The oxygenation of flavonol (flaH) using Cu(II)(fla)2 and Cu(I)(fla)(PPh3)2 catalysts results in oxidative cleavage of the heterocyclic ring to give O-benzoylsalicylic acid (O-bsH) and CO as primary products. The oxygenolysis of flavonol catalyzed by Cu(II)(fla)2 in DMF was followed by electronic spectroscopy and the rate law was found to be - d[flaH]/dt = k(obs)[flaH][Cu(II)(fla)2][O2]. The rate constant, activation energy, activation enthalpy and entropy at 393 K are as follows: k(obs)/s-1 mol-2 dm-6 = (2.02 ± 0.07) x 103, E(a)/kJ mol-1 = 142 ± 6, ΔH(+)/kJ mol-1 = 139 ± 5, and ΔS(+)/J mol-1 K-1 = 168 ± 13. The results of the kinetic measurements of the Cu(I)(fla)(PPh3)2-catalyzed oxygenation shows that in the presence of a large excess of the substrate, the Cu(I)(fla)(PPh3)2 reacts with flavonol in an irreversible step to Cu(II)(fla)2, and, then, the mechanism of the oxygenation is the same as that with the Cu(II)(fla)2-catalyzed reaction. (C) 2000 Elsevier Science B.V.
- Flavonolate complexes
ASJC Scopus subject areas
- Process Chemistry and Technology
- Physical and Theoretical Chemistry