Mechanistic studies of milled and Kraft lignin oxidation by radical species

2020 ◽  
Vol 22 (4) ◽  
pp. 1182-1197 ◽  
Author(s):  
Maryam Davaritouchaee ◽  
William C. Hiscox ◽  
Evan Terrell ◽  
Rock J. Mancini ◽  
Shulin Chen
Keyword(s):  
Lignin Degradation ◽  
Kraft Lignin ◽  
Mechanistic Studies ◽  
Scientific Interest ◽  
Radical Species ◽  
Lignin Oxidation

Accomplishing selective lignin degradation in a controlled manner by breaking C–O and C–C bonds is of great scientific interest although technically challenging.

Degradation of natural and Kraft lignins by the microflora of soil and water

1977 ◽  
Vol 23 (4) ◽  
pp. 434-440 ◽  
Author(s):  
Don L. Crawford ◽  
Suellen Floyd ◽  
Anthony L. Pometto III ◽  
Ronald L. Crawford
Keyword(s):  
Molecular Weight ◽  
Microbial Degradation ◽  
Lignin Degradation ◽  
Kraft Lignin ◽  
Lignin Biodegradation ◽  
Incubation Periods ◽  
Molecular Weight Fractions ◽  
Soil And Water ◽  
Different Molecular Weight ◽  
Microbial Attack

The comparative rates of microbial degradation 14C-lignin-labeled lignocelluloses and 14C-Kraft lignins were investigated using selected soil and water samples as sources of microorganisms. Natural lignocelluloses containing 14C primarily in their lignin components were prepared by feeding plants uniformly labeled L-[14C]phenylalanine through their cut stems. 14C-Kraft lignins were prepared by pulping lignin-labeled lignocelluloses. Rates of lignin biodegradation were determined by monitoring 14CO2 evolution from incubation mixtures over incubation periods of up to 1000 h. Observed rates of lignin degradation were slow in all cases. Kraft lignins appeared more resistant to microbial attack than natural lignins, even though they were decomposed more rapidly during the first 100–200 h of incubation. Similar degradation patterns were observed in both soil and water. Individual samples, however, varied greatly in their overall rates of degradation of either lignin type. A Kraft-lignin preparation was separated into a variety of molecular weight fractions by column chromatography on LH-20 Sephadex and the biodegradability of the different molecular weight fractions determined. The lower molecular weight fractions of the Kraft lignin were decomposed at a significantly faster rate by the microflora of soil than were the fractions of higher molecular weight.

Mechanistic studies of base-catalysed lignin depolymerisation in dimethyl carbonate

2018 ◽  
Vol 20 (1) ◽  
pp. 170-182 ◽  
Author(s):  
Saumya Dabral ◽  
Julien Engel ◽  
Jakob Mottweiler ◽  
Stephanie S. M. Spoehrle ◽  
Ciaran W. Lahive ◽  
...  
Keyword(s):  
Dft Calculations ◽  
Lignin Degradation ◽  
Dimethyl Carbonate ◽  
Analytical Techniques ◽  
Mechanistic Studies

Various analytical techniques and DFT calculations have been applied in studying base-catalysed lignin degradation in dimethyl carbonate.

Kinetics of Vanillin Production from Kraft Lignin Oxidation

1996 ◽  
Vol 35 (1) ◽  
pp. 28-36 ◽  
Author(s):  
Claire Fargues ◽  
Álvaro Mathias ◽  
Alírio Rodrigues
Keyword(s):  
Kraft Lignin ◽  
Lignin Oxidation ◽  
Kinetics Of

Ozonation of pine kraft lignin in alkaline solution. Part 1: Ozonation, characterization of kraft lignin and its ozonated preparations

Holzforschung ◽  
2004 ◽  
Vol 58 (6) ◽  
pp. 622-630 ◽  
Author(s):  
Rui Wang ◽  
Chen-Loung Chen ◽  
Josef S. Gratzl
Keyword(s):  
Molecular Mass ◽  
Sodium Hydroxide Solution ◽  
Group Analysis ◽  
Kraft Lignin ◽  
Oxygen Radical ◽  
Active Oxygen ◽  
Radical Species ◽  
Average Molecular Mass ◽  
Air Stream ◽  
Ph Range

Abstract Pine kraft lignin was purified to obtain a kraft lignin preparation (KL) with weight average molecular mass (Mw) of 5500. The KL was then ozonated with an ozone-air stream containing 2–2.5% of ozone in 0.1 M sodium hydroxide solution to prepare ozonated kraft lignin preparations with ozone consumption of 10, 25, 30 and 40% per KL; Oz-10-KL, Oz-25-KL, Oz-30-KL and Oz-40-KL, respectively. The pH of reaction mixture was decreased with increasing ozone consumption, while the carboxylic acid content and the Mw of resulting ozonated lignins increase with increasing ozone consumption. The KL and its ozonated preparations were then characterized by elemental composition, functional group analysis, molecular mass distribution and nitrobenzene-K4MnO4 oxidation. The results showed that the KL extensively undergoes oxidative cleavage of both side chains and aromatic moieties without decrease in the Mw as well as dehydrogenationive coupling of phenolic degraded fragments by active oxygen radical species, such as hydroperoxyl and hydroxyl radicals. The formation of these active oxygen radical species are produced by way of a series of reactions initiated by the reaction of ozone with hydroxide anions at pH range of 12.4–10.5, producing superoxide (-O2•) and hydroperoxyl (HOO•) radicals.

scholarly journals Site-Fixed Hydroboration of Alkenes under Metal-Free Conditions: Scope and Mechanistic Studies

2021 ◽  
Author(s):  
Sida Li ◽  
Chenyang Hu ◽  
Xin Cui ◽  
Liu Leo Liu ◽  
Lipeng Wu
Keyword(s):  
Reaction Pathway ◽  
Original Position ◽  
Side Reactions ◽  
Single Electron Transfer ◽  
Mechanistic Studies ◽  
Radical Species ◽  
Metal Free ◽  
Proton Source ◽  
Alkene Oligomerization ◽  
Metal Catalyzed

An unprecedented and general metal-free hydroboration of alkenes with BBr3 as the boration reagent in the presence of iPr2NEt is reported. The addition of iPr2NEt not only suppresses alkene oligomerization and bromoboration side reactions, but also provides a proton source for hydroboration. More importantly, the site-fixed installation of a boryl group at the original position of the internal double-bond is easily achieved using our strategy as compared with traditional transition-metal-catalyzed hydroboration processes. Preliminary studies on the mechanism revealed a distinct reaction pathway that involves radical species and may operate through frustrated-Lewispair-type single-electron transfer.

Crystallization of vanillin from kraft lignin oxidation

2020 ◽  
Vol 247 ◽  
pp. 116977 ◽  
Author(s):  
E.D. Gomes ◽  
A.E. Rodrigues
Keyword(s):  
Kraft Lignin ◽  
Lignin Oxidation

Lignin oxidation mechanisms under oxygen delignification conditions. Part 1. Results from direct analyses

Holzforschung ◽  
2011 ◽  
Vol 65 (4) ◽  
Author(s):  
Anna Kalliola ◽  
Susanna Kuitunen ◽  
Tiina Liitiä ◽  
Stella Rovio ◽  
Taina Ohra-aho ◽  
...  
Keyword(s):  
Lignin Degradation ◽  
Mechanistic Model ◽  
Quantitative Information ◽  
Kraft Lignin ◽  
Oxygen Delignification ◽  
Analysis Techniques ◽  
Softwood Kraft Lignin ◽  
Lignin Reactivity ◽  
Oxidation Mechanisms ◽  
Reactor Pressure

Abstract Oxidation of softwood and hardwood kraft lignins was observed under conditions of oxygen delignification (90°C and 110°C; 0.6 and 0.9 MPa) as a function of time by means of a number of analysis techniques and quantitative information was obtained on the degradation and formation of various compounds and structures. The decrease in reactor pressure was monitored during a 4-h reaction period. During the first 60 min, lignin reactivity was high, while a very intense stage took place during the first 20 min. The reactions decelerated after the first 60 min and after 120 min the reactions did not significantly advance. The oxygen consumption after 4-h reaction was 1.3–1.5 mole O2 per 1 mole lignin depending on the conditions. In the first 20 min, 50%–60% of the oxygen was consumed and the consumption increased only slightly after 60 min. At 90°C, the changes in all observed quantities were smaller throughout the whole 4-h reaction period than at 110°C. Under the studied conditions, increasing the reaction temperature, rather than the pressure, had primary significance in the increasing rate of lignin degradation. Hardwood kraft lignin was more reactive than softwood kraft lignin. The results obtained in this study are the basis for the development of a mechanistic model for the oxygen delignification process of pulps to be published in subsequent papers.

Electrochemical reduction of dodecylpyridinium bromide in aprotic solvents: Mechanistic studies

2011 ◽  
Vol 76 (12) ◽  
pp. 1895-1908 ◽  
Author(s):  
Magdaléna Hromadová ◽  
Lubomír Pospíšil ◽  
Romana Sokolová ◽  
Viliam Kolivoška
Keyword(s):  
Pyrolytic Graphite ◽  
Mercury Electrode ◽  
Reduction Process ◽  
Ex Situ ◽  
Aprotic Solvents ◽  
Mechanistic Studies ◽  
Radical Species ◽  
Scanning Tunnelling ◽  
Tunnelling Microscopy ◽  
Adsorption Phenomena

Reduction mechanism of 1-dodecylpyridin-1-ium bromide (DPBr) in dimethylsulfoxide has been studied on mercury electrode. Based on the classical polarographic methods as well as on the use of AC techniques it was shown that DPBr is reduced in a reversible one electron transfer step followed by dimerization of the corresponding radical species. Reduction process is accompanied by the adsorption phenomena even in the non-aqueous solvents. Possible modes of DPBr adsorption have been studied by the ex situ scanning tunnelling microscopy (STM) imaging of these molecules on highly oriented pyrolytic graphite.

Carbon–Oxygen Homocoupling of 2-Naphthols through Electrochemical Oxidative Dearomatization

Synlett ◽  
2019 ◽  
Vol 30 (08) ◽  
pp. 903-909
Author(s):  
Ting Chen ◽  
Song Chen ◽  
Shaomin Fu ◽  
Song Qin ◽  
Bo Liu
Keyword(s):  
Organic Synthesis ◽  
Ruthenium Complex ◽  
Mechanistic Studies ◽  
Radical Species ◽  
Oxidative Dearomatization ◽  
Scale Experiment ◽  
Homocoupling Reaction

A homocoupling reaction of 2-naphthols with formation of a C–O bond through electrochemical oxidative dearomatization in the presence of catalytic amounts of ferrocene and a ruthenium complex was developed. Mechanistic studies revealed that the reaction might proceed through coupling between two identical radical species. Moreover, a gram-scale experiment was performed to illustrate the potential practicability of this methodology in organic synthesis.

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