Accelerated photo-oxidation of concentrated p-coumaric acid in homogeneous solution. Mechanistic studies, intermediates and precursors formed in the dark

This study shows that p-coumaric acid undergoes accelerated degradation via photo-assisted Fenton reactions. Simulated solar radiation (90 mW/cm(2)) promotes the full mineralization of a concentrated solution of p-coumaric acid (420 mg C/l) in less than 15 min when suitable times for the oxidant addition were used in the presence of very low Fe-ion concentration (4 mg Fe-ion/l). The mineralization of p-coumaric acid has been studied as a function of the common variables as pH, concentration of reagents and of the substrate used. The reduction of the total organic compound (TOC) was observed to be a function of the surface-to-volume (s/v) ratio on the reaction vessel due to the formation of light induced radicals in the solution surface. Decoloration of these concentrated solutions were observed in <1 min by stopped-flow techniques. The most important reaction intermediates were determined by HPLC, GC-MS and FTIR suggesting a reaction network for the degradation process. The Fenton reagent is shown to form precursor intermediates which are susceptible to degradation under light. Degradation performed via alternate dark and light cycles showed the importance of the dark precursor species. Implications of this observation as an energy saving device during the mineralization process is accounted for in this study. (C) 1998 Elsevier Science B.V.