromine looping. This novel active phase is finely dispersed on appropriate carriers and scaled up to technical extrudates, enhancing the utilization of the europium phase while preserving the performance. This catalytic system paves the way for sustainable valorization of stranded natural gas via bromine chemistry.     

Zur Calorimetrie der Bismutoxidhalogenide. II. Bismutoxidbromide

Calorimetry of Bismuth Oxidhalides. II. Bismuth Oxidebromides The heat solution of all known solid phases in the system Bi₂O₃/BiBr₃ in 4n HBr were investigated. To compare the data they were converted to the standardized formula Bi₂O_3?y/2Br_yBr_y with 0 ? y ? 2. The enthalphies of formation of the complex bismuthoxidebromides are based on the enthalpies of Bi₂O_3,f HBr_,Lsg and H₂O circumventing the value for Bi(OH)_3,Lsg.     

HBr or not HBr? That is the question: crystal structure of 6‐hydroxy‐1,4‐diazepane‐1,4‐diium dibromide redetermined

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.     

Investigation on the mechanism and applications of the reaction Cl2+2HBr=2HCl+Br2

The mechanism of reaction Cl₂+2HBr=2HCl+Br₂ has been carefully investigated with density functional theory (DFT) at B3LYP/6-311G^** level. A series of three-centred and four-centred transition states have been obtained. The activation energy (138.96 and 147.24 kJ/mol, respectively) of two bimolecular elementary reactions Cl₂+HBr→HCl+BrCl and BrCl+HBr→HCl+Br₂ is smaller than the dissociation energy of Cl₂, HBr and BrCl, indicating that it is favorable for the title reaction occurring in the bimolecular form. The reaction has been applied to the chemical engineering process of recycling Br₂ from HBr. Gaseous Cl₂ directly reacts with HBr gas, which produces gaseous mixtures containing Br₂, and liquid Br₂ and HCl are obtained by cooling the mixtures and further separated by absorption with CCl₄. The recovery percentage of Br₂ is more than 96%, and the Cl₂ remaining in liquid Br₂ is less than 3.0%. The paper provides a good example of solving the difficult problem in chemical engineering with basic theory.     

Kinetics of the R + HBr RH + Br (CH3CHBr, CHBr2 or CDBr2) equilibrium. Thermochemistry of the CH3CHBr and CHBr2 radicals

The kinetics of the reaction of the CH₃CHBr, CHBr₂ or CDBr₂ radicals, R, with HBr have been investigated in a temperature-controlled tubular reactor coupled to a photoionization mass spectrometer. The CH₃CHBr (or CHBr₂ or CDBr₂) radical was produced homogeneously in the reactor by a pulsed 248 nm exciplex laser photolysis of CH₃CHBr₂ (or CHBr₃ or CDBr₃). The decay of R was monitored as a function of HBr concentration under pseudo-first-order conditions to determine the rate constants as a function of temperature. The reactions were studied separately from 253 to 344 K (CH₃CHBr + HBr) and from 288 to 477 K (CHBr₂ + HBr) and in these temperature ranges the rate constants determined were fitted to an Arrhenius expression (error limits stated are 1σ + Student’s t values, units in cm³ molecule⁻¹ s⁻¹, no error limits for the third reaction): k(CH₃CHBr + HBr) = (1.7 ± 1.2) × 10⁻¹³ exp[+ (5.1 ± 1.9) kJ mol⁻¹/RT], k(CHBr₂ + HBr) = (2.5 ± 1.2) × 10⁻¹³ exp[−(4.04 ± 1.14) kJ mol⁻¹/RT] and k(CDBr₂ + HBr) = 1.6 × 10⁻¹³ exp(−2.1 kJ mol⁻¹/RT). The energy barriers of the reverse reactions were taken from the literature. The enthalpy of formation values of the CH₃CHBr and CHBr₂ radicals and an experimental entropy value at 298 K for the CH₃CHBr radical were obtained using a second-law method. The result for the entropy value for the CH₃CHBr radical is 305 ± 9 J K⁻¹ mol⁻¹. The results for the enthalpy of formation values at 298 K are (in kJ mol⁻¹): 133.4 ± 3.4 (CH₃CHBr) and 199.1 ± 2.7 (CHBr₂), and for α-C–H bond dissociation energies of analogous compounds are (in kJ mol⁻¹): 415.0 ± 2.7 (CH₃CH₂Br) and 412.6 ± 2.7 (CH₂Br₂), respectively.     

Simultaneous determination of mercury and selenium in biological materials by radiochemical neutron activation analysis

A simple and sensitive radiochemical neutron activation analysis (RNAA) method has been developed for the simultaneous determination of mercury and selenium in biological materials. The radiochemical procedure is based upon the digestion of irradiated samples with sulphuric and nitric acids followed by subsequent extractions of mercury and selenium into toluene, first of mercury from 7.5 M H₂SO₄-0.01M HBr media and after of selenium from 7M H₂SO₄-1 M HBr media. After washing of the organic phases with similar media, the mercury bromide was back-extracted into 0.034M EDTA in 5% aqueous ammonia and the selenium bromide into 0.14M H₂O₂ in aqueous solution. The¹⁹⁷Hg and the⁷⁵Se were counted on a Ge(Li) detector. The precision and accuracy of the method was checked by analysing NBS Standard Reference Materials: orchard leaves and bovine liver.     

Catalysis by HBr in the bromination of o-xylene in acetic acid

Hydrogen bromide is known to inhibit the bromination of aromatic substrates (ArH), either by fixing up bromine as HBr₃ or ArH as ArH · HBr. However, there is catalysis by HBr in the bromination of mesitylene in acetic acid. The bromination of o-xylene in acetic acid in the dark is found to be autocatalytic, and the reaction is overall third order, first order in o-xylene with the orders in Br₂ and HBr depending on the concentrations. A composite rate expression involving Br₂ and HBr as electrophiles has been proposed and verified using iodine bromide as a catalyst where the orders are one in each of the reactants, irrespective of the concentrations used.     

Extraction of99Mo-molybdophosphate and99mTc-pertechnetate from various acid solutions by bis/2-ethylhexyl/ phosphoric acid

The extractability of⁹⁹Mo-molybdophosphoric acid H₃/PMo₁₂O₄₀/ and^99mTc-pertechnetic acid /PTcO₄/ in 20% (v/v) bis /2-ethylhexyl/ phosphoric acid /HDEHP/ in benzene has been investigated at different concentrations of HCl, HBr and HNO₃ acids. The effect of extractant concentration and diluent on the extractability of molybdophosphoric and pertechnetic acids with 20% (v/v) HDEHP in benzene from different concentrations of HCl acid has also been studied.⁹⁹Mo-molybdo-phosphoric acid was found to be selectively extracted and separated from^99mTc-pertechnetic acid with 20% HDEHP in benzene at an acidity of about 0.49M HCl, HBr and HNO₃. The extractability of H₃/PMo₁₂O₄₀/ from these acids generally follows the decreasing order HBr>HCl>HNO₃. The separation factors /K_d molybdophosphoric/K_d pertechnetic/ were found to be 12.9×10⁵ and 7.6×10⁵ for HBr and HCl, respectively. The extractability of pertechnetic acid follows the order HCl>HBrHNO₃. Benzene is the diluent due to its radiation stability. A new procedure for the separation of^99mTc from⁹⁹Mo was suggested.     

Reaction of bis(trimethylsilyl) sulfate with hydrogen halides and with phosphorus and sulfur halides and oxyhalides

Conclusions The reaction of bis(trimethylsilyl) sulfate (BTS) with HBr leads to trimethylbromosilane, hexamethyldisiloxane, and free bromine. Its reaction products with HI are hexamethyldisiloxane and free iodine. The reaction of BTS with PCl₃ leads to the formation of Me₃SiCl, SO₂, and a polymeric product whose composition approximates [(CH₃)₃SiO]₈Cl₂O₂₇P₈S₄. The reaction of SOCl₂ with BTS gives in high yield Me₃SiOSO₂Cl, Me₃SiCl, and SO₂. POCl₃ and SO₂Cl₂ do not react with BTS under analogous conditions.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 696–698, March, 1982.