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The inter-and intramolecular selectivity of the carbonate radical anion in its reactions with lignin and carbohydrates
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In the present thesis, the effects of the carbonate radical anion on lignin and cellulose were investigated.

The carbonate radical has a rather high reactivity towards aromatic lignin constituents. It reacts especially fast with phenolates. All these reactions occur by way of electron transfer. Small carbohydrates react with CO3 •- much slower than aromatics. These reactions are hydrogen transfer reactions. However, in very basic media, where the carbohydrates deprotonate to some extent, their anions react with CO3 •- by way of electron transfer and the rates approach those of non-phenolic aromatics. These findings suggest that in neutral or slightly alkaline media CO3 •- might serve as an excellent delignifying agent of pulp down to very low lignin contents. With small carbohydrates possessing one or two glucosidic bonds, CO3 •- abstracts hydrogen predominantly from C1 – H bonds, which results in rupture of the glucosidic linkage. Interestingly, however, the glucosidic bonds in cotton linters are rather resistent towards CO3 •-. This has probably morphological reasons. These results imply that, even at very low lignin contents, where CO3 •- is bound to react with cellulose, the reactions will not lead to substantial decrease in pulp viscosity.

At present the cheapest and most practical way of producing CO3 •- radicals in the presence of pulp is to mix the latter with peroxynitrite and CO2. We have performed such experiments on pulp with very promising results. The Kappa number decreased substantially, brightness increased, while the viscosity remained high. This confirms the predicted excellent properties of the carbonate radical.

However, before the peroxynitrite method can be implemented in the pulp industry, a number of technical problems has to be solved. Chief among them is a slow and steady dosage of peroxynitrite to minimise side reactions of the radicals with peroxynitrite and the nitrite impurity. The fate of the NO2 radical, the coproduct of CO3 •-, has also to be assessed. NO2 will probably have to be removed by vigorous degassing in order to block the possible nitration of cellulose.

Place, publisher, year, edition, pages
Stockholm: KTH , 2005. , 62 p.
Series
Trita-KKE, ISSN 0349-6465 ; 0501
Keyword [en]
Chemistry, nuclear chemistry
Keyword [sv]
Kemi
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-257ISBN: 91-7178-098-X (print)OAI: oai:DiVA.org:kth-257DiVA: diva2:8210
Public defence
2005-06-15, Sal E3, Lindstedtsvägen 3, Stockholm, 14:00 (English)
Opponent
Supervisors
Note
QC 20101001Available from: 2005-06-02 Created: 2005-06-02 Last updated: 2010-10-01Bibliographically approved
List of papers
1. Reactivity of the carbonate radical anion towards carbohydrate and lignin model compounds
Open this publication in new window or tab >>Reactivity of the carbonate radical anion towards carbohydrate and lignin model compounds
2003 (English)In: Journal of wood chemistry and technology, ISSN 0277-3813, E-ISSN 1532-2319, Vol. 23, no 1, 47-69 p.Article in journal (Refereed) Published
Abstract [en]

The kinetic selectivity for the reaction of the carbonate radical anion towards lignin and carbohydrate model compounds was determined by pulse radiolysis in the pH-span 8-13. For the cellulose model compound methyl-β-D-glucopyranoside a pKA-value of 14.4 was estimated.

Keyword
Bleaching, Carbonate radical anion, Pulp, Selectivity, electron reduction potentials; phenoxyl radicals; rate constants; peroxynitrite; cations; dioxide; water; chemistry; acidity; damage
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-5265 (URN)10.1081/WCT-120018615 (DOI)
Note
QC 20100812Available from: 2005-06-02 Created: 2005-06-02 Last updated: 2017-12-04Bibliographically approved
2. The Carbonate Radical as One-Electron Oxidant of Carbohydrates in Alkaline media
Open this publication in new window or tab >>The Carbonate Radical as One-Electron Oxidant of Carbohydrates in Alkaline media
2005 (English)In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 59, no 2, 143-146 p.Article in journal (Refereed) Published
Abstract [en]

The mechanism by which the carbonate radical anion reacts with D-glucose in alkaline aqueous solutions has been studied by means of gamma-radiolysis. From the product analysis it is concluded that the reaction sequence is initiated by a one-electron transfer between the carbonate radical anion and deprotonated D-glucose. In the presence of molecular oxygen, the major, if not only products of this reaction sequence are formic acid, arabinose and gluconic acid and reaction schemes are proposed to account for the observed formation of these products.

Keyword
carbonate radical, deprotonated glucose, one-electron transfer, beta-scission, 1, 2 H-shift
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-5266 (URN)10.1515/HF.2005.021 (DOI)000227384700006 ()2-s2.0-14844314191 (Scopus ID)
Note
QC 20100812Available from: 2005-06-02 Created: 2005-06-02 Last updated: 2017-12-04Bibliographically approved
3. D-gluco-Hexodialdose in Aqueous Solution: Determination of the Main Forms by NMR spectroscopy
Open this publication in new window or tab >>D-gluco-Hexodialdose in Aqueous Solution: Determination of the Main Forms by NMR spectroscopy
Show others...
(English)Manuscript (preprint) (Other academic)
Keyword
Glucose dialdehyde, gluco-Hexodialdose, Hydrates of gluco-hexodialdose, Dimers of gluco-hexodialdose, NMR data
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-5267 (URN)
Note
QC 20101001Available from: 2005-06-02 Created: 2005-06-02 Last updated: 2010-10-01Bibliographically approved
4. A selectivity study of reaction of the carbonate radical anion with methyl beta- D-cellobioside and methyl beta-D-glucoside in oxygenated aqueous solutions
Open this publication in new window or tab >>A selectivity study of reaction of the carbonate radical anion with methyl beta- D-cellobioside and methyl beta-D-glucoside in oxygenated aqueous solutions
2006 (English)In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 60, no 2, 130-136 p.Article in journal (Refereed) Published
Abstract [en]

In the presence of oxygen, radiolytically generated carbonate radical anions, CO3.-, were reacted with methyl beta-D-cellobioside and methyl beta-D-glucoside. From the ensuing product pattern, it was concluded that CO3 center dot- abstracts hydrogen atoms predominantly from glucosidic C1 - H bonds. This high intramolecular selectivity was rationalised mainly in terms of a polar effect on the transition state of the hydrogen abstraction reaction. The present findings are in sharp contrast to the relative inertness of CO3(center dot-) towards glucosidic C1 - H bonds previously observed in cotton linters. The reasons for this discrepancy are discussed in light of a possible future role of CO3 center dot- as a bleaching agent for pulp.

Keyword
carbohydrate, carbonate radical, glucosidic cleavage, hydrogen abstraction, intramolecular, model compounds, selectivity
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-5268 (URN)10.1515/HF.2006.021 (DOI)000236203100003 ()2-s2.0-33644925334 (Scopus ID)
Note
QC 20101001. Uppdaterad från manuskript till artikel (20101001). Tidigare titel: A Selectivity Study of the Carbonate Radical Anion Reacting with Methyl-β-D-cellobioside and Methyl-β-D-glucoside in Oxygenated Aqueous Solutions Available from: 2005-06-02 Created: 2005-06-02 Last updated: 2017-12-04Bibliographically approved
5. A comparative study on the degradation of cotton linters induced by carbonate and hydroxyl radicals generated from peroxynitrite
Open this publication in new window or tab >>A comparative study on the degradation of cotton linters induced by carbonate and hydroxyl radicals generated from peroxynitrite
2005 (English)In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 59, no 2, 132-142 p.Article in journal (Refereed) Published
Abstract [en]

Carbonate (CO3.(-)) and hydroxyl (HO.) radicals were chemically produced in cotton linter suspensions using peroxynitrite as a radical precursor. Both radicals could degrade cotton linters, as shown by viscosity and GPC-SEC measurements. As evidenced by the viscosity measurements, the presence of oxygen during the cotton linter treatments slightly increased cellulose degradation by both radicals. For the carbonate radical, more than 90% of the viscosity losses could be recovered by reductive NaBH4 treatment before measuring the viscosity, whereas only approximately 40% of the viscosity was recovered after hydroxyl radical degradation and subsequent NaBH4 treatment. This indicates that carbonate radicals mainly abstract H-atoms adjacent to hydroxyl groups, i.e., at C-2, C-3 and C-6. This intramolecular selectivity may reflect a polar effect, whereby hydrogen atom abstractions from these positions are favoured. In addition, abstraction at C-6 would be sterically and statistically favoured.

Keyword
carbonate radical; cellulose; cotton linters; degradation; fibre; hydroxyl radical; intramolecular selectivity; peroxynitrite; pulse-radiolysis; hydrogen-peroxide; aqueous-solution; pernitrous acid; nitric-oxide; decomposition; oxidations; homolysis; peroxonitrite; chemistry
National Category
Chemical Process Engineering
Identifiers
urn:nbn:se:kth:diva-5269 (URN)10.1515/HF.2005.020 (DOI)000227384700005 ()2-s2.0-14844313731 (Scopus ID)
Note
QC 20100812Available from: 2005-06-02 Created: 2005-06-02 Last updated: 2017-12-04Bibliographically approved
6. Peroxynitrite mediated delignification of pulp: A comparative study on the bleaching properties of the carbonate and hydroxyl radicals
Open this publication in new window or tab >>Peroxynitrite mediated delignification of pulp: A comparative study on the bleaching properties of the carbonate and hydroxyl radicals
2004 (English)In: Journal of wood chemistry and technology, ISSN 0277-3813, E-ISSN 1532-2319, Vol. 24, no 2, 83-98 p.Article in journal (Refereed) Published
Abstract [en]

Oxygen delignified pulps were bleached with hydroxyl and carbonate radicals produced from peroxynitrite. The carbonate radical treated pulps showed better selectivity and an increase in brightness. For both radicals, good kappa reductions were obtained. This study shows that the carbonate radical anion is a possible green oxidant for future delignification technologies.

Keyword
Delignification, Hydroxyl and carbonate radicals, Kappa, viscosity, and brightness values, Peroxynitrite
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-5270 (URN)10.1081/WCT-200026553 (DOI)000223809300001 ()2-s2.0-4544345768 (Scopus ID)
Note
QC 20100812Available from: 2005-06-02 Created: 2005-06-02 Last updated: 2017-12-04Bibliographically approved

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