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| - Kinetics and Mechanism of the Base-Catalyzed Oxygenation ofFlavonol in DMSO−H2O Solution
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| - The kinetics of the base-catalyzed oxygenation of flavonol have been investigated in 50% DMSO−H2O solution in the pH range 6.4−10.8 and an ionic strength of 0.1 mol L-1 using spectrophotometrictechniques at temperatures between 70 and 90 °C. The rate law −d[flaH]/dt = kobs [OH-][flaH][O2](kobs = kK1/[H2O]) describes the kinetic data. The rate constant, activation enthalpy, and entropyat 353.16 K are as follows: k/mol-1 L s-1 = (4.53 ± 0.07) × 10-2, ΔH⧧/kJ mol-1= 59 ± 4, ΔS⧧/Jmol-1 K-1 = −110 ± 11. The reaction showed specific base catalysis. It fits a Hammett linear freeenergy relationship for 4‘-substituted flavonols and electron-releasing substituents enhanced thereaction rate. The linear correlation between the oxidation potential of the flavonols and the rateconstants supports that a higher electron density on the flavonolate ion makes them morenucleophilic and the electrophilic attack of O2 easier.
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