Simulated autohydrolysis of aspen milled wood lignin in the presence of aromatic additives: Structural modifications

In a previous article the authors have described changes in molecular weight which occur when aspen milled wood lignin is subjecte to autocatalyzed hydrolysis (autohydrolysis) in the presence of three aromatic additives: 2-naphthol, resorcinol, and p-hydroxybenzoic acid. In the present work, the reactions of these additives have been studied from the viewpoint of their effect on the structure of the lignin. The use of milled wood lignin instead of aspen wood served to distinguish those reactions between the additives and the lignin, without involving the other wood components. The reaction products have been charactrized by elemental analysis and UV and IR spectroscopy. It was concluded that keto groups, generated on the lignin side-chain during autohydrolysis, condense with the additives, which become incorporated into the lignin. This occurs most probably through an aromatic eletrophilic substitution reaction. While 2-naphthol condensed primarily with the β-keto carbonyl groups, resorcinol attacked also the α-keto carbonyl groups. When p-hydroxybenzoic acid was the additive, its incorporation was accompanied by an increase in lignin carboxylic acid groups.     

Aromatic Products from Reaction of Lignin Model Compounds with UV-Alkaline Peroxide

A series of guaiacyl and syringyl lignin model compounds and their methylated analogues were reacted with alkaline hydrogen peroxide while irradiating with UV light at 254 nm. The aromatic products obtained were investigated by gas chromatography-mass spectrometry (GC-MS). Guaiacol, syringol and veratrol gave no detectable aromatic products. However, syringol methyl ether gave small amounts of aromatic products, resulting from ring substitution and methoxyl displacement by hydroxyl radicals. Reaction of vanillin and syringaldehyde gave the Dakin reaction products, methoxy-1,4-hydroquinones, while reaction of their methyl ethers yielded benzoic acids. Acetoguaiacone, acetosyringone and their methyl ethers afforded several hydroxylated aromatic products, but no aromatic products were identified in the reaction mixtures from guaiacylpropane and syringylpropane. In contrast, veratrylpropane gave a mixture from which 17 aromatic hydroxylated compounds were identified. It is concluded that for phenolic lignin model compounds, particularly those possessing electron-donating aromatic ring substituents, ring-cleavage reactions involving superoxide radical anions are dominant, whereas for non-phenolic lignin models, hydroxylation reactions through attack of hydroxyl radicals prevail.     

Study of Structure of Industrial Acid Hydrolysis Lignin,Oxidized in the H2O2-H2SO4 System

Products of oxidation of industrial acid hydrolysis lignin in the H₂O₂-H₂SO₄ system were studied using ¹³C NMR (in solution and solid state), MALDI-MS, and MS(ESI) techniques. Oxidation of hydrolysis lignin leads to the opening of aromatic rings of lignin, yielding carboxylic groups. Alkyl aryl ether linkages (β-O-4-bonds) between lignin phenyl propane units are not significantly affected by the oxidation. The structure of oxidized hydrolysis lignin is proposed. The basic structural unit of oxidized hydrolysis lignin is a muconic acid derivative.     

Reactivity of Lignin and Lignin Models Towards UV-Assisted Peroxide

The comparative reactivities of a series of guaiacyl and syringyl lignin model compounds and their methylated analogues towards alkaline peroxide and UV-alkaline peroxide were investigated. The overall reaction was followed by monitoring the reduction of the substrate as a function of time, and in every case, the reaction showed pseudo-first-order kinetics. The reaction rates of most lignin models having identical sidechains with alkaline peroxide and with UV-alkaline peroxide were in the order syringyl > guaiacyl > 3,4,5-trimethoxyphenyl > veratryl. Thus phenols react faster than their methyl ethers, and an extra ortho methoxyl group promotes the reaction. Lignin models possessing electron-donating side-chains had generally higher reaction rates than those with electron-withdrawing sidechains. The reaction rates of the series of benzoic acids were 2–4 times higher at pH 11 than at pH 5. UV-peroxide degradation of a eucalypt kraft lignin was faster than that of a pine kraft lignin, and degradation was 1.4–1.6 times faster at pH 11 than at pH 5. The data are consistent with the formation of higher amounts of reactive radicals under alkaline conditions, and aromatic rings with greater electronegativities promoting reactions with the radicals.     

Lignin Structural Changes During Liquefaction in Acidified Ethylene Glycol

Abstract

Beech (Fagus Sylvatica) milled-wood lignin was used as a model substrate in a study of lignin-catalyzed liquefaction in the presence of p-toluene sulfonic acid monohydrate (PTSA) or sulphuric acid as the catalysts. The structural changes that lignin undergoes during the treatment were studied by NMR spectroscopy, FTIR, size-exclusion chromatography, and high-performance liquid chromatography. For the sulphuric acid-catalyzed liquefaction, it was shown that the greater hydronium ion concentration in the reaction mixture induced formation of more condensed structures compared to the ones obtained after PTSA-catalyzed liquefaction. In addition, lignin during the PTSA-catalyzed liquefaction suffered degradation and was functionalized by the ethylene glycol. Gradual introduction of the ethylene glycol moieties into the lignin structure formed a condensed lignin-based polymeric material with predominant aromatic hydroxyl groups. HPLC and NMR analysis of the liquefied lignin with low-molecular mass fraction confirmed the presence of lignin monomers and further conversion of initially identified products into the aliphatic, aromatic (syringyl- and guaiacyl-based) esters and acids.     

Mass spectrometric analysis of polymers derived from N-aryl-α-amino acid initiators

Previous studies have demonstrated that the interaction of carboxylic acids with aryl amines produces free radicals that can initiate the polymerization of acrylic monomers. N-Aryl-α-amino acids (NAAA) represent a special class of this type of initiator that combines in one molecule the carboxylic acid and aryl amine functionalities necessary for the generation of radical species. The mechanism(s) of radical formation in these molecules is thought to involve both electron transfer and hydrogen abstraction reactions that can occur by intra- and intermolecular pathways. Acrylic monomers, i.e., methyl methacrylate (MMA) and 2-hydroxyethyl methacrylate (HEMA), were activated with various amounts of several NAAAs. Specific NAAAs investigated include N-phenylglycine (NPG) and N-p-tolylglycine (NTG). Polymerization was conducted at ambient or near ambient temperatures, and the polymers then were analyzed by electron impact mass spectrometry. Results indicate that these polymers have end groups derived directly from the NAAA initiators. © 1997 John Wiley & Sons, Inc. J Appl Polm Sci 65:561–565, 1997     

In Situ Reflection–Absorption Infrared Spectroscopy at the Liquid–Solid Interface: Decomposition of Organic Molecules on Polycrystalline Platinum Substrates

The room-temperature adsorption and surface chemistry of several categories of organic molecules used as reactants or solvents in liquid-phase catalysis, of carboxylic acids, esters, aldehydes, acetone, alcohols and ethers in particular, were characterized in situ on polycrystalline Pt in the presence of the liquid phase by reflection-absorption infrared spectroscopy (RAIRS). For carboxylic acids and esters it was found that the propensity for decomposition and CO formation follows a formic acid ? methyl formate, ethyl formate > acetic acid, propionic acid, acrylic acid, ethyl acetate sequence. For aldehydes and acetone, the observed trend is formaldehyde ? acetaldehyde > acrolein, crotonaldehyde > propionaldehyde, acetone. Virtually no adsorbed CO was detected when Pt surfaces were exposed to liquid solutions of either alcohols or ethers. The observed trends could be correlated with the corresponding molecular structures. They are discussed in the context of previous results obtained from studies under ultrahigh vacuum (UHV) and under electro-oxidation conditions.     

Direct polymer reaction of poly(styrene‐co‐maleic anhydride): Polymeric imidization

Using direct polymer reaction of poly(styrene‐co‐maleic anhydride) (SMA), a synthesis of copolymer of styrene and N‐aryl succinimide (SMI) has been investigated. SMI copolymers were synthesized from SMA copolymers by a concerted two‐step reaction, which consisted of the condensation reaction (step 1) of SMA with aromatic amine to prepare a precursor, succinamic acid, for imide formation and the cyclodehydration reaction (step 2) of succinamic acid. In this article, the application of Searle's preparation method of N‐aryl or N‐alkyl maleimide to the direct polymer reaction for SMI was attempted. Compared with synthesis of monomeric imides, the imide formation in polymeric condition appeared to be a little more sensitive to the reaction condition. The optimum condition for maximum conversion was examined in terms of time, temperature, and the amount of reactants. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1187–1196, 1999     

Rhodium‐Catalyzed Oxidative ortho‐Acylation of Aryl Ketone O‐Methyl Oximes with Aryl and Alkyl Aldehydes

The rhodium‐catalyzed oxidative ortho‐acylation of aryl ketone O‐methyl oximes with aryl and alkyl aldehydes via C H bond activation is described. The cross‐coupling reaction exhibits high functional group tolerance and regioselectivity under relatively mild conditions and constitutes a versatile route to a diverse library of diaryl ketones, which are difficult to obtain by the classical Friedel–Crafts acylation. Moreover, this reaction proceeds via an unprecedented Rh‐catalyzed oxidative ortho‐acylation of aryl ketone O‐methyl oximes with highly electron‐deficient aryl aldehydes followed by a direct addition of the second ortho C H bond to aldehydes in a one‐pot reaction, to generate two C C bonds simultaneously.     

Pyrolysis of model compounds of the flame retardant poly(N-dimethylphosphonomethyl acrylamide)

An investigation of the thermal decomposition of N-dimethylphosphonomethyl amides has shown that the major volatile products for decomposition above 300°C are methanol, the methyl ester of the carboxylic acid, the nitrile, the carboxylic acid, the N-methyl amide, and the N,N-dimethyl amide. Also, benzoic acid was the only volatile product detected in the decomposition of α-benzamidomethylphosphonic acid. A mass balance for the decomposition of N-dimethylphosphonomethyl benzamide at 420°C showed methanol and methyl benzoate to be the major volatile products. Methanol and benzonitrile formation increased with an increase in temperature at a faster rate than the other volatile products. The reaction of amides and phosphonates was further studied using sealed tubes in a furnace. Reaction of N-methylbenzamide with dimethyl methylphosphonate at 307°C in a sealed tube produced methyl benzoate and N,N-dimethylbenzamide. N,N-dimethylbenzamide and dimethylmethylphosphonate were also shown to produce methyl benzoate at 310°C. After a 5-min period more methyl benzoate was produced in the N,N-dimethylbenzamide reaction than in the N-methylbenzamide reaction. Also, addition of ethanol to the N,N-dimethylbenzamide/dimethyl methylphosphonate reaction resulted in less ethyl benzoate methyl benzoate after heating at 310°C.     

Unique Versatility of Ionic Liquids as Clean Decarboxylation Catalyst Cum Solvent: A Metal‐ and Quinoline‐Free Paradigm towards Synthesis of Indoles,Styrenes, Stilbenes and Arene Derivatives under Microwave Irradiation in Aqueous Conditions

Ionic liquids have been found to provide a new platform for metal‐ and quinoline‐free decarboxylation of various N‐heteroaryl and aryl carboxylic acids under microwave irradiation in aqueous condition. The method was found to possess a wide substrate scope towards the synthesis of various pharmacologically and industrially important aromatic compounds including indoles, styrenes, stilbenes, and nitro‐ or hydroxyarene derivatives. The decarboxylation of indole and α‐phenylcinnamic acids proceeded well without addition of any catalyst in neat 1‐hexyl‐3‐methylimidazolium bromide ([hmim]Br) and 1‐methylimidazolium p‐toluenesulfonic acid ([Hmim]PTSA), respectively, while addition of a mild base like aqueous sodium hydrogen carbonate (NaHCO₃) to [hmim]Br further improved the decarboxylation of hydroxylated cinnamic and aromatic acid substrates. The developed methodology not only precludes the usage of toxic metal/quinoline and harsh organic bases but also offers several inherent benefits like recyclability of reagent system, reduction in waste and hazards, short reaction time besides ease of product recovery.     

Thermal cracking of coal model diaryl ethers in aromatic solvent

Thermal cracking of nine diaryl ethers in a hydrogen donor solvent or 1-methylnaphthalene was studied kinetically. The rate of conversion of the diaryl ethers was first order with respect to the substrate concentration and increased with increase in size of the aryl structure. The relative rate constant of aryloxygen bond cleavage calculated on the basis of first order reaction has indicated that the ease of cracking depends strongly on the aromatic structure and the position of substitution. The conversion rate of 2, 2′-dinaphthyl ether was remarkably enhanced in the presence of hydrogen donor solvent, for example by a factor of ten in the presence of 9, 10-dihydroanthracene. The activation energy of thermal conversion of 2, 2′-dinaphthyl ether was 214 kJ/mole in methylnaphthalene, 151 kJ/mole in tetralin and 88 kJ/mole in dihydroanthracene. The enhancing effect of the hydrogen donor was considered due to hydrogen transfer to the aromatic nucleus of the diaryl ether from the hydrogen donor and successive fast decomposition of hydrogenated ethers.     

Nickel‐Catalyzed Cross‐Coupling of Arene‐ or Heteroarenecarbonitriles with Aryl‐ or Heteroarylmanganese Reagents through C?CN Bond Activation

The nickel‐catalyzed cross‐coupling reaction of arene‐ or heteroarenecarbonitriles with aryl‐ or heteroarylmanganese reagents via C CN bond activation has been developed. Both electron‐rich and electron‐deficient nitriles can be employed as the electrophilic substrates. The reaction tolerates a range of functional groups and aromatic heterocycles.     

Lewis Acid Catalyzed Additions to Unsaturated Fatty Compounds. II: Alkylaluminium Halide Catalyzed Ene Reactions of Unsaturated Fatty Compounds and Formaldehyde

We are presenting our results on the alkylaluminium halide catalyzed ene addition of formaldehyde to readily available unsaturated fatty compounds to give primary homoallylic alcohols. The reaction of oleic acid and 10-undecenoic acid with formaldehyde gives (E)-9(10)-(hydroxymethyl)octadec-10(8)-enoic acid and 12-hydroxydodec-9-enoic acid, respectively, in high yields. Formaldehyde can be added also to oleyl alcohol to give the very interesting diol (E)-9(10)-(hydroxymethyl)oxtadec-10(8)-en-l-ol. Me₂AlCl and EtAl-sesquichloride are the most suitable catalysts for these reactions. The addition of formaldehyde to methyl oleate and methyl 10-undecenoate, respectively, to give the corresponding ene products is catalyzed by EtAlCl₂.     

The Characteristics and Reactivity of Acid-Labile Aryl Ether Units in Wood Lignin

Wood lignin contains significant amounts of acid-labile aryl ether units, which play a significant role in lignin modification or delignification processes. We have evaluated the rate and reaction kinetics on the acid-catalyzed cleavages of aryl ether structures for wood lignin in situ based on the formation of phenolic hydroxyl groups. The content of acid-labile aryl ether units was quite uniform for a variety of softwood wood lignins (～4% per C₉ unit) and it varied appreciably among hardwood species, ranging from 4% for aspen to 9% for beech wood lignin. These variations, however, appear to be related to the content of syringyl units in wood lignin. The reactivity of these reactive aryl ether structures was noticeably higher for the spruce than for the aspen wood lignin. This difference in reactivity, based on the behavior of lignin model compound reactions, can be attributed to the influence of syringyl moieties in aspen wood lignin. It appears that most of the acid-labile aryl ether units in hardwood were associated with the syringy moiety being present as a benzyl unit, which is much less reactive than the corresponding guaiacyl moiety.     

Structure of polycondensates from hydroxymethylphenols

The structure of oligomers obtained from mono‐hydroxymethylphenols in melt condensation at 120°C was determined using ¹³C NMR spectra in CD₃OD solution. Alongside of methylene region of spectrum, valuable information was obtained from signals of aromatic carbons. Noncatalytic conditions promote the formation of dihydroxydibenzyl ethers in equilibrium with ortho‐ and para‐benzoquinones of oxymethylene derivatives. The final methylene linked oligomers are formed, mainly, by splitting the ether intermediates with free aromatic positions. In alkaline conditions, highly nucleophilic phenoxide ions of ortho‐hydroxymethyl compounds are responsible for substitution in free aromatic positions. The most favored reaction in the mixture of both hydroxymethylphenols is the formation of p,p′‐methylene. In condensation of para‐hydroxymethylphenol, formation of p,p′‐methylene groups occurs with simultaneous release of formaldehyde. High content of alkali stabilized ortho‐hydroxymethyl groups of fully substituted methylene linked oligomers determines the curing behavior of resol phenol–formaldehyde resins. The role of hemiformals in reactions was insignificant. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

全氟羧酸酯乙烯基醚的合成研究

全氟羧酸酯乙烯基醚用于多种含氟聚合物的改性,合成全氟羧酸离子交换树脂等高性能含氟聚合物,也可以合成含氟醚类的绿色可降解表面活性剂。采用3-羧酸甲酯全氟丙酰氟与六氟环氧丙烷进行加成反应,然后脱羧制备全氟羧酸酯乙烯基醚。     

Polarographically Active Structural Fragments of Lignin. I. Monomeric Model Compounds

Abstract

Electrochemical properties of compounds modeling typical structural units of lignin were determined by differential pulse polarography in dimethylsulfoxide with tetrabutylammonium perchlorate as a supporting electrolyte. p-Quinonemethides; derivatives of cinnamyl aldehyde and cinnamic acid; aromatic aldehydes, ketones, diketones, and carboxylic acids; isoeugenol; and coniferyl alcohol were studied. Structural effects on the reduction potentials of lignin units were estimated. The potentials, which correspond to the first polarographic peak, varied from -0.8 (p-quinonemethide) to -2.8 V (coniferyl alcohol). The compounds containing nonconjugated carbonyl or carboxyl groups were not polarographically active. The autoprotonation reaction had a profound effect on the electrochemical reduction of compounds containing hydroxyl groups.     

Composition of the silk lipids of the spider Nephila clavipes

A detailed analysis of the lipids of spider silk is given for the first time. Extracts of the silk from the golden orb weaver, Nephila clavipes, were studied by gas chromatography, mass spectrometry, and chemical derivatizations. The major group of the lipids consisted of methyl-branched 1-methoxyalkanes (methyl ethers) with up to four methyl groups in the chain (chain length between C₂₈ and C₃₄), which are unique to spiders. The position of the methyl branches was determined by conversion into cyanides, which allowed easy location of methyl branches. The second-largest group included alkanes with a wide structural variety; 2-methyl-branched, even-numbered hydrocarbons predominated. A general numerical method for the estimation of retention indices of alkanes and their derivatives is presented. Further components of the web included alkanols and alkanediols, fatty acids, and glyceryl ethers. Some comments on the biosynthesis of these compounds are also given.     

A GC–MS study of the addition reaction of aryl amines with acrylic monomers

Previous studies have shown that the interaction of carboxylic acid groups with the amine functionalities of aryl amines, especially secondary and tertiary aryl amines, can lead to the free-radical polymerization of acrylic monomers such as methyl methacrylate. In this study, the Michael addition reaction of primary and secondary aryl amines with acrylic monomers such as acrylic acid (AA) was investigated. Equivalent amounts of either p-toluidine (PT) or N-phenylglycine (NPG) and AA were combined in polar solvents such as ethanol. The reactions were conducted at ambient (23°C) or near-ambient (37–60°C) temperatures. Samples (about 3–5 mg) of these products were then trimethylsilylated with a solution consisting of 0.4 mL of bis(trimethylsilyl)trifluoroacetamide (BSTFA) and 0.4 mL of acetonitrile by heating for 30 min at 140°C under N₂. These derivatives were characterized by gas chromatography–mass spectrometry (GC–MS). The GC–MS analyses suggest that 1 mol of the primary amine PT had reacted with 2 mol of AA to yield the expected N-p-tolyliminodipropionic acid. Similarly, the secondary amine NPG added to 1 mol of AA yielded the corresponding mixed iminodiacid, N-phenyliminoacetic–propionic acid. It would appear that the Michael reaction of primary and secondary amines with acrylic monomers may offer a general, facile synthetic route to a variety of tertiary amines. Aryl amino acids of the type synthesized in this study may find use in a number of dental applications, e.g., as surface-active adhesive agents and as polymerization initiators or activators. © 1998 John Wiley & Sons, Inc. J Appl Polm Sci 67:1545–1551, 1998