from first principles PP-I-1

OP-II-3Mechanism for the Reduction of Dioxygen by Diethylhydroxylamine(DEHA) Organocatalyzed by Natural PolyphenolsAubry J.M., Nardello-Rataj V.Université de Lille Nord de France, Laboratoire de Chimie Moléculaire et Formulation,EA-4478, Cité Scientifique, F-59652 Villeneuve d’Ascq CEDEX, Francejean-marie.aubry@univ-lille1.frA reduction of dioxygen dissolved in water by diethylhydroxylamine (DEHA) in the presenceof hydroquinones or quinones as organocatalysts was investigated with regard to reaction rateand catalyst turnover. Eleven p-benzoquinone derivatives bearing various electron-donating,electron-withdrawing and bulky substituents were studied. The catalytic activity of fourbenzenediols (hydroquinone, resorcinol, catechol and 4-tert-butylcatechol) and of fourbenzenetriols (hydroxyquinol, phloroglucinol, pyrogallol and 5-tert-butylpyrogallol) iscompared.Mechanistic and kinetic studies indicate that therate-determining step is the regeneration ofhydroquinones through the reduction of thecorresponding benzoquinones by DEHA.Then, eight natural polyphenols were tested as alternative catalysts to the potential carcinogenhydroquinone. Four of them (purpurin, myricetin, gallic acid and propyl gallate) exhibitedsome catalytic activity and gallic acid was shown to be even more efficient than hydroquinoneitself.A further improvement of the catalytic system was achieved by adding catalase todisproportionate the generated hydrogen peroxide, which is detrimental for the catalyst. Thus,the oxygen scavenging system DEHA–gallic acid–catalase has been found to be not onlygreener but also more efficient than the current system DEHA–hydroquinone since it giveswater instead of hydrogen peroxide as the final reduction product of dioxygen.Reference:[1] R. Lebeuf , Y. Zhu , V. Nardello-Rataj , J.P. Lallier and J.M. AubryGreen Chem. (2012) DOI: 10.1039/C2GC16503A38