Kinetics and mechanism of the oxygenation of potassium flavonolate. Evidence for an electron transfer mechanism

László Barhács, J. Kaizer, G. Speier

Research output: Contribution to journalArticle

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Abstract

The oxygenation of the potassium salt of flavonol (flaH) in absolute DMF leads to potassium O-benzoylsalicylate and carbon monoxide in 95% yield at 40 °C. Kinetic measurements resulted in the rate law -d[flaK]/dt = k2[flaK][O2]. The rate constant, activation enthalpy, and entropy at 313.16 K are as follows: k2/M-1 s-1 = (3.28 ± 0.10) x 10-1, ΔH(+)/kJ mol- 1 = 29 ± 2, ΔS(+)/J mo1-1 K-1 = -161 ± 6. The reaction fits a Hammett linear free energy relationship for 4'-substituted flavonols, and electron- releasing groups make the oxygenation reaction faster. The anodic oxidation wave potentials Ea of the 4'-substituted flavonolates correlate well with reaction rates. At more negative Ea values faster reaction rates were observed. EPR spectrum of the reaction mixture (g = 2.0038, dH = 1.8 G, a(H)= 0.9 G) showed the presence of flavonoxyl radical as a result of a SET from the flavonolate to dioxygen.

Original languageEnglish
Pages (from-to)3449-3452
Number of pages4
JournalJournal of Organic Chemistry
Volume65
Issue number11
DOIs
Publication statusPublished - Jun 2 2000

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Oxygenation
Reaction rates
Potassium
Flavonols
Kinetics
Electrons
Anodic oxidation
Carbon Monoxide
Free energy
Paramagnetic resonance
Enthalpy
Rate constants
Entropy
Salts
Chemical activation
Oxygen
3-hydroxyflavone

ASJC Scopus subject areas

  • Organic Chemistry

Cite this

Kinetics and mechanism of the oxygenation of potassium flavonolate. Evidence for an electron transfer mechanism. / Barhács, László; Kaizer, J.; Speier, G.

In: Journal of Organic Chemistry, Vol. 65, No. 11, 02.06.2000, p. 3449-3452.

Research output: Contribution to journalArticle

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N2 - The oxygenation of the potassium salt of flavonol (flaH) in absolute DMF leads to potassium O-benzoylsalicylate and carbon monoxide in 95% yield at 40 °C. Kinetic measurements resulted in the rate law -d[flaK]/dt = k2[flaK][O2]. The rate constant, activation enthalpy, and entropy at 313.16 K are as follows: k2/M-1 s-1 = (3.28 ± 0.10) x 10-1, ΔH(+)/kJ mol- 1 = 29 ± 2, ΔS(+)/J mo1-1 K-1 = -161 ± 6. The reaction fits a Hammett linear free energy relationship for 4'-substituted flavonols, and electron- releasing groups make the oxygenation reaction faster. The anodic oxidation wave potentials Ea of the 4'-substituted flavonolates correlate well with reaction rates. At more negative Ea values faster reaction rates were observed. EPR spectrum of the reaction mixture (g = 2.0038, dH = 1.8 G, a(H)= 0.9 G) showed the presence of flavonoxyl radical as a result of a SET from the flavonolate to dioxygen.

AB - The oxygenation of the potassium salt of flavonol (flaH) in absolute DMF leads to potassium O-benzoylsalicylate and carbon monoxide in 95% yield at 40 °C. Kinetic measurements resulted in the rate law -d[flaK]/dt = k2[flaK][O2]. The rate constant, activation enthalpy, and entropy at 313.16 K are as follows: k2/M-1 s-1 = (3.28 ± 0.10) x 10-1, ΔH(+)/kJ mol- 1 = 29 ± 2, ΔS(+)/J mo1-1 K-1 = -161 ± 6. The reaction fits a Hammett linear free energy relationship for 4'-substituted flavonols, and electron- releasing groups make the oxygenation reaction faster. The anodic oxidation wave potentials Ea of the 4'-substituted flavonolates correlate well with reaction rates. At more negative Ea values faster reaction rates were observed. EPR spectrum of the reaction mixture (g = 2.0038, dH = 1.8 G, a(H)= 0.9 G) showed the presence of flavonoxyl radical as a result of a SET from the flavonolate to dioxygen.

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