Epimerization and degradation of 2-O-(4-O-methyl-α-d-glucopyranosyluronic acid)-d-xylitol in alkaline medium

Johansson, Mats H.; Samuelson, Olof

doi:10.1016/s0008-6215(00)84821-1

Cited by 54 publications

(22 citation statements)

References 5 publications

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“…From 4-O-methyl glucopyranosiduronic acid, HexA formation was suggested to occur through b-elimination of methanol, leaving a double bond that is always placed regioselectively towards C-5, thus resulting in a conjugated a,b-unsaturated acid structure (see Scheme 1) (Clayton 1963). Further studies were able to confirm these early findings (Johansson and Samuelson 1977), establishing definite knowledge of the structure of HexA, when enzymatic hydrolysis was applied to kraft pulps by Teleman et al (1995). The role of HexA in decreasing brightness has been thoroughly investigated, as were the bleaching conditions that permit its minimization (Teleman et al 1995;Sjostrom 2006).…”

Section: Introductionmentioning

confidence: 81%

“…Acidic pulping conditions, e.g. at 130°C for 2-3 h with 0.05 M H 2 SO 4 (Johansson and Samuelson 1977), or at 80 to 140°C and pH 3.0-3.5 for 2-5 h (Chakar et al 2000;Clavijo et al 2012), allow the removal of possible HexA side groups, but also result in the occurrence of furanoid primary degradation products, e.g. 2-furancarboxylic acid and 5-formyl-2-furancarboxylic acid that lead to the formation of hitherto unidentified chromophoric compounds (Clavijo et al 2012;Teleman et al 1996).…”

Section: Introductionmentioning

confidence: 99%

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Chromophores from hexeneuronic acids: identification of HexA-derived chromophores

et al. 2017

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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-Omethylglucuronic 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 HexAderived chromophores, are reported here for the first time. The compounds are ladder-type, mixed quinoidaromatic 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 1-13 C-4-deoxy-b-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 ( 13 C) in combination with NMR spectroscopy and mass spectrometry served for structure elucidation, and final confirmation was provided by X-ray structure analysis.13 C-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 Chromophores in cellulosic materials. Part XVI.

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Section: Introductionmentioning

confidence: 81%

Section: Introductionmentioning

confidence: 99%

Chromophores from hexeneuronic acids: identification of HexA-derived chromophores

et al. 2017

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“…Removal of HexA residues in bleaching sequences is done in so-called ''A stages'', which work with acid at elevated temperatures (Chakar et al 2000;Johansson and Samuelson 1977;Clavijo et al 2012). Under those conditions, dark colored chromophores are very rapidly formed (seconds to few minutes) from HexA, and these processes are too fast for any detailed mechanistic or kinetic studies.…”

Section: Discussionmentioning

confidence: 99%

“…(Chakar et al 2000) Samuelsson using dimeric model compounds (Johansson and Samuelson 1977). Acid treatments of HexA-containing pulps caused degradation of the proposed unsaturated uronic acids and only xylans and ''tar'' were found in the hydrolysate (Chakar et al 2000;Johansson and Samuelson 1977;Teleman et al 1995;Shimizu 1981).…”

Section: Introductionmentioning

confidence: 99%

“…Acidic conditions, e.g. at 130°C for 2-3 h with 0.05 M H 2 SO 4 , (Johansson and Samuelson 1977) or at 80-140°C and pH 3.0-3.5 for 2-5 h, (Chakar et al 2000;Clavijo et al 2012) allowed removal of the HexA side groups, but also caused occurrence of furanoid primary products, e.g. 2-furancarboxylic acid and 5-formyl-2-furancarboxylic acid, which gave rise to unidentified chromophoric compounds (Clavijo et al 2012;Teleman et al 1996).…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2017

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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 (Astage) 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 ( 13 C) 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.

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Chemical Composition and Properties of Wood

Stevanović

2016

Lignocellulosic Fibers and Wood Handbook

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Epimerization and degradation of 2-O-(4-O-methyl-α-d-glucopyranosyluronic acid)-d-xylitol in alkaline medium

Cited by 54 publications

References 5 publications

Chromophores from hexeneuronic acids: identification of HexA-derived chromophores

Chromophores from hexeneuronic acids: identification of HexA-derived chromophores

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

Chemical Composition and Properties of Wood

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