Rate constants for the reactions of free radicals with oxygen in solution

Maillard, B.; Ingold, K. U.; Scaiano, J. C.

doi:10.1021/ja00353a039

Cited by 465 publications

(315 citation statements)

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“…Ph 2 CH • reacts effectively with O 2 . 59,63 Given the concentration of O 2 in airsaturated acetonitrile at ambient temperature (1.9 mM) 64 and a first order lifetime of 350 ns, a rate constant for the consumption of benzyl by O 2 was roughly estimated at 1.5 × 10 9 M -1 s -1 , which compares well with reported values. 63 Further evidence for the assignment of the transient absorption spectrum in Figure 3 is the observation of fluorescence of Ph 2 -CH • .…”

Section: Chartsupporting

confidence: 79%

Generation and Decay of Aryl Sulfinyl and Sulfenyl Radicals: A Transient Absorption and Computational Study

et al. 1997

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Absorption spectra and extinction coefficients of phenylsulfinyl and phenylsulfenyl (thiyl) radicals are determined by nanosecond laser photolysis in various solvents. Direct observation and characterization of arylsulfinyl radicals from the photolysis of several aromatic sulfoxides provides the strongest evidence to date for R-cleavage as the predominant primary photochemical process for these compounds. The absorption spectrum of phenylsulfinyl, with λ max ) 300 and 450 nm and ) 1.1 × 10 4 and 1.3 × 10 3 M -1 cm -1 , is practically independent of solvent. Quantum yields of free sulfinyl radicals range from 0.09 to 0.18 in various solvents. Recombination rate constants very near diffusion control indicate that there is a large spin-orbital coupling in the radical pair. Rate constants for the reactions of arylsulfinyl radicals with stable nitroxide radicals are among the fastest known, but reactivity with O 2 is very modest. Computations indicate that the singly occupied molecular orbital is a π* orbital largely localized on the sulfur and oxygen atoms.

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Section: Chartsupporting

confidence: 79%

Generation and Decay of Aryl Sulfinyl and Sulfenyl Radicals: A Transient Absorption and Computational Study

et al. 1997

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“…The dissolved oxygen seems to play an active role leading to peroxy-radicals, ROO • (R = H, alkyl, aryl) [24][25][26] and peroxy-radicals serve as chain propagators and oxidize organic materials either by hydrogen abstraction or electron transfer process [28][29][30]. Under light irradiation, the additional generation OH • -radicals improve the kinetics of the Orange II mineralization (20) as reported earlier for Fenton systems [7,26].…”

Section: Influence Of the Gas Atmosphere On The Orange II Mineralizatmentioning

confidence: 93%

Bleaching and photobleaching of Orange II within seconds by the oxone/Co2+ reagent in Fenton-like processes

Fernández

Maruthamuthu

Renken

et al. 2004

Applied Catalysis B: Environmental

125

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Accelerated bleaching, photobleaching and mineralization of the non-biodegradable azo-dye, Orange II, was observed with oxone in solutions with Co 2+ -ions. The bleaching rate of Orange II in the dark was found to follow a first-order kinetics with respect to [Co 2+ ] with a rate constant of 20 M −1 s −1 . Fitting of the Orange II photobleaching experimental points in the presence of the Co 2+ /oxone reagent was carried out and followed the trend known for reactions presenting a chain radical branched mechanism. The photobleaching trace could be fitted by a single mathematical expression with an error <5% with respect to the experimental data. The bleaching trace observed for the Orange II solution in the dark followed zero-order decay kinetics. In a typical run, Orange II (0.20 mM or TOC 30 mg C/l) in the presence of oxone and Co 2+ was bleached under visible light within ∼15 s. The Co 2+ -ion concentrations necessary to catalyze the Orange II mineralization by oxone was observed to be ∼100 times lower than the oxone concentration. A 100% TOC decrease, under visible light irradiation, was attained for an Orange II (0.2 mM) solution in the presence of Co 2+ -ions (0.06 mM) and oxone (20 mM) within times ∼70 min for solutions purged with oxygen. Under visible light irradiation, Orange II mineralization in the presence of O 2 involves the photo-dissociation of reaction intermediates leading to organic peroxides in the second step of the mineralization process.

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“…This reaction, which is essentially a radical-radical coupling reaction, produces a lipid peroxyl radical and proceeds under normal oxygen pressure at or near the diffusion-controlled rate of approximately 10 9 M -1 s -1 (Ingold 1969;Maillard et al 1983). As a result, the peroxyl radical is the main chain-carrying species in the autoxidation reaction mixture provided that oxygen is present in sufficient concentration.…”

Section: Figurementioning

confidence: 99%

“…This mechanistic proposal has been critically viewed. First, direct isomerization of the allyl radicals is considered unlikely because the rearrangement of the allyl radical from cis to trans is thermodynamically unfavourable (Gardner 1989) and because under normal oxygen pressures the allyl radials are trapped by molecular oxygen at or near the diffusion controlled rate (Ingold 1969;Maillard et al 1983). Secondly, this mechanism fails to give an adequate explanation for the observed isomeric distribution or its dependency on the concentration of hydrogen atom donors added to the autoxidation mixture (Porter et al 1994a).…”

Section: Hydroperoxide Formation During Autoxidation Of Monoene Fattymentioning

confidence: 99%

Autoxidation of Conjugated Linoleic Acid Methyl Ester in the Presence of α‐Tocopherol: The Hydroperoxide Pathway

Pajunen

Johansson

Hase

et al. 2008

Lipids

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The autoxidation of conjugated linoleic acid (CLA) is poorly understood in spite of increasing interest in the beneficial biological properties of CLA and growing consumption of CLA-rich foods. In this thesis, the autoxidation reactions of the two major CLA isomers, 9-cis,11-transoctadecadienoic acid and 10-trans,12-cis-octadecadienoic acid, are investigated. The results contribute to an understanding of the early stages of the autoxidation of CLA methyl ester, and provide for the first time a means of producing and separating intact CLA methyl ester hydroperoxides as well as basic knowledge on lipid hydroperoxides and their hydroxy derivatives.Conjugated diene allylic monohydroperoxides were discovered as primary autoxidation products formed during autoxidation of CLA methyl esters in the presence and absence oftocopherol. This established that one of the autoxidation pathways of CLA methyl ester is the hydroperoxide pathway.Hydroperoxides were produced from the two major CLA methyl esters by taking advantage of the effect of -tocopherol to promote hydroperoxide formation. The hydroperoxides were analysed and separated first as methyl hydroxyoctadecadienoates and then as intact hydroperoxides by HPLC. The isolated products were characterized by UV, GC-MS, and NMR techniques. In the presence of a high amount of -tocopherol, the autoxidation of CLA methyl ester yields six kinetically-controlled conjugated diene monohydroperoxides and is diastereoselective in favour of one particular geometric isomer as a pair of enantiomers. The primary autoxidation products produced from the two major CLA isomers include new positional isomers of conjugated diene monohydroperoxides, the 8-, 10-, 12-, and 14-hydroperoxyoctadecadienoates. Furthermore, two of these new positional isomers have an unusual structure for a cis,trans lipid hydroperoxide where the allylic methine carbon is adjacent to the cis instead of the usual trans double bond.The 1 H and 13 C NMR spectra of nine isomeric methyl hydroxyoctadecadienoates and of ten isomeric methyl hydroperoxyoctadecadienoates including the unusual cis,trans hydroperoxides, i.e. Me 8-OOH-9c,11t and Me 14-OOH-10t,12c, were fully assigned with the aid of 2D NMR spectroscopy. The assigned NMR data enabled determination of the effects of the hydroxyl and hydroperoxyl groups on the carbon chemical shifts of CLA isomers, identification of diagnostic signals, and determination of chemical shift differences of the olefinic resonances that may help with the assignment of structure to as yet unknown lipid hydroperoxides either as hydroxy derivatives or as intact hydroperoxides.A mechanism for the hydroperoxide pathway of CLA autoxidation in the presence of a high amount of -tocopherol was proposed based on the characterized primary products, their relative distribution, and theoretical calculations. This is an important step forward in CLA research, where exact mechanisms for the autoxidation of CLA have not been presented before. Knowledge of these hydroperoxide formation steps is of cr...

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Rate constants for the reactions of free radicals with oxygen in solution

Cited by 465 publications

References 3 publications

Generation and Decay of Aryl Sulfinyl and Sulfenyl Radicals: A Transient Absorption and Computational Study

Generation and Decay of Aryl Sulfinyl and Sulfenyl Radicals: A Transient Absorption and Computational Study

Bleaching and photobleaching of Orange II within seconds by the oxone/Co2+ reagent in Fenton-like processes

Autoxidation of Conjugated Linoleic Acid Methyl Ester in the Presence of α‐Tocopherol: The Hydroperoxide Pathway

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