Chromophores in cellulosics, XVIII. Degradation of the cellulosic key chromophore 5,8-dihydroxy-[1,4]-naphthoquinone under conditions of chlorine dioxide pulp bleaching: a combined experimental and theoretical study

Hosoya, Takashi; Zwirchmayr, Nele Sophie; Klinger, Karl Michael; Reiter, Heidemarie; Spitzbart, Martin; Dietz, Thomas H.; Eibinger, Klaus; Kreiner, Wolfgang; Mahler, Arnulf Kai; Winter, Heribert; Röder, Thomas; Potthast, Antje; Elder, Thomas; Rosenau, Thomas

doi:10.1007/s10570-018-1912-2

Cited by 7 publications

(5 citation statements)

References 30 publications

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“…We had just observed a similar kinetic behavior for the reaction of another key chromophore, 5,5-dihydroxy-1,4-naphthoquinone (DHNQ), with ClO 2 (Hosoya et al 2018). Its degradation kinetics could be explained by the occurrence of an unstable intermediate that was slowly reconverted into the starting material.…”

Section: Influence Of the Ratio Dhbq/clomentioning

confidence: 83%

“…In the case of the ClO 2 oxidation of DHNQ we had observed a modest kinetic H/D isotope effect (Hosoya et al 2018), and therefore we also performed the reaction of DHBQ in D 2 O instead of H 2 O. The effect was more drastic than in the case of DHNQ: the reaction rate was more than halved, and complete consumption of DHBQ at a 1:1 ratio of DHBQ/ClO 2 was only reached after 8.5 min (instead of 4 min in H 2 O).…”

Section: Influence Of the Ratio Dhbq/clomentioning

confidence: 85%

“…Possible examples for such processes are proton shifts (keto-enol tautomerism), addition reactions, eliminations after protonation of the leaving group (HO -/DO -), or hydrogen atom (H Á ) abstraction reactions, which would all show a kinetic isotope effect. In particular the last alternative seemed likely since the initial reactions of ClO 2 are often H Á abstractions (or transfer of an electron and a proton, formally giving H Á ), as also observed in the case of DHNQ (Hosoya et al 2018). 50°C).…”

Section: Influence Of the Ratio Dhbq/clomentioning

confidence: 87%

“…The BaCl 2 test confirmed the gas to be CO 2 , which was confirmed by flushing into diluted NaOH and 13 C NMR (carbonate peak). NMR of the acidic mother solution provided only one 13 C peak, which was identified as oxalic acid based on previous experiments (Hosoya et al 2018) and by spiking with an authentic sample. The final reaction products of the degradation of RhA (and thus indirectly of DHBQ) were thus oxalic acid (COOH) 2 and CO 2 .…”

Section: Influence Of the Ratio Dhbq/clomentioning

confidence: 93%

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Degradation of the cellulosic key chromophore 2,5-dihydroxy-[1,4]-benzoquinone (DHBQ) under conditions of chlorine dioxide pulp bleaching: formation of rhodizonate as secondary chromophore—a combined experimental and theoretical study

et al. 2020

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2,5-Dihydroxy-[1,4]-benzoquinone (DHBQ, 1) is the most prominent representative of cellulosic key chromophores, which occur almost ubiquitously in all types of aged cellulosics. The degradation of DHBQ by chlorine dioxide under conditions of industrial pulp bleaching (''D stage'') was studied, i.e. in moderately acidic medium (pH 3) at temperatures between 50 and 90°C. The degradation in the presence of excess ClO 2 generates rhodizonic acid (RhA, 5,6-dihydroxycyclohex-5-ene-1,2,3,4-tetrone, 2) as a secondary chromophore which is even more stable and more potent as a chromophore than the starting DHBQ, especially in the form of its salts. At least a threefold ClO 2 excess is needed for complete DHBQ consumption. The reaction from DHBQ to RhA involves pentahydroxybenzene (PHB, I) as an intermediate which is either readily further oxidized to RhA by excess ClO 2 or slowly reconverted to DHBQ in the absence of ClO 2. The RhA yield after 30 min reaction time had a maximum of 83% at a DHBQ/ ClO 2 molar ratio of 1:5, and decreased with increasing ClO 2 charge, reaching 38% at a DHBQ/ClO 2 ratio of

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Section: Influence Of the Ratio Dhbq/clomentioning

confidence: 83%

Section: Influence Of the Ratio Dhbq/clomentioning

confidence: 85%

Section: Influence Of the Ratio Dhbq/clomentioning

confidence: 87%

Section: Influence Of the Ratio Dhbq/clomentioning

confidence: 93%

See 2 more Smart Citations

Degradation of the cellulosic key chromophore 2,5-dihydroxy-[1,4]-benzoquinone (DHBQ) under conditions of chlorine dioxide pulp bleaching: formation of rhodizonate as secondary chromophore—a combined experimental and theoretical study

et al. 2020

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“…The latter was thus a genuine reaction product of the DHBQ ''chlorination''. Analogous to the bleaching chemistry of the cellulosic key chromophores with chlorine dioxide (D stage bleaching) (Hosoya et al 2018), radical processes, in particular a single-electron transfer from the electron rich DHBQdianion to the electron-deficient chlorine cation, are likely involved as initial steps, which are followed by the reaction of the resulting DHBQ radical species with excess water to eventually form rhodizonic acid.…”

Section: Reaction Behavior Of Dhbq With Chlorinating Agentsmentioning

confidence: 99%

Pitfalls in the chemistry of cellulosic key chromophores

et al. 2018

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The chemistry of cellulosic key chromophores is challenging because of the usually very low concentration of the colored compounds in realworld cellulosic matrices. It offers many surprises and positive outcomes; unfortunately there are also pitfalls and disappointments. This report discusses eight examples or surprising chemistry out of the realm of cellulosic key chromophores. The reactions have either taken unforeseen paths or provided unexpected products. The reaction mechanisms of the ''strange'' processes are described and the products are comprehensively analytically characterized. Given that the seemingly obvious approaches have failed, alternatives for obtaining the desired products are provided, wherever possible.Hubert Hettegger and Hassan Amer have contributed equally to this work.

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Degradation of cellulosic key chromophores by ozone: a mechanistic and kinetic study

et al. 2021

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Chromophores, colored substances of rather high stability that reduce brightness, are present in all kinds of cellulosic products, such as pulp, fibers, aged cellulosic material, and even in very low concentrations in highly bleached pulps. Thus, they are the prime targets of industrial pulp bleaching. In this study, the three cellulosic key chromophores 2,5-dihydroxy-1,4-benzoquinone (DHBQ, 1), 5,8-dihydroxy-1,4-naphthoquinone (DHNQ, 2), and 2,5-dihydroxyacetophenone (DHAP, 3) were bleached with ozone at pH 2 resembling industrial conditions (Z-stage). Bleaching kinetics were followed by UV/Vis spectrophotometry. The chemical structures of the degradation products were analyzed using NMR spectroscopy as well as GC/MS and confirmed by comparison with authentic reference compounds. The main, stable intermediates in the ozonation reactions have been elucidated by employing ozone not in excess but roughly stoichiometric amounts: mesoxalic acid (4) from DHBQ (1), rhodizonic acid (5) from DHNQ (2), and hydroxy-[1,4]-benzoquinone (8) from DHAP (3). As the final products at a large excess of ozone, a complex mixture of carboxylic acids (C1 to C4) was obtained, with the C4 acids being formed by subsequent condensation of smaller fragments (malonic acid and mesoxalic acid) rather than directly as ozonation products. At shorter reaction times and lower ozone excess, some aldehydes and ketones (C2 and C3) were contained in addition. The mixture of the degradation products was not completely stable but tended to undergo further changes, such as decarboxylation and condensation reactions. The reaction mechanisms of degradation by ozone, intermediate formation and re-condensation are described and discussed. Graphic abstract

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Chromophores in cellulosics, XVIII. Degradation of the cellulosic key chromophore 5,8-dihydroxy-[1,4]-naphthoquinone under conditions of chlorine dioxide pulp bleaching: a combined experimental and theoretical study

Cited by 7 publications

References 30 publications

Degradation of the cellulosic key chromophore 2,5-dihydroxy-[1,4]-benzoquinone (DHBQ) under conditions of chlorine dioxide pulp bleaching: formation of rhodizonate as secondary chromophore—a combined experimental and theoretical study

Degradation of the cellulosic key chromophore 2,5-dihydroxy-[1,4]-benzoquinone (DHBQ) under conditions of chlorine dioxide pulp bleaching: formation of rhodizonate as secondary chromophore—a combined experimental and theoretical study

Pitfalls in the chemistry of cellulosic key chromophores

Degradation of cellulosic key chromophores by ozone: a mechanistic and kinetic study

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