Abstract
When heated under anaerobic conditions, aqueous solutions of the polyoxometalate anion a-[SiVW11O4]5- (POMox, 1), supplied as the salt K5[SiVW11O4] · 12H2O, selectively delignify unbleached mixed-pine kraft pulps. During delignification, 1 is reduced by residual lignin to α-[SiVW11O40]6- (POMred' 2): α-[SiVW11O40]5-+ le-→α-[SiVW11O40]6-, Eo = + 0.69V vs. NHE. Model studies suggest that phenolic (hydroxylated phenyl) groups present in residual lignin are substrates for the reduction of 1. Reactions of 1 with phenolic arylglycerol β-aryl ethers and other phenolic lignin models suggest that anaerobic POM degradation of residual lignin may occur via sequential single-electron oxidation reactions of phenolic substructures, first to cyclohexadienyl radicals and subsequently to cyclohexadienyl cations. Hydrolysis of these cationic intermediates results in alkyl-side-chain cleavage, a likely route to polymer degradation.
Original language | English |
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Pages (from-to) | 311-318 |
Number of pages | 8 |
Journal | Holzforschung |
Volume | 52 |
Issue number | 3 |
DOIs | |
State | Published - 1 Jan 1998 |
Externally published | Yes |
Keywords
- Bleaching
- Delignification
- Kraft pulp
- Lignin
- Oxidation
- Oxygen
- Phenol
- Polyoxometalate
ASJC Scopus subject areas
- Biomaterials