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Cory Camasta - One of the best experts on this subject based on the ideXlab platform.
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Electronic Structures and Spin Density Distributions of BrO2 and (HO)2BrO Radicals. Mechanisms for Avoidance of Hypervalency and for Spin Delocalization and Spin Polarization
2016Co-Authors: Rainer Glaser, Cory CamastaAbstract:The results are reported of an ab initio study of bromine dioxide BrO2, 1, and of the T-shaped trans- and cis-dihydroxides 2 and 3 of dihydrogen bromate (HO)2BrO. The thermochemistry has been explored of potential synthetic routes to (HO)2BrO involving water addition to BrO2, hydroxyl addition to bromous acid HOBrO, 4, protonation/reduction of bromic acid HOBrO2, 5, via tautomers 6–8 of protonated bromic acid, and by reduction/protonation of bromic acid via radical anion [HOBrO2]−, 9. The potential energy surface analyses were performed at the MP2(full)/6-311G* level (or better) and with the consideration of aqueous solvation at the SMD(MP2(full)/6-311G*) level (or better), and higher-level energies were computed at levels up to QCISD(full,T)/6-311++G(2df,2pd)//MP2. The addition of RO radical to bromous acid or Bromite esters and the reduction of protonated bromic acid or protonated bromate esters are promising leads for possible synthetic exploration. Spin density distributions and molecular electrostatic potentials were computed at the QCISD(full)/6-311G*//MP2(full)/6-311G* level to characterize the electronic structures of 1–3. Both radicals employ maximally occupied (pseudo) π-systems to transfer electron density from bromine to the periphery. While the formation of the (3c-5e) π-system suffices to avoid hypervalency in 1, the formation of the (4c-7e) π-system in 2 or 3 still leaves the bromine formally hypervalent and (HO)2BrO requires delocalization of bromine density into σ*-SMOs over the trans O–Br–O moiety. Molecular orbital theory is employed to describe the mechanisms for the avoidance of hypervalency and for spin delocalization and spin polarization. The (4c-7e) π-system in 2 is truly remarkable in that it contains five π-symmetric spin molecular orbitals (SMO) with unique shapes
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Electronic Structures and Spin Density Distributions of BrO2 and (HO)2BrO Radicals. Mechanisms for Avoidance of Hypervalency and for Spin Delocalization and Spin Polarization
Inorganic chemistry, 2013Co-Authors: Rainer Glaser, Cory CamastaAbstract:The results are reported of an ab initio study of bromine dioxide BrO2, 1, and of the T-shaped trans- and cis-dihydroxides 2 and 3 of dihydrogen bromate (HO)2BrO. The thermochemistry has been explored of potential synthetic routes to (HO)2BrO involving water addition to BrO2, hydroxyl addition to bromous acid HOBrO, 4, protonation/reduction of bromic acid HOBrO2, 5, via tautomers 6–8 of protonated bromic acid, and by reduction/protonation of bromic acid via radical anion [HOBrO2]−, 9. The potential energy surface analyses were performed at the MP2(full)/6-311G* level (or better) and with the consideration of aqueous solvation at the SMD(MP2(full)/6-311G*) level (or better), and higher-level energies were computed at levels up to QCISD(full,T)/6-311++G(2df,2pd)//MP2. The addition of RO radical to bromous acid or Bromite esters and the reduction of protonated bromic acid or protonated bromate esters are promising leads for possible synthetic exploration. Spin density distributions and molecular electrostati...
Johanna Rollin - One of the best experts on this subject based on the ideXlab platform.
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The occurrence of bromate and perbromate on BDD anodes during electrolysis of aqueous systems containing bromide: first systematic experimental studies
Journal of Applied Electrochemistry, 2011Co-Authors: M. E. Henry Bergmann, Tatiana Iourtchouk, Johanna RollinAbstract:Bromide electrolysis was carried out on laboratory-scale cells in the range of 1–1,005 mg [Br^−] dm^−3 using boron-doped diamond (BDD) anodes. These studies were part of fundamental research activities on drinking water electrolysis for disinfection. Synthetic water systems were mostly used in the experiments, which varied the temperature between 5 and 30 °C, the current density between 50 and 700 A m^−2, and the rotation rate of the rotating anode between 100 and 500 rpm (laminar regime). HypoBromite and bromate were found as by-products, as expected. Bromite was not detected. Higher bromate levels were formed at higher current density, but no clear relationship was observed between bromate concentration and the rotation rate or temperatures between 5 and 30 °C. Bromate yields higher than 90% were found at higher charge passed. Perbromate was found as a new potential synthesis or disinfection by-product (DBP), but no perbromate was detected at the lowest bromide concentrations and under drinking water conditions. The perbromate yield was about 1%, and somewhat lower when bromate was used as a starting material instead of bromide. At a temperature of 5 °C more perbromate was detected compared with experiments at 20°. Approximately 20 times more perchlorate was formed compared with perbromate formation in the presence of chloride ions of equimolar concentration. State of mechanistic considerations is presented and a mechanism for perbromate formation is proposed. The reaction from bromate to perbromate was found to be limited that is in contrast to the earlier studied chlorate-to-perchlorate conversion. In the measured concentration range, reduction processes at the mixed oxide cathode showed a much higher impact on the resulting concentration for perbromate than for bromate.
Rainer Glaser - One of the best experts on this subject based on the ideXlab platform.
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Electronic Structures and Spin Density Distributions of BrO2 and (HO)2BrO Radicals. Mechanisms for Avoidance of Hypervalency and for Spin Delocalization and Spin Polarization
2016Co-Authors: Rainer Glaser, Cory CamastaAbstract:The results are reported of an ab initio study of bromine dioxide BrO2, 1, and of the T-shaped trans- and cis-dihydroxides 2 and 3 of dihydrogen bromate (HO)2BrO. The thermochemistry has been explored of potential synthetic routes to (HO)2BrO involving water addition to BrO2, hydroxyl addition to bromous acid HOBrO, 4, protonation/reduction of bromic acid HOBrO2, 5, via tautomers 6–8 of protonated bromic acid, and by reduction/protonation of bromic acid via radical anion [HOBrO2]−, 9. The potential energy surface analyses were performed at the MP2(full)/6-311G* level (or better) and with the consideration of aqueous solvation at the SMD(MP2(full)/6-311G*) level (or better), and higher-level energies were computed at levels up to QCISD(full,T)/6-311++G(2df,2pd)//MP2. The addition of RO radical to bromous acid or Bromite esters and the reduction of protonated bromic acid or protonated bromate esters are promising leads for possible synthetic exploration. Spin density distributions and molecular electrostatic potentials were computed at the QCISD(full)/6-311G*//MP2(full)/6-311G* level to characterize the electronic structures of 1–3. Both radicals employ maximally occupied (pseudo) π-systems to transfer electron density from bromine to the periphery. While the formation of the (3c-5e) π-system suffices to avoid hypervalency in 1, the formation of the (4c-7e) π-system in 2 or 3 still leaves the bromine formally hypervalent and (HO)2BrO requires delocalization of bromine density into σ*-SMOs over the trans O–Br–O moiety. Molecular orbital theory is employed to describe the mechanisms for the avoidance of hypervalency and for spin delocalization and spin polarization. The (4c-7e) π-system in 2 is truly remarkable in that it contains five π-symmetric spin molecular orbitals (SMO) with unique shapes
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Electronic Structures and Spin Density Distributions of BrO2 and (HO)2BrO Radicals. Mechanisms for Avoidance of Hypervalency and for Spin Delocalization and Spin Polarization
Inorganic chemistry, 2013Co-Authors: Rainer Glaser, Cory CamastaAbstract:The results are reported of an ab initio study of bromine dioxide BrO2, 1, and of the T-shaped trans- and cis-dihydroxides 2 and 3 of dihydrogen bromate (HO)2BrO. The thermochemistry has been explored of potential synthetic routes to (HO)2BrO involving water addition to BrO2, hydroxyl addition to bromous acid HOBrO, 4, protonation/reduction of bromic acid HOBrO2, 5, via tautomers 6–8 of protonated bromic acid, and by reduction/protonation of bromic acid via radical anion [HOBrO2]−, 9. The potential energy surface analyses were performed at the MP2(full)/6-311G* level (or better) and with the consideration of aqueous solvation at the SMD(MP2(full)/6-311G*) level (or better), and higher-level energies were computed at levels up to QCISD(full,T)/6-311++G(2df,2pd)//MP2. The addition of RO radical to bromous acid or Bromite esters and the reduction of protonated bromic acid or protonated bromate esters are promising leads for possible synthetic exploration. Spin density distributions and molecular electrostati...
Torsten C. Schmidt - One of the best experts on this subject based on the ideXlab platform.
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a new reaction pathway for Bromite to bromate in the ozonation of bromide
Environmental Science & Technology, 2015Co-Authors: Alexandra Fischbacher, Clemens Von Sonntag, Katja Loppenberg, Torsten C. SchmidtAbstract:Ozone is often used in the treatment of drinking water. This may cause problems if the water to be treated contains bromide as its reaction with ozone leads to the formation of bromate, which is considered to be carcinogenic. Bromate formation is a multistep process resulting from the reaction of ozone with Bromite. Although this process seemed to be established, it has been shown that ozone reacts with Bromite not by the previously assumed mechanism via O transfer but via electron transfer. Besides bromate, the electron-transfer reaction also yields O3•–, the precursor of OH radicals. The experiments were set up in such a way that OH radicals are not produced from ozone self-decomposition but solely by the electron-transfer reaction. This study shows that hydroxyl radicals are indeed generated by using tBuOH as the OH radical scavenger and measuring its product, formaldehyde. HOBr and bromate yields were measured in systems with and without tBuOH. As OH radicals contribute to bromate formation, higher br...
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A New Reaction Pathway for Bromite to Bromate in the Ozonation of Bromide
2015Co-Authors: Alexandra Fischbacher, Clemens Von Sonntag, Katja Löppenberg, Torsten C. SchmidtAbstract:Ozone is often used in the treatment of drinking water. This may cause problems if the water to be treated contains bromide as its reaction with ozone leads to the formation of bromate, which is considered to be carcinogenic. Bromate formation is a multistep process resulting from the reaction of ozone with Bromite. Although this process seemed to be established, it has been shown that ozone reacts with Bromite not by the previously assumed mechanism via O transfer but via electron transfer. Besides bromate, the electron-transfer reaction also yields O3•–, the precursor of OH radicals. The experiments were set up in such a way that OH radicals are not produced from ozone self-decomposition but solely by the electron-transfer reaction. This study shows that hydroxyl radicals are indeed generated by using tBuOH as the OH radical scavenger and measuring its product, formaldehyde. HOBr and bromate yields were measured in systems with and without tBuOH. As OH radicals contribute to bromate formation, higher bromate and HOBr yields were observed in the absence of tBuOH than in its presence, where all OH radicals are scavenged. On the basis of the results presented here, a pathway from bromide to bromate, revised in the last step, was suggested
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Formation of bromate in sulfate radical based oxidation: mechanistic aspects and suppression by dissolved organic matter.
Water Research, 2014Co-Authors: Holger V. Lutze, Rani Bakkour, Nils Kerlin, Clemens Von Sonntag, Torsten C. SchmidtAbstract:Sulfate radical based oxidation is discussed being a potential alternative to hydroxyl radical based oxidation for pollutant control in water treatment. However, formation of undesired by-products, has hardly been addressed in the current literature, which is an issue in other oxidative processes such as bromate formation in ozonation of bromide containing water (US-EPA and EU drinking water standard of bromate: 10 μg L−1). Sulfate radicals react fast with bromide (k = 3.5 × 109 M−1 s−1) which could also yield bromate as final product. The mechanism of bromate formation in aqueous solution in presence of sulfate radicals has been investigated in the present paper. Further experiments were performed in presence of humic acids and in surface water for investigating the relevance of bromate formation in context of pollutant control. The formation of bromate by sulfate radicals resembles the well described mechanism of the hydroxyl radical based bromate formation. In both cases hypobromous acid is a requisite intermediate. In presence of organic matter formation of bromate is effectively suppressed. That can be explained by formation of superoxide formed in the reaction of sulfate radicals plus aromatic moieties of organic matter, since superoxide reduces hypobromous acid yielding bromine atoms and bromide. Hence formation of bromate can be neglected in sulfate radical based oxidation at typical conditions of water treatment.
Roberto B. Faria - One of the best experts on this subject based on the ideXlab platform.
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Modeling the complex bromate-iodine reaction.
The journal of physical chemistry. A, 2009Co-Authors: Priscilla B. Machado, Roberto B. FariaAbstract:In this article, it is shown that the FLEK model (ref 5) is able to model the experimental results of the bromate−iodine clock reaction. Five different complex chemical systems, the bromate−iodide clock and oscillating reactions, the Bromite−iodide clock and oscillating reactions, and now the bromate−iodine clock reaction are adequately accounted for by the FLEK model.
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Systematic design of chemical oscillators. 86. Combined mechanism explaining nonlinear dynamics in bromine(III) and bromine(V) oxidations of iodide ion
The Journal of Physical Chemistry, 1993Co-Authors: Roberto B. Faria, Irving R. Epstein, Istvan Lengyel, Kenneth KustinAbstract:A mechanism is presented that explains the full range of dynamics exhibited in the oxidations of iodide ion by both bromine(III) (Bromite) and bromine(V) (bromate) in closed and open reactors, including clock reactions and oscillations. This comprehensive model comprises 28 steps and 14 species, includes IBr as a reactive intermediate, and contains a reaction sequence autocatalytic in HOBr. Kinetics curves and phase diagrams simulated with this model show very good agreement with experiment.
