Pulse radiolysis of aqueous CNS? solutions and the rates of hydroxyl-radical reactions

Baxendale, J. H.; Stott, D. A.

doi:10.1039/c19670000699

Cited by 10 publications

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“…The oxidation product of thiocyanate anions following the reaction with OH radicals in aqueous solution was first studied by Adams et al, 11,12 who identified the SCN radical as an absorber. Subsequently, more detailed studies 13,14 of the formation of the transient species at low SCN À concentration demonstrated that the product is (SCN) 2…”

Section: Competition Methodsmentioning

confidence: 99%

Kinetics of reactions of OH with organic carbonyl compounds in aqueous solution

Gligorovski

Herrmann

2004

Phys. Chem. Chem. Phys.

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The OH radical plays an important role in tropospheric chemistry. The OH radical is a very strong oxidant and its reactivity contributes to the atmospheric degradation of volatile organic compounds in aqueous solution. In this work the temperature dependencies of the rate constants for the reactions of OH with the following organic carbonyl compounds, (1) methyl ethyl ketone (MEK), (2) acetonylacetone, (3) isobutyraldehyde, (4) ethyl formate and (5) diacetyl are studied. By means of laser flash photolysis and applying a competition kinetics method the following Arrhenius expressions were obtained: Reaction of OH with methyl ethyl ketone : k 1 ðTÞ ¼ ð5:1 AE 0:6Þ Â 10 11 exp À1804 AE 914 T M À1 s À1 Reaction of OH with acetonylacetone : k 2 ðTÞ ¼ ð1:1 AE 0:1Þ Â 10 11 exp À1485 AE 542 T M À1 s À1 Reaction of OH with isobutyraldehyde : k 3 ðTÞ ¼ ð3:0 AE 0:1Þ Â 10 10 exp À700 AE 347 T M À1 s À1 Reaction of OH with ethyl formate : k 4 ðTÞ ¼ ð1:8 AE 0:1Þ Â 10 10 exp À1194 AE 447 T M À1 s À1 Reaction of OH with diacetyl : k 5 ðTÞ ¼ ð4:3 AE 0:3Þ Â 10 12 exp À2880 AE 590 T M À1 s À1The errors stated throughout this study are statistical errors for a confidence interval of 95%. Reaction mechanisms are discussed and Evans-Polanyi correlations are presented.

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Section: Competition Methodsmentioning

confidence: 99%

Kinetics of reactions of OH with organic carbonyl compounds in aqueous solution

Gligorovski

Herrmann

2004

Phys. Chem. Chem. Phys.

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“…The selected value from Buxton [3] was not considered since it is an averaged and not an experimentally obtained value. Furthermore, the value from Adams [64] was not included since it was later shown by Baxendale [65] that the reported value from Adams refers to R4 rather than to R2. The reported rate constant for R2 from Baxendale 1967 [65] and 1968 [66] is significantly larger than all the other available rate constants for reaction R2.…”

Section: Kineticsmentioning

confidence: 99%

Tropospheric Aqueous‐Phase Free‐Radical Chemistry: Radical Sources, Spectra, Reaction Kinetics and Prediction Tools

et al. 2010

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The most important radicals which need to be considered for the description of chemical conversion processes in tropospheric aqueous systems are the hydroxyl radical (OH), the nitrate radical (NO(3)) and sulphur-containing radicals such as the sulphate radical (SO(4)(-)). For each of the three radicals their generation and their properties are discussed first in the corresponding sections. The main focus herein is to summarize newly published aqueous-phase kinetic data on OH, NO(3) and SO(4)(-) radical reactions relevant for the description of multiphase tropospheric chemistry. The data compilation builds up on earlier datasets published in the literature. Since the last review in 2003 (H. Herrmann, Chem. Rev. 2003, 103, 4691-4716) more than hundred new rate constants are available from literature. In case of larger discrepancies between novel and already published rate constants the available kinetic data for these reactions are discussed and recommendations are provided when possible. As many OH kinetic data are obtained by means of the thiocyanate (SCN(-)) system in competition kinetic measurements of OH radical reactions this system is reviewed in a subchapter of this review. Available rate constants for the reaction sequence following the reaction of OH+SCN(-) are summarized. Newly published data since 2003 have been considered and averaged rate constants are calculated. Applying competition kinetics measurements usually the formation of the radical anion (SCN)(2)(-) is monitored directly by absorption measurements. Within this subchapter available absorption spectra of the (SCN)(2)(-) radical anion from the last five decades are presented. Based on these spectra an averaged (SCN)(2)(-) spectrum was calculated. In the last years different estimation methods for aqueous phase kinetic data of radical reactions have been developed and published. Such methods are often essential to estimate kinetic data which are not accessible from the literature. Approaches for rate constant prediction include empirical correlations as well as structure activity relationships (SAR) either with or without the usage of quantum chemical descriptors. Recently published estimation methods for OH, NO(3) and SO(4)(-) radical reactions in aqueous solution are finally summarized, compared and discussed.

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“…7,8 The rate coefficient corresponding to reaction 1 was reported to be 2.8 × 10 10 M -1 s -1 , and the equilibrium constant was K 2 ) 2 × 10 5 M -1 . The effect of ionic strength proved that (SCN) 2 •-is involved in a second-order reaction to give (SCN) 2 and SCN -.…”

Section: Introductionmentioning

confidence: 99%

Pulse Radiolysis of Aqueous Thiocyanate Solution

Milosavljevic

LaVerne

2004

J. Phys. Chem. A

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The pulse radiolysis of N 2 O saturated aqueous solutions of KSCN was studied under neutral pH conditions. The observed optical absorption spectrum of the SCN • radical in solution is more complex than previously reported, but it is in good agreement with that measured in the gas phase. Kinetic traces at 330 and 472 nm corresponding to SCN • and (SCN) 2•-, respectively, were fit using a Monte Carlo simulation kinetic model. The rate coefficient for the oxidation of SCN -ions by OH radicals, an important reaction used in competition kinetics measurements, was found to be (1.4 ( 0.1) × 10 10 M -1 s -1 , about 30% higher than the normally accepted value. A detailed discussion of the reaction mechanism is presented.

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Pulse radiolysis of aqueous CNS? solutions and the rates of hydroxyl-radical reactions

Cited by 10 publications

References 0 publications

Kinetics of reactions of OH with organic carbonyl compounds in aqueous solution

Kinetics of reactions of OH with organic carbonyl compounds in aqueous solution

Tropospheric Aqueous‐Phase Free‐Radical Chemistry: Radical Sources, Spectra, Reaction Kinetics and Prediction Tools

Pulse Radiolysis of Aqueous Thiocyanate Solution

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