A time-resolved kinetic study on the hydrogen atom abstraction reactions from a series of tertiary amines by the cumyloxyl (CumO•) and benzyloxyl (BnO•) radicals was carried out. With the sterically hindered triisobutylamine, comparable hydrogen atom abstraction rate constants (kH) were measured for the two radicals (kH(BnO•)/kH(CumO•) = 2.8), and the reactions were described as direct hydrogen atom abstractions. With the other amines, increases in kH(BnO•)/ kH(CumO•) ratios of 13 to 2027 times were observed. kH approaches the diffusion limit in the reactions between BnO• and unhindered cyclic and bicyiclic amines, whereas a decrease in reactivity is observed with acyclic amines and with the hindered cyclic amine 1,2,2,6,6-pentamethylpiperidine. These results provide additional support to our hypothesis that the reaction proceeds through the rate-determining formation of a C H/N hydrogen-bonded prereaction complex between the benzyloxyl R-C H and the nitrogen lone pair wherein hydrogen atom abstraction occurs, and demonstrate the important role of amine structure on the overall reactionmechanism. Additional mechanistic information in support of this picture is obtained from the study of the reactions of the amines with a deuterated benzyloxyl radical (PhCD2O•, BnO•-d2) and the 3,5-di-tert-butylbenzyloxyl radical.

Salamone, M., Dilabio, G., Bietti, M. (2011). Hydrogen Atom Abstraction Reactions from Tertiary Amines by Benzyloxyl and Cumyloxyl Radicals: Influence of Structure on the Rate-Determining Formation of a Hydrogen Bonded Pre-reaction Complex. JOURNAL OF ORGANIC CHEMISTRY, 76, 6264-6270 [10.1021/jo201025j].

Hydrogen Atom Abstraction Reactions from Tertiary Amines by Benzyloxyl and Cumyloxyl Radicals: Influence of Structure on the Rate-Determining Formation of a Hydrogen Bonded Pre-reaction Complex

SALAMONE, MICHELA;BIETTI, MASSIMO
2011-06-29

Abstract

A time-resolved kinetic study on the hydrogen atom abstraction reactions from a series of tertiary amines by the cumyloxyl (CumO•) and benzyloxyl (BnO•) radicals was carried out. With the sterically hindered triisobutylamine, comparable hydrogen atom abstraction rate constants (kH) were measured for the two radicals (kH(BnO•)/kH(CumO•) = 2.8), and the reactions were described as direct hydrogen atom abstractions. With the other amines, increases in kH(BnO•)/ kH(CumO•) ratios of 13 to 2027 times were observed. kH approaches the diffusion limit in the reactions between BnO• and unhindered cyclic and bicyiclic amines, whereas a decrease in reactivity is observed with acyclic amines and with the hindered cyclic amine 1,2,2,6,6-pentamethylpiperidine. These results provide additional support to our hypothesis that the reaction proceeds through the rate-determining formation of a C H/N hydrogen-bonded prereaction complex between the benzyloxyl R-C H and the nitrogen lone pair wherein hydrogen atom abstraction occurs, and demonstrate the important role of amine structure on the overall reactionmechanism. Additional mechanistic information in support of this picture is obtained from the study of the reactions of the amines with a deuterated benzyloxyl radical (PhCD2O•, BnO•-d2) and the 3,5-di-tert-butylbenzyloxyl radical.
29-giu-2011
Pubblicato
Rilevanza internazionale
Articolo
Esperti anonimi
Settore CHIM/06 - CHIMICA ORGANICA
English
Con Impact Factor ISI
Salamone, M., Dilabio, G., Bietti, M. (2011). Hydrogen Atom Abstraction Reactions from Tertiary Amines by Benzyloxyl and Cumyloxyl Radicals: Influence of Structure on the Rate-Determining Formation of a Hydrogen Bonded Pre-reaction Complex. JOURNAL OF ORGANIC CHEMISTRY, 76, 6264-6270 [10.1021/jo201025j].
Salamone, M; Dilabio, G; Bietti, M
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2108/76311
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