- Kinetics of sulfur oxide, sulfur fluoride, and sulfur oxyfluoride anions with atomic species at 298 and 500 K
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The rate constants and product-ion branching ratios for the reactions of sulfur dioxide (SO2-), sulfur fluoride (SF n-), and sulfur oxyfluoride anions (SOxF y-) with H, H2, N, N2, NO, and O have been measured in a selected-ion flow tube (SIFT). H atoms were generated through a microwave discharge on a H2/He mixture, whereas O atoms were created via N atoms titrated with NO, where the N had been created by a microwave discharge on N2. None of the ions reacted with H 2, N2 or NO; thus, the rate constants are -12 cm3 s-1. SOxFy - ions react with H by only fluorine-atom abstraction to form HF at 298 and 500 K. Successive F-atom removal does not occur at either temperature, and the rate constants show no temperature dependence over this limited range. SO2- and F- undergo associative detachment with H to form a neutral molecule and an electron. Theoretical calculations of the structures and energetics of HSO2- isomers were performed and showed that structural differences between the ionic and neutral HSO 2 species can account for at least part of the reactivity limitations in the SO2- + H reaction. All of the SOxF y- ions react with O; however, only SO2 - reacts with both N and O. SOxFy- reactions with N (SO2- excluded) have a rate constant limit of -11 cm3 s-1. The rate constants for the SOxFy- reactions with H and O are ≤25% of the collision rate constant, as seen previously in the reactions of these ions with O3, consistent with a kinetic bottleneck limiting the reactivity. The only exceptions are the reactions of SO2 - with N and O, which are much more efficient. Three pathways were observed with O atoms: F-atom exchange in the reactant ion, F- exchange in the reactant ion, and charge transfer to the O atom. No associative detachment was observed in the N- and O-atom reactions.
- Midey, Anthony J.,Viggian
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p. 1852 - 1859
(2008/10/09)
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- Reactivity and role of SO5?- radical in aqueous medium chain oxidation of sulfite to sulfate and atmospheric sulfuric acid generation
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This study reevaluates the role of peroxymonosulfate anion radical (-O3SOO? or SO5?-) intermediate during radical-induced chain oxidation of HSO3-/SO32- in oxygenated aqueous solution. The SO5?- radical absorption band in the UV is weak: ε = 1065 ± 80 M-1 cm-1 at λmax (260-265 nm). The SO5?- radical takes part in two radical-radical and four radical-solute reactions, partially producing the other chain carrier, the SO4?- radical, in either case. In this study, employing the pulse-radiolysis technique but adopting a new approach, these two types of reactions of the SO5?- radical have been separately quantified (at room temperature). For example, over pH 3.5-12, the branching ratio of (SO5?- + SO5?-) reactions giving rise to either the SO4?- radical or S2O82- is found to remain ~1. The respective reaction rate constants for I → 0 are (2.2 ± 0.3) and (2.1 ± 0.3) × 108 M-1 s-1. The (SO5?- + HSO3-) reactions in acid pH follow two paths, forming the SO4?- radical in one and regenerating the SO3?- radical in the other, with respective rates of ca. (6.0 ± 0.4) and (3.0 ± 0.3) × 107 M-1 s-1. In alkaline pH (for SO5?- + SO32- reactions), the rates for similar reactions are ca. (5.6 ± 0.6) and (1.0 ± 0.1) × 108 M-1 s-1. From only these results, the earlier prediction of chain length reaching a few thousands could be supported in simulation studies (Bigelow, S. L. Z. Phys. Chem. 1898, 28, 493. Young, S. W. J. Am. Chem. Soc. 1902, 24, 297. Titoff, A. Z. Phys. Chem. 1903, 45, 641. Ba?ckstro?m, H. L. J. J. Am. Chem. Soc. 1927, 49, 1460. Alyea, H. N.; Ba?ckstro?m, H. L. J. J. Am. Chem. Soc. 1929, 51, 90). To explore the feasibility of controlling S(IV) chain oxidation to sulfuric acid in liquid hydrometeors, the effect of radical scavenging on each SOx?- radical (x = 3, 4, 5) was simulated. The results show that for the SO5?- radical a scavenger reactivity of ~100 s-1 may be enough to reduce the chain length by >98%. However, in the case SO4?- radical scavenging under similar conditions, only ~75-80% reduction in acid production was observed. These results suggest a fresh modeling of sulfuric acid generation in atmospheric liquid hydrometeors.
- Das, Tomi Nath
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p. 9142 - 9155
(2007/10/03)
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- Temperature Dependence of the Rate Constants for Reaction of Dihalide and Azide Radicals with Inorganic Reductants
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Rate constants for several reactions of inorganic radicals with inorganic reductants in aqueous solutions have been measured by pulse radiolysis as a function of temperature, generally between 5 and 75 deg C.The reactions studied were of the dihalide radicals, Cl2.-, Br2.-, and I2.-, the (SCN).- radical, and the neutral radical N3., reacting with the substitution-inert metal complexes, Fe(CN)6(4-), Mo(CN)8(4-), and W(CN)8(4-), and with the anions SO3(2-), HSO3(1-), NO2(1-), and ClO2(1-).The rate constants measured were in the range of 1E6 to 5E9 M-1 s-1and the calculated Arrhenius activation energies ranged from 5 to 35 kJ mol-1.The preexponential factors also varied considerably, with log A ranging from 8.9 to 13.1.The temperature dependence of the reaction rate constant is correlated to the reaction exothermicity for the metal complexes, which apparently react by outer-sphere electron transfer.The simple anions, however, have lower activation energies, which do not correlate well with the exothermicities, suggesting that these anions probably react by inner-sphere mechanism.
- Shoute, L. C. T.,Alfassi, Z. B.,Neta, P.,Huie, R. E.
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p. 3238 - 3242
(2007/10/02)
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- Electron Transfer From Indoles, Phenol, and Sulfite (SO32-) to Chlorine Dioxide (ClO2.)
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With the ClO2/ClO2- couple as reference the one-electron-reduction potentials have been determined for four methylated indolyl radical cations.Their Eo values are 1.23 V (N-Me), 1.10 V (2-Me), 1.07 V (3-Me), and 0.93 V (2,3-diMe).Eo values were also measured for the following: tryptophylH.+/trypH 1.24 V, SO3.-/SO32- 0.76 V, and phenoxy./phenolate 0.80 V.The redox potentials were obtained from purely kinetic data (for tryptophan and 2-, 3-, and N-methylindole) or from combined kinetic and thermodynamic measurements.
- Merenyi, Gabor,Lind, Johan,Shen, Xinhua
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p. 134 - 137
(2007/10/02)
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- Gas-phase reactions of the hydroperoxide and performate anions
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The flowing afterglow technique has been used to study the reactions of HO2- and HCO3- in the gas phase.The hydroperoxide ion reacts slowly with CO to form HO-, and oxidizes CO2, OCS, CS2, NO, SO2, CH3NCS in fast reactions to form CO3-, CO2S-, COS2-, NO2-, SO3-, CH3NCO2-, and CH3NCOS-, respectively.Reactions of HO2- with certain amides and esters provide synthetic routes for a number of interesting peracyl anions.One of these, the peroxyformate ion, HCO3-, reacts with CO and NO in slow oxidation reactions to form the formate ion HCO2-.It also forms HCO2- upon reaction with acetone and pivalaldehyde, perhaps by Baeyer-Villiger oxidation.
- Bowie, John H.,DePuy, Charles H.,Sullivan, Sally A.,Bierbaum, Veronica M.
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p. 1046 - 1050
(2007/10/02)
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