Liquefaction Mechanism of β-O-4 Lignin Model Compound in the Presence of Phenol under Acid Catalysis. Part 2. Reaction Behaviour and Pathways

Holzforschung ◽  
2001 ◽  
Vol 55 (6) ◽  
pp. 625-630 ◽  
Author(s):  
L. Lin ◽  
S. Nakagame ◽  
Y. Yao ◽  
M. Yoshioka and N. Shiraishi ◽  
N. Shiraishi
Keyword(s):  
High Performance ◽  
Model Compound ◽  
Structural Characteristics ◽  
Gel Permeation Chromatography ◽  
Main Reaction ◽  
Reaction Products ◽  
Reaction Behavior ◽  
Lignin Model Compound ◽  
Lignin Model ◽  
Acid Catalyzed

Summary By means of high performance liquid chromatography (HPLC) and gel permeation chromatography (GPC), the yields of the main reaction products and the polymeric portion formed in the reaction of guaiacylglycerol-β-guaiacyl ether (GG) under various acid-catalyzed conditions were quantified as a function of reaction time. Based on their forming sequence and reaction behavior, as well as their structural characteristics, an acid-catalyzed reaction mechanism of GG with phenol was proposed.

Liquefaction Mechanism of β-O-4 Lignin Model Compound in the Presence of Phenol under Acid Catalysis. Part 1. Identification of the Reaction Products

Holzforschung ◽  
2001 ◽  
Vol 55 (6) ◽  
pp. 617-624 ◽  
Author(s):  
L. Lin ◽  
Y. Yao ◽  
N. Shiraishi
Keyword(s):  
High Performance ◽  
Model Compound ◽  
Structural Characteristics ◽  
Main Reaction ◽  
Reaction Products ◽  
Lignin Model Compound ◽  
H Nmr ◽  
Lignin Model ◽  
Oxalic Acids ◽  
C Nmr

Summary Guaiacylglycerol-β-guaiacyl ether (GG) was used as a lignin model compound to study the liquefaction reaction mechanism of lignin in the presence of phenol under the catalysis of several typical acids such as sulfuric, phosphoric and oxalic acids. The reaction products were isolated by silicagel column chromatography and high performance liquid chromatography (HPLC). The structures of the obtained compounds were identified by means of GC-MS, 1H-NMR, 13C-NMR, 1H-1H COSY, HMBC and HMQC. As a result, about 30 compounds were obtained as the main reaction products. It was found that their structural characteristics were significantly different from those yielded at the non-catalyzed liquefaction (Lin et al. 1997a), and independent on the acid species. The dominant products were guaiacylglycerol-α-phenyl-β-guaiacyl ethers, followed by guaiacol, triphenylethanes, diphenylmethanes, benzocyclobutanes and phenylcoumarans. The structural characteristics and yields of these main reaction products indicated that condensation between phenol and GG in its C-α and further cleavages in both the β-O-4 linkage and Cβ–Cγ bonding could be the dominant reaction pathways.

Reaction kinetics of strong nucleophiles with a dimeric non-phenolic lignin model compound with α-carbonyl functionality (adleron) in aqueous alkali solution

Holzforschung ◽  
2016 ◽  
Vol 70 (9) ◽  
pp. 811-818 ◽  
Author(s):  
Olesya Fearon ◽  
Susanna Kuitunen ◽  
Tapani Vuorinen
Keyword(s):  
Hydrogen Sulfide ◽  
Model Compound ◽  
Degradation Kinetics ◽  
Reaction Products ◽  
Lignin Model Compound ◽  
Vis Spectroscopy ◽  
Soda Pulping ◽  
Lignin Model ◽  
Kinetics Of ◽  
Sulfite Ion

Abstract The degradation kinetics of a non-phenolic lignin model compound with α-carbonyl functionality (adlerone) has been studied by varying temperature and concentrations of sodium hydroxide, sodium hydrogen sulfide, and sodium sulfite. The kinetics of adlerone degradation and formation of its reaction products were monitored by UV-Vis spectroscopy and their structures were analyzed by GC/MS. The two step degradation of adlerone was studied in two separate experimental setups. In the first alkali catalyzed step, adlerone is converted to a β-elimination product that reacts further in the second step with hydrogen sulfide or sulfite ion. The Arrhenius kinetic parameters were derived by the KinFit software. The activation energy for the 1st step was 69.1 kJ mol-1, and for the 2nd step with sulfide 42.4 kJ mol-1 and with sulfite ion 35.8 kJ mol-1. The reaction mechanisms presented are in line with those published earlier: β-ether bonds of structures having α-carbonyl functionality do not cleave under soda pulping conditions, whereas in kraft and sulfite pulping the cleavage of β-ether bonds proceeds via nucleophile attack and addition. The combination of hydroxyl and sulfite ions gives the fastest cleavage of β-ether bonds in non-phenolic lignin structures with the α-carbonyl functionality.

Delignification Mechanism during High-Boiling Solvent Pulping. Part 1. Reaction of Guaiacylglycerol-β-Guaiacyl Ether

Holzforschung ◽  
2001 ◽  
Vol 55 (6) ◽  
pp. 611-616 ◽  
Author(s):  
T. Kishimoto ◽  
Y. Sano
Keyword(s):  
Model Compound ◽  
Reaction Products ◽  
Aryl Ether ◽  
Lignin Model Compound ◽  
First Order ◽  
Order Rate ◽  
High Boiling Solvent ◽  
Lignin Model ◽  
Rate Behavior ◽  
Pseudo First Order

Summary A phenolic β-O-4 type lignin model compound, guaiacylglycerol-β-guaiacyl ether (1) was treated with 70 wt% aq 1,3-butanediol solution at 160–200°C to investigate the delignification mechanism under HBS (high-boiling solvent) pulping conditions. The following compounds were identified from the reaction products by use of GC-MS: guaiacol (2), coniferyl alcohol (3), γ-etherified coniferyl alcohols (4) and α-etherified guaiacylglycerol-β-guaiacyl ethers (5), but acidolysis products, such as Hibbert's ketones were not detected. These results strongly suggest that the phenolic β-O-4 linkage was cleaved homolytically under HBS pulping conditions. The cleavage of β-ether exhibited a pseudo first-order rate behavior. The pseudo first-order rate constants were as follows: k = 0.94 × 10−2 min−1 at 160 °C; k = 1.97 × 10−2 min−1 at 170°C; k = 3.22 × 10−2 min−1 at 180 °C; k = 9.76 x 10−2 min−1 at 200 °C. The activation energy was 98.3 kJmol−1. The formation of higher molecular weight compounds was confirmed by GPC. It is highly probable that the oligomeric products were derived from the recombination of phenoxy radicals formed by homolysis of the β-aryl ether.

Delignification Mechanism during High-Boiling Solvent Pulping. Part 2. Homolysis of Guaiacylglycerol-β-Guaiacyl Ether

Holzforschung ◽  
2002 ◽  
Vol 56 (6) ◽  
pp. 623-631 ◽  
Author(s):  
T. Kishimoto ◽  
Y. Sano
Keyword(s):  
Model Compound ◽  
Quinone Methide ◽  
Radical Mechanism ◽  
Reaction Products ◽  
Aryl Ether ◽  
Lignin Model Compound ◽  
High Boiling Solvent ◽  
Lignin Model ◽  
Phenoxy Radicals

Summary A phenolic β-O-4 type lignin model compound, guaiacylglycerol-β-guaiacyl ether, was treated with 70 wt % aq 1,4-butanediol solution at 180°C to investigate the delignification mechanism under high-boiling solvent (HBS) pulping conditions. Thirteen compounds including four monomers, six dimers, two trimers and a tetramer were isolated from the reaction products. Most of these products were generated by recombination of phenoxy radicals formed by homolysis of the β-aryl ether. The results suggest that phenolic β-O-4 linkages in lignin are cleaved homolytically (radical mechanism) via quinone methide intermediates under HBS pulping conditions.

scholarly journals Revisiting the mechanism of β-O-4 bond cleavage during acidolysis of lignin VII: acidolyses of non-phenolic C6-C2-type model compounds using HBr, HCl and H2SO4, and a proposal on the characteristic action of Br− and Cl−

2020 ◽  
Vol 66 (1) ◽  
Author(s):  
Qiaoqiao Ye ◽  
Tomoya Yokoyama
Keyword(s):  
Model Compound ◽  
Bond Cleavage ◽  
Type Model ◽  
Enol Ether ◽  
Lignin Model Compound ◽  
Benzyl Cation ◽  
Acid Type ◽  
Unstable Compound ◽  
Lignin Model ◽  
Acidolysis Reaction

AbstractA non-phenolic C6-C2-type lignin model compound with the β-O-4 bond, 2-(2-methoxyphenoxy)-1-(3,4-dimethoxyphenyl)ethanol (I), was acidolyzed in aqueous 82% 1,4-dioxane containing HBr, HCl, or H2SO4 with a concentration of 0.2 mol/L at 85 ℃ to examine the differences between these acidolyses. Compound I primarily converted to an enol ether compound, 1-(2-methoxyphenoxy)-2-(3,4-dimethoxyphenyl)ethene (II), via the benzyl cation followed by acidolytic β-O-4 bond cleavage regardless of the acid-type, although the disappearance rates of compound I were remarkably different (HBr > HCl >> H2SO4). Acidolyses of compound II using these acids under the same conditions showed a similar tendency, but the rate differences were much smaller than in the acidolyses of compound I. Acidolyses of the α-methyl-etherified derivative of compound I (I-α-OMe) using these acids under the same conditions suggested that the formation rates of the benzyl cation from compound I-α-OMe (also from compound I) are not largely different between the acidolyses using these acids, but those of compound II from the benzyl cation are remarkably different. Acidolysis of the α-bromo-substituting derivative of compound I (I-α-Br) using HBr under the same conditions showed a characteristic action of Br¯ in the acidolysis. Br¯ adds to the benzyl cation generated from compound I or I-α-OMe to afford unstable compound I-α-Br, resulting in acceleration of the formation of compound II and of the whole acidolysis reaction.

scholarly journals Model compounds-based study on adsorption and dispersion properties of lignin-based superplasticizer

2021 ◽  
Vol 104 (1) ◽  
pp. 003685042098062
Author(s):  
Shuangping Ma ◽  
Qingjun Ding ◽  
Fen Zhou ◽  
Huaxiong Zhu
Keyword(s):  
Molecular Structure ◽  
Zeta Potential ◽  
Model Compound ◽  
Research Work ◽  
Structure Activity Relationship ◽  
Activity Relationship ◽  
Lignin Model Compound ◽  
Structure Activity ◽  
Lignin Model ◽  
Relationship Of

The chemical modifications of lignin-based superplasticizers have attracted extensive attentions during recent years. The comprehending of the structure-activity relationship of lignin-based superplasticizer is important to promote the modification and application research of lignin resources. However, lignin features complex and variable molecular structure, which is not conducive to study on structure-activity relationship of lignin-based superplasticizer as well as development and application of new lignin-based superplasticizer. However, the related research work can be simplified by selecting small molecular compound with appropriate molecular structure as the lignin model compound. This article intends to study the structure-activity relationship of lignin-based superplasticizer by using dihydroeugenol as the lignin model compound. Through the substitution of lignin by dihydroeugenol during the synthesis process, a model compound lignin-based superplasticizer (DAFS) was synthesized. The adsorption and dispersion properties of this superplasticizer and reference sample (LAFS) were investigated by fluidity test, Zeta-potential measurement, Total organic carbon analysis and others. The results suggest that the adsorption behavior of both DAFS and LAFS conformed to the Langmuir isotherms and Pseudo-second order kinetic. In cement paste, added with 1 g/L of LAFS and DAFS, Zeta potential were reduced from +3.5 to −15.2 mV and −18.7 mV, respectively. The substitution of lignin by dihydroeugenol has no significantly influence on the dispersive property, but differences on rheological properties which need to be optimized in the future. All the tests confirmed that dihydroeugenol is suitable to replace lignin on exploring the structure-activity relationship of lignin-based superplasticizer. This research work provides new insight on model study of lignin-based superplasticizer.

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