Flavonols, autoxidation

Copper complexes were used as efficient catalysts for selective autoxidations of flavonols (HFLA) to the corresponding o-benzoyl salicylic acid (o-BSH) and CO in non-aqueous solvents and at elevated temperatures (124-128). The oxidative cleavage of the pyrazone ring is also catalyzed by some cobalt complexes (129-131). 

A comparison of the rate constants for the [Cun(FLA)(IDPA)]+-cata-lyzed autoxidation of 4/-substituted derivatives of flavonol revealed a linear free energy relationship (Hammett) between the rate constants and the electronic effects of the para-substituents of the substrate (128). The logarithm of the rate constants linearly decreased with increasing Hammett o values, i.e. a higher electron density on the copper center yields a faster oxidation rate. 

Flavonol quercetin (Q) (3,5,7,3 4 -pentahydroxyflavone) (Scheme 1) due to its phenolic structure is a strong antioxidant and free radical scavenger [1]. Oxidation of quercetin during its antioxidative functions is usually accompanied by the production of the quercetin radical anion, superoxide, and hydrogen peroxide [2]. Quercetin undergoes autoxidation—the nonenzymatic reaction with atmospheric... 

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