Author:
Evtuguin D.V.,Neto C. Pascoal,Rocha J.
Abstract
Summary
The behaviour of lignin in wood delignification by oxygen in acidic media in the presence of the molybdovanadophosphate
heteropolyanion [PMO7V5O40]8−as studied using wet chemistry methods, solid
and liquid state 13C NMR spectroscopy. Lignin is oxidised by [PMO7V5O40]8− almost completely to
carbon dioxide, with a minor yield of intermediate low-molecular weight aromatic products. The analysis
of the reaction products shows that the lignin acidolysis and homolysis involving the oxygen participation
in oxidation take place. The residual lignin in the wood residue is more “condensed” and richer
in guaiacyl structural units than that in the initial wood. The analysis of “condensed” structures issued
from permanganate oxidation of residual lignins suggests that these are formed predominantly by acid-catalysed
reactions. The use of an organic solvent, such as ethanol, in the pulping solution favours the
oxidative delignification, protecting the lignin against competing reactions (condensation).
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