ESR study of reactions of cellulose with ·OH generated by Fe+2/H2O2

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Abstract
It was demonstrated by ESR spectroscopy that the Fe+2/H2O2 system gave a reactive species which generated an ESR triplet spectrum or sorbitol similar to that generated by hydroxyl radicals from the Ti+3/H3O2 system. An ESR spectrum was obtained for the hydroxyl radicals generated by the latter system. However, the lifetime of hydroxyl radicals, generated by the Fe+2/H2O2 system, was apparently very short, and an ESR spectrum for the hydroxyl radicals, generated by this system, was not observed. The Fe+2/H2O2 system also generated triplet spectra with cotton cellulose I, cotton cellulose II, and microcrystalline cellulose, suggesting that a hydrogen atom had been abstracted from the hydroxyl group on carbon C6, or possibly the hydrogen atom on carbon C5. The ESR spectrum generated on microcrystalline cellulose was less intense than those generated on cellulose I and II. On initiation of graft polymerization of the activated cellulose with acrylonitrile, the triplet spectrum disappeared and was replaced by two strong singlet spectra. One of the singlet spectra was likely generated on carbon C1 or C4 on depolymerization of the cellulose molecule, and the other was probably generated on the end of the growing polyacrylonitrile molecular chain. The absence of a triplet spectrum gave direct evidence for the order in which the acrylonitrile monomer was being grafted onto the cellulose molecule. The mechanisms proposed by Haber and Weiss for the reactions generated in the Fe+2/H2O2 system were generally supported.