- State-specific low temperature reactions of DBr+2 i(v+) + (D2, DBr) → D2Br+
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State-specific reactions of DBr+(2 i, v+) with D2 and DBr were studied in a low temperature free jet flow reactor. The selected spin-orbit and vibrational states of the DBr+ ion were prepared by resonance-enhanced multiphoton ionization. All of the reactant and product ions were monitored using time-of-flight mass spectrometry. Rate coefficients for the DBr+/DBr reaction are ~1.4 × 10-9 cm3 s-1 independent of the ion internal state, similar to those for the HBr+/HBr reaction. Rate coefficients of the DBr+/D2 reaction rise from 0 (lower spin-orbit-vibrational states) to 2 × 10-11 cm3 s-1 (highest energy states) and are observed to follow a mass independent threshold function similar to the HBr+/H2 reaction.
- Belikov, Andrey E.,Smith, Mark A.
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- Kinetics of CN(X 2Σ+) radical reactions with HCN, BrCN and CH3CN
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Absolute rate constants were obtained for CN (X 2Σ+) radical reactions with HCN, BrCN and CH3CN. The CN radical relative concentration was followed by laser-induced fluorescence (LIF) with a cw ring dye laser on the A 2Π-X 2Σ+ (4, 0) band at 621.5 nm. CN radicals were generated by laser photolysis of ICN at 266 nm. The following Arrhenius parameters were obtained over the temperature range 296-578 K: CN+HCN, k=10-11.41±0.15 exp[-(670±100)/T] cm3 s-1; CN+BrCN, k=10-10.7±0.4 × exp[-(1340±330)/T] cm3 s-1; CN+CH3CN, k=10-10.19±0.10 exp[-(1190±70)/T] cm3 s-1. The rates meas and that of Szekely et al. for CN+HCN could be well fitted by the form, k=10-16.20T1.57 exp (-50/T) cm3 s-1 over the range 300-3000 K, allowing extrapolation to the combustion temperature regime. The measured rates and those of Kayes and Levitt and Clark et al. for the CN+BrCN reaction could be fitted by the form, k=10-14.18T1.16 exp(-940/T) cm3 s-1 the temperature range 300-3000 K. In addition, the non-linearity of these data over a wide range of temperature could be satisfactorily accounted for by transition-state theory calculations for both of these reactions.
- Zabarnick,Lin
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- Electrochemistry of Br-/Br2 Redox Couple in Acetonitrile, Methanol and Mix Media of Acetonitrile-Methanol: An Insight into Redox Behavior of Bromide on Platinum (Pt) and Gold (Au) Electrode
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Electro-oxidation of Br- on platinum and gold electrode was studied in acetonitrile, methanol and mix media of acetonitrile-methanol. The mechanism of Br- oxidation in these media was investigated using CV, Semi Integration Cyclic Vo
- Tariq, Muhammad
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- On the mechanism of the BrO+HBr reaction
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The reaction of the bromine oxide radical, BrO, with HBr has been examined with coupled-cluster methods. The HO+HCl reaction is also examined and is used to calibrate the results for the BrO+HBr reaction. The heat of reaction and activation energy barrier
- Hansen, Jaron C.,Li, Yumin,Li, Zhuangjie,Francisco, Joseph S.
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- Dual-frequency oscillations induced by acidity in Belousov-Zhabotinskii reactions with aldosugars as substrates
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Depending on the initial concentration of H2SO4, two types of dual-frequency oscillations have been observed in Belousov-Zhabotinskii type reactions catalyzed by Mn2+ with acetone and aldosugars (arabinose, glucose, galactose, lactose or maltose) as coupled substrates in a batch reactor. No such dual-frequency oscillations have been found when a ketosugar like fructose was used instead of an aldosugar as the substrate; or acetone was replaced by N2 flow. No oscillations were observed when Ce3+ was used instead of Mn2+. The reaction products of aldosugars in different oscillating regimes have been analyzed. The dual-frequency oscillatory patterns have been discussed according to the roles of the substrates and their derivatives formed at different acidity.
- Li, Hexing,Jin, Ronghua,Dai, Weilin,Deng, Jingfa
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- Experimental and theoretical determination of the magnetic dipole transition moment for the Br(4p5)(2P1/2←2P3/2) fine-structure transition and the quantum yield of Br(2P1/2) from the 193 nm photolysis of BrCN
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The integrated-absorption coefficients of several hyperfine lines of the magnetic dipole allowed transition of the bromine atom, Br, center at 3685.2 cm-1 were measured, and a value for the square of the magnetic dipole transition moment of the Br atom was determined. A theoretical calculation for the magnetic dipole transition moment was also carried out using a relativistic ab initio atomic structure formulation. The theoretical value was in excellent agreement with the value predicted assuming pure LS coupling, and in reasonable agreement with experiment. The Br atom was generated in equal concentration with the cyano radical (CN) by the 193 nm photolysis of cyanogen bromine, BrCN. The CN radicals were titrated by the rapid reaction with C3H8 to generate HCN and a small amount of HNC. Both time-resolved and frequency-scanned infrared absorption spectroscopy were used to monitor the Br, HCN, and HNC species. The photolysis of BrCN at 193 nm produced both the ground state Br(2P3/2) and the spin-orbit excited Br(2P1/2) atoms, and the yield for the production of Br(2P1/2) atoms was measured to be 0.31±0.01. The rate constants for the quenching of Br(2P1/2) by BrCN and C3H8 at 293 K were also determined.
- He,Seth, Michael,Tokue,Macdonald, R. Glen
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- Pt embedded in carbon rods of N-doped CMK-3 as a highly active and stable catalyst for catalytic hydrogenation reduction of bromate
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A novel Pt-based catalyst with fine and homogeneous Pt particles embedded in carbon rods of N-doped CMK-3 was fabricated by a two-step infiltration method using SBA-15 as the template. Due to its fine particle size, N-containing functionality and effective embedment of Pt particles in carbon rods, the catalyst exhibited superior catalytic activity and stability in the liquid phase catalytic hydrogenation of bromate in water.
- Li, Minghui,Hu, Yuan,Fu, Heyun,Qu, Xiaolei,Xu, Zhaoyi,Zheng, Shourong
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- Kinetics and Thermochemistry of the sec-C4H9 + HBr n-C4H10 + Br Equilibrium
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The kinetics of the sec-C4H9 + HBr reaction was studied in a tubular reactor coupled to a photoionization mass spectrometer.The sec-C4H9 radicals were produced homogeneously in the reactor by pulsed UV laser photolysis.Radical decays in the presence of different HBr concentrations were monitored in time-resolved experiments.Rate constants were obtained as a function of temperature (229 - 533 K) and were fit to an Arrhenius expression: 1.7(+/-0.6)*10-12exp-1/RT> cm3 molecule-1 s-1.This kinetic information was combined with knowledge of the rate constant of the reverse reaction to obtain both the entropy -1 K-1> and heat of formation -1> of the sec-C4H9 radical at 298 K in a second law determination.The secondary C-H bond energy in n-C4H10 derived from this heat of formation is 411 (+/-3) kJ mol-1.This value is in excellent agreement with the secondary C-H bond energy in C3H8 determined previously both in an investigation of a comparable equilibrium involving HBr -1> and in investigations of dissociation-recombination equilibria involving i-C3H7 -1>.This study also provides a reconciliation of the formerly disparate sec-C4H9 heats of formation that were derived from studies of differnet kinds of chemical equilibria.
- Seetula, Jorma A.,Gutman, David
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- Kinetics of the Reactions of F- with CF3Br and CF3I as a Function of Temperature, Kinetic Energy, Internal Temperature, and Pressure
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The reactions of F- with CF3Br and CF3I have been studied at several temperatures as functions of pressure and ion-neutral average center-of-mass kinetic energy (cm>).Rate constants and product branching fractions were measured by using a variable temperature-selected ion flow drift tube apparatus.Both title reactions involve two product pathway: displacement and association, the latter being the major channel under most experimental conditions.The rate constants for displacement are governed by total energy, regardless of the relative contributions by translational and internal energy, indicating that the displacement reactions behave statistically.In contrast, the rate constants for association depend strongly on the internal energy of CF3X (rotations and vibrations) compared with the relatively weak effect of translational collision energy.For CF3Br the rate constants for the association channel increase with increasing pressure while those for displacement are independent of pressure, indicating that the additional reactivity leading to more association at higher pressure appears not to compete with the displacement pathway.This lack of competition may be the result of two different reaction intermediates.The more efficient CF3I reaction is at or near the high-pressure limit for association, showing no pressure dependence in both the association and displacement channels.Therefore, there appears to be no competition between these channels for CF3I as well, but the data are less definitive in this case.
- Morris, Robert A.,Viggiano, A. A.
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- Temperature dependence of electron attachment to CH2ClBr: Competition between Cl- and Br- formation
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Dissociative electron attachment (DEA) to CH2ClBr has been studied in a crossed electron/molecular beams experiment in the electron energy range between 0 and 2 eV and in the gas temperature range between 328 and 449 K. In this electron energy range we find the two negative fragment ions Cl- and Br- which are both formed from a prominent low energy resonant feature (≈0 eV). While the Br- ion yield (recorded at ≈0 eV) considerably increases with the temperature, that of Cl- slightly decreases resulting in an overall increase of ion formation at low electron energy. The temperature dependence is interpreted by the relative disposition of the involved potential energy surfaces. For the exothermic Br- channel an activation energy of 107 ± 10 meV for the DEA reaction is obtained. Using absolute rates from swarm data the total cross section for the DEA to CH2ClBr has been calibrated to absolute values leading to 5 × 10-21m2 at 0.5 eV.
- Matejcik,Ipolyi,Illenberger
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- Photo-response of the bromate-sulfite chemical oscillator with tris-(bipyridine)ruthenium(II) as a catalyst
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Photo-response of the chemical oscillator composed of BrO3-, SO32- and Ru(bpy)32+ in the acidic aqueous solution was examined in a flow system. After establishing the dark state diagram, state diagrams have been determined taking P (the illumination light power) as one of the external parameters. In the P versus [SO32-] plane, the bifurcation between the reduced steady state and the oscillatory or oxidized steady state was found to be independent of P, occurring at a fixed critical concentration of SO32-. Qualitative discussions are given for this and other characteristic features in the system containing SO32- as a reductant.
- Matsuyama,Okazaki,Tanimoto,Hanazaki
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- Negative ion production in collisions between K(nd) Rydberg atoms and CF3Br and CF2Br2
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Negative ion production via electron transfer in collisions between K(nd) Rydberg atoms and CF3Br and CF2Br2 has been investigated over a wide range of of n (10n70).For both species, the major negative ion observed is Br-, although with C
- Kalamarides, A.,Marawar, R. W.,Ling, Xi,Walter, C. W.,Lindsay, B. G.,et al.
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- Discharge Flow Kinetic Study of the Reactions of NO3 with Br, BrO, HBr, and HCl
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The reactions of NO3 with Br, BrO, HBr, and HCl have been studied at 298 K by using the discharge-flow EPR method.In the study of the reactions of NO3 with Br and BrO, where NO3 and BrO were flowed separately in the presence of excess NO3, the following r
- Mellouki, A.,Poulet, G.,Bras, G. Le,Singer, R.,Burrows, J. P.,Moortgat, G. K.
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- Simple and Complex pH Oscillations and Bistability in the Phenol-Perturbed Bromite-Hydroxylamine Reaction
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The unbuffered reaction between bromite and hydroxylamine at pH 3-7 has been studied under closed and open conditions.The stoichiometry of the batch system depends on the initial concentration ratio of the reactants and on the starting pH.The reaction is strongly autocatalytic in H+.Under flow conditions the reaction exhibits bistability between two steady states but does not oscillate.If the flow system is perturbated by an input of phenol, it shows oscillatory behavior in pH, potential of a Pt electrode, and color.A qualitative explanation of the batch and oscillatory behaviors is suggested.The bromite-hydroxylamine-phenol flow system can be characterized as a large-amplitude, long-period, pH-driven oscillator.
- Orban, Miklos,Epstein, Irving R.
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- Complex Kinetics in the Bromate-Iodide Reaction: A Clock Reaction Mechanism
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A reinvestigation of the kinetics and mechanism of the bromate-iodide reaction in acidic medium has been undertaken.The stoichiometry of the reaction in excess iodide concentrations over bromate is BrO3(1-)+9I(1-)+6H(1+)->Br(1-)+3I3(1-)+3H2O (A), and in excess bromate concentrations the stoichiometry is BrO3(1-)+6I(1-)+6H(1+)->Br(1-)+3I2+3H2O (B).In excess bromate concentrations a second reaction is observed in which the iodine produced by reaction B is consumed rapidly and suddenly in a typical clock reaction fashion according to the reaction 2BrO3(1-)+I2->2IO3(1-)+Br2 (C).Reaction C does not commence until reaction B is complete, i.e., when all the iodide ions have been consumed.This is explained via a combination of kinetic factors which favor the production of iodine and the fact that higher oxidation states of iodine are thermodinamically unstable with respect to iodine in the presence of iodide ions in acidic media.At 25+/-0.1 deg C and ionic strength 0.2 M (NaClO4), the rate low in both high iodide and high bromide environments was found to be -d/dt-k02, with k0=44.3+/-1.1 M-3 s-1.The postulated mechanism involves an initial nucleophilic attack on the protonate bromate species by iodide, followed by elimination of HOI.
- Simoyi, Reuben H.,Masvikeni, Patricia,Sikosana, Angela
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- Oxygen-induced wavefront instabilities and disorder in the Belousov-Zhabotinsky reaction
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Wavefront instabilities leading to spatiotemporal disorder in a convection-free and horizontally homogeneous Ru(bpy)32+-catalyzed Belousov-Zhabotinsky reagent had previously been measured and simulated. Necessary conditions in a 20% O2 atmosphere (air) were: high light intensities (I>150 mW/m2) and low catalyst concentrations (≤1 mM). Here, we show that at sufficiently high O2 concentrations, comparable instabilities and disorder appear even in the dark or at high (≥1 mM) catalyst concentrations. In contrast, in the ferroin-catalyzed reagent such dynamic processes are not observed at any value of I in air, although they do occur - independently of I - at sufficiently high O2 concentrations.
- Markus, Mario,Czajka, Andre
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- A novel polyoxometalate-encapsulating 3D polycatenated metal-organic framework
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A novel polyoxometalate-encapsulating polycatenated metal-organic framework, (bib)0.5[Cu2(bib)3.5(GeW12O40)]·H2O (1) (bib = 1,4-bis(1-imidazol-yl)-2,5-dimethyl benzene), has been synthesize
- Li, Shaobin,Lu, Borong,Xin, Jianjiao,Zhang, Li,Pan, Jing,Chen, Yue,Tan, Xiaoguo
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- Vibrational product states from reactions of CN- with the hydrogen halides and hydrogen atoms
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Infrared chemiluminescence is observed from the C-H stretch manifold v3 of HCN formed in the gas phase ion-molecule reactions: CN- + HX -> HCN(v3) + X-, with (X=Cl, Br, I), and for CN- + H -> HCN(vsu
- Maricq, M. Matti,Smith, Mark A.,Simpson, C. J. S. M.,Ellison, G. Barney
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- State-to-state dynamics of H+HX collisions. II. The H+HXHX(excit.)+H (X = Cl,Br,I) reactive exchange and inelastic collisions at 1.6 eV collision energy
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We report measurement of product state distributions for the rotationally and/or vibrationally excited HX formed in collisions of translationally hot H atoms with HX (X = Cl, Br, and I) at 1.6 eV collision energy.The product state distributions are probed
- Aker, Pamela M.,Germann, Geoffrey J.,Tabor, Kevin D.,Valentini, James J.
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- Reactive cross section as a function of reagent energy. II. H(D) + HBr(DBr) -> H2(HD,D2) + Br
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A crossed molecular beam study has been made of reactive cross section as a function of collision energy Sr(ET) for all isotopic variants of the absorption reaction H' + H''Br -> H'H'' + Br.The apparatus incorporates, for reagent preparation, a supersonic source of variable-energy H or D atoms, and, for product detection, a tunable vacuum ultraviolet laser to obtained laser-induced fluorescence of Br.The cross-section functions indicate that the threshold energy for reaction is T=7 kcal/mol,the observed order of reactivity in the isotopic series designated (H',H'') was (D,H)>(D,D)>(H,H)>(H,D).As noted in a previous report from this laboratory the favorable kinematics for (D,H) as compared with (H,D) can be understood in terms of lengthened interaction time for D atom reaction (compared with H) and diminution in the time required for HBr (compared with DBr) to rotate into the preferred alignment for reaction.The effect is illustrated here in terms of a simple model of reaction.The experimental data obtained in this work at low collision energy, in conjunction with 300 K rate constants obtained by others, suggest that close to threshold, kinematic effects are supplanted by threshold effects, yielding Sr(H,D) > Sr(D,H), the inverse of the principal isotope effect at enhanced collision energy.
- Hepburn, J. W.,Klimek, D.,Liu, K.,Macdonald, R. G.,Northrup, F. J.,Polanyi, J. C.
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- Spectrophotometric reaction rate method for determination of barbituric acid by inhibition of the hydrochloric acid-bromate reaction.
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A new kinetic-spectrophotometric method was developed for the determination of barbituric acid. The method is based on its inhibition effect on the reaction between hydrochloric acid and bromate. The decolorization of methyl orange by the reaction products was used to monitor the reaction spectrophotometrically at 510 nm. The variable affecting the rate of the reaction was investigated. The method is simple, rapid, relatively sensitive and precise. The limit of detection is 7.9x10(-7) M and calibration rang is 1x10(-6)-6.0x10(-4) M barbituric acid. The linearity range of the calibration graph is depends on bromate concentration. The relative standard deviation of seven replication determination of 5.6x10(-6) M barbituric acid was 1.8%. The influence of potential interfering substance was studied.
- Ensafi, Ali A,Movahedinia
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- Recombination of Br2- photodissociated within mass selected ionic clusters
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Photofragmentation studies of mass selected Br2-*(CO2)n, na supersonic expansion crossed with an electron beam.Thesc ionic clusters are mass analyzed in a time-of-flight mass spectrometer prior to photodissociation of the Br2- absorber in the cluster.Mass analysis of the ionic photofragments shows that in some cases the photodissociated Br2- has recombined and in other cases a Br atom has escaped from the cluster.The branching ratio for recombination depends on both the size of the initial cluster ion and the photodissociation wavelength.The photofragmentation data are consistent with a recombination mechanism dominated by attractive forces in the smaller clusters and repulsive interactions in the larger clusters.
- Alexander, Michael L.,Levinger, Nancy E.,Johnson, M. A.,Ray, Douglas,Lineberger, W. C.
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- Bisulfite-driven autocatalysis in the bromate-thiosulfate reaction in a slightly acidic medium
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The thiosulfate-bromate reaction has been studied by high-performance liquid chromatography, monitoring the concentrations of thiosulfate and tetrathionate simultaneously. It is found that concentration-time curves of both species display a sigmoidal shape in a slightly acidic, well-buffered medium. Unlike the previously reported complex reaction systems involving bromate, this nonlinear dynamical behavior originates from neither proton nor bromine(III) autocatalysis under our experimental conditions. We demonstrated that sulfur(IV) species significantly accelerates the reaction; therefore, it acts as an autocatalyst. To the best of our knowledge, no reaction system has yet been reported among the pH-driven oxysulfur-oxyhalogen systems, where sulfur(IV) has such a remarkable role. On the basis of the simultaneous evaluation of [S 2O32-] and [S4O6 2-] time series, an eight-step kinetic model is proposed to account for the experimental observations. The model employed here may serve as a solid starting point to extend it for other oxysulfur-oxyhalogen systems where such a seemingly general phenomenon may become observable.
- Wang, Zhen,Gao, Qingyu,Pan, Changwei,Zhao, Yuemin,Horvath, Attila K.
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- Kinetic study of the reaction of atomic chlorine with hydrogen bromide
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The reaction Cl + HBr --> HCl + Br was studied by a competitive method using the reaction Cl + C2H6 --> HCl + C2H5 as a reference reaction.Experiments to determine ratios of rate constants kCl+HBr/kCl+C2H6 in the temperature range 222-504 K were carried out in a fast flow system with mass spectrometric analysis of the reaction mixture.The results fit the Arrhenius expression: kCl+HBr/kCl+C2H6 = (0.53+/-0.03)exp.A comparison is made with values calculated from reported results for the individual rate constants kCl+HBr and kCl+C2H6.
- Rubin, Rachamim,Persky, Avigdor
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- Temperature dependence and kinetic isotope effects for the OH + HBr reaction and H/D isotopic variants at low temperatures (53-135 K) measured using a pulsed supersonic laval nozzle flow reactor
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The reactions of OH + HBr and all isotopic variants have been measured in a pulsed supersonic Laval nozzle flow reactor between 53 and 135 K, using a pulsed DC discharge to create the radical species and laser induced fluorescence on the A 2∑ ←X 2π(v′ = 1 ←v″ = 0) transition. All reactions are found to possess an inverse temperature dependence, in accord with previous work, and are fit to the form k = A(T/298)-n, with k1 (OH + HBr) = (10.84 ±0.31) × 10-12(T/298)(-0.67±0-02) cm3/s, k2 (OD + HBr) = (6.43 ±2.60) × 10-12(T/298) (-1.19±026) cm3/s, k3 (OH + DBr) = (5.89 ±1.93) × 10-12(T/298)(-0.76±22) cm3/s, and k4 (OD + DBr) = (4.71 ±1.56) × 10-12(T/298)(-1.09±0.21) cm3/s. A global fit of k vs T over the temperature range 23-360 K, including the new OH + HBr data, yields k(T) = (1.06 ±0.02) × 10-11(T/298) (-0.90±0.11) cm3/s, and (0.96 ±0.02) × 10-11(T/298)(-0.90±0.03)exp(((-2.88±1.82K)/T) cm 3/s, in accord with previous fits. In addition, the primary and secondary kinetic isotope effects are found to be independent of temperature within experimental error over the range investigated and take on the value of (kH/kD)AVG =1.64 for the primary effect and (kH/kD)AVG =0.87 for the secondary effect. These results are discussed within the context of current experimental and theoretical work.
- Mullen, Christopher,Smith, Mark A.
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- Kinetics and mechanisms of S(IV) reductions of bromite and chlorite ions
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The reaction of bromite with aqueous S(IV) is first order in both reactants and is general-acid catalyzed. The reaction half-lives vary from 5 ms (p[H+] 5.9) to 210 s (p[H+] 13.1) for 0.7 mM excess S(IV) at 25°C. The proposed mechanism includes a rapid reaction (k1 = 3.0 × 107 M-1 s-1) between BrO2- and SO32- to form a steady-state intermediate, (O2BrSO3)3-. General acids assist the removal of an oxide ion from (O2BrSO3)3- to form OBrSO3-, which hydrolyzes rapidly to give OBr- and SO42-. Subsequent fast reactions between HOBr/OBr- and SO32- give Br- and SO42- as final products. In contrast, the chlorite reactions with S(IV) are 5-6 orders of magnitude slower. These reactions are specific-acid, not general-acid, catalyzed. In the proposed mechanism, ClO2- and SO3H-/SO2 react to form (OClOSO3H)2- and (OClOSO2)- intermediates which decompose to form OCl- and SO42-. Subsequent fast reactions between HOCl/OCl- and S(IV) give Cl- and SO42- as final products. SO2 is 6 orders of magnitude more reactive than SO3H-, where k5(SO2/ClO2-) = 6.26 × 106 M-1 s-1 and k6(SO3H-/ClO2-) = k6(SO3H-/ClO2-) = 5.5 M-1 s-1. Direct reaction between ClO2- and SO32- is not observed. The presence or absence of general-acid catalysis leads to the proposal of different connectivities for the initial reactive intermediates, where a Br-S bond forms with BrO2- and SO32-, while an O-S bond forms with ClO2- and SO3H-.
- Huff Hartz, Kara E.,Nicoson, Jeffrey S.,Wang, Lu,Margerum, Dale W.
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- Palladium nanoparticles encapsulated in core-shell silica: A structured hydrogenation catalyst with enhanced activity for reduction of oxyanion water pollutants
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Noble metal nanoparticles have been applied to mediate catalytic removal of toxic oxyanions and halogenated hydrocarbons in contaminated water using H2 as a clean and sustainable reductant. However, activity loss by nanoparticle aggregation and
- Wang, Yin,Liu, Jinyong,Wang, Peng,Werth, Charles J.,Strathmann, Timothy J.
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- Dissociation energy of the molecule AIBr from equilibrium measurements
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The dissociation equilibrium AlBr = Al + Br was studied by effusion beam mass spectrometry over the range 1970 to 2260 K and the dissociation energy D00 (AlBr) was derived as 4.41 0.06 eV.This value is in general agreement with other fragme
- Hildenbrand, D. L.,Lau, K. H.
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- Photodissociation of carbonic dibromide at 267 nm: Observation of three-body dissociation and molecular elimination of Br2
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The photodissociation of Br2CO at 267 nm was studied by ion velocity imaging and TOF-MS method. Bimodal kinetic energy distributions of bromine atoms were found. In general, the results indicate that the transition dipole moment of Br2/su
- Xu, Dadong,Huang, Jianhua,Francisco, Joseph S.,Hansen, Jaron C.,Jackson, William M.
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- H Atom Reactions in the Sonolysis of Aqueous Solutions
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Aqueous solutions of the spin trap 5,5-dimethylpyrroline N-oxide (DMPO) and or Br2, I2, MnO4-, AuCl4-, and Ag+ were irradiated with 1-MHz ultrasound under argon-hydrogen mixtures of various compositions.DMPO was found to trap only very small amounts of hydrogen atoms while substantially greater amounts could be scavenged by the other solutes.The yield of H atoms as measured by the ESR signal of the DMPO adduct decreased with increasing H2 concetration in the gas mixture.The yields of the reduction products of the other solutes passed through a maximum at about 20 vol percent H2.The efficiency of scavenging did not correlate to the rate constant of reaction with H in homogeneous solution.It seems that the ability of a solute to be accumulated at the liquid-gas interface cavitation bubbles strongly influences the scavenging efficiency.Thallium ions are reduced in solutions of high pH.This reduction is attributed to hydrated electrons which are formed in the reaction of the H atoms with OH- anions.It is concluded that the local concetration of H atoms in the interfacial region of the cavitation spots is about 10-3 M and that hydrated electrons are not primary products of sonolysis.
- Gutierrez, Maritza,Henglein, Arnim,Dohrmann, Jurgen K.
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- Negative ion-molecule reactions of SF4
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A study of some negative ion-molecule reactions involving SF4 has been carried ot by the flowing afterglow technique at ambient temperature.By ezamining a series of charge exchange reactions of SF4 and SF4-, the electron affinity of SF4 has been determined to be 2.35+/-0.1 eV.Rate coefficients for the charge exchange reactions of HS-, S-, OH-, and O- with SF4 and of SF4- with Cl2 and NO2 are reported.In addition, the fluoride transfer reactions of SF4- and SF6- with SF4 to produce SF5- have been examined.That both reactions proceed indicates that the fluoride affinity of SF4 is greater than that of SF3 or SF5.A lower limit of 3.7 eV for the electron affinity of SF5 may also be deduced from the fluoride transfer reactions.The two body addition of halide ions (X-) to SF4 to form the adduct SF4X- proceeds at near the collision limit (k=9.7*10-10cm3molecule-1s-1) for F-, very slowly (k=2.6*10-11cm3molecule-1s-1) for Cl-1, and not at all within experimental limits (k-12cm3molecule-1s-1) for Br-1.
- Babcock, Lucia M.,Streit, Gerald E.
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- Reinvestigation of the kinetics of reduction of bromite by hexacyanoferrate(II) in slightly basic solution
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The reaction BrO2- + 4 Fe(CN)64- + 2H2O → Br- + 4Fe(CN)63- + 4OH- has been studied by spectrophotometry at 30, 40 and 50°C and both with equivalent amounts of reactants and with an excess of bromite. It follows the kinetic expression dξ/dt = kobs[BrO2-] [Fe(CN)64-]2 with kobs = 8.2 M-2 s-1 at 25°C, ΔH≠ = 66 kJ mol-1 and ΔS≠ = -121.7 J K-1 mol-1. The proposed mechanism is a two-stage process, the first, rate-determining stage being reduction of bromite to hypobromous acid, the second further reduction to bromide. Either stage consists of two bimolecular reactions. The major contribution to the energy barriers comes from electrostatic repulsion between negative ions.
- Lundager Madsen, Hans E.
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- Simultaneous evaluation of different types of kinetic traces of a complex system: Kinetics and mechanism of the tetrathionate - bromine reaction
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The bromine-tetrathionate reaction has been studied in the presence of phosphoric acid/dihydrogen phosphate buffer at T = 25 ± 0.1°C and at I = 0.5 M ionic strength with both stopped-flow technique and a conventional diode array spectrophotometer. The sto
- Varga, Denes,Horvath, Attila K.
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- Extraction and stripping of platinum (IV) from acidic chloride media using guanidinium ionic liquid
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The extraction and stripping behaviors of Pt(IV) from acidic chloride media by 2,2-diheptyl-1,1,3,3-tetramethylguanidinium bromide were investigated. The extraction of Pt(IV) was carried out by modulating various parameters such as concentration of the extractant, temperature, and concentration of HCl solution. Based on the characterization of experimental results such as Job's method data, UV–vis spectra and fourier transform infrared spectra analysis, the anion exchange mechanism was confirmed. Quantum chemical calculations were performed to provide theoretical support for the mechanism. The ionic liquid showed outstanding selectivity for Pt(IV) over the base metals. Furthermore, the organic phase could be easily used for four extraction-stripping cycles by reductive stripping process using 0.5 M CS(NH2)2/0.5 M HCl. The numbers of theoretical stages needed for the effective extraction and stripping of Pt(IV) has been determined by McCabe Thiele's diagram. Under the selected counter-current extraction and stripping stages, the extraction efficiency and stripping efficiency could reach 99.5% and 99.0%, respectively. Therefore, the system is highly effective, selective and recyclable to extract Pt(IV). On the basis of the extraction protocol, the system may be a promising candidate for highly selective extraction of Pt(IV).
- Wang, Ning,Wang, Qi,Lu, Wenjuan,Ru, Miaoyan,Yang, Yanzhao
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- Visible Light Driven Bromide Oxidation and Ligand Substitution Photochemistry of a Ru Diimine Complex
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The complex [Ru(deeb)(bpz)2]2+ (RuBPZ2+, deeb = 4,4′-diethylester-2,2′-bipyridine, bpz = 2,2′-bipyrazine) forms a single ion pair with bromide, [RuBPZ2+, Br-]+, with Keq = 8400 ± 200 M-1 in acetone. The RuBPZ2+ displayed photoluminescence (PL) at room temperature with a lifetime of 1.75 μs. The addition of bromide to a RuBPZ2+ acetone solution led to significant PL quenching and Stern-Volmer plots showed upward curvature. Time-resolved PL measurements identified two excited state quenching pathways, static and dynamic, which were operative toward [RuBPZ2+, Br-]+ and free RuBPZ2+, respectively. The single ion-pair [RuBPZ2+, Br-]+? had a lifetime of 45 ± 5 ns, consistent with an electron transfer rate constant, ket = (2.2 ± 0.3) × 107 s-1. In contrast, RuBPZ2+? was dynamically quenched by bromide with a quenching rate constant, kq = (8.1 ± 0.1) × 1010 M-1 s-1. Nanosecond transient absorption revealed that both the static and dynamic pathways yielded RuBPZ+ and Br2?- products that underwent recombination to regenerate the ground state with a second-order rate constant, kcr = (2.3 ± 0.5) × 1010 M-1 s-1. Kinetic analysis revealed that RuBPZ+ was a primary photoproduct, while Br2?- was secondary product formed by the reaction of a Br? with Br-, k = (1.1 ± 0.2) × 1010 M-1 s-1. Marcus theory afforded an estimate of the formal reduction potential for E0(Br?/-) in acetone, 1.42 V vs NHE. A 1H NMR analysis indicated that the ion-paired bromide was preferentially situated close to the RuII center. Prolonged steady state photolysis of RuBPZ2+ and bromide yielded two ligand-substituted photoproducts, cis- and trans-Ru(deeb)(bpz)Br2. A photochemical intermediate, proposed to be [Ru(deeb)(bpz)(κ1-bpz)(Br)]+, was found to absorb a second photon to yield cis- and trans-Ru(deeb)(bpz)Br2 photoproducts.
- Li, Guocan,Brady, Matthew D.,Meyer, Gerald J.
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p. 5447 - 5456
(2018/05/01)
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- Enhancing the anion affinity of urea-based receptors with a Ru(terpy) 22+ chromophore
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Covalent linking of a Ru(terpy)22+ substituent improves recognition and sensing properties of the urea subunit toward anions. Urea's anion affinity is enhanced by the electrostatic attraction exerted by the RuII cation and by the electron-withdrawing effect exerted by the entire polypyridine-metal complex. Such an enhancement of the anion affinity, which results from the combination of a through-space and a through-bond effect, is greater than that exerted by the classical neutral electron-withdrawing substituent nitrophenyl. Small yet significant modifications of π-π* and MLCT bands of the Ru(terpy)22+ chromophore, detected through UV-vis spectrophotometric titrations, allowed the determination of the constants for the formation of receptor-anion H-bond complexes in diluted MeCN solution. On 1H NMR titration experiments, carried out under more concentrated conditions, the interaction of a second Cl- ion was observed, taking place through an outer-sphere mechanism. The Ru(terpy) 22+ substituent favors the deprotonation of a urea N-H fragment on addition of a second equivalent of fluoride, with formation of HF2-.
- Baggi, Giorgio,Boiocchi, Massimo,Ciarrocchi, Carlo,Fabbrizzi, Luigi
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p. 5273 - 5283
(2013/06/26)
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- Reaction of Br2 with adsorbed CO on Pt, studied by the surface interrogation mode of scanning electrochemical microscopy
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(Chemical Equation Presented) Scanning electrochemical microscopy surface interrogation (SI-SECM) in the cyclic voltammetry mode was successfully used to detect and quantify adsorbed CO on a Pt electrode by reaction with electrogenerated Br2. T
- Wang, Qian,Rodriguez-Lopez, Joaquin,Bard, Allen J.
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p. 17046 - 17047
(2010/03/25)
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- Pulse radiolysis study of the oxidation of the I- ions with the radical anions Br2 >=- In an aqueous solution: Formation and properties of the radical anion BrI>=-
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The radiation chemical redox transformations in solutions of bromides in the presence of minor additives of iodides were studied by pulse radiolysis. The change in the concentrations of the Br- and I- ions changes the ratio of the formed short-lived radical anions Br2 ?-, BrI?-, and I2 ?-. The spectrum of the mixed radical anion BrI?- contains a broad optical band at 370 nm with 370 = 9650 L mol-1 cm -1. The reduction potential of the BrI?-/Br -, I- pair is 1.25 V. The rate constants for the forward and backward reactions Br2 ?- + I- BrI?- + Br- are k f = 4.3?10 9 and k r = 1.0?105 L mol-1 s-1, respectively; for the reactions BrI?- Br - + I?, k f = 5.7?108 s-1 and k r = 1.0?1010 L mol-1 s-1.
- Ershov,Janata,Gordeeva
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p. 1821 - 1826
(2009/12/02)
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- Kinetics and mechanism of oxidation of some thioacids by benzyltrimethylammonium chlorobromate
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The oxidation of some thioacids, viz., thioplycollic, thiolactic and thiomalic acids by benzyltrimethylammonium chlorobromate (BTMACB) has been studied in acetic acid. The reaction is first order with respect to BTMACB. Michaelis-Menten type of 'kinetics have been observed with respect to the reductants. The reaction has been studied in solvents of different compositions of acetic acid and water. The solvent composition effect has been analysed using Grunwald-Weinstein equation. A mechanism involving the formation of an intermediate complex in the pre-equilibrium and its subsequent decomposition in slow step has been proposed.
- Tiwari, Vandana,Kumbhani,Shastri,Sharma, Vinita
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p. 1520 - 1523
(2009/05/16)
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- Homogeneous catalysis of manganese(II) in the oxidation of citric acid by acid bromate: A novel kinetic behaviour of citric acid
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The kinetic and mechanistic studies on Mn(II)-catalysed oxidation of citric acid by acid bromate in presence of Hg(II) as a scavenger have been carried out under varying conditions. The reaction exhibits 1.5 order each in [bromate] and [acid], and less than unit order in [Mn(II)]. The kinetic behaviour of citric acid is novel, being 0.30 order in the lower [citric acid] range and tending to -0.25 order at higher [citric acid], Hg(OAc)2 and D2O have insignificant effect on the reaction rate. Formal redox potential for the Mn(II)/Mn(III)-citric acid couple is determined as 0.32 V (vs SCE) and 0.58 V (vj NHE). These findings are accounted quantitatively by the formation of 1:1 (MnCt) and 1:2 (MnCt2) manganese(II)-citric acid complexes of which only 1:1 (MnCt) complex is kinetically active towards the bromate oxidation. In the envisaged mechanism, acid bromate reacts with the 1:1 (MnCt) complex, whose formation is precedent to the Mn(II)-Br(V) reaction. It results in an intermediate complex, which subsequently decomposes to the products. At higher [citric acid], the ratio of 1:2 and 1:1 Mn(II)-citric acid complexes reached 1.98. The effects of [pyrophosphate], [LiF], dielectric constant of the media and ionic strength are also in accordance with the proposed mechanism. Reaction constants involved in the proposed mechanism have been evaluated and thermodynamic parameters computed.
- Reddy, Cherkupally Sanjeeva
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p. 407 - 415
(2008/02/09)
-
- Oxidation of Chlorine(III) by Hypobromous Acid: Kinetics and Mechanism
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The kinetics and mechanism of the chlorine(III)-HOBr reaction were studied by the stopped-flow method under acidic conditions, pH 1.0-3.0, in 1.0 M NaClO4 and at 25.0 °C. The overall redox process occurs in two consecutive steps via the formation of the BrClO2 intermediate. The electron transfer reactions are coupled with bromine hydrolysis, the formation of the tribromide ion, and the protolytic equilibrium of chlorine(III). On the basis of simultaneous evaluation of the kinetic traces, the following rate constants were obtained for the redox steps: HClO2 + HOBr ? BrClO2 + H2O, k3 = (3.34 ± 0.02) × 104 M-1 s-1, k-3 = (3.5 ± 1.3) × 103 s-1; BrClO2 + ClO2- ? 2ClO2 + Br-, k 4 = (2.9 ± 1.0) × 107 M-1 s -1. The second step was practically irreversible under the conditions applied, and the value of k-4 could not be determined. The equilibrium constant for the formation of BrClO2, K3 = 9.5 M-1, was calculated from the kinetic results, and it was confirmed that this species is a very powerful oxidant. The redox potential was also estimated for the BrClO2 + e- = Br- + ClO2 reaction: ε0o ~ 1.70 V.
- Toth, Zsuzsanna,Fabian, Istvan
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p. 2717 - 2723
(2008/10/09)
-
- A systematic study of spirals and spiral turbulence in a reaction-diffusion system
-
A study was conducted of the spiral behaviors in a reaction-diffusion system using the BZ reaction and observed certain new phenomena. Transition from the D type spiral turbulence to the T type turbulence on the D-T boundary can be readily explained by the change of the BZ reaction from excitable to oscillatory. A well established method, the hierarchical structure theory can be applied to identify this transition.
- Guo, Hongyu,Li, Liang,Ouyang, Qi,Liu, Jian,She, Zhensu
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p. 5038 - 5044
(2007/10/03)
-
- Indazole compounds and pharmaceutical compositions for inhibiting protein kinases, and methods for their use
-
Indazole compounds that modulate and/or inhibit the activity of certain protein kinases are described. These compounds and pharmaceutical compositions containing them are capable of mediating tyrosine kinase signal transduction and thereby modulate and/or inhibit unwanted cell proliferation. The invention is also directed to the therapeutic or prophylactic use of pharmaceutical compositions containing such compounds, and to methods of treating cancer and other disease states associated with unwanted angiogenesis and/or cellular proliferation, such as diabetic retinopathy, neovascular glaucoma, rheumatoid arthritis, and psoriasis, by administering effective amounts of such compounds.
- -
-
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- The reactivity of 2,2'-bipyridine complexes in the electrochemical reduction of organohalides
-
Nickel(0) complexes coordinatively unsaturated with 2,2'-bipyridine (bpy) are more reactive in the oxidative addition to organic halides than the saturated analogs. ?-Organonickel complexes formed as intermediates of catalytic cycles were prepared in high
- Yakhvarov, D. G.,Samieva, E. G.,Tazeev, D. I.,Budnikova, Yu. G.
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p. 796 - 804
(2007/10/03)
-
- Temperature-dependent kinetic isotope effects in the gas-phase reaction: OH + HBr
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The temperature dependence of the hydrogen transfer rate coefficients for the reactions: OH + HBr (Reaction 1), OD + HBr (Reaction 2), OH + DBr (Reaction 3), and OD + DBr (Reaction 4) have been investigated at temperatures between 120 and 224K using a pulsed uniform supersonic flow monitoring hydroxyl reactive loss. The lack of observed isotopic scrambling indicates the reaction occurs by H/D atom transfer from HBr/ DBr at all temperatures. The rate coefficients demonstrate little temperature dependence above 200 K, but strong inverse temperature behavior below 200 K. The current work provides unequivocal experimental evidence of temperature dependent and inverse primary and secondary kinetic isotope effects (kH/kD H/kD, at 120 K are for primary substitution on HBr; k1/k3 = 1.00 (±0.17) and k2/k4 = 0.46 (±0.08), while for secondary substitution on OH; k1/k2 = 0.94 (±0.20) and k3/k4 = 0.43 (±0.05). At the lowest temperature employed (120 K), deuterated reactants react as fast or faster than their natural hydrogen isotopomer and there is no significant difference between the primary and secondary kinetic isotope effect. The results are discussed within the framework of recent theoretical models.
- Jaramillo, Veronica I.,Smith, Mark A.
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p. 5854 - 5859
(2007/10/03)
-
- Kinetics and mechanism of the OH and OD reactions with BrO
-
The kinetics and mechanism of the reactions OH + BrO → products (1) and OD + BrO → products (2) have been studied in the temperature ranges of 230-355 K and 230-320 K, respectively, and at total pressure of 1 Torr of helium using the discharge-flow mass s
- Bedjanian, Yuri,Riffault, Veronique,Le Bras, Georges,Poulet, Gilles
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p. 6154 - 6166
(2007/10/03)
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- Kinetics and products of the IO + BrO reaction
-
The kinetics and products of the IO + BrO reaction were discussed. The reaction was studied using the technique of laser flash photolysis with kinetic ultraviolet (UV) absorption spectroscopy. No direct measurement of I or Br was performed. IBr was observed as a minor product (klb/kl ld/kl 0.15). The results were compared with previous studies of the IO + BrO reaction, and the atmospheric implications were briefly discussed.
- Rowley, David M.,Bloss, William J.,Cox, R. Anthony,Jones, Roderic L.
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p. 7855 - 7864
(2007/10/03)
-
- Measurement of the rate coefficient for the reaction of OH with BrO
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We report the rate coefficient for the reaction OH + BrO → Products (1) at 298 K to be k1(298 K) = (4.5 ± 1.8) × 10-11 cm3 molecule-1 s-1. Reaction 1 was studied in an excess of BrO, generated in a flow tube, and measured via its UV-vis absorption. OH, produced by laser photolysis, was monitored by laserinduced fluorescence. Quoted uncertainties include estimated uncertainties in the BrO concentration and that due to the unavoidable concurrent reaction of OH with Br2. Our measured value of k1 is compared with that previously reported by Bogan et al.
- Gilles, Mary K.,McCabe, David C.,Burkholder, James B.,Ravishankara
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p. 5849 - 5853
(2007/10/03)
-
- Kinetics and mechanism of the initial phase of the bromine - chlorite ion reaction in aqueous solution
-
The kinetics and mechanism of the chlorine(III)-bromine reaction are studied by the stopped-flow method under acidic conditions in 1.0 M NaClO4 and at 25.0 °C. There are two kinetically well-separated phases in this reaction. A detailed mechanism is proposed for the first phase of the reaction, in which Br2 oxidizes ClO2- to chlorine dioxide. It is confirmed that the oxidation occurs via competing parallel reaction steps. The autoinhibition observed in the reaction is attributed to a backward shift in the reversible initial step as the oxidation proceeds. On the basis of simultaneous evaluations of the kinetic traces, the following forward rate constants are obtained for the kinetically significant reaction steps: Br2 + ClO2- = ClO2 + Br2-, k1 = (1.3 ± 0.2) x 103 M-1 s-1 (k-1 = 1.1 x 109 M-1 s-1); Br2- + ClO2- = ClO2 + 2Br-, k2 = (4.0 ± 0.1) x 106 M-1 s -1; Br + ClO2- = ClO2 + Br-, k8 = (2.3 ± 0.7) x 108 M-1 s-1; HOBr + HClO2 = BrClO2 + H20 (BrClO2 + ClO2- = Br- + 2ClO2, very fast), k9 = (1.9 ± 0.1) x 105 M-1 s-1. The possible kinetic role of the reactive BrClO2 intermediate is discussed in detail.
- Toth, Zsuzsanna,Fabian, Istvan
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p. 4608 - 4614
(2008/10/08)
-
- Synthesis, properties and crystal structure of some polyoxometallates containing the tris(hydroxymethyl)-aminomethane cation
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Polyoxometallates [(CH2OH)3CNH3]3PMo12O40·5H2O, [(CH2OH)3CNH3]3PW12O40·11H2O, [(CH2OH)3CNH3]2H2SiW12O40·10H2O, [(CH2OH)3CNH3]4GeW12O40·9H2O, [C4H12NO3]4SiMo12O40·5H2O, [(CH2OH)3CNH3]2H4P2W18O62·3H2O and [(CH2OH)3CNH3]3H3As2W18O62·4H2O have been synthesized for the first time, purified, and structurally characterized by means of elemental analyses, IR spectrum, electronic spectrum, cyclic voltammogram, 31P NMR and X-ray diffraction. The crystal structure of [(CH2OH)3CNH3]4PMo12O40·5H2O has been determined by X-ray diffraction. Hydrogen bonding between (CH2OH)3CNH2 and PMo12O40/3- was inferred from heavy atom distances. The solid reflectance electronic spectra and IR spectra indicate that there is interaction between the H3PMo12O40 and the organic substrate. The complexes have photosensitivity under irradiation of sunlight to result in charge transfer by oxidation of (CH2OH)3CNH2 and the reduction of the polyoxometallates. We also found that [(CH2OH)3CNH3]3PMo12O40·5H2O and [(CH2OH)3CNH3]3 PW12O40·11H2O exhibited substantial catalytic activity toward the electro-reduction of bromate and nitrite, respectively. (C) 2000 Elsevier Science S.A.
- Bi, LiHua,Wang, EnBo,Xu, Lin,Huang, RuDan
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p. 163 - 171
(2008/10/08)
-
- B-Z oscillator with fructose and tartaric acid as organic substrates
-
Experimental studies on fructose (F) + tartaric acid (TA) + Ce4+ + BrO3- + H2SO4 system are reported by keeping either of the two organic substrates at a fixed concentration and varying the concentration of the other. An attempt has been made to investigate the oscillatory behaviour and the mechanism of the reaction. The change in [Br2] during the course of reaction has been monitored spectrophotometrically while [Br-] has been estimated electrometrically. Effect of addition of fructose and BrO3-after the cessation of oscillation has also been investigated. The results confirm the earlier conclusion that the oscillations are non-[Br-] controlled.
- Rastogi,Husain,Chand,Das
-
p. 679 - 684
(2007/10/03)
-
- The role of 3Π0+ in the photodissociation of BrCl at 235 nm
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The photodissociation of BrCl has been investigated at 235 nm using a two-dimensional photofragment ion imaging technique. Three direct dissociation channels were observed with the quantum yields of Φ[Br(2P1/2)+Cl(2P 3/2)]=0.58±0.05, Φ[Br(2P3/2)+Cl(2P 1/2)]=0.16±0.05, and Φ[Br(2P3/2)+Cl(2P 3/2)]=0.26±0.05, and angular distributions were represented by anisotropy parameters, β=1.98±0.05, -1.04±0.05, and 1.88±0.05, respectively. The results indicate that the 2341 3Π0+ state plays a key role in the dissociation dynamics after absorbing a photon. Based on the results of BrCl and newly found probe lines for Br atoms, the ionization probability ratios of Cl(2P3/2 or 2P1/2) to Br(2P3/2 or 2P1/2) were determined.
- Park, Moon-Soo,Jung, Young-Jae,Lee, Sung-Hae,Kim, Dong-Chan,Jung, Kyung-Hoon
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p. 429 - 438
(2008/10/08)
-
- Aqueous solutions of hypovalent gallium; reductions using gallium(I)
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Solutions 0.2 mol dm-3 in Ga1, prepared by dissolving Ga2Cl4 in dry acetonitrile, are stable for more than seven days and may be diluted 300- to 1000-fold with O2-free water to give Ga(I) preparations
- Swavey,Gould
-
p. 2159 - 2160
(2007/10/03)
-
- Kinetics and mechanisms of the oxidation of hydrazinium ion (N2H5+) by aqueous Br2, Cl2, and BrCl. Electrophilicity scale for halogens and interhalogens
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Very rapid oxidations of N2H5+ by Br2, Cl2, and BrCl are measured by stopped-flow and pulsed-accelerated-flow methods in acidic solutions with excess N2H5+. Second-order rate constants (M-1 s-1) at 25.0 °C, μ = 1.0 M are 1.49 x 107, 1.01 x 108, and 5.6 x 108 for the reactions with Br2, Cl2, and BrCl, respectively. The reactions are postulated to proceed by nucleophilic reaction of N2H5+ with XY electrophiles (XY = Br2, Cl2, BrCl) to form XN2H4+ with Y- and H+ release in the rate-determining step. In the subsequent reactions, we propose that XN2H4+ eliminates X- and H+ rapidly to form N2H3+ and diazine, N2H2, which is oxidized by a second Br2, Cl2, or BrCl to form N2 in fast steps. The stoichiometries are measured and confirmed to be 1:2 for the Cl2 and BrCl reactions. The relative reactivities for the oxidation of N2H5+ by halogens and interhalogens (BrCl > Cl2 > Br2 > ICl >> IBr >> I2) are used to establish an electrophilicity scale (E(XY)) for this type of reaction in aqueous solution.
- Jia, Zhongjiang,Salaita, Murad G.,Margerum, Dale W.
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p. 1974 - 1978
(2008/10/08)
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- Kinetics and mechanisms of the oxidation of hydrazinium ion (N2H5+) by ICI and IBr; determination of the protonation constant of N2H5+
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The kinetics of N2H5+ oxidation by ICl and IBr in 0.1-1.0 M [H+] is investigated by following the formation of I2Cl- and I2Br- with excess ICl2- and IBr2-, respectively, when total hydrazine is the limiting reactant. Highly acidic solutions are needed to suppress the rates of N2H4 reactions and to avoid hydrolysis of the interhalogens. Protonation constants of N2H5+, KP2 = [N2H62+]/[N2H5 +][H+], measured spectrophotometrically at 25.0 °C with picric acid as an indicator, are 1.61 M-1 (μ = 0.50 M) and 1.72 M-1 (μ = 1.00 M). In the proposed mechanisms, ICl and IBr react by an I+ transfer process to N2H5+ with loss of H+ (k1) to form a steady-state species, IN2H4+, that eliminates I- and H+ to give N2H3+ (k2). Subsequent reactions consume a second interhalogen, as diazine (N2H2) is rapidly oxidized to N2. Rate constants (25.0 °C, μ = 1.00 M) for the ICl/N2H5+ reaction are k1 = 4.12 × 106 M-1 s-1, k-1/k2 = 1.9 M-2 and for the IBr/N2H5+ reaction are k1 = 7.6 × 104 M-1 s-1, k-1/k2 = 28 M-2. The relative rates of oxidation of N2H5+ are ICl ? IBr ? I2.
- Jia, Zhongjiang,Margerum, Dale W.
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p. 5374 - 5378
(2008/10/08)
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- Kinetics and mechanism of the oxidation of ammineruthenium(II) complexes by bromine
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The reactions of Ru(NH3)5py2+, Ru(NH3)4bpy2+, Ru2(NH3)10pz5+,RuRh(NH 3)10pz5+ and Ru(NH3)5pz2+ with bromine are first-order in ruthenium and first-order in bromine. The rates decrease with increasing bromide ion concentration and, except for Ru(NH3)5pz2+, are independent of hydrogen ion concentration. The reactions are postulated to proceed via outer-sphere, one-electron transfer from Ru(II) to Br2 with the formation of Br2- as a reactive intermediate. The bromide inhibition is ascribed to the formation of Br3- which is unreactive in outer-sphere reactions because of the barrier imposed by the need to undergo reductive cleavage. The reaction of Ru (NH3)5pz2+ is inhibited by hydrogen ions. The hydrogen ion dependence shows that Ru(NH3)5pzH3+ has a pKa of 2.49 and is at least 500 times less reactive than Ru(NH3)5pz2+. The reaction of Ru2(NH3)10pz4+ with bromine is biphasic. The second phase has a rate identical to that of the Ru2(NH3)10pz5+-Br2 reaction. A detailed analysis shows that the reaction of Ru2(NH3)10pz4+ with bromine proceeds by a sequence of one-electron steps, Br2- being produced as an intermediate. A linear free energy relationship between rate constants and equilibrium constants, obeyed for all the reactions studied, provides an estimate of ~ 1.5×102 M-1 s-1 for the self-exchange rate constant of the Br2/Br2- couple.
- Plotkin, Stuart,Haim, Albert
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p. 189 - 196
(2008/10/08)
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- Kinetics and mechanism of oxidation of heterocyclic aldehydes by acid bromate
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The kinetics and mechanism of oxidation of some heterocyclic aldehydes viz. furan-2-aldehyde, pyrrole-2-aldehyde and thiophene-2-aldehyde by acid bromate in H2SO4 - HOAc medium have been studied. The reaction is first order each in [BrO3 -] and [substrate] and second order in [H+]. The products of oxidation are the corresponding carboxylic acids. From the study of effect of hetero atom of the molecule on rate, HBrO3 and protonated heteroaldehyde have been established as the reactive species. The order of reactivity is found to be furan-2-aldehyde > pyrrole-2- aldehyde > thiophene-2-aldehyde. A suitable mechanism has been proposed and discussed.
- Veeraiah,Sondu
-
p. 328 - 330
(2007/10/03)
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- Temperature dependence of the rate constants and branching ratios for the reactions of Cl- (D2O)1-3 with CH3Br and thermal dissociation rates for Cl-(CH3Br)
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The rate constants and products for the reactions of Cl-(D2O)(n) + CH3Br (n = 1-3) have been measured. The n = 1 reaction was studied from 238 to 478 K. The rate constant is well described by k = (6.0 x 10-10) exp(-1270/T) cm3 s-1. We determined the reaction mechanism to be ligand switching to produce Cl-(CH3Br) followed by thermal decomposition of the complex. Cl-(CH3Br) decomposition produces greater than 90% Br- + CH3Cl with the remainder being Cl- + CH3Br. The Cl-(CH3Br) + He rate constant is well described by k = (4.5 x 10-10) exp(-2260/T) cm3 s-1. RRKM theory was used to model the decomposition of Cl-(CH3Br). The results are consistent with our experimental results if a central barrier height of 22.5 kJ mol-1 is used. The n = 2 and 3 reactions also proceed by ligand switching followed by thermal decomposition. The n = 2 reaction was studied from 203 to 298 K. The rate constant is well-described by (4.4 x 10-9) exp(-1329/T) cm3 s-1. The main product observed was Cl-(D2O) with a smaller amount of Cl-(D2O)(CH3Br) also detected. The n = 3 reaction was studied from 188 to 203 K. The reaction was about a factor of 1.8 faster than the n = 2 reaction. The main product was Cl-(D2O)2 with smaller amounts of Cl-(D2O)2(CH3Br) and Cl-(D2O)(CH3Br) also observed.
- Seeley, John V.,Morris, Robert A.,Viggiano,Wang, Haobin,Hase, William L.
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p. 577 - 584
(2007/10/03)
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- Equilibrium and Kinetics of Bromine Hydrolysis
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Equilibrium constants for bromine hydrolysis, K1 = [HOBr][H+][Br-]/[Br2(aq)], are determined as a function of ionic strength (μ) at 25.0 °C and as a function of temperature at μ ? 0 M. At μ ? 0 M and 25.0 °C, K1 = (3.5 ± 0.1) × 10-9 M2 and ΔH° = 62 ± 1 kJ mol-1. At μ = 0.50 M and 25.0 °C, K1 = (6.1 ± 0.1) × 10-9 M2 and the rate constant (k-1 for the reverse reaction of HOBr + H+ + Br- equals (1.6 ± 0.2) × 1010 M-2 s-1. This reaction is general-acid-assisted with a Bronsted a value of 0.2. The corresponding Br2(aq) hydrolysis rate constant, k1, equals 97 s-1, and the reaction is general-base-assisted (β = 0.8).
- Beckwith, Richard C.,Wang, Tian Xiang,Margerum, Dale W.
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p. 995 - 1000
(2008/10/09)
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- A gaskinetic investigation of HOBr reactions with Cl(2P), O(3P) and OH(2Π). the reaction of BrCl with OH(2Π)
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The reactions of HOBr with atomic chlorine (1), with oxygen (2) and with hydroxyl radicals (3) have been investigated at 300 K using the discharge flow technique with mass-spectrometric detection. The rate constants based on HOBr consumption have been determined to be k, = (8.0±0.4) · 10-11 and k2 = (3.1±0.2)· 10-11. For the reaction with OH radicals k3-13 was obtained. All rate constants are given in units cm3 molecule-1 s-1. The reactions of HOBr with Cl and with O are shown to proceed via bromine abstraction with formation of BrCl and BrO, respectively. The predominant channel in the reaction of OH with BrCl was identified to be step (4a) OH + BrCl → HOBr + Cl (4a) Based on the present kinetic investigation the heat of formation for HOBr at T = 300 K was evaluated to be ΔHf0 (HOBr) = -(60.22 ± 2) kJ · mol-1. VCH Verlagsgesellschaft mbH, 1996.
- Kukui,Kirchner,Benter, Th,Schindler
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p. 455 - 461
(2007/10/03)
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- Very Low Pressure Reactor Study of the H + HBr ->/<- H2 + Br Reaction
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The reaction of H atoms, generated by microwave discharge of H2/Ar gas mixtures, with HBr has been studied employing the very low pressure reactor (VLPR) technique.Reactants and reaction products were followed by mass spectrometry.Rate constants of (5.4 +/- 0.7) x 1E-12, (6.3 +/- 0.8) x 1E-12, and (6.8 +/- 0.4) x 1E-12 cm3 molecule-1 s-1 were extracted for the title reaction at 268, 298, and 333 K, respectively.Difficulties were encountered in obtaining mass balance closure for molecular hydrogen, owing to its production from the internal surfaces of the phosphoric acid coated quartz microwave tube.Formation of very small amounts of molecular bromide, detected at m/e 158, 160, and 162, appeared due to some back-diffusion of HBr into the microwave tube.Br2 formation was observed to be a function of discharge power and, at sufficiently high powers, could be reduced below detection limits.Under these conditions, bromine mass balances (Br2, Br, and HBr)were around (95 +/- 5)percent.A transtion state calculation provides an estimated preexponential factor for the reaction in good agreement with our experimental results and with those available from the other most recent temperature-dependent studies.The temperature dependence of reaction 1 can be expressed by k1/cm3 molecule -1 s-1 = 9.96 x 1E-13T0.5 exp(-300/T) over the temperature range 200-1000 K.
- Mitchell, Terence J.,Gonzalez, Alicia C.,Benson, Sidney W.
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p. 16960 - 16966
(2007/10/02)
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- Syntheses, Characterization, and Properties of Vanadium(III) Complexes Containing Tripodal Tetradentate Ligands with Single Pyridyl Groups
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The syntheses, characterization, and properties of (1a), (1b), (2), and Br2 (3) are described, where pda (N-(2-pyridylmethyl)iminodiacetate), bpg (N,N-bis(2-pyridylmethyl)glycinate), and tpa (tris(2-pyridylmethyl)amine) are tripodal tetradentate ligands with single pyridyl groups.Complexes 1a, 1b, and 2 were characterized on the basis of their electronic and Raman spectra.The structure of 3 was determined by X-ray crystallography.Complex 3 crystallizes in the P space group with the following unit cell dimensions: a=11.505(5), b=11.509(5), c=16.348(7) Angstroem, α=103.73(2) deg, β=103.71(2) deg, γ=93.26(3) deg, and Z=2.The V-O-V angle is 175.3(2) deg and the V-μ-O distances are 1.783(2) and 1.784(2) Angstroem.In complex 3, the four unpaired electrons are ferromagnetically coupled.It was found that there is a positive correlation between 2 * νas(V-O-V) and the energy of the oxo-to- V(III) charge-transfer transition for single oxo-bridged dinuclear vanadium(III) complexes including the present complexes.This correlation is discussed in terms of the ? character of the V(III)-μ-O bond that is affected by the remaining donor groups.
- Kanamori, Kan,Kameda, Eiji,Kabetani, Takatsugu,Suemoto, Taiko,Okamoto, Ken-ichi,Kaizaki, Sumio
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p. 2581 - 2590
(2007/10/03)
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