Author:
Evtuguin D.V.,Neto C. Pascoal,Carapuça H.,Soares J.
Abstract
Summary
Vanillyl and veratryl alcohols were used as monomeric lignin model compounds in experiments aiming
to enhance the understanding of the lignin oxidation mechanisms involved in the oxygen delignification
in acidic media catalysed by [PMo7V5O40]8− (HPA-5) heteropolyanion. Based on the model compound
experiments, the first step of lignin oxidation is suggested to be a one-electron oxidation by the catalyst.
This step is followed by coupling reactions and/or by further oxidation by the catalyst. The ratio of coupling/oxidation reaction products depends on the oxidation conditions and decreases with temperature
raise. The higher oxidation rate of vanillyl alcohol as compared to the veratryl alcohol in the reaction
system O2/HPA-5 was explained by the redox properties of the catalyst. The insufficiently high redox
potential of HPA-5 did not allow the efficient oxidation of veratryl alcohol. The former was oxidised by
VO2
+ ions dissociated from the HPA-5 under the acidic conditions. The reactivity of different lignin
structural units in the reaction system O2/HPA-5 was estimated by electrochemical methods using various
lignin model compounds.
Cited by
31 articles.
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