Studies on electro-oxidation of lignin and lignin model compounds. Part 2: N-Hydroxyphthalimide (NHPI)-mediated indirect electro-oxidation of non-phenolic lignin model compounds

Holzforschung ◽  
2012 ◽  
Vol 66 (3) ◽  
Author(s):  
Takumi Shiraishi ◽  
Toshiyuki Takano ◽  
Hiroshi Kamitakahara ◽  
Fumiaki Nakatsubo
Keyword(s):  
Hydrogen Atom Transfer ◽  
High Yield ◽  
Cyclic Voltammogram ◽  
Model Compounds ◽  
Lignin Model Compounds ◽  
Lignin Model Compound ◽  
Reaction Proceeds ◽  
Lignin Model ◽  
Electro Oxidation ◽  
High Yields

Abstract The N-hydroxyphthalimide (NHPI)-mediated indirect electro-oxidation of non-phenolic lignin model compounds has been investigated for selective Cα-carbonylation of lignin. A cyclic voltammogram of NHPI in 0.1 M LiClO4/CH3CN with 2,6-lutidine interpreted that NHPI can act as a mediator in the indicated process in the range 0.5–0.8 V vs. Ag/Ag+. The corresponding Cα-carbonyl compounds was obtained in high yields (85–97%) in the case of the monomer 1-(4-ethoxy-3-methoxyphenyl) ethanol in 0.1 M LiClO4/CH3CN or 0.1 M LiClO4/(CH3CN/H2O=7/3) with a small amount of 2,6-lutidine at 0.7 V vs. Ag/Ag+. The processing of the dimeric lignin model compound (4-ethoxy-3-methoxyphenylglycerol-β-guaiacyl ether) also gave the corresponding Cα-carbonyl compound in high yield (88–92%). The reaction proceeds through hydrogen atom transfer in the NHPI-mediated electro-oxidation. On the other hand, the direct electro-oxidation and indirect electro-oxidation mediated by ABTS [2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonate)] of the dimeric compound preferentially gave the corresponding Cα-Cβ cleavage product in low or moderate yields (5–40%). The conclusion is that NHPI is an excellent mediator for selective Cα-carbonylation of non-phenolic β-O-4 structures in lignin in electronic mediator system.

Studies on electrooxidation of lignin and lignin model compounds. Part 1: Direct electrooxidation of non-phenolic lignin model compounds

Holzforschung ◽  
2012 ◽  
Vol 66 (3) ◽  
Author(s):  
Takumi Shiraishi ◽  
Toshiyuki Takano ◽  
Hiroshi Kamitakahara ◽  
Fumiaki Nakatsubo
Keyword(s):  
Electron Transfer ◽  
Cyclic Voltammetry ◽  
Carbonyl Compounds ◽  
Model Compounds ◽  
Lignin Model Compounds ◽  
Bulk Electrolysis ◽  
Lignin Model ◽  
Dimeric Compound ◽  
High Yields ◽  
Short Time

Abstract The direct anodic oxidation of non-phenolic lignin model compounds was investigated to understand their basic behaviors. The results of cyclic voltammetry (CV) studies of monomeric model, such as 1-(4-ethoxy-3-methoxyphenyl)ethanol, are interpreted as the oxidation for Cα-carbonylation did not proceed in the reaction without a catalyst, but a base promotes this reaction. Indeed, the bulk electrolyses of the monomeric lignin model compounds with 2,6-lutidine afforded the corresponding Cα-carbonyl compounds in high yields (60–80%). It is suggested that deprotonation at Cα-H in the ECEC mechanism (E=electron transfer and C=chemical step) is important for Cα-carbonylation. In the uncatalyzed bulk electrolysis of a β-O-4 model dimeric compound, 4-ethoxy-3-methoxyphenylglycerol-β-guaiacyl ether, the corresponding Cα-carbonyl compound was not detected but as a result of Cα-Cβcleavage 4-O-ethylvanillin was found in 40% yield. In the electrolysis reaction in the presence of 2,6-lutidine (as a sterically hindered light base), the reaction stopped for a short time unexpectedly. These results indicate the different electrochemical behavior of simple monomeric model compounds and dimeric β-O-4 models. The conclusion is that direct electrooxidation is unsuitable for Cα-carbonylation of lignin.

Comparison of a series of laccase mediators in the electro-oxidation reactions of non-phenolic lignin model compounds

2013 ◽  
Vol 106 ◽  
pp. 440-446 ◽  
Author(s):  
Takumi Shiraishi ◽  
Yumi Sannami ◽  
Hiroshi Kamitakahara ◽  
Toshiyuki Takano
Keyword(s):  
Oxidation Reactions ◽  
Model Compounds ◽  
Lignin Model Compounds ◽  
Lignin Model ◽  
Electro Oxidation

scholarly journals Effect of lignin structure on adsorbable organic halogens formation in chlorine dioxide bleaching

2019 ◽  
Vol 6 (2) ◽  
pp. 182024 ◽  
Author(s):  
Lisheng Shi ◽  
Jiayan Ge ◽  
Shuangxi Nie ◽  
Chengrong Qin ◽  
Shuangquan Yao
Keyword(s):  
Chlorine Dioxide ◽  
Model Compound ◽  
Pulp Bleaching ◽  
Model Compounds ◽  
Lignin Model Compounds ◽  
Lignin Model Compound ◽  
Lignin Model ◽  
Organic Halogens ◽  
Adsorbable Organic Halogens ◽  
Lignin Structure

Adsorbable organic halogens (AOX) are formed in pulp bleaching as a result of the reaction of residual lignin with chlorine dioxide. The natural structure of lignin is very complex and it tends to be damaged by various extraction methods. All the factors can affect the study about the mechanism of AOX formation in the reaction of lignin with chlorine dioxide. Lignin model compounds, with certain structures, can be used to study the role of different lignin structures on AOX formation. The effect of lignin structure on AOX formation was determined by reacting phenolic and non-phenolic lignin model compound with a chlorine dioxide solution. Vanillyl alcohol (VA) and veratryl alcohol (VE) were selected for the phenolic and non-phenolic lignin model compound, respectively. The pattern consumption of lignin model compounds suggests that both VA and VE began reacting with chlorine dioxide within 10 min and then gradually steadied. The volume of AOX produced by VE was significantly higher than that produced by VA for a given initial lignin model compound concentration. In a solution containing a combination of VA and VE in chlorine dioxide, VE was the dominant producer of AOX. This result indicates that the non-phenolic lignin structure was more easily chlorinated, while the phenolic lignin structure was mainly oxidized. In addition, AOX content produced in the combined experiments exceeded the total content of the two separate experiments. It suggested that the combination of phenolic and non-phenolic lignin structure can promote AOX formation.

The Reactions of Lignin Model Compounds with Hydrogen Peroxide at Low pH

Holzforschung ◽  
2003 ◽  
Vol 57 (1) ◽  
pp. 52-88 ◽  
Author(s):  
T. Kishimoto ◽  
J. F. Kadla ◽  
H.-m. Chang ◽  
H. Jameel
Keyword(s):  
Hydrogen Peroxide ◽  
Reaction System ◽  
Model Compounds ◽  
Reaction Conditions ◽  
Lignin Model Compounds ◽  
Lignin Model Compound ◽  
Lignin Model ◽  
Decreasing Ph ◽  
Hydroxyl Compounds ◽  
Acidic Hydrogen

Summary In peroxymonosulfuric acid bleaching, the presence of hydrogen peroxide is dependent on the reaction conditions and the conversion ratios used to generate the peroxy acid. Substantial amounts of hydrogen peroxide may be present in the reaction system under certain conditions. An understanding of the reactions of hydrogen peroxide under these conditions would be beneficial. Therefore, several simple lignin model compounds were reacted with acidic hydrogen peroxide, pH 1-3, at 70°C. In all cases the phenolic lignin model compounds reacted much faster than their non-phenolic counterparts. In fact, the extent of reaction was very much dependent on the structure of the lignin model compound. The α-hydroxyl compounds, 4-(1-Hydroxy-ethyl)-2-methoxy-phenol and 1-(3,4-Dimethoxy-phenyl)-ethanol, reacted faster than the corresponding α-carbonyl compounds with both reacting much faster than the aromatic compounds, with simple alkyl substituents. A new reaction mechanism for α-hydroxyl compounds is proposed, in which benzyl carbocation formation is followed by nucleophilic addition of hydrogen peroxide. Unlike the mechanisms proposed in the past, no evidence of aromatic hydroxylation via perhydronium ion was observed. The reactivities were very pH dependent, in that higher reactivity was associated with lower pH. Decreasing pH further increased the amount of condensation products identified, such that condensation was competitive with degradation. These condensation reactions were also present under the Caro's acid bleaching conditions at pH below 2. However, under all conditions the reactivity of acidic peroxide was found to be much less than that of peroxymonosulfuric acid.

Thermal stability of lignin in ground pulp (GP) and the effect of lignin modification on GP’s thermal stability: TGA experiments with dimeric lignin model compounds and milled wood lignins

Holzforschung ◽  
2019 ◽  
Vol 73 (5) ◽  
pp. 493-499 ◽  
Author(s):  
Daisuke Ando ◽  
Fumiaki Nakatsubo ◽  
Hiroyuki Yano
Keyword(s):  
Thermal Stability ◽  
Model Compound ◽  
Pinus Densiflora ◽  
Wood Fiber ◽  
Model Compounds ◽  
Lignin Model Compounds ◽  
Oh Groups ◽  
Lignin Model Compound ◽  
Lignin Model ◽  
Thermal Stability Of

Abstract For ground pulp (GP) utilization in wood fiber composites as reinforced material, its thermal behavior is relevant. The contribution of lignin to thermal performance of GP from Pinus densiflora was the focus of the present study. Dimeric lignin model compounds and isolated milled wood lignins (MWLs) from three sources were submitted for thermogravimetric analysis (TGA). The temperatures leading to 1% weight loss (T per 1% WL) for the material were determined. The thermal stability of β-O-4 models was the lowest. Among the MWLs, the abaca MWL with its high β-O-4 content was the least thermostable. An acetylated nonphenolic β-O-4 lignin model compound showed that acetylation improves the thermal stability of this type of dimeric models. The acetylation of benzylic OH groups in β-O-4 linkages is especially relevant for the thermal resistance, which was also shown based on pre-acetylated benzylic OH groups in the GP before the total acetylation.

Free radical reaction promoted by ionic liquid: a route for metal-free oxidation depolymerization of lignin model compound and lignin

2015 ◽  
Vol 51 (19) ◽  
pp. 4028-4031 ◽  
Author(s):  
Yingying Yang ◽  
Honglei Fan ◽  
Jinliang Song ◽  
Qinglei Meng ◽  
Huacong Zhou ◽  
...  
Keyword(s):  
Ionic Liquid ◽  
Model Compound ◽  
Radical Reaction ◽  
Free Radical Reaction ◽  
Model Compounds ◽  
Lignin Model Compounds ◽  
Lignin Model Compound ◽  
Organosolv Lignin ◽  
Lignin Model ◽  
Free Oxidation

Ionic liquid can efficiently promote the transformation of lignin model compounds and organosolv lignin.

TEMPO-mediated electro-oxidation reactions of non-phenolic β-O-4-type lignin model compounds

Holzforschung ◽  
2017 ◽  
Vol 71 (2) ◽  
pp. 109-117 ◽  
Author(s):  
Yumi Sannami ◽  
Hiroshi Kamitakahara ◽  
Toshiyuki Takano
Keyword(s):  
Phosphate Buffer ◽  
Model Compound ◽  
Catalytic Efficiency ◽  
High Yield ◽  
Oxidation Reactions ◽  
Lignin Model Compound ◽  
Carbonate Buffer ◽  
Mediator System ◽  
Lignin Model ◽  
Electro Oxidation

Abstract Oxidation reactions of a non-phenolic β-O-4-type lignin model compound [4-ethoxy-3-methoxyphenylglycerol-β-guaiacyl ether (1)] were conducted in an electrolytic mediator system (EMS) using 2,2,6,6-tetramethyl-1-piperidinyloxyl radical (TEMPO) or 4-acetoamido-TEMPO (AcNH-TEMPO) as mediators. The results revealed that the electrolytes strongly influenced the chemoselectivity between Cα-carbonylation and Cγ-carboxylation of compound 1. The Cα-carbonylation proceeded preferentially in the EMS oxidation conducted in the LiClO4/CH3CN-H2O system, although the yield of the resulting Cα-carbonyl compound 2 was low (1.9%–11.1%). In contrast, Cγ-carbonylation was preferred, if the EMS oxidation reactions were conducted in the dioxane-carbonate buffer (pH 10.0), dioxane-borate buffer (pH 10.0), and dioxane-phosphate buffer (pH 7.0). Especially, the Cγ-carboxyl compound 3 was obtained in a high yield (72.0%–93.2%), when the dioxane-phosphate buffer served as the electrolyte. The catalytic efficiency of AcNH-TEMPO was higher than that of TEMPO for the EMS oxidation reactions. The conclusion is that AcNH-TEMPO-EMS oxidation reaction in dioxane-phosphate buffer could be used for the chemoselective Cγ-carboxylation of lignins.

Synthesis of lignin model compound containing a β-O-4 linkage

2017 ◽  
Vol 72 (2) ◽  
pp. 119-124 ◽  
Author(s):  
Asma Mukhtar ◽  
Muhammad Zaheer ◽  
Muhammad Saeed ◽  
Wolfgang Voelter
Keyword(s):  
Structural Feature ◽  
Model Compound ◽  
Raw Materials ◽  
Value Added ◽  
Model Compounds ◽  
Lignin Model Compounds ◽  
Lignin Model Compound ◽  
Efficient Conversion ◽  
Lignin Model

AbstractDevelopment of catalysts for efficient conversion of lignin polymer to value-added materials requires appropriately-functionalized lignin model compounds. The predominant structural feature of lignin biopolymer is an extensive network of β-O-4 linkages. Access to large amounts of a model compound containing the β-O-4 linkage is crucial for the valorisation of lignin biopolymer to aromatic raw materials. Starting from commercially available vanillin, synthesis of dilignol model compound, containing a β-O-4 linkage, is accomplished in good overall yield.

Polyoxometalate (POM) oxidation of lignin model compounds

Holzforschung ◽  
2008 ◽  
Vol 62 (1) ◽  
pp. 38-49 ◽  
Author(s):  
Yong Sik Kim ◽  
Hou-min Chang ◽  
John F. Kadla
Keyword(s):  
Reaction Rate ◽  
Model Compound ◽  
Reaction Rates ◽  
Hydroxyl Group ◽  
Model Compounds ◽  
Lignin Model Compounds ◽  
Lignin Model Compound ◽  
First Order ◽  
Resonance Stabilization ◽  
Lignin Model

Abstract Various lignin model compounds were oxidized with polyoxometalate (POM), K5[SiVW11O40]·12 H2O, in sodium acetate buffer (I=0.2 M, pH 5.0) and the reaction kinetics were investigated. The reactions were found to have second order reaction rates, first order with regards to both lignin model compound and POM. A dramatic increase in reactivity was observed upon addition of methoxyl groups in ortho-positions to the phenolic hydroxyl group. Syringyl units reacted faster than guaiacyl units. Reaction rates of para-substituted guaiacyl and syringyl model compounds showed a strong dependency on the nature of the substituents. The reaction rate of a 5-5′ dimer lignin model compound was extremely fast. The addition of the ortho-phenol substituent not only increased the electron density of the aromatic ring, but also helped stabilize the intermediate phenoxy radical through resonance stabilization and delocalization.

Recyclable ionic liquid tagged Co(salen) catalysts for the oxidation of lignin model compounds

2013 ◽  
Vol 91 (12) ◽  
pp. 1258-1261 ◽  
Author(s):  
Kenson Ambrose ◽  
Bitu B. Hurisso ◽  
Robert D. Singer
Keyword(s):  
Ionic Liquid ◽  
Liquid Phase ◽  
Model Compound ◽  
Veratryl Alcohol ◽  
Pure Oxygen ◽  
Model Compounds ◽  
Imidazolium Ionic Liquid ◽  
Lignin Model Compounds ◽  
Lignin Model Compound ◽  
Lignin Model

Ionic liquid tagged salen ligands containing two proximal 1,3-disubstituted imidazolium ionic liquid cores form cobalt(III) complexes capable of selectively oxidizing veratryl alcohol, a lignin model compound, to veratraldehyde using air or pure oxygen as the source of oxygen. Entrainment of these catalysts in either 1-butyl-3-methylimidazolium hexafluorophosphate, [bmim][PF6], or 1-butyl-3-methylimidazolium bistriflimide, [bmim][NTf2], hydrophobic ionic liquid solvents, results in biphasic reactions when water is used as the second solvent allowing the catalyst/ionic liquid phase to be recycled.

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