THE FATE OF PEROXYL RADICALS IN AQUEOUS-SOLUTION

The reactions of peroxyl radicals occupy a central role in oxidative d egradation. Under the term Advanced Oxidation Processes in drinking-wa ter and wastewater processing, procedures are summarized that are base d on the formation and high reactivity of the OH radical. These react with organic matter (DOG). With O-2, the resulting carbon-centered rad icals O-2 give rise to the corresponding peroxyl radicals. This reacti on is irreversible in most cases. An exception is hydroxycyclohexadien yl radicals which are formed from aromatic compounds, where reversibil ity is observed even at room temperature. Peroxyl radicals with strong ly electron-donating substituents eliminate O-2, those with an OH-grou p in a-position HO2. Otherwise organic peroxyl radicals decay bimolecu larly. The tetroxides formed in the first step are very short-lived in termediates and decay by various pathways, leading to molecular produc ts (alcohols, ketones, esters and acids, depending on the precursor), or to oxyl radicals, which either fragment by scission of a neighbouri ng C-C bond or, when they carry an a-hydrogen, undergo a (water-assist ed) 1,2-H-shift. (C) 1997 IAWQ Published by Elsevier Science Ltd.