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T. Kishimoto, J. F. Kadla, H.-m. Chang, H. Jameel
The Reactions of Lignin Model Compounds with Hydrogen Peroxide at Low pH
In peroxymonosulfuric acid bleaching, the presence of hydrogen peroxide is dependent on the reaction
conditions and the conversion ratios used to generate the peroxy acid. Substantial amounts
of hydrogen peroxide may be present in the reaction system under certain conditions. An understanding
of the reactions of hydrogen peroxide under these conditions would be beneficial. Therefore,
several simple lignin model compounds were reacted with acidic hydrogen peroxide, pH 1-3,
at 70°C. In all cases the phenolic lignin model compounds reacted much faster than their non-phenolic
counterparts. In fact, the extent of reaction was very much dependent on the structure of the
lignin model compound. The ?-hydroxyl compounds, 4-(1-Hydroxy-ethyl)-2-methoxy-phenol and
1-(3,4-Dimethoxy-phenyl)-ethanol, reacted faster than the corresponding ?-carbonyl compounds
with both reacting much faster than the aromatic compounds, with simple alkyl substituents. A
new reaction mechanism for ?-hydroxyl compounds is proposed, in which benzyl carbocation formation
is followed by nucleophilic addition of hydrogen peroxide. Unlike the mechanisms proposed
in the past, no evidence of aromatic hydroxylation
Holzforschung, Walter de Gruyter
Print ISSN: 0018-3830
Volume: 57, 01/2003
Pages: 52 - 88