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Thermally initiated radical reactions of K 2 S 2 O 8 : EPR spin trapping investigations
Author(s) -
Staško Andrej,
Brezová Vlasta,
Liptáková Mária,
Šavel Jan
Publication year - 2000
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/1097-458x(200011)38:11<957::aid-mrc765>3.0.co;2-g
Subject(s) - chemistry , adduct , spin trapping , electron paramagnetic resonance , radical , selectivity , photochemistry , radical initiator , aqueous solution , decomposition , organic chemistry , catalysis , polymer , nuclear magnetic resonance , polymerization , physics
The thermally initiated decomposition of K 2 S 2 O 8 radical initiator coupled with EPR spin trapping represents a very powerful source of reactive free radicals which can be effectively used to initiate and to monitor various radical processes, as we were able to demonstrate in the characterization of the antioxidant properties of wine samples. The spin trapping agent α‐phenyl‐ N ‐ tert ‐butylnitrone (PBN) is a very effective trap, but with low selectivity. 5,5‐Dimethyl‐1‐pyrroline‐ N ‐oxide (DMPO), which has higher selectivity and a very pronounced dependence of adduct formation on the temperature (the formal activation energy of · DMPO–OH formation is 81.1 kJ mol −1 ), offers more advantages. In pure aqueous solutions, formation of the · DMPO–OH adduct dominates. In mixed water–ethanol solvents, carbon‐centred DMPO radical adducts are increasingly evident with higher CH 3 CH 2 OH ratios, and at very high ethanol ratios the formation of · DMPO–OOR adduct prevails. Copyright © 2000 John Wiley & Sons, Ltd.