Studies on the condensation of lignins in alkaline media. Part II. The formation of stilbene and arylcoumaran structures through neighbouring group participation reactions

1977 ◽  
Vol 55 (4) ◽  
pp. 593-599 ◽  
Author(s):  
Josef Gierer ◽  
Ingegerd Pettersson
Keyword(s):  
Phenolic Compounds ◽  
Alkaline Media ◽  
Aryl Ether ◽  
Model Compounds ◽  
Ether Linkage ◽  
Group Participation ◽  
Condensation Products ◽  
Neighbouring Group Participation ◽  
Alkaline Delignification ◽  
Aryl Participation

The alkaline condensation of p-hydroxyarylglycerol-β-aryl ether units in lignin with other phenolic structures and the subsequent reactions of the condensation products have been elucidated using appropriate model compounds. It is shown that the primary condensation of simple phenols (2,6-xylenol or resorcinol) into the α-position of phenolic compounds of the β-aryl ether type is followed by an aryl participation (A1-3) reaction resulting in the cleavage of the β-aryl ether bond and formation of the corresponding stilbene derivative. When resorcinol is used as reaction partner, the condensation is also followed by the cleavage of the β-aryl ether linkage through another type of neighbouring group participation reaction involving the phenolate anion ortho to the site of condensation and giving rise to the corresponding aryl-coumaran derivative.The consequences of these findings for the course of alkaline delignification processes are briefly discussed.

Neighbouring group participation of thiol through aldehyde group assisted thiolysis of active ether: ratiometric and vapor phase fast detection of hydrogen sulfide in mixed aqueous media

2015 ◽  
Vol 39 (7) ◽  
pp. 5669-5675 ◽  
Author(s):  
Avijit Kumar Das ◽  
Shyamaprosad Goswami ◽  
Ching Kheng Quah ◽  
Hoong-Kun Fun
Keyword(s):  
Hydrogen Sulfide ◽  
Vapor Phase ◽  
Aqueous Media ◽  
Aldehyde Group ◽  
Nucleophilic Attack ◽  
Ether Linkage ◽  
Fast Detection ◽  
Group Participation ◽  
Neighbouring Group Participation

Ratiometric and fast detection of H2S via NGP of thiol rather than direct nucleophilic attack to cleave active ether linkage.

Photocatalytic oxidation of phenolic compounds in wastewater from oil shale treatment

1997 ◽  
Vol 35 (4) ◽  
pp. 165-174 ◽  
Author(s):  
Sergei Preis ◽  
Yelena Terentyeva ◽  
Aleksei Rozkov
Keyword(s):  
Phenolic Compounds ◽  
Uv Irradiation ◽  
Oil Shale ◽  
Photocatalytic Oxidation ◽  
Alkaline Media ◽  
Treated Wastewater ◽  
Model Compounds ◽  
Hollow Glass Microspheres ◽  
Irradiation Intensity ◽  
Untreated Wastewater

Experimental research into the photooxidation of aqueous solutions and wastewaters containing phenolic compounds was undertaken. Titanium dioxide under near-UV irradiation was selected as a photocatalyst. Phenol, p-cresol, resorcinol and 5-methylresorcinol (5-MR) were chosen as model compounds for the experiments with synthetic phenolic solutions. The photooxidative treatment of phenolic solutions was found to be more effective in acidic and strongly alkaline media. No difference was found between shortwave and near-UV irradiation photooxidation abilities. Methylated phenolic substitutes (p-cresol, 5-MR) yield better to photooxidation than non-methylated compounds. The higher the irradiation intensity the lower the photooxidation efficiency. The results obtained from the experiments with model compounds were compared with the results of photooxidative purification of wastewaters produced from the thermal treatment of oil shale in Estonia. Being heavily polluted, the wastewater yields better to photooxidation when slightly diluted with potable water in a 3:1 ratio. Anatase, immobilised onto the surface of buoyant hollow glass microspheres, was less effective than when suspended in a slurry. The photooxidatively pre-treated wastewater showed better biodegradability and lower toxicity to bacteria than untreated wastewater.

Neighbouring Group Participation of C-6 Substituents of Glucose Derivatives on the Stereoselectivity of the N-Glycosidic Linkage of Glycopeptides

1999 ◽  
Vol 54 (5) ◽  
pp. 692-698 ◽  
Author(s):  
Hong Zhang ◽  
Yali Wang ◽  
René Thürmer ◽  
Khalid Parvez ◽  
Iqbal Choudhary ◽  
...  
Keyword(s):  
Amino Acid ◽  
Total Synthesis ◽  
Carbohydrate Chain ◽  
Protecting Groups ◽  
Glycosidic Linkage ◽  
Group Participation ◽  
Condensation Products ◽  
Neighbouring Group Participation ◽  
Chain Lengths ◽  
Glucose Derivatives

The first example of a glycopeptide with a direct N-α-glycosidic linkage between the trisaccharide and the amino acid residue was found in the glomerular basement membrane of rats. In connection with the total synthesis of nephritogenoside, glycosyl azides with different protecting groups and carbohydrate chain lengths are synthesized, reduced to the corresponding glycosyl amines and coupled with Z-Asp-OBzl. Remarkable differences in the α:β ratio of the condensation products are observed, caused by neighbouring group participation.

scholarly journals In VitroEnzymatic Depolymerization of Lignin with Release of Syringyl, Guaiacyl, and Tricin Units

2017 ◽  
Vol 84 (3) ◽  
Author(s):  
Daniel L. Gall ◽  
Wayne S. Kontur ◽  
Wu Lan ◽  
Hoon Kim ◽  
Yanding Li ◽  
...  
Keyword(s):  
Aromatic Compounds ◽  
Renewable Resource ◽  
Plant Secondary Metabolite ◽  
Enzymatic System ◽  
Reaction Products ◽  
Aryl Ether ◽  
Terrestrial Plants ◽  
Model Compounds ◽  
Ether Linkage

ABSTRACTNew environmentally sound technologies are needed to derive valuable compounds from renewable resources. Lignin, an abundant polymer in terrestrial plants comprised predominantly of guaiacyl and syringyl monoaromatic phenylpropanoid units, is a potential natural source of aromatic compounds. In addition, the plant secondary metabolite tricin is a recently discovered and moderately abundant flavonoid in grasses. The most prevalent interunit linkage between guaiacyl, syringyl, and tricin units is the β-ether linkage. Previous studies have shown that bacterial β-etherase pathway enzymes catalyze glutathione-dependent cleavage of β-ether bonds in dimeric β-ether lignin model compounds. To date, however, it remains unclear whether the known β-etherase enzymes are active on lignin polymers. Here we report on enzymes that catalyze β-ether cleavage from bona fide lignin, under conditions that recycle the cosubstrates NAD+and glutathione. Guaiacyl, syringyl, and tricin derivatives were identified as reaction products when different model compounds or lignin fractions were used as substrates. These results demonstrate anin vitroenzymatic system that can recycle cosubstrates while releasing aromatic monomers from model compounds as well as natural and engineered lignin oligomers. These findings can improve the ability to produce valuable aromatic compounds from a renewable resource like lignin.IMPORTANCEMany bacteria are predicted to contain enzymes that could convert renewable carbon sources into substitutes for compounds that are derived from petroleum. The β-etherase pathway present in sphingomonad bacteria could cleave the abundant β–O–4-aryl ether bonds in plant lignin, releasing a biobased source of aromatic compounds for the chemical industry. However, the activity of these enzymes on the complex aromatic oligomers found in plant lignin is unknown. Here we demonstrate biodegradation of lignin polymers using a minimal set of β-etherase pathway enzymes, the ability to recycle needed cofactors (glutathione and NAD+)in vitro, and the release of guaiacyl, syringyl, and tricin as depolymerized products from lignin. These observations provide critical evidence for the use and future optimization of these bacterial β-etherase pathway enzymes for industrial-level biotechnological applications designed to derive high-value monomeric aromatic compounds from lignin.

scholarly journals Neighbouring Group Participation in the Methanolysis of a Vicinal Diepoxide

1999 ◽  
Vol 23 (6) ◽  
pp. 356-357
Author(s):  
James R. Hanson ◽  
Peter B. Hitchcock ◽  
Ismail Kiran
Keyword(s):  
Hydroxy Group ◽  
Group Participation ◽  
Neighbouring Group Participation

The tetracyanoethylene catalysed methanolysis of 17β-acetoxy-4β,5β:6α,7α-diepoxyandrostane afforded 17β-acetoxy-4α,7α-oxido-5β-hydroxy-6β-methoxyandrostane in which the methanolysis product of the 6α,7α-epoxide has participated in the cleavage of the 4β,5β-epoxide; the reaction is modified however by an adjacent 3β-hydroxy group.

Insights into the electrochemical degradation of phenolic lignin model compounds in protic ionic liquid-water system

2021 ◽  
Author(s):  
Guangyong Liu ◽  
Qian Wang ◽  
Dongxia Yan ◽  
Yaqin Zhang ◽  
Chenlu Wang ◽  
...  
Keyword(s):  
Water System ◽  
Value Added ◽  
Electrochemical Degradation ◽  
Aryl Ether ◽  
Model Compounds ◽  
Protic Ionic Liquid ◽  
Lignin Model Compounds ◽  
Mild Conditions ◽  
System P ◽  
Lignin Model

Cleavage of aryl ether (Caryl-O) bonds is crucial for conversion and value-added utilization of lignin and its derivatives, but remains extremely challenging under mild conditions due to strong Caryl-O linkages....

Tailored Mesoporous Silicas: From Confinement Effects to Catalysis

2009 ◽  
Vol 1217 ◽  
Author(s):  
A. C. Buchanan, III ◽  
Michelle K. Kidder
Keyword(s):  
Chemical Reactivity ◽  
High Surface ◽  
High Surface Area ◽  
Mesoporous Silicas ◽  
Surface Immobilization ◽  
Product Selectivity ◽  
Aryl Ether ◽  
Ether Linkage ◽  
Synthetic Methodologies ◽  
The Impact

AbstractOrdered mesoporous silicas continue to find widespread use as supports for diverse applications such as catalysis, separations, and sensors. They provide a versatile platform for these studies because of their high surface area and the ability to control pore size, topology, and surface properties over wide ranges. Furthermore, there is a diverse array of synthetic methodologies for tailoring the pore surface with organic, organometallic, and inorganic functional groups. In this paper, we will discuss two examples of tailored mesoporous silicas and the resultant impact on chemical reactivity. First, we explore the impact of pore confinement on the thermochemical reactivity of phenethyl phenyl ether (PhCH2CH2OPh, PPE), which is a model of the dominant β-aryl ether linkage present in lignin derived from woody biomass. The influence of PPE surface immobilization, grafting density, silica pore diameter, and presence of a second surface-grafted inert “spacer” molecule on the product selectivity has been examined. We will show that the product selectivity can be substantially altered compared with the inherent gas-phase selectivity. Second, we have recently initiated an investigation of mesoporous silica supported, heterobimetallic oxide materials for photocatalytic conversion of carbon dioxide. Through surface organometallic chemistry, isolated M-O-M’ species can be generated on mesoporous silicas that, upon irradiation, form metal to metal charge transfer bands capable of converting CO2 into CO. Initial results from studies of Ti(IV)-O-Sn(II) on SBA-15 will be presented.

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