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.

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.

scholarly journals Aromatic–hydroxyl interaction of an alpha-aryl ether lignin model-compound on SBA-15, present at pyrolysis temperatures

2014 ◽  
Vol 16 (44) ◽  
pp. 24188-24193 ◽  
Author(s):  
M. V. Kandziolka ◽  
M. K. Kidder ◽  
L. Gill ◽  
Z. Wu ◽  
A. Savara
Keyword(s):  
Hydrogen Bonds ◽  
Model Compound ◽  
Vibrational Frequencies ◽  
Aryl Ether ◽  
Lignin Model Compound ◽  
Surface Hydroxyls ◽  
Lignin Model

BPEa hydrogen bonds to SBA-15 surface hydroxylsviaan aromatic–hydroxyl interaction characterized by a redshift of >100 cm−1in the OH and CH vibrational frequencies. Surprisingly, this aromatic–hydroxyl interaction is present until ∼400 °C.

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.

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.

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.

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