Quantitative P NMR Detection of Radical Species in Peroxide Bleaching, 2002 International Pulp Bleaching Conference Proceedings

Kamilah N. Smith and Dimitris S. Argyropoulos

In this effort, we demonstrate that quantitative 31P NMR spin trapping techniques can be used as effective tools for the detection and quantification of radical species involved in bleaching reactions. Initially our work was focused at assigning the 31P NMR signals for hydroxyl and superoxide radicals and at identifying the quantitative reliability of such techniques. Our conclusions indicate that the radical adduct reaction products of hydroxyl(HO) and superoxide (O2-) radicals, of phosphorus containing nitroxides, are relatively stable and their structures can be detected and quantified using 31P NMR. The application of this novel methodology showed that superoxide radicals are in equilibrium with aqueous hydrogen peroxide when in contact with air or oxygen. Furthermore, the concentration of superoxide radicals in peroxide solutions at neutral and alkaline pH’s was determined to be substantial and significantly greater than that of hydroxyl radicals. Consequently, superoxide radicals were shown to be key species, participating in aqueous hydrogen peroxide chemistry, most likely playing a more significant role in alkaline peroxide bleaching processes, than originally thought.