Chromophores from hexeneuronic acids (HexA): synthesis of model compounds and primary degradation intermediates

Chromophores from hexeneuronic acids (HexA): synthesis of model compounds and primary degradation... Hexeneuronic acid (HexA) is formed under pulping conditions from 4-O-methyl-glucuronic acid residues in xylans by methanol elimination. It is usually removed by an acidic washing treatment (A-stage) within the pulp bleaching sequence. Hexeneuronic acid has long been recognized as a source of color generation in pulps, but the chemical structure of the actual chromophoric compounds remained elusive. We report the synthesis of isotopically (13C) labeled HexA model units carrying a label at any of the six carbon atoms. Confirming pertinent literature accounts, it is shown that HexA forms three primary degradation intermediates, 2-furancarboxylic acid, 5-formyl-2-furancarboxylic acid, and formic acid, under mildly acidic conditions, and their formation mechanism is discussed. 2-Furancarboxylic acid is demonstrated to be deformylation product of 5-formyl-2-furancarboxylic acid. The three primary intermediates are colorless and do not represent chromophores themselves. Their mixture, upon thermal or acidic treatment, gives rise to the same chromophores that are also directly formed from HexA. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Cellulose Springer Journals

Chromophores from hexeneuronic acids (HexA): synthesis of model compounds and primary degradation intermediates

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Publisher
Springer Journals
Copyright
Copyright © 2017 by The Author(s)
Subject
Chemistry; Bioorganic Chemistry; Physical Chemistry; Organic Chemistry; Polymer Sciences; Ceramics, Glass, Composites, Natural Materials; Sustainable Development
ISSN
0969-0239
eISSN
1572-882X
D.O.I.
10.1007/s10570-017-1396-5
Publisher site
See Article on Publisher Site

Abstract

Hexeneuronic acid (HexA) is formed under pulping conditions from 4-O-methyl-glucuronic acid residues in xylans by methanol elimination. It is usually removed by an acidic washing treatment (A-stage) within the pulp bleaching sequence. Hexeneuronic acid has long been recognized as a source of color generation in pulps, but the chemical structure of the actual chromophoric compounds remained elusive. We report the synthesis of isotopically (13C) labeled HexA model units carrying a label at any of the six carbon atoms. Confirming pertinent literature accounts, it is shown that HexA forms three primary degradation intermediates, 2-furancarboxylic acid, 5-formyl-2-furancarboxylic acid, and formic acid, under mildly acidic conditions, and their formation mechanism is discussed. 2-Furancarboxylic acid is demonstrated to be deformylation product of 5-formyl-2-furancarboxylic acid. The three primary intermediates are colorless and do not represent chromophores themselves. Their mixture, upon thermal or acidic treatment, gives rise to the same chromophores that are also directly formed from HexA.

Journal

CelluloseSpringer Journals

Published: Jul 13, 2017

References

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