title: Hydroxylamines as oxidation catalysts: thermochemical and kinetic studies.
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.
authors.affiliation: Dipartimento di Chimica Organica A. Mangini, Università degli Studi di Bologna, Via S. Donato 15, 40127 Bologna, Italy.
authors.forename: Riccardo
authors.initials: R
authors.lastname: Amorati
authors.forename: Marco
authors.initials: M
authors.lastname: Lucarini
authors.forename: Veronica
authors.initials: V
authors.lastname: Mugnaini
authors.forename: Gian Franco
authors.initials: GF
authors.lastname: Pedulli
authors.forename: Franceso
authors.initials: F
authors.lastname: Minisci
authors.forename: Francesco
authors.initials: F
authors.lastname: Recupero
authors.forename: Francesca
authors.initials: F
authors.lastname: Fontana
authors.forename: Paola
authors.initials: P
authors.lastname: Astolfi
authors.forename: Lucedio
authors.initials: L
authors.lastname: Greci