Reactions Of Lignin Model Compounds Research Articles

Reaction of lignin model compounds sequentially with chlorine dioxide and sodium hydroxide

Reaction of lignin model compounds sequentially with chlorine dioxide and sodium hydroxide

Reactions of lignin model compounds with pulp bleaching chemicals. Cannizzaro-type reaction of tetrachloro-o-benzoquinone with alkali

Reaction of tetrachloro-o-benzoquinone 1 with aqueous sodium hydroxide resulted in a Cannizzaro-type disproportionation into tetrachloromuconic acid and tetrachlorocatechol. The tetrachloromuconic acid was isolated and identified by X-ray crystallography as the methyl ester of the cyclized lactone 3. Crystals of C7H3Cl3O4, 4, are orthorhombic, a = 9.991 (2), b = 7.981 (1), c = 24.626(2) Å, Z = 8, space group Pna21. The structure was solved by direct methods and was refined by full-matrix least-squares procedures to R = 0.033 for 1609 reflections with I ≥ 3σ(I).

Reactions of lignin model compounds with pulp bleaching chemicals. Reactions of 4-methyltrichlorocatechol

Aqueous chlorination of 4-methyltrichlorocatechol 2 gave the tetrachlorohydroxycyclohexenone 4, which crystallized as the hydrate 5. Reaction of 4 with aqueous sodium hydroxide resulted in a benzilic acid rearrangement to the tetrachlorodihydroxycyclopentenecarboxylic acid 6. These reactions have important implications with respect to understanding how lignin is removed during pulp bleaching. Crystals of the tetrachlorotrihydroxycyclohexenone 5 are monoclinic, a = 11.4420(6), b = 7.5873(9), c = 12.6443(6) Å, β = 101.266(4)°, Z = 4, space group P21/c, and those of the methyl tetrachlorodihydroxycyclopentenecarboxylate 7 are monoclinic, a = 28.447(1), b = 6.929(1), c = 12.597(1) Å, β = 103.074(5)°, Z = 8, space group C2/c. The structures were solved by direct methods and were refined by full-matrix least-squares procedures to R = 0.028 and 0.034 for 1716 and 2164 reflections with I ≥ 3σ(I), respectively.

Veratryl Alcohol as a Mediator in Lignin Model Compound Biodegradation

Veratryl alcohol and 1,4-dimethoxybenzene were found to be ineffective mediators for the oxidation of anisyl alcohol by the lignin peroxidase model, iron meso-tetra(2,6-dichloro-3-sulfonatophenyl)porphyrin chloride (TDCSPPFeCl). However, veratryl alcohol can mediate the electrochemical oxidation of the polymeric dye Poly B-411. The TDCSPPFeCl catalyzed reactions of lignin model compounds were found to be dependent on pH and the solvent being used. The importance of the mediating role of veratryl alcohol in lignin degradation is discussed

Biomimetic Approach to Lignin Degradation II. The Mechanism of Oxidative C—C Bond Cleavage Reactions of Lignin Model Compounds with Natural Iron (III) Porphyrin Chloride as a Heme-Enzyme Model System

Article Biomimetic Approach to Lignin Degradation II. The Mechanism of Oxidative C—C Bond Cleavage Reactions of Lignin Model Compounds with Natural Iron (III) Porphyrin Chloride as a Heme-Enzyme Model System was published on January 1, 1987 in the journal Holzforschung (volume 41, issue 5).

The Condensation Reactions of Lignin Model Compounds in Alkaline Pulping Liquors

Abstract The significance of condensation reactions at the 5-position of the aromatic ring of lignin to the overall pulping process has been evaluated using lignin model compounds. Reactions of 5-hydroxymethylcreosol, as a model for 5-substituted lignins formed when formaldehyde is released during pulping, have shown that such groups will react via ortho-quinonemethides to give alkali-stable carbon-carbon bonded condensation products. The amount of condensation depends on the type of pulping liquor used, with less formed in the kraft and soda-anthraquinone (AQ) processes than in the soda process. In these liquors the hydrosulphide or anthrahydroquinone (AHQ) ions present can compete effectively with phenoxide ion for the reactive o-quinonemethide intermediate. Reduced AQ reacts with the o-quinonemethide to form oxanthrone- and anthrone-adducts which are still detectable at 170°C. Such reactions, particularly the reduction of AQ to its anthrone oxidation state, may be one of the reasons why AQ is consumed during pulping. Degradation products of glucose have also been found to decrease the amount of lignin-lignin type condensation products.

PROBABILISTIC MODELLING OF LIGNIN LIQUEFACTION

ABSTRACT The results of the thermal and catalytic reactions of lignin model compounds are used in the a priori prediction of its liquefaction. Lignin was defined probabilistically as an ensemble of single ring aromatics with substituents on each of their six ring positions. Elements in a substituent vector x1, for each ring position i, were matched into all possible combinations to describe lignin. Initial number fractions, or probabilities, for each vector element were ascertained through inspection of lignin structural data. The reaction of lignins altered the probabilities within each substituent vector, and reaction products were also calculated by matching all combinations of vector elements for each ring position. Model compound results provided the identities and rates of change of vector elements. This simulation of lignin liquefaction predicted the yields of permanent gases, aqueous liquids, single- and two-ring phenolic products, and a carbonaceous residue. The impact of the distribution of oligomeric sizes on catalyst effectiveness was probed.

Structural/Reactivity Studies (I): Soda Reactions of Lignin Model Compounds

Abstract Lignin model compounds containing a phenolic “A” ring, α-OH, and β-aryl (ring “B”) ether, with different substituents located on rings A and B, have been synthesized and degraded under a variety of conditions in sodium hydroxide-water (soda). Substituent changes on ring B had a large effect on fragmentation reactions of the models; changes on ring A showed only small effects. These substituent-reactivity relationships indicate that the slow step in the mechanism for model fragmentation under soda conditions is cleavage of the β-aryl ether bond. Vinyl ether formation, a reaction which competes with model fragmentation, is more prominent at low alkali concentration.

Structural/Reactivity Studies (II): Reactions of Lignin Model Compounds with Pulping Additives

Abstract Lignin model compounds, capable of forming quinonemethides and having different substituents on the quinonemethide (A) rings and β-aryl ether (B) rings, have been degraded under a variety of conditions in the presence of NaOH (soda), NaOH/Na2S (kraft), NaOH/glucose, and NaOH/AHQ (soda/AQ). Substituent changes on ring B had no effect on the extent of model fragmentation in the presence of excess AHQ and NaSH. Substituent changes on ring A had large effects on fragmentation under soda/AQ and kraft conditions. These substituent-reactivity relationships indicate that the slow step in the mechanism for model fragmentation under soda/AQ and kraft conditions is quinonemethide formation. Conditions aimed at demonstrating the existence of electron-transfer fragmentation of the model compounds gave results which were inconclusive, but demonstrated that equilibrium reactions between quinonemethide intermediates exist.

Fiber Surface Modification. Part III. The Reaction of Lignin Model Compounds and Other Phenols with Cyanuric Chloride.

Fiber Surface Modification. Part III. The Reaction of Lignin Model Compounds and Other Phenols with Cyanuric Chloride.