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)

Gábor Bellér, Mária Szabó, G. Lente, I. Fábián

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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 1H NMR and ESI-MS methods. The results presented here offer the possibility of designing an experimental protocol for preparing phenO2.

Original languageEnglish
Pages (from-to)5345-5353
Number of pages9
JournalJournal of Organic Chemistry
Volume81
Issue number13
DOIs
Publication statusPublished - Jul 1 2016

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Phenanthrolines
Ions
Oxidation
Kinetics
Oxides
1,10-phenanthroline
potassium peroxymonosulfuric acid
Rate constants
Hydrogen bonds
Nuclear magnetic resonance
Atoms
Substrates

ASJC Scopus subject areas

  • Organic Chemistry

Cite this

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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 1H NMR and ESI-MS methods. The results presented here offer the possibility of designing an experimental protocol for preparing phenO2.",
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T1 - Formation of 1,10-phenanthroline-N,N′-dioxide under mild conditions

T2 - The kinetics and mechanism of the oxidation of 1,10-phenanthroline by peroxomonosulfate ion (Oxone)

AU - Bellér, Gábor

AU - Szabó, Mária

AU - Lente, G.

AU - Fábián, I.

PY - 2016/7/1

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N2 - 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 1H NMR and ESI-MS methods. The results presented here offer the possibility of designing an experimental protocol for preparing phenO2.

AB - 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 1H NMR and ESI-MS methods. The results presented here offer the possibility of designing an experimental protocol for preparing phenO2.

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