Thermally initiated radical reactions of K2S2O8: EPR spin trapping investigations

The thermally initiated decomposition of K2S2O8 radical initiator coupled w ith EPR spin trapping represents a very powerful source of reactive free ra dicals which can be effectively used to initiate and to monitor various rad ical processes, as we were able to demonstrate in the characterization of t he antioxidant properties of wine samples. The spin trapping agent alpha -p henyl-N-tert-butylnitrone (PBN) is a very effective trap, but with low sele ctivity. 5,5-Dimethyl-1-pyrroline-N-oxide (DMPO), which has higher selectiv ity and a very pronounced dependence of adduct formation on the temperature (the formal activation energy of (DMPO)-D-.-OH formation is 81.1 kJ mol(-1 )), offers more advantages. In pure aqueous solutions, formation of the (DM PO)-D-.-OH adduct dominates. In mixed water-ethanol solvents, carbon-centre d DMPO radical adducts are increasingly evident with higher CH3CH2OH ratios , and at very high ethanol ratios the formation of (DMPO)-D-.-OOR adduct pr evails. Copyright (C) 2000 John Wiley & Sons, Ltd.