title: Formation of 1,10-Phenanthroline-N,N'-dioxide under Mild Conditions: The Kinetics and Mechanism of the Oxidation of 1,10-Phenanthroline by Peroxomonosulfate Ion (Oxone).
abstract: This paper confirms the unexpected formation of 1,10-phenanthroline-N,N'-dioxide (phenO2) when 1,10-phenanthroline (phen) is oxidized by peroxomonosulfate ion (PMS) in a neutral aqueous solution. The kinetics of oxidation of phen by PMS features a complex pH dependence. In 1.00 M H2SO4, 1,10-phenanthroline-mono-N-oxide (phenO) is the sole product of the reaction. The rate of the N-oxidation is highly dependent on pH with a maximum at pH ∼6.7. The formation of phenO occurs via two parallel pathways: the rate constant of the oxidation of phen (k = 3.1 ± 0.1 M(-1) s(-1)) is significantly larger than that of Hphen(+) [k = (4.1 ± 0.3) × 10(-3) M(-1) s(-1)] because the two N atoms are open to oxidative attack in the deprotonated substrate while an internal hydrogen bond hinders the oxidation of the protonated form. With an excess of PMS, four consecutive oxidation steps were found in nearly neutral solutions. In the early stage of the reaction, the stepwise oxidation results in the formation of phenO, which is converted into phenO2 in the second step. The formation of phenO2 was confirmed by (1)H NMR and ESI-MS methods. The results presented here offer the possibility of designing an experimental protocol for preparing phenO2.
authors.affiliation: MTA-DE Homogeneous Catalysis and Reaction Mechanisms Research Group, University of Debrecen , H-4032 Debrecen, Egyetem tér 1, Hungary.
authors.forename: Gábor
authors.initials: G
authors.lastname: Bellér
authors.affiliation: MTA-DE Homogeneous Catalysis and Reaction Mechanisms Research Group, University of Debrecen , H-4032 Debrecen, Egyetem tér 1, Hungary.
authors.forename: Mária
authors.initials: M
authors.lastname: Szabó
authors.affiliation: Department of Inorganic and Analytical Chemistry, University of Debrecen , H-4032 Debrecen, Egyetem tér 1, Hungary.
authors.forename: Gábor
authors.initials: G
authors.lastname: Lente
authors.affiliation: Department of Inorganic and Analytical Chemistry, University of Debrecen , H-4032 Debrecen, Egyetem tér 1, Hungary.
authors.forename: István
authors.initials: I
authors.lastname: Fábián