Selective transition-metal catalysis of oxygen delignification using water-soluble salts of polyoxometalate (POM) anions. Part II. Reactions of α-[SiVW11O40]5- with phenolic lignin-model compounds

Ira A. Weinstock, Kenneth E. Hammel, Mark A. Moen, Lawrence L. Landucci, Sally Ralph, Cindy E. Sullivan, Richard S. Reiner

Research output: Contribution to journalArticlepeer-review

61 Scopus citations

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 languageEnglish
Pages (from-to)311-318
Number of pages8
JournalHolzforschung
Volume52
Issue number3
DOIs
StatePublished - 1 Jan 1998
Externally publishedYes

Keywords

  • Bleaching
  • Delignification
  • Kraft pulp
  • Lignin
  • Oxidation
  • Oxygen
  • Phenol
  • Polyoxometalate

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