Studies on the Degradation of Phenolic Lignin Units of the beta-Aryl Ether Type with Oxygen in Alkaline Media.

Gierer, Josef; Imsgard, Finn; Norén, Isa; Stilkerieg, B.; Christensen, A.; Schroll, Gustav

doi:10.3891/acta.chem.scand.31b-0561

Cited by 60 publications

(62 citation statements)

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“…The spiroepoxide moiety of 6 was established by the carbon chemical shifts of C-1 (68.2 ppm) and C-1Ј (59.2 ppm), showing that both were connected to oxygen, and the proton chemical shift of H1 at 3.28 ppm (33). The ring attached to the epoxide was oxidized to a quinone (C-4Ј as a carbonyl at 184.0 ppm), resulting in chemical shifts of H-2Ј, H-5Ј, and H-6Ј compatible with double bonds rather than an aromatic ring.…”

Section: Isolation and Characterization Of Curcumin Autoxidationmentioning

confidence: 99%

Unraveling Curcumin Degradation

Gordon

Luis

Sintim

et al. 2015

Journal of Biological Chemistry

139

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Background:The bioactive metabolites of curcumin are not well defined. Results: Using [14 C]curcumin as tracer, degradation products and unstable reaction intermediates were isolated and identified. Conclusion: The spontaneous degradation of curcumin is an autoxidation that yields electrophilic and nucleophilic products. Significance: The unexpected chemical diversity of its metabolites may explain the polypharmacology of curcumin.

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Section: Isolation and Characterization Of Curcumin Autoxidationmentioning

confidence: 99%

Unraveling Curcumin Degradation

Gordon

Luis

Sintim

et al. 2015

Journal of Biological Chemistry

139

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“…The first phase of the oxidative ammonolysis is likely associated with the reactions of phenolic moieties of the original lignin, because their reactivity is much higher than etherified moieties. [16,17] About 60% of the maximum nitrogen uptake being incorporated in the first reaction phase correlates with amount of phenolic hydroxyl groups (70%) in Repap lignin reported by Faix et al [18] The second phase of the reaction is likely associated with original non-phenolic moieties. The original non-phenolic moieties could participate in the oxidative ammonolysis by their conversion to phenolic moieties via oxidative cleavage of side chains resulting in cleavage of alkyl-O-aryl bonds.…”

Section: The Reaction Mechanisms Of Oxidative Ammonolysis Of Ligninmentioning

confidence: 85%

Oxidative Ammonolysis of Technical Lignins. Part 4. Effects of the Ammonium Hydroxide Concentration and pH

Capanema

Balakshin

Chen

et al. 2006

Journal of Wood Chemistry and Technology

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The effects of ammonium hydroxide concentration and pH on the kinetics and reaction mechanism of oxidative ammonolysis of Repap organosolv lignin were studied. The reactions were carried out at 1008C with an oxygen pressure of 8 bar (116 psi) and 0.4-1.6 M [NH 4 OH] and 9 -12.7 pH. The resulting N-modified lignins were analyzed for elemental composition and methoxyl group content. An increase in ammonium hydroxide concentration increased the rate of nitrogen incorporation, oxygen consumption, CO 2 formation, and lignin dissolution. The rate of nitrogen incorporation was 0.5 order with respect to NH 4 OH concentration. The amount of oxygen consumed, oxygen incorporated into the lignin, CO 2 formed, and OMe groups eliminated per mole of nitrogen incorporated decreased with increasing ammonium hydroxide concentration indicating that the increase in [NH 4 OH] accelerated nitrogen incorporation more than lignin oxidation. The dependence of the rate of nitrogen incorporation on the reaction pH went through a maximum leading to the This article is dedicated to the memory of Josef S. Gratzl.conclusion that HO 2 competes with ammonia in reactions with electrophilic lignin centers resulting in interruption of nitrogen incorporation into the lignin.

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“…Quinoide compounds seem to be important key intermediates in the natural formation of humic substances. They can be formed via both, homolytic (Kratzl et al 1967) and heterolytic processes (Gierer et al 1977) from any (substituted: guaiacyl, syringyl type) phenylpropane unit that bears a free phenolic group. Although these studies were based on lignin, lignite still contains phenylpropane units bearing free phenolic OH groups as lignin does (Wender 1976).…”

Section: Phenanthrene Sorptionmentioning

confidence: 99%

Effect of ammonoxidation on lignite properties

et al. 2009

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Oxidised lignite is a potential alternative source of N fertilizers. Ammonoxidation is the reaction of a given substrate with oxygen in aqueous ammonia. Lignite ammonoxidation is used for converting low-rank lignite into slowly nitrogen-releasing artificial humic matter. A lignite sample is compared before and after ammonoxidation in terms of geochemical and petrological properties, as well as the acid-base and physical hydrophobic sorptive behavior. The most obvious change caused by ammonoxidation is the decrease of attrinite, texto-ulminite and textinite in favor mainly of densinite and gelohuminite. In general, the ammonoxidative reactions promote the destruction of the structured humic macerals (texto-ulminite, textinite), and the formation of gels, which resulted in the cementation of the freely fine humic particles (attrinite). The pzc values are 3.4 and 4.3 for oxidised and nonoxidised lignite, respectively. After ammonoxidation the contents of carboxylic and free phenolic groups are found to be lower. The oxidised lignite shows a statistically lower sorptive capacity and affinity than the original sample due to a possible decrease in the hydrophobicity of the lignite.

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Studies on the Degradation of Phenolic Lignin Units of the beta-Aryl Ether Type with Oxygen in Alkaline Media.

Cited by 60 publications

References 0 publications

Unraveling Curcumin Degradation

Unraveling Curcumin Degradation

Oxidative Ammonolysis of Technical Lignins. Part 4. Effects of the Ammonium Hydroxide Concentration and pH

Effect of ammonoxidation on lignite properties

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