Kinetic Study of the Hydrogen Abstraction Reaction of the Benzotriazole-N-oxyl Radical (BTNO) with H-Donor Substrates (Articolo in rivista)

Type
Label
  • Kinetic Study of the Hydrogen Abstraction Reaction of the Benzotriazole-N-oxyl Radical (BTNO) with H-Donor Substrates (Articolo in rivista) (literal)
Anno
  • 2005-01-01T00:00:00+01:00 (literal)
Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#doi
  • 10.1021/jo051615n (literal)
Alternative label
  • Brandi P.; Galli C.; Gentili P. (2005)
    Kinetic Study of the Hydrogen Abstraction Reaction of the Benzotriazole-N-oxyl Radical (BTNO) with H-Donor Substrates
    in Journal of organic chemistry
    (literal)
Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#autori
  • Brandi P.; Galli C.; Gentili P. (literal)
Pagina inizio
  • 9521 (literal)
Pagina fine
  • 9528 (literal)
Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#numeroVolume
  • 70 (literal)
Rivista
Note
  • ISI Web of Science (WOS) (literal)
Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#affiliazioni
  • Dipartimento di Chimica and IMC-CNR Sezione Meccanismi di Reazione, Universita` 'La Sapienza' (literal)
Titolo
  • Kinetic Study of the Hydrogen Abstraction Reaction of the Benzotriazole-N-oxyl Radical (BTNO) with H-Donor Substrates (literal)
Abstract
  • The aminoxyl radical (>N-O¥) BTNO (benzotriazole-N-oxyl) has been generated by the oxidation of 1-hydroxybenzotriazole (HBT; >N-OH) with a CeIV salt in MeCN. BTNO presents a broad absorption band with ìmax 474 nm and ? 1840 M-1 cm-1, and spontaneously decays with a firstorder rate constant of 6.3 ? 10-3 s-1 in MeCN at 25 °C. Characterization of BTNO radical by EPR, laser flash photolysis, and cyclic voltammetry is provided. The spontaneous decay of BTNO is strongly accelerated in the presence of H-donor substrates such as alkylarenes, benzyl and allyl alcohols, and alkanols, and rate constants of H-abstraction by BTNO from a number of substrates have been spectroscopically investigated at 25 °C. The kinetic isotope effect confirms the H-abstraction step as rate-determining. Activation parameters have been measured in the 15-40 °C range with selected substrates. A correlation between Ea and BDE(C-H) (C-H bond dissociation energy) for a small series of H-donors has been obtained according to the Evans-Polanyi equation, giving R ) 0.44. From this plot, the experimentally unavailable BDE(C-H) of benzyl alcohol can be extrapolated, as ca. 79 kcal/mol. With respect to the H-abstraction step, peculiar differences in the ¢Sq parameter emerge between an alkylarene, ArC(H)R2, and a benzyl alcohol, ArC(H)(OH)R. The data acquired on the H-abstraction reactivity of BTNO are compared with those recently reported for the aminoxyl radical PINO (phthalimide-N-oxyl), generated from N-hydroxyphthalimide (HPI). The higher reactivity of radical PINO is explained on the basis of the higher energy of the NO-H bond of HPI, as compared with that of HBT (88 vs ca. 85 kcal/mol, respectively), which is formed on H-abstraction from the RH substrate. (literal)
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