Kinetics and mechanism of the base-catalyzed oxygenation of flavonol in DMSO-H(2)O solution.
The kinetics of the base-catalyzed oxygenation of flavonol have been investigated in 50% DMSO-H(2)O solution in the pH range 6.4-10.8 and an ionic strength of 0.1 mol L(-1) using spectrophotometric techniques at temperatures between 70 and 90 degrees C. The rate law -d[flaH]/dt = k(obs) [OH(-)][flaH][O(2)] (k(obs) = kK(1)/[H(2)O]) describes the kinetic data. The rate constant, activation enthalpy, and entropy at 353.16 K are as follows: k/mol(-1) L s(-1) = (4.53 +/- 0.07) x 10(-2), DeltaH/kJ mol(-1)= 59 +/- 4, DeltaS/J mol(-1) K(-1) = -110 +/- 11. The reaction showed specific base catalysis. It fits a Hammett linear free energy relationship for 4'-substituted flavonols and electron-releasing substituents enhanced the reaction rate. The linear correlation between the oxidation potential of the flavonols and the rate constants supports that a higher electron density on the flavonolate ion makes them more nucleophilic and the electrophilic attack of O(2) easier.
Balogh-Hergovich E
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Research Group for Petrochemistry, Hungarian Academy of Sciences, 8201 Veszprém, Hungary.
Speier
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D002384:Catalysis; D004121:Dimethyl Sulfoxide; D005419:Flavonoids / Q000737:chemistry*; D044948:Flavonols; D006863:Hydrogen-Ion Concentration; D006878:Hydroxides / Q000737:chemistry; D007700:Kinetics; D010084:Oxidation-Reduction; D012996:Solutions; D013816:Thermodynamics; D014867:Water
D005419:Flavonoids; D044948:Flavonols; D006878:Hydroxides; D012996:Solutions; D014867:Water; D004121:Dimethyl Sulfoxide