摘要:

AbstractAbsolute rate constants for the one electron oxidation of guanine, guanosine, uric acid, xanthine, hypoxanthine, tyrosine, and thymine by various halogenated peroxyl radicals in aqueous solutions have been determined using the technique of pulse radiolysis. Roughly, linear correlations have been observed between the logarithm of these rate constants and Taft's inductive parameter (σ*) for the radicals. However, the rate constants for the radical CBr3O 2˙are slightly higher than those for CCl3O 2˙for most of these compounds. © John Wiley&So

ISSN:0538-8066    

DOI:10.1002/kin.550241202

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe kinetics of the solvolysis of [Co(CN)5Cl]3−ions have been investigated in mixtures formed by the addition of ethane‐1,2‐diol or ethanonitrile to water where the physical properties indicate little enhancement of structure in water‐rich conditions. The effect on the kinetics of this solvolysis of this lack of structural change in the solvent shows in the linearity of the variation of log (rate constant) with the reciprocal of the dielectric constant for the addition of ethane‐1,2‐diol to water and the absence of any prominent extrema in the enthalpy or entropy of activation using either co‐solvent. However, the effect of changes in solvation on the solvolysis with these two co‐solvents appears to operate in a similar manner to the effects found when the hydrophobic co‐solvent propan‐2‐ol is added to water. The application of a free energy cycle to the process of the initial state going to the transition state for this dissociative process suggests that, with both co‐solvents, [Co(CN)5]2−in the transition state is more stable than [Co(CN)5Cl]3−in the initial st

ISSN:0538-8066    

DOI:10.1002/kin.550241203

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe reaction of permanganate ion with pyruvic acid and lactic acid has been studied in aqueous solutions containing 0.10–2.0 mol dm−3alkali. In this range of HO−concentration the reaction\documentclass{article}\pagestyle{empty}\begin{document}$$ 2{\rm MnO}_4 ^- + {\rm Substrate} \to {\rm 2MnO}_{\rm 4} ^{2-} + {\rm product} $$\end{document}is followed slowly by the reduction of manganate, thus, the above process can be studied separately. In the case of lactic acid (LA), the reactive species is alkoxy anion, and the deprotonation constant could be calculated from the kinetic data. A mechanism based on electron abstraction from the alkoxy anion has been proposed. In the case of pyruvic acid (PA) oxidation may proceed with participation of enolate anion, or hydrate anion, or an adduct. These three possibilities have been investigated. © John Wiley&Son

ISSN:0538-8066    

DOI:10.1002/kin.550241204

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractData on the tropospheric degradation of proposed substitutes for ozone depleting CFCs were obtained by conducting photochemical oxidation studies of HCFCs and HFCs using long path Fourier transform infrared spectroscopy. The hydrogen abstraction reactions were initiated using Cl radicals rather than OH radicals because of the rather unreactive nature of the compounds. The experimental product yields at T = 25 ± 3°C and 700 Torr of dry air were: CHClF2(1.11 ± 0.06 C(O)F2); CClFHCF3(1.00 ± 0.04 CF3C(O)F); CF3CHF2(1.09 ± 0.05 C(O)F2); CClF2CH3(0.98 ± 0.03 C(O)F2); CHF2CH3(1.00 ± 0.05 C(O)F2); CF3CH2F (0.16 ± 0.03 CF3CF(O), and 0.83 ± 0.22 HFC(O)), where all standard deviations are 2σ. For each compound, the critical step in determining the oxidation products was the decomposition of a halogenated alkoxy radical. For HCFC‐22 and HCFC‐124, the major alkoxy radical decomposition route was Cl elimination. The HFC‐125 product data were consistent with CC cleavage of a two carbon alkoxy radical as the major decomposition route whereas both CC cleavage and H abstraction by O2were significant contributors to the decomposition of the HFC‐134a alkoxy radical. Secondary Cl reactions in the HCFC‐142b and HFC‐152a experiments prevented an unambiguous determination of the decomposition modes; the data are consistent with both CC bond scission and Cl reactions with halogenated aldehydes producing the oxidation product C(O)F2. With the exception of the HFC‐134a and HFC‐125 data, the proposed mechanisms can account for the major oxidation products. For HFC‐134a and HFC‐125, a number of product bands could not be identified. The bands are likely due to products from reactions involving the C

ISSN:0538-8066    

DOI:10.1002/kin.550241205

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractA study is made of the kinetic salt effects upon the outer‐sphere electron transfer reaction between hexacyanoferrate(II) and 4‐pyridinecarboxylatopentaamminecobalt(III). The observed salts effects are analyzed, taking into account the possible association of the reactants with the ions of the supporting electrolyte, though no conclusive results could be obtained. A correlation has been established between the logarithm of the observed second‐order rate constants and the logarithm of the rate constants for a related innersphere electron transfer reaction. From this correlation the conclusion can be drawn that the observed salt effects in concentrated electrolyte solutions are mainly due to the effects on the electron transfer step. © John Wiley&Son

ISSN:0538-8066    

DOI:10.1002/kin.550241206

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractWe studied the kinetics of theN‐chlorination of 2‐aminobutyric, 3‐aminoisobutyric, and 4‐aminobutyric acids by sodium hypoclorite in strongly alkaline aqueous solution. As in the case of other amines, the rate of formation of the fourN‐chloroamino acids was proportional to the concentrations of hypochlorite and amino acid, and inversely proportional to the concentration of hydroxyl ions. A reaction mechanism compatible with these results is proposed and discussed. © John Wiley

ISSN:0538-8066    

DOI:10.1002/kin.550241207

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractWe have found in our recent kinetic study of the oxidation of HCN by NO2in the temperature range 623–773 K that HNCO and CO2are very important early products. The measured kinetic data cannot be accounted for by a “conventional” mechanism involving HCN reactions with NO2, O, and OH. However, the introduction of the isomerization reaction HCN → HNC, followed by the rapid oxidation of HNC by NO2, O, and OH, can quantitatively simulate all measured kinetic data. A similar study of the NO2+ HCN reaction in shock waves at temperatures between 1500 and 2400 K also required the inclusion of HNC reactions in order to quantitatively account for measured product distributions. The effects of the HNC molecule on the high temperature HCN chemistry are discussed in terms of the predicted rate constants for HNC reactions with O and OH employing the BAC‐MP4 method. © John Wiley

ISSN:0538-8066    

DOI:10.1002/kin.550241208

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

ISSN:0538-8066    

DOI:10.1002/kin.550241209

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

ISSN:0538-8066    

DOI:10.1002/kin.550241210

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

ISSN:0538-8066    

DOI:10.1002/kin.550241201

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY