Theoretical and Experimental Investigation on the Oxidation of Gallic Acid by Sulfate Radical Anions

PAULA CAREGNATO; PEDRO DAVID GARA; GABRIELA BOSIO; MONICA GONZALEZ; NINO RUSSO; MARIA DEL CARMEN MICHELINI; DANIEL MARTIRE

JOURNAL OF PHYSICAL CHEMISTRY A

AMER CHEMICAL SOC

Año: 2008 p. 1188 - 1194

1089-5639

By monitoring the decay of SO4.- after flash photolysis of aqueous solutions of S2O8 2- at different pH values, the kinetics of the reaction of SO4.- radicals with gallic acid and the gallate ion was investigated. The bimolecular rate constants for the reactions of the sulfate radicals with gallic acid and the gallate ion were found to be (6.3± 0.7) x 108 and (2.9± 0.2) x 109 M-1 s-1 respectively. On the basis of the oxygenindependent second-order decay kinetics and on their absorption spectra, the organic radicals formed as intermediates of these reactions were assigned to the corresponding phenoxyl radicals. DFT calculations in the gas phase and aqueous solution support formation of the phenoxyl radicals by H abstraction from the phenols to the sulfate radical anion. The observed recombination of the phenoxyl radicals of gallic acid to yield substituted biphenyls and quinones is also supported by the calculations. HPLC/MS product analysis showed ormation of one of the predicted quinones.