Bond dissociation enthalpies (BDE) of hydroxylamines containing alkyl, aryl, vinyl, and carbonyl substituents at the nitrogen atom have been determined by using the EPR radical equilibration technique in order to study the effect of the substituents on the O−H bond strength of these compounds. It has been found that substitution of an alkyl group directly bonded to the nitrogen atom with vinyl or aryl groups has a small effect, while substitution with acyl groups induces a large increase of the O−H BDE value. Thus, dialkyl hydroxylamines have O−H bond strengths of only ca. 70 kcal/mol, while acylhydroxylamines and N-hydroxyphthalimide (NHPI), containing two acyl substituents at nitrogen, are characterized by BDE values of ca. 80 and 88 kcal/mol, respectively. Since the phthalimide N-oxyl radical (PINO) has been recently proposed as an efficient oxidation catalyst of hydrocarbons or other substrates, the large BDE value found for the parent hydroxylamine (NHPI) justifies this proposal. Kinetic studies, carried out in order to better understand the mechanism of the NHPI-catalyzed aerobic oxidation of cumene, are consistent with a simple kinetic model where the rate-determining step is the hydrogen atom abstraction from the hydroxylamine by cumylperoxyl radicals.

(2003). Hydroxylamines as Oxidation Catalysts: Thermochemical and Kinetic Studies [journal article - articolo]. In JOURNAL OF ORGANIC CHEMISTRY. Retrieved from http://hdl.handle.net/10446/121708

Hydroxylamines as Oxidation Catalysts: Thermochemical and Kinetic Studies

Fontana, F.;
2003-01-01

Abstract

Bond dissociation enthalpies (BDE) of hydroxylamines containing alkyl, aryl, vinyl, and carbonyl substituents at the nitrogen atom have been determined by using the EPR radical equilibration technique in order to study the effect of the substituents on the O−H bond strength of these compounds. It has been found that substitution of an alkyl group directly bonded to the nitrogen atom with vinyl or aryl groups has a small effect, while substitution with acyl groups induces a large increase of the O−H BDE value. Thus, dialkyl hydroxylamines have O−H bond strengths of only ca. 70 kcal/mol, while acylhydroxylamines and N-hydroxyphthalimide (NHPI), containing two acyl substituents at nitrogen, are characterized by BDE values of ca. 80 and 88 kcal/mol, respectively. Since the phthalimide N-oxyl radical (PINO) has been recently proposed as an efficient oxidation catalyst of hydrocarbons or other substrates, the large BDE value found for the parent hydroxylamine (NHPI) justifies this proposal. Kinetic studies, carried out in order to better understand the mechanism of the NHPI-catalyzed aerobic oxidation of cumene, are consistent with a simple kinetic model where the rate-determining step is the hydrogen atom abstraction from the hydroxylamine by cumylperoxyl radicals.
journal article - articolo
1-gen-2003
Amorati, R.; Lucarini, M.; Mughaini, V.; Pedulli, G. F.; Minisci, F.; Recupero, F.; Fontana, Francesca; Astolfi, P.; Greci, L.
(2003). Hydroxylamines as Oxidation Catalysts: Thermochemical and Kinetic Studies [journal article - articolo]. In JOURNAL OF ORGANIC CHEMISTRY. Retrieved from http://hdl.handle.net/10446/121708
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10446/121708
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