- Spectral properties and absolute rate constants for β-scission of ring-substituted cumyloxyl radicals. A laser flash photolysis study
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A laser flash photolysis study of the spectral properties and β-scission reactions of a series of ring-substituted cumyloxyl radicals has been carried out. All cumyloxyl radicals display a broad absorption band in the visible region of the spectrum, which decays on the microsecond time scale, leading to a strong increase in absorption in the UV region of the spectrum, which is attributed to the corresponding acetophenone formed after β-scission of the cumyloxyl radicals. The position of the visible absorption band is red-shifted by the presence of electron-donating ring substituents, while a blue-shift is observed in the presence of electron-withdrawing ring substituents, suggesting that + R ring substituents promote charge separation in the excited cumyloxyl radical through stabilization of the partial positive charge on the aromatic ring of an incipient radical zwitterion. Along this line, an excellent Hammett-type correlation between the experimentally measured energies at the visible absorption maxima of the cumyloxyl radicals and σ+ substituent constants is obtained. A red-shift is also observed on going from MeCN to MeCN/H2O for all cumyloxyl radicals, pointing toward a specific effect of water. The ring substitution does not influence to a significant extent the rate constants for β-scission of the cumyloxyl radicals, which varies between 7.1 × 105 and 1.1 × 106 s-1, a result that suggests that cumyloxyl radical β-scission is not governed by the stability of the resulting acetophenone. Finally, κβ increases on going from MeCN to the more polar MeCN/H2O 1:1 for all cumyloxyl radicals, an observation that reflects the increased stabilization of the transition state for β-scission through increased solvation of the incipient acetophenone product.
- Baciocchi, Enrico,Bietti, Massimo,Salamone, Michela,Steenken, Steen
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p. 2266 - 2270
(2007/10/03)
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- Catalytic selective oxidation of alkyl arenes to aryl tert. butyl peroxides with TBHP over Ru-exchanged Montmorillonite K10
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A mild and efficient catalytic method for the benzylic oxidation of alkyl arenes to the corresponding tert. butyl aryl peroxides is described using a catalytic amount of reusable solid, Ru(III)-exchanged Montmorillonite K10 and 70% tert. butyl hydroperoxide (TBHP) as oxidant.
- Nikalje, Milind D.,Sudalai
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p. 5903 - 5908
(2007/10/03)
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- Steric and Electronic Substituent Effects in Tertiary Alkyl Peroxide Decompositions
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Rate constants for the homolysis of aryl- substituted α-cumyl tert-butyl peroxides (X-PhCMe2OOCMe3) produce a Hammett plot with a ρ value of -0.22 +/- .04.Both steric and electronic parameters influence the decomposition rate constants of tertiary alkyl peroxides with bulky substituents: log krel = (-0.40 +/- .08)Σ?* - (0.43 +/- .02)ΣEsc.
- Hendrickson, William H.,Nguyen, Chi C.,Nguyen, Jackie T.,Simons, Kim T.
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p. 7217 - 7220
(2007/10/02)
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- New Syntheses of Mixed Peroxides under Gif-Barton Oxidation of Alkylbenzenes, Conjugated Alkenes and Alkanes; a Free-radical Mechanism
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Syntheses of mixed peroxides are performed under Gif oxidation of alkylaromatics, electron-rich conjugated alkenes (styrene, α-methylstyrene) or cyclohexane and acrylonitrile; chemical and kinetic evidence support a free-radical redox chain mechanism.
- Minisci, Francesco,Fontana, Francesca,Araneo, Silvia,Recupero, Francesco
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p. 1823 - 1824
(2007/10/02)
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