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Rosenau, T; Potthast, A; Zwirchmayr, NS; Hettegger, H; Plasser, F; Hosoya, T; Bacher, M; Krainz, K; Dietz, T.
(2017): Chromophores from hexeneuronic acids: identification of HexA-derived chromophores
CELLULOSE. 2017; 24(9): 3671-3687. FullText FullText_BOKU

Hexeneuronic acids (HexA) have long been known as triggers for discoloration processes in glucuronoxylan-containing cellulosic pulps. They are formed under the conditions of pulping from 4-O-methylglucuronic acid residues, and are removed in an "A stage" along the bleaching sequences, which mainly comprises acidic washing treatments. The chemical structures of HexA-derived chromophoric compounds 4-8, which make up 90% of the HexA-derived chromophores, are reported here for the first time. The compounds are ladder-type, mixed quinoid-aromatic oligomers of the bis(furano)-[1,4]benzoquinone and bis(benzofurano)-[1,4]benzoquinone type. The same chromophoric compounds are generated independently of the starting material, which can be either a) HexA in pulp, b) the HexA model compound methyl 1-C-13-4-deoxy-beta-L-threo-hex-4-enopyranosiduronic acid (1) or c) a mixture of the primary degradation intermediates of 1, namely 5-formyl-furancarboxylic acid (2) and 2-furancarboxylic acid (3). Isotopic labeling (C-13) in combination with NMR spectroscopy and mass spectrometry served for structure elucidation, and final confirmation was provided by X-ray structure analysis. C-13-Isotopic labeling was also used to establish the formation mechanisms, showing all the compounds to be composed of condensed, but otherwise largely intact, 2-carbonylfuran and 2-carbonylfuran-5-carboxylic acid moieties. These results disprove the frequent assumption that HexA-derived or furfural-derived chromophores are linear furanoid polymers, and might have a direct bearing on structure elucidation studies of "humins", which are formed as dark-colored byproducts in depolymerization of pentosans and hexosans in different biorefinery scenarios.
Authors BOKU Wien:
Bacher Markus
Hettegger Hubert
Hosoya Takashi
Potthast Antje
Rosenau Thomas
Zwirchmayr Nele Sophie
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Find related publications in this database (Keywords)
Hexeneuronic acids
Furancarboxylic acid
Ladder-type oligomers

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