Degradation Of Lignin Model Compounds Research Articles

T-BuOK promoted C–C bond oxidative cleavage of β-O-4 and β-1 lignin models to benzoic acids at room temperature

Benzoic acids and phenols were obtained through a tBuOK–O2 system realizing the degradation of lignin model compounds through continuous oxidation. The process is carried out at room temperature without the participation of a metal catalyst.

Molecular identification of native Egyptian Actinobacteria: Screening for lignin utilization and degradation of lignin model compounds

Phylum Actinobacteria covers a broad group of bacteria that are well-known for their applications in pharmaceutical industries. The majority of Actinobacteria found to produce extracellular peroxidases belong to the Streptomycetaceae family, and the majority of the peroxidases produced have been detected in experiments focusing on phenol and/or lignin degradation. In the current study, twenty-three native Egyptian Actinobacteria strains were isolated for lignin utilization. The results indicate that 17 out of 23 were successfully utilizing lignin as sole carbon source on lignin agar medium. Also, they showed ability to degrade lignin model compounds such as vanillic acid, veratric acid and guaiacol. Molecular identification of the 17 isolates by 16S rDNA gene sequencing was carried out. Data analyzed using Blast from Genbank and accession numbers were acquired, and phylogenetic trees were constructed.

Microwave-assisted chemistry: parametric optimization for catalytic degradation of lignin model compounds in imidazolium-based ILs

Lignin, a readily available form of biomass with a potential source of aromatic chemical compounds, has not been fully utilized due to its complex structure. Hence, this study aims to elaborate and optimize the effects of parametric microwave conditions for the catalytic degradation of lignin model compounds. In addition to that, 41 types of imidazolium-based Ionic liquids were employed for the conversion of lignin model compounds such as guaiacol and benzyl phenyl ether. The microwave-assisted conversion of lignin model compounds in imidazolium-based ionic liquids was performed at optimum applied microwave power 700 W and 30-min irradiation time. The percentages conversion and yield were quantified using high-performance liquid chromatography (HPLC) analysis. Results revealed that the chloride anion-based ionic liquids exhibited better nucleophilic behavior and catalyzed the cleavage of ether-based compounds efficiently under microwave irradiation. Among the imidazolium-based ionic liquids, 1H-methylimidazolium chloride ([1H-MIM][Cl]) exhibited better performance with guaiacol conversion and catechol yield of 99% and 81%, respectively. Therefore, the microwave-assisted technique was found to be more promising than conventional methods for the ionic liquid-based catalytic degradation of lignin model compounds.

A two-phase reaction system for selective oxidative degradation of lignin model compounds

Lignin depolymerization through an oxidation method could provide value-added products, but it is challenging in terms of recovering catalysts or separating products in time to avoid over-oxidation. In this study, a process of selectively oxidative degradation of lignin model compounds was operated in a two-phase reaction system. Lignin model compounds of 4-benzyloxyphenol (PBP) or guaiacylglycerol-β-guaiacyl ether (GGE) in a bottom phase of 1-butyl-3-methylimidazole chloride ([BMIM]Cl) ionic liquid were selectively oxidized by H2O2 in the presence of a solid acid (SO42-/Fe2O3-ZrO2), and the degradation products immediately diffused into the upper organic solvent phase (butyl acetate). In this kind of reaction system, the yield of the products was improved due to the prolonged life of ∙OH in ionic liquid, and the product selectivity was maintained due to the timely product separation, and the ionic liquid and the catalyst were easily recycled.

Bacillus amyloliquefaciensCotA degradation of the lignin model compound guaiacylglycerol-β-guaiacyl ether

The cotA gene from Bacillus amyloliquefaciens MN-13 was cloned and expressed in Escherichia coli Transetta. Nucleotide sequence analysis showed an open reading frame of 1542bp encoding a polypeptide comprised of 513 amino acids. The degradation of lignin model compounds by recombinant CotA was investigated by HPLC-MS with guaiacylglycerol-β-guaiacyl ether as the substrate. The compounds including guaiacol, 3-(4-hydro-3-methoxyphenyl)-3-oxo-propanol and 4-hydro-3-methoxy acetophenone detected by HPLC-MS verified the rupture of β-O-4 bond and oxidation Cα bond of guaiacylglycerol-β-guaiacyl ether by CotA. 4-vinylguaiacol and 1-(4-hydroxy-3-methoxyl phenyl)-1-(2-methoxyl) phenoxyl ethylene were first time found in the degradation products of guaiacylglycerol-β-guaiacyl ether. The appearance of 4-vinylguaiacol and 4-hydro-3-methoxy acetophenone confirmed the cleavage of Cβ-Cγ bond. 1-(4-hydroxy-3-methoxyl phenyl)-2-(2-methoxyl) phenoxyl ethylene was coupled by the radical reaction of 4-vinylguaiacol with guaiacol. Otherwise, no corresponding degradation product was found to give a proof of cleavage of Cα-Cβ bond in guaiacylglycerol-β-guaiacyl ether by CotA.

Electrochemical Generation of ROS in Ionic Liquid for the Degradation of Lignin Model Compound

p-benzyloxyl phenol (PBP), as a lignin model compound, was electrochemically degraded in [BMIM]BF4 ionic liquid (IL) using an oxygen reduction reaction (ORR) cathode. The utilization of this kind of aprotic IL made it possible to identify which kind of reactive oxygen species (ROS) played an important role in the electrochemical depolymerization of lignin. Electrochemical study confirmed that superoxide radical (·O2−), the one-electron reductive product of dioxygen, is the main resultant of ORR in [BMIM]BF4. However, the generated ·O2− radical transformed into hydroperoxyl radical (·OOH) in the presence of protons donated by PBP, and then received one more electron to form H2O2, which then attacked and broke down the alkyl-O-aryl bonds in PBP molecules. The continuous electrolysis of PBP in [BMIM]BF4 provided indirect evidence to reveal that the in situ generated H2O2 on ORR cathode was responsible for the cleavage of ether bonds in PBP.

Ligninolytic activity of bacteria of the genera Azospirillum and Niveispirillum

Capacity of associative soil bacteria of the genera Azospirillum and Niveispirillum for degradation of lignin model compounds was demonstrated. Lignin and Mn-peroxidases were detected in the culture liquid of the type strains of these genera. The data on involvement of nonspecific bacterial peroxidases in lignin degradation were obtained.

Microwave-Assisted Oxidative Degradation of Lignin Model Compounds with Metal Salts

A systematic study on microwave-assisted oxidative degradation of lignin model compounds, such as 2-phenoxy-1-phenylethanol, vanillyl alcohol, and 4-hydroxybenzyl alcohol, was performed by evaluating the catalytic activity of 14 types of metal salts. The acidity of each metal salt solution for the oxidative degradation of 2-phenoxy-1-phenylethanol, vanillyl alcohol, and 4-hydroxybenzyl alcohol under the microwave irradiation and conventional heating conditions was measured and compared. The results showed that CrCl3 and MnCl2 were the most effective for the degradation of the lignin model compounds. The acidity of metal salt is in favor of the catalytic activity for the degradation of 2-phenoxy-1-phenylethanol, vanillyl alcohol, and 4-hydroxybenzyl alcohol, and microwave irradiation is able to accelerate the degradation rate in a large scale. The possible mechanisms for the degradation of 2-phenoxy-1-phenylethanol, vanillyl alcohol, and 4-hydroxybenzyl alcohol are proposed on the basis of the product dist...

ChemInform Abstract: Solar Photochemical Oxidation of Alcohols Using Catalytic Hydroquinone and Copper Nanoparticles under Oxygen: Oxidative Cleavage of Lignin Models.

Alcohols are converted into to their corresponding carbonyl compounds using catalytic amounts of 1,4-hydroquinone with a copper nanoparticle electron transfer mediator with oxygen as the terminal oxidant in acetone as solvent under visible light irradiation. These conditions employing biorenewable hydroquinone as reagent were developed from initial experiments using stoichiometric amounts of 1,4-benzoquinone as oxidant. A range of benzylic and aliphatic primary and secondary alcohols are oxidized, affording the corresponding aldehydes or ketones in moderate to excellent yields. The methodology is also applicable to the oxidative degradation of lignin model compounds that undergo C–C bond cleavage to give simple aromatic compounds.

Photocatalytic Degradation of Lignin Model Compounds and Kraft Pine Lignin by CdS/TiO2 under Visible Light Irradiation

Cadium sulfide/titanium dioxide (CdS/TiO2) catalyst was prepared by two different methods: microemulsion-mediated solvothermal hydrolyzation (CdS/TiO2 (SH)) and in-situ sulfurization under supercritical conditions (CdS/TiO2 (SS)). The photocatalysts were characterized by nitrogen adsorption-desorption, X-ray diffraction, X-ray photoelectron spectra, UV-Vis absorption spectra, and PL spectra. Photodegradation reactions of three monomeric and one dimeric lignin model compounds, and kraft pine lignin (Indulin AT) were carried out at room temperature in a weak alkaline aqueous system by visible light irradiation with air bubbling. Quantitative results showed that these lignin model compounds and kraft lignin were effectively degraded. While both phenolic and non-phenolic lignin units are reactive, the phenolic units appeared to react faster and preferentially reacted.

Solar photochemical oxidation of alcohols using catalytic hydroquinone and copper nanoparticles under oxygen: oxidative cleavage of lignin models.

Alcohols are converted into to their corresponding carbonyl compounds using catalytic amounts of 1,4-hydroquinone with a copper nanoparticle electron transfer mediator with oxygen as the terminal oxidant in acetone as solvent under visible light irradiation. These conditions employing biorenewable hydroquinone as reagent were developed from initial experiments using stoichiometric amounts of 1,4-benzoquinone as oxidant. A range of benzylic and aliphatic primary and secondary alcohols are oxidized, affording the corresponding aldehydes or ketones in moderate to excellent yields. The methodology is also applicable to the oxidative degradation of lignin model compounds that undergo C-C bond cleavage to give simple aromatic compounds.

Microwave-Assisted Degradation of Lignin Model Compounds in Imidazolium-Based Ionic Liquids

A systematic study of microwave-assisted degradation of lignin model compounds such as benzyl phenyl ether (BPE) and guaiacol, in imidazolium-based ionic liquids, was performed by evaluating the catalytic activity of 29 types of ionic liquids as both solvent and catalyst. After measuring and comparing the acidity of each ionic liquid solution for BPE and guaiacol degradation under the microwave irradiation and conventional heating conditions, it was found that the ionic liquid 1-butyl-3-methylimidazolium hydrogen sulfate ([BMIM]HSO4) was the most effective for decomposing the lignin model compounds. The experimental results indicate that ionic liquid acidity is in favor of the catalytic activity for BPE and guaiacol degradation, microwave irradiation could accelerate the degradation rate by 650% for BPE and 1120% for guaiacol and significantly increase the reaction selectivity. It was also found in experiments that the ionic liquid [BMIM]HSO4 could be used for 5 times without any loss of catalytic activity. The possible mechanisms for BPE and guaiacol degradation are proposed based on the product distributions.

Catalytic degradation of lignin model compounds in acidic imidazolium based ionic liquids: Hammett acidity and anion effects

Ionic liquids based on the 1-methylimidazolium cation with chloride, bromide, hydrogen sulfate, and tetrafluoroborate counterions along with 1-butyl-3-methylimidazolium hydrogen sulfate were employed to degrade two lignin model compounds, guaiacylglycerol-β-guaiacyl ether and veratrylglycerol-β-guaiacyl ether. The acidity of each ionic liquid was approximated using 3-nitroaniline as an indicator to measure the Hammett acidity (H0). While all of the tested ionic liquids were strongly acidic (H0 between 1.48 and 2.08), the relative acidity did not correlate with the ability of the ionic liquid to catalyze β-O-4 ether bond hydrolysis. The reactivity of the model compounds in the ionic liquids is dependent not only on the acidity, but also on the nature of the ions and their interaction with the model compounds.

Non‐Oxidative Vanadium‐Catalyzed CO Bond Cleavage: Application to Degradation of Lignin Model Compounds

Richtungswechsel: Durch Änderung der Ligandenstruktur kann die Reaktivität von Vanadium(V)-Oxo-Komplexen von der Alkohol-Oxidation zu einer neuartigen nichtoxidativen C-O-Spaltung umgelenkt werden. Damit steht eine Methode für die selektive Bildung von hoch funktionalisierten Arylenonen aus Lignin-Modellverbindungen durch Vanadium-katalysierte Spaltung der β-O-4-Verknüpfung zur Verfügung (siehe Schema; N blau, O rot).

Non-oxidative vanadium-catalyzed C-O bond cleavage: application to degradation of lignin model compounds.

New direction: Changes in the ligand structure divert the reactivity of vanadium(V) oxo complexes from alcohol oxidation to a novel non-oxidative CO bond cleavage. Thus, highly functionalized aryl enones can be selectively generated from lignin model compounds by vanadium-catalyzed cleavage of the β-O-4 linkage (see scheme; N blue, O red).

Simulation of Lignin Degradation During Chlorine Dioxide Delignification Stage

The chlorine dioxide reaction with residual lignin of chemical pulp during delignification stage was simulated using phenolic and non-phenolic lignin model compounds applying various amounts of chlorine dioxide. Based on the reaction of model compounds and measurement of inorganic chlorinated species, three reaction phases were established for degradation of lignin model compounds. It was found that after the degradation of free phenolic units, the reaction of primary oxidized products by ClO2 competed with the oxidation of non-phenolic aromatic structure. The results obtained by lignin model compounds were compared with the pulp delignification results. This comparison indicated two special phases for the reduction of the kappa number. The initial phase corresponded to the oxidation of phenolic units without secondary reactions. The second phase corresponded to the oxidation of the non-phenolic units in competing with secondary reactions. The results of this confirmed the over consumption of chlorine dioxide by primary oxidized lignin in the secondary reactions.

Reactions of Lignin with Peroxymonophosphoric Acid: The Degradation of Lignin Model Compounds

Summary Peroxymonophosphoric acid (Pp) has been shown to be an excellent delignification chemical for kraft pulps. However, the reaction mechanism of Pp with lignin has not been elucidated. Therefore, the reactions of Pp with non-phenolic lignin model compounds have been investigated at 70 and 90°C and compared to those of peroxymonosulfuric acid (Px). Pp and Px appear to follow similar reaction pathways, however, the reaction kinetics are significantly different. Both Pp and Px react with 1,2-Dimethoxy-4-methyl-benzene as electrophiles, with aromatic hydroxylation being the main initial reaction. For 1-(3,4-Dimethoxy-phenyl)-ethanone, both Px and Pp react via the Baeyer-Villiger reaction, in which the initial step is nucleophilic attack by the peracid.The reaction with 1-(3,4-Dimethoxy-phenyl)-ethanol occurs primarily via carbocation formation followed by subsequent reactions with the peracid. Changes in pH dramatically affect the reaction rates of Pp with all the model compounds investigated, whereas with the exception of the Baeyer-Villiger reaction, changes in pH did not affect the Px reactions. Below pH 2, Pp is a better electrophile than Px, but above pH 2, Px is better. In addition, while Px remains reactive, Pp is not reactive at pH above 7 for the model compounds investigated.

Degradation of lignin and lignin model compound under sulfate reducing condition

The release of depolymerization products of lignin during the degradation of lignocellulsic material under sulfate reducing condition was investigated. In addition, we investigated the fate of the most common (beta-O-4) link present in lignin under sulfate reducing condition, using a lignin model compound. The method of investigation was based on the selective inhibition of microbial uptake of released aromatic phenolic compounds, depolymerization product of lignin, by toluene. Eight different aromatic phenolic compounds were identified. Until day 17 only 3 phenolic compounds were regularly detected, thereafter 7 aromatic phenolic compounds could be regularly identified. The accumulation of identified phenolic acid was not linear with time. The lignin model compound was completely degraded within 13 days when either Avicel cellulose or newspaper was present as alternate source of carbon. On the other hand when lignin model compound was present as the sole source of carbon, it took more than 22 days for its complete degradation. But in either case complete degradation of lignin model compound was observed. Four degradation byproducts of lignin model compound were identified, but the two most significant compounds identified were vanillic acid and 3-methoxy-4-hydroxy benzene propionic acid. The GC/MS analysis of the degradation by products of lignin model compound indicated that beta-O-4 link was cleaved under sulfate reducing condition and the presence of additional carbon source enhanced this process.

Structural modifications induced during biodegradation of wheat lignin by Lentinula edodes

The structural modifications occurring during wheat straw lignin biodegradation were evaluated by the concerted use of 31P-, 1H- and 2D homo- and heteronuclear NMR spectroscopies. Straw lignin was found to be oxidatively degraded via stereoselective side-chain oxidation as evidenced by a lower erythro/threo ratio. Significantly lower amounts of phenolic hydroxy and methoxy groups in the decayed lignin may be indicative that its structure after the fungal treatment contained a lower amount of aromatic units. In addition an increase in carboxylic acids content, that cannot be explained only on the basis of side-chain oxidation reactions, was also apparent. This evidence, coupled with pertinent data collected during this effort, suggests the occurrence of aromatic ring cleavage reactions. In fact the oxidative degradation of lignin model compounds by fungi has been reported to occur via the 3-oxoadipate pathway which is known to cause aromatic ring cleavage with the formation of aliphatic chains. The presence of aliphatic moieties in the decayed lignin was confirmed by detailed 1H- and 2D NMR spectroscopic analyses.

Reactions of Lignin with Cyanamide Activated Hydrogen Peroxide. Part 1. The Degradation of Lignin Model Compounds

Monomeric lignin model compounds representing various functional groups found in residual lignins were reacted with cyanamide activated hydrogen peroxide. Non-phenolic lignin model compounds failed to react even under extreme reaction conditions (90°C), while phenolic lignin model compounds underwent rapid oxidation. Reaction optimization studies reveal that these reactions are strongly dependent on pH and the cyanamide-to-peroxide ratio, while temperature is not a factor. Through the use of electron paramagnetic resonance (EPR) spectroscopy free radical involvement has been demonstrated. In contrast to previous literature, a predominately free-radical mechanism exists, and on the basis of the reactions carried out in the presence of superoxide dismutase, the presence of .O 2 - has been determined.