Reactions Of Free Radicals In Solution Research Articles

21] Electron and hydrogen atom transfer reactions: Determination of free radical redox potentials by pulse radiolysis

Pulse radiolysis technique is proving to be, particularly useful for the kinetic and thermodynamic study of free-radical reactions in solution. A large variety of free-radical reactions relevant to biochemistry, biology, and medicine can be observed directly. Electron-transfer cascades, catalytic action of glutathione and related thiols in linking hydrogen transfer and electron-transfer reactions, and protection of vitamin E by vitamin C are just three examples. In the study of hydrogen atom and electron-transfer reactions, most of the experiments to date, particularly those linked to biology, have been undertaken in systems in which water is the principal component. The choice and concentrations of the selective free-radical scavengers to be used depend on the type of reaction to be studied and on the relative rates of reaction of the compounds of interest compared to those for the other solutes under study. In principle, in any multisolute system the proportion of a particular radical reacting with a particular component will depend on the rate constants of the individual reactions and the respective solute concentrations. Typical scavengers used in the studies of electron- and hydrogen-transfer reactions together with the absolute rate constants of the initial interactions, that must be used when designing the composition of solutions to be irradiated, are available.

Free radical reactions in solution : VIII. Radical-initiated addition of trialkylsilanes across alkene CC bonds

Difficulties in carrying out the free-radical addition of trialkylsilanes (as opposed to trichlorosilane) to alkene CC bonds are partly due to telomerization competing with the radical transfer step. This can be overcome by the use of a large excess of trialkylsilane, when good yields of adduct are obtained from mono-substituted and 1,2-disubstituted alkenes.

Free radical reactions in solution VIII. Radical-initiated addition of trialkylsilanes across alkene C=C bonds

Summary Difficulties in carrying out the free-radical addition of trialkylsilanes (as opposed to trichlorosilane) to alkene C=C bonds are partly due to telomerization competing with the radical transfer step. This can be overcome by the use of a large excess of trialkylsilane, when good yields of adduct are obtained from mono-substituted and 1,2-disubstituted alkenes.

ChemInform Abstract: FREE RADICAL REACTIONS IN SOLUTION. PART 7. SUBSTITUENT EFFECTS ON FREE RADICAL REACTIONS: COMPARISON OF THE Σ· SCALE WITH OTHER MEASURES OF RADICAL STABILIZATION

Chemischer InformationsdienstVolume 12, Issue 47 Preparative Organic Chemistry ChemInform Abstract: FREE RADICAL REACTIONS IN SOLUTION. PART 7. SUBSTITUENT EFFECTS ON FREE RADICAL REACTIONS: COMPARISON OF THE Σ· SCALE WITH OTHER MEASURES OF RADICAL STABILIZATION S. DINCTUERK, Search for more papers by this authorR. A. JACKSON, Search for more papers by this author S. DINCTUERK, Search for more papers by this authorR. A. JACKSON, Search for more papers by this author First published: November 24, 1981 https://doi.org/10.1002/chin.198147108AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume12, Issue47November 24, 1981 RelatedInformation

ChemInform Abstract: FREE RADICAL REACTIONS IN SOLUTION. PART 6. THERMAL DECOMPOSITION OF SUBSTITUTED DIBENZYL MERCURIALS IN SOLUTION. AN IMPROVED Σ· SCALE

Chemischer InformationsdienstVolume 12, Issue 47 Preparative Organic Chemistry ChemInform Abstract: FREE RADICAL REACTIONS IN SOLUTION. PART 6. THERMAL DECOMPOSITION OF SUBSTITUTED DIBENZYL MERCURIALS IN SOLUTION. AN IMPROVED Σ· SCALE S. DINCTUERK, S. DINCTUERKSearch for more papers by this authorR. A. JACKSON, R. A. JACKSONSearch for more papers by this authorM. TOWNSON, M. TOWNSONSearch for more papers by this authorH. AGIRBAS, H. AGIRBASSearch for more papers by this authorN. C. BILLINGHAM, N. C. BILLINGHAMSearch for more papers by this authorG. MARCH, G. MARCHSearch for more papers by this author S. DINCTUERK, S. DINCTUERKSearch for more papers by this authorR. A. JACKSON, R. A. JACKSONSearch for more papers by this authorM. TOWNSON, M. TOWNSONSearch for more papers by this authorH. AGIRBAS, H. AGIRBASSearch for more papers by this authorN. C. BILLINGHAM, N. C. BILLINGHAMSearch for more papers by this authorG. MARCH, G. MARCHSearch for more papers by this author First published: November 24, 1981 https://doi.org/10.1002/chin.198147107Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume12, Issue47November 24, 1981 RelatedInformation

Free radical reactions in solution. Part 6. Thermal decomposition of substituted dibenzyl mercurials in solution. An improved σ˙ scale

The kinetics of the decomposition of ten substituted dibenzylmercury compounds in solution have been determined in the temperature range 126–156°. From the relative rates at 140.2°, a new scale of substituent constants σ˙ applicable to free radical reactions is derived. E.s.r. spectra for seven substituted benzyl radicals show a reasonable correlation of aα–CH2 with σ˙.

Free radical reactions in solution. Part 7. Substituent effects on free radical reactions: comparison of the σ˙ scale with other measures of radical stabilization

The σ˙ scale of radical stabilization derived from the thermal decomposition of substituted dibenzyl mercurials is compared with other proposed scales. By using the σ˙ scale, the parameter ρ˙ can be used as a probe for the amount of radical character developed or destroyed in the transition state of a free radical reaction.

Free radical reactions in solution. Part 4. Radical-initiated reduction of acid chlorides to alkanes by tri-n-propylsilane: removal of unwanted carboxy-groups from organic molecules

Aliphatic acyl chlorides RCOCl react with tripropylsilane in the presence of t-butyl peroxide at 140–170° to give the corresponding alkane RH. Yields are good when R is a primary or secondary alkyl group, poor when R is tertiary or benzylic, and zero when R is phenyl. A radical chain reaction is postulated. The reaction should be synthetically useful for removing carboxy-groups from carboxylic acids RCO2H, where R is a primary or secondary alkyl group.

Free radical reactions in solution. Part 3. The decomposition of dibenzylmercury in toluene

Dilute solutions of dibenzylmercury decompose on heating in toluene solution to give mercury and bibenzyl as the main products, along with traces of 1,2,3-triphenylpropane and stilbene. Phenyl-p-tolylmethane was absent. The decomposition of dilute solutions of the mercurial initially follows first-order kinetics in the temperature range 130–160°. Arrhenius parameters are log10A 16.0 ± 0.3; E 38.5 ± 0.5 kcal mol–1. The rate-determining process is probably homolysis of one benzyl–mercury bond. In concentrated solutions, particularly at the higher temperatures, the kinetics of the decomposition are more complex.

Kinetic applications of ESR spectroscopy to some reactions of the t-butoxy radical in solution

Kinetic studies of free radical reactions in solution are often laborious and difficult to carry out over a wide range of temperature. As a result, the literature contains relatively few reports of Arrhenius parameters for these reactions. We have tried to devise simple ESR techniques for studying key steps in radical reactions with a view to measuring activation parameters. The study of unimolecular radical decompositions, which are often not readily accommodated by conventional techniques, is particularly suited to the ESR method. We would like to illustrate the ESR method with three examples. Bimolecular homolytic substitution (S,2) reactions occurring at metal centres in organometallic compounds have been the subject of a good deal of recent interest (I, 2). This prompted us to attempt a kinetic study of the reactions of t-butoxy radicals with organoboron compounds, with a view to elucidating some of the factors which influence the rates of these substitution processes. t-Butoxy radicals may be generated in the cavity of the ESR spectrometer by photolysis of di-t-butyl peroxide (3) or thermolysis of di-t-butyl hyponitrite (4) solutions (Eqs. [l and 21). In the presence of an alkylboron compound a rapid displacement reaction takes place, producing a readily observable concentration of alkyl radicals (Eq. [3]). These reactions provide a facile method of generating specific alkyl radicals for ESR study [5].

1007. Kinetics of free-radical reactions in solution. Part I. Evaluation of rate constants for transfer reactions in systems with varying radical concentrations

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Free radical chemistry in solution

Considers the general characteristics of free radical reactions in solution, types of free radical reactions, and the effect of structure on bond dissociation energies.

Free radical reactions in solution initiated by heavy metal ions

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Some recent developments in the chemistry of free-radical reactions in solution

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The autoxidation of tetralin

The autoxidation of tetralin can be photosensitized by suitable vat dyes. This reaction can therefore be investigated by standard photochemical techniques. The kinetics have in this way been shown to conform to the scheme suggested by Bolland & Gee (1946) for autoxidations. The absolute velocity constants for the elementary processes have been evaluated, and the activation energies and frequency factors estimated (table 4). The frequency factors of free radical reactions in solution have been discussed. It is suggested that the ‘normal’ frequency factor for such a reaction is about 107. It is pointed out that the techniques described in this paper should be generally applicable to the study of free radical reactions in solution.