- Are quinone methides responsible for yellowing of paper in light?
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Irradiation of tetrahydrofuran solutions of quinone methide 1 at 350 nm resulted in the formation of yellow oligomeric products and guaiacol. The rate constants determined for the disappearance of the starting compound and those of guaiacol formation show
- Dolenc, Jozica,Sket, Boris,Strlic, Matija
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- One-pot synthesis of β-O-4 lignin models: Via the insertion of stable 2-diazo-1,3-dicarbonyls into O-H bonds
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Because lignin is a macromolecule that is a sustainable source of aromatic compounds, model substrates are commonly used to increase our understanding of its complex structure. However, few methods have been described for the synthesis of these models. Herein, we describe a new route towards the synthesis of β-O-4 lignin models by intermolecular O-H insertion reactions with simple and stable diazocarbonyls. The benefits of this developed method were shorter reaction times and high yields, as well as mild and environmentally friendly conditions. This journal is
- Burtoloso, Antonio C. B.,De Oliveira, Gabriela P.,Dias, Rafael Mafra P.
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p. 4815 - 4823
(2020/07/13)
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- Transition-metal-free conversion of lignin model compounds to high-value aromatics: Scope and chemoselectivity
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An efficient and straightforward reaction protocol for the conversion of lignin model compounds was developed based on a simple system consisting of a base, oxygen, and a green solvent under mild conditions in the absence of metals. This protocol was successfully applied to the cleavage of both 'β-O-4' dimeric and trimeric compounds, and a controlled selective degradation was achieved depending on the bond type. The feasibility of this method to provide aromatic compounds in high yields from lignin by a sequential oxidative dehomologation reaction was clearly demonstrated.
- Lee, Tae Woo,Yang, Jung Woon
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p. 3761 - 3771
(2018/08/21)
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- Iridium-catalysed primary alcohol oxidation and hydrogen shuttling for the depolymerisation of lignin
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Lignin is a potentially abundant renewable resource for the production of aromatic chemicals, however its selective depolymerisation is challenging. Here, we report a new catalytic system for the depolymerisation of lignin to novel, non-phenolic monoaromatic products based on the selective β-O-4 primary alcohol dehydrogenation with a Cp?Ir-bipyridonate catalyst complex under basic conditions. We show that this system is capable of promoting the depolymerisation of model compounds and isolated lignins via a sequence of selective primary alcohol dehydrogenation, retro-aldol (Cα-Cβ) bond cleavage and in situ stabilisation of the aldehyde products by transfer (de)hydrogenation to alcohols and carboxylic acids. This method was found to give good to excellent yields of cleavage products with both etherified and free-phenolic lignin model compounds and could be applied to real lignin to generate a range of novel non-phenolic monomers including diols and di-acids. We additionally show, by using the same catalyst in a convergent, one-pot procedure, that these products can be selectively channelled towards a single di-acid product, giving much simpler product mixtures as a result.
- Lancefield, Christopher S.,Teunissen, Lucas W.,Weckhuysen, Bert M.,Bruijnincx, Pieter C. A.
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p. 3214 - 3221
(2018/07/31)
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- Method for synthesizing guaiacyl glycerol-beta-guaiacyl ether from lignin beta-O-4 linkage dimer model compound
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The invention provides a method for synthesizing guaiacyl glycerol-beta-guaiacyl ether from a lignin beta-O-4 linkage dimer model compound. The content of beta-O-4 linkages in all linkages of lignin is highest and about 40-60%, so research of the beta-O-4 linkage lignin model compound plays an important role in research of the structure of lignin and the reaction mechanism of lignin in reaction. The method is simple, reaction conditions are mild, the yield is high, and the production period is short.
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Paragraph 0065; 0066; 0080; 0081; 0095; 0096
(2017/08/25)
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- SELECTIVE AEROBIC ALCOHOL OXIDATION METHOD FOR CONVERSION OF LIGNIN INTO SIMPLE AROMATIC COMPOUNDS
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Described is a method to oxidize lignin or lignin sub-units. The method includes oxidation of secondary benzylic alcohol in the lignin or lignin sub-unit to a corresponding ketone in the presence of unprotected primarily aliphatic alcohol in the lignin or lignin sub-unit. The optimal catalyst system consists of HNO3 in combination with another Br?nsted acid, in the absence of a metal-containing catalyst, thereby yielding a selectively oxidized lignin or lignin sub-unit. The method may be carried out in the presence or absence of additional reagents including TEMPO and TEMPO derivatives.
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- Chemoselective metal-free aerobic alcohol oxidation in lignin
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An efficient organocatalytic method for chemoselective aerobic oxidation of secondary benzylic alcohols within lignin model compounds has been identified. Extension to selective oxidation in natural lignins has also been demonstrated. The optimal catalyst system consists of 4-acetamido-TEMPO (5 mol %; TEMPO = 2,2,6,6-tetramethylpiperidine-N-oxyl) in combination with HNO3 and HCl (10 mol % each). Preliminary studies highlight the prospect of combining this method with a subsequent oxidation step to achieve C-C bond cleavage.
- Rahimi, Alireza,Azarpira, Ali,Kim, Hoon,Ralph, John,Stahl, Shannon S.
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supporting information
p. 6415 - 6418
(2013/06/05)
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- Hydrogenolysis of lignosulfonate into phenols over heterogeneous nickel catalysts
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We report a strategy for the catalytic conversion of lignosulfonate into phenols over heterogeneous nickel catalysts. Aryl-alkyl bonds (C-O-C) and hydroxyl groups (-OH) are hydrogenated to phenols and alkanes, respectively, without disturbing the arenes. The catalyst is based on a naturally abundant element, and is recyclable and reusable. The Royal Society of Chemistry 2012.
- Song, Qi,Wang, Feng,Xu, Jie
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supporting information; experimental part
p. 7019 - 7021
(2012/08/14)
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- Alkoxyl- and carbon-centered radicals as primary agents for degrading non-phenolic lignin-substructure model compounds
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Lignin degradation by white-rot fungi proceeds via free radical reaction catalyzed by oxidative enzymes and metabolites. Basidiomycetes called selective white-rot fungi degrade both phenolic and non-phenolic lignin substructures without penetration of extracellular enzymes into the cell wall. Extracellular lipid peroxidation has been proposed as a possible ligninolytic mechanism, and radical species degrading the recalcitrant non-phenolic lignin substructures have been discussed. Reactions between the non-phenolic lignin model compounds and radicals produced from azo compounds in air have previously been analysed, and peroxyl radical (PR) is postulated to be responsible for lignin degradation (Kapich et al., FEBS Lett., 1999, 461, 115-119). However, because the thermolysis of azo compounds in air generates both a carbon-centred radical (CR) and a peroxyl radical (PR), we re-examined the reactivity of the three radicals alkoxyl radical (AR), CR and PR towards non-phenolic monomeric and dimeric lignin model compounds. The dimeric lignin model compound is degraded by CR produced by reaction of 2,2′-azobis(2-amidinopropane) dihydrochloride (AAPH), which under N2 atmosphere cleaves the α-β bond in 1-(4-ethoxy-3-methoxyphenyl)-2-(2-methoxyphenoxy)-1,3-propanediol to yield 4-ethoxy-3-methoxybenzaldehyde. However, it is not degraded by the PR produced by reaction of Ce4+/tert-BuOOH. In addition, it is degraded by AR produced by reaction of Ti3+/tert-BuOOH. PR and AR are generated in the presence and absence of veratryl alcohol, respectively. Rapid-flow ESR analysis of the radical species demonstrates that AR but not PR reacts with the lignin model compound. Thus, AR and CR are primary agents for the degradation of non-phenolic lignin substructures.
- Ohashi, Yasunori,Uno, Yukiko,Amirta, Rudianto,Watanebe, Takahito,Honda, Yoichi,Watanabe, Takashi
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body text
p. 2481 - 2491
(2011/05/14)
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- Co(salen)/SBA-15 catalysed oxidation of a β-O-4 phenolic dimer under microwave irradiation
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The microwave-assisted oxidative degradation of a lignin model phenolic dimer [1-(4-hydroxy-3-methoxyphenoxy)-2-(2-methoxyphenoxy)-propane-1,3-diol, 1] catalysed by Co(salen)/SBA-15 is reported. The investigated model compound 1 was prepared through a multistep synthesis and characterized by 1H, 13C NMR, and GC-MS studies. The catalyst was prepared by immobilizing [N,N′-bis(salicylidene)ethane-1,2-diaminato]Cobalt(II), Co(salen) complex onto the periodic mesopore channels of siliceous SBA-15. The activity of the Co(salen)/SBA-15 was investigated in the oxidation of 1 in the presence of hydrogen peroxide as oxidant, both under microwave irradiation and conventional heating. The phenolic dimer was selectively oxidized to 2-methoxy phenol with very high TON under microwave activation conditions. Comparatively, reactions run under conventional heating led to oligomerisation of the dimer and resulted in a mixture of products.
- Badamali, Sushanta K.,Luque, Rafael,Clark, James H.,Breeden, Simon W.
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scheme or table
p. 993 - 995
(2012/02/14)
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- Chloroaniline/lignin conjugates as model system for nonextractable pesticide residues in crop plants
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In vitro lignins formed by the peroxidase/H2O2-mediated polymerization of coniferyl alcohol in the presence of 3,4-dichloroaniline or [15N]aniline were studied by 1H, 13C, and 15N NMR spectroscopy. The anilines were >95% bound to the benzylic α-position of lignin side chains. Mild acid hydrolysis under simulated stomach conditions (0.1 M HCl, 37 °C) was studied as a first estimate of animal bioavailability. The two extremes of facile or slow acid hydrolysis that are known for chloroaniline/lignin complexes could be reproduced by using low or high incorporation ratios of aniline to coniferyl alcohol (10 or 40 mol %, respectively). The case of facile acid hydrolysis and high animal bioavailability may be due to the high mole ratios used and may not be relevant for pesticidal crop plant residue levels of 3,4- dichloroaniline. The latter are typically in the parts per million range. On the basis of 15N NMR spectral fine structure, we propose that the acid- labile linkage may be due to anchimeric assistance in conformers formed at the high aniline molar ratio. The optimized methods presented here allow the use of in vitro lignin copolymers as a reference system for the structural features and the bioavailability of nonextractable pesticide residues in crop plants. In vitro lignins formed by the peroxidase/H2O2-mediated polymerization of coniferyl alcohol in the presence of 3,4-dichloroaniline or [15N]aniline were studied by 1H,13C, and 15N NMR spectroscopy. The anilines were >95% bound to the benzylic α-position of lignin side chains. Mild acid hydrolysis under simulated stomach conditions (0.1 M HCl, 37 °C) was studied as a first estimate of animal bioavailability. The two extremes of facile or slow acid hydrolysis that are known for chloroaniline/lignin complexes could be reproduced by using low or high incorporation ratios of aniline to coniferyl alcohol (10 or 40 mol %, respectively). The case of facile acid hydrolysis and high animal bioavailability may be due to the high mole ratios used and may not be relevant for pesticidal crop plant residue levels of 3,4-dichloroaniline. The latter are typically in the parts per million range. On the basis of 15N NMR spectral fine structure, we propose that the acid-labile linkage may be due to anchimeric assistance in conformers formed at the high aniline molar ratio. The optimized methods presented here allow the use of in vitro lignin copolymers as a reference system for the structural features and the bioavailability of nonextractable pesticide residues in crop plants.
- Lange, B. Markus,Hertkorn, Norbert,Sandermann Jr., Heinrich
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p. 2113 - 2118
(2007/10/03)
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- The incorporation of 3,4-dichloroaniline, a pesticide metabolite, into dehydrogenation polymers of coniferyl alcohol (DHPs)
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A mechanism by which pesticide metabolites may become incorporated into plant lignins has been studied with the aid of 3,4-dichloroaniline (DCA) and lignin model compounds. DCA was found to react rapidly with a quinone methide representing an intermediate in lignin biosynthesis. The resulting benzylamine group was stable to mild acidolysis under simulated stomach conditions. Addition of DCA to dehydrogenative polymerizations of coniferyl alcohol yielded DHPs containing covalently bonded DCA. NMR spectroscopy showed that the DCA had become bonded to the benzylic position in arylglycerol-β-guaiacyl ether structures. The majority of these structures were phenolic. This observation and the fact that the DCA accumulates in the low molecular weight fraction of the DHP indicates that the DCA functions as a trap for quinone methides and stops the further growth of the polymer. Acta Chemica Scandinavica 1998.
- Brunow, Goesta,Raiskila, Sanni,Sipilae, Jussi
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p. 1338 - 1342
(2007/10/03)
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- Singlet oxygen in the photodegradation of lignin models
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The photochemical oxidation of lignin models in the presence of singlet oxygen was studied. The treatment of the non-phenolic β-O-4 aryl ether derivatives 6, 7, and 8 in the presence of both oxygen and Rose Bengal gave products deriving from a formal β-C-O cleavage formation. By this way. the derivatives 12, 13, and 15 were obtained. The photochemical oxidation of the phenolic β-O-4 aryl ether 9 gave the same type of product confirming that, in this case, the presence of the carbonyl group is not indispensable to have the cleavage reaction. The use of the model compound 10 showed that, when the phenoxy part of the molecule shows a lower reactivity towards singlet oxygen, the oxidation of the phenol moiety to hydroquinone call occur. The photochemical behaviour of these model compounds can be rationalised from a reaction of singlet oxygen with the phenoxy part of the molecule.
- Crestini, Claudia,D'Auria, Maurizio
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p. 7877 - 7888
(2007/10/03)
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- Electroorganic Reactions. 38. Mechanism of Electrooxidative Cleavage of Lignin Model Dimers
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The mechanisms for oxidative cleavage of several phenolic ethers, models for lignins, have been investigated by a detailed comparison of the results of anodic oxidation at nickel anodes in alkaline electrolyte with that of oxidation in acetonitrile in the presence of a triarylamine redox catalyst.The latter reaction is unambiguously initiated by single-electron transfer (SET), and in this case the major product of cleavage is aldehyde (vanillin or syringaldehyde derivatives).At nickel anodes polymerization is predominant although the aldehydes are formed together with larger amounts of the corresponding carboxylic acids.Combinations of 4-hydroxyl, α-keto, β-O-aryl, and β-hydroxymethyl functionality are shown to be crucial for the oxidation at nickel; the carboxylic acid formation probably involves a route with initial hydrogen atom abstraction at the surface.Important chemical conversions precede and accompany oxidation in alkaline media, and these are associated with the propensity for polymerization.
- Pardini, Vera L.,Smith, Carmen Z.,Utley, James H. P.,Vargas, Reinaldo R.,Viertler, Hans
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p. 7305 - 7313
(2007/10/02)
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- Oxidation of Lignin Model Compounds Using Single-Electron-Transfer Catalysts
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The single-electron-transfer oxidation of model compounds representative of the arylglycerol β-aryl ether and 1,2-diarylpropane linkages of lignin has been examined by using Co(II), Mn(II), or Co(II)/Mn(II) as catalysts.Catalytic oxidation of 1-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)propane-1,3-diol (DMMP) in 80percent acetic acid with 500 psi of 4percent oxygen in nitrogen and at 170 deg C resulted predominantly in products of Cα-Cβ bond cleavage when using Co(II)/Mn(II) as catalyst.Cα-Cβ bond cleavage of DMMP results from an initial single-electron oxidation toproduce an intermediate aromatic radical cation; in the absence of oxygen and catalyst, acid-catalyzed β-aryl ether cleavage was the predominant reaction pathway.Dihydroanisoin (DHA) and 1,2-bis(4-methoxyphenyl)propane-1,3-diol (BMPD) were oxidized by stoichiometric quantities of Co(III) to give solely products of Cα-Cβ bond cleavage but produced only acid-catalyzed dehydration products under reaction conditions necessary for catalytic oxidation.The application of this oxidation reaction as a replacement for chlorine bleaching of paper pulp is discussed.
- DiCosimo, Robert,Szabo, Hsiao-Chiung
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p. 1673 - 1679
(2007/10/02)
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- Stereoselective Syntheses of Lignin Model Compounds of the β-0-4 and β-1 Types
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The preparation of erythro forms of lignin model compounds of the β-0-4 type by hydroboration of α-aryloxycinnamic acids, using a borate dimethyl sulfide complex as a reagent, has been studied.The erythro form of 1-(4-hydroxy-3-methoxyphenyl)-2-(2-methoxyphenoxy)-1,3-propanediol was obtained in a yeild of about 50percent.Acid-catalyzed rearangements of chalcone oxides result in the formation of α-formyldesoxibenzoins which give 1,2-diaryl-1,3-propanediols on borohydride reduction.The synthesis of the erythro forms of 1,2-bis(4-hydroxy-3-methoxyphenyl)-1,3-propanediol and 1,2-bis(4-hydroxy-3,5-dimethoxyphenyl)-1,3-propanediol by this reaction route is discribed; 1,2-diaryl-1,3-propanediols represent lignin model compounds for the β-1 type of structure.
- Ahvonen, Toivo,Brunow, Goesta,Kristersson, Per,Lundquist, Knut
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p. 845 - 850
(2007/10/02)
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