A time-resolved kinetic study on the hydrogen abstraction reactions from a series of primary and secondary amines by the cumyloxyl (CumO•) and benzyloxyl (BnO•) radicals was carried out. The results were compared with those obtained previously for the corresponding reactions with tertiary amines. Very different hydrogen abstraction rate constants (kH) and intermolecular selectivities were observed for the reactions of the two radicals. With CumO•, kH was observed to decrease on going from the tertiary to the secondary and primary amines. The lowest kH values were measured for the reactions with 2,2,6,6-tetramethylpiperidine (TMP) and tert-octylamine (TOA), substrates that can only undergo N H abstraction. The opposite behavior was observed for the reactions of BnO•, where the kH values increased in the order tertiary < secondary < primary. The kH values for the reactions of BnO• were in all cases significantly higher than those measured for the corresponding reactions of CumO•, and no significant difference in reactivity was observed between structurally related substrates that could undergo exclusive α-C H and N H abstraction. This different behavior is evidenced by the kH(BnO•)/kH(CumO•) ratios that range from 55 85 and 267 673 for secondary and primary alkylamines up to 1182 and 3388 for TMP and TOA. The reactions of CumO• were described in all cases as direct hydrogen atom abstractions. With BnO• the results were interpreted in terms of the rate-determining formation of a hydrogenbonded prereaction complex between the radical α-C H and the amine lone pair wherein hydrogen abstraction occurs. Steric effects and amine HBA ability play a major role, whereas the strength of the substrate α-C H and N H bonds involved appears to be relatively unimportant. The implications of these different mechanistic pictures are discussed.

Salamone, M., Dilabio, G., Bietti, M. (2011). Hydrogen Atom Abstraction Selectivity in the Reactions of Alkylamines with the Benzyloxyl and Cumyloxyl Radicals. The Importance of Structure and of Substrate-Radical Hydrogen Bonding. JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 133, 16625-16634 [10.1021/ja206890y].

Hydrogen Atom Abstraction Selectivity in the Reactions of Alkylamines with the Benzyloxyl and Cumyloxyl Radicals. The Importance of Structure and of Substrate-Radical Hydrogen Bonding

SALAMONE, MICHELA;BIETTI, MASSIMO
2011-09-06

Abstract

A time-resolved kinetic study on the hydrogen abstraction reactions from a series of primary and secondary amines by the cumyloxyl (CumO•) and benzyloxyl (BnO•) radicals was carried out. The results were compared with those obtained previously for the corresponding reactions with tertiary amines. Very different hydrogen abstraction rate constants (kH) and intermolecular selectivities were observed for the reactions of the two radicals. With CumO•, kH was observed to decrease on going from the tertiary to the secondary and primary amines. The lowest kH values were measured for the reactions with 2,2,6,6-tetramethylpiperidine (TMP) and tert-octylamine (TOA), substrates that can only undergo N H abstraction. The opposite behavior was observed for the reactions of BnO•, where the kH values increased in the order tertiary < secondary < primary. The kH values for the reactions of BnO• were in all cases significantly higher than those measured for the corresponding reactions of CumO•, and no significant difference in reactivity was observed between structurally related substrates that could undergo exclusive α-C H and N H abstraction. This different behavior is evidenced by the kH(BnO•)/kH(CumO•) ratios that range from 55 85 and 267 673 for secondary and primary alkylamines up to 1182 and 3388 for TMP and TOA. The reactions of CumO• were described in all cases as direct hydrogen atom abstractions. With BnO• the results were interpreted in terms of the rate-determining formation of a hydrogenbonded prereaction complex between the radical α-C H and the amine lone pair wherein hydrogen abstraction occurs. Steric effects and amine HBA ability play a major role, whereas the strength of the substrate α-C H and N H bonds involved appears to be relatively unimportant. The implications of these different mechanistic pictures are discussed.
6-set-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 Selectivity in the Reactions of Alkylamines with the Benzyloxyl and Cumyloxyl Radicals. The Importance of Structure and of Substrate-Radical Hydrogen Bonding. JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 133, 16625-16634 [10.1021/ja206890y].
Salamone, M; Dilabio, G; Bietti, M
Articolo su rivista
File in questo prodotto:
File Dimensione Formato  
jacs2011.pdf

solo utenti autorizzati

Licenza: Copyright dell'editore
Dimensione 1.53 MB
Formato Adobe PDF
1.53 MB Adobe PDF   Visualizza/Apri   Richiedi una copia

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2108/76289
Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus 46
  • ???jsp.display-item.citation.isi??? 45
social impact