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Dehydropolymerization of p-hydroxycinnamyl alcohols with manganese(III) acetate in either aqueous acetic acid or pyridine resulted in dehydropolymers (DHPs) that more closely approximate the structure of natural lignins than do DHPs produced by enzymic techniques. The 13C NMR spectrum of a “biomimetic” guaiacyl-DHP (G-DHP) from coniferyl alcohol was very similar to that of a lignin isolated from spruce wood, unlike a corresponding spectrum of a G-DHP prepared by a conventional enzymic technique. A similar comparison between a biomimetic guaiacyl/syringyl DHP (GS-DHP), a conventional GS-DHP, and a natural lignin from elm wood also confirmed a closer resemblance between the biomimetic DHP and the natural lignin. Likewise, a biomimetic S-DHP prepared from sinapyl alcohol was remarkably similar to a high syringyl fraction of lignin isolated from birch wood. The flexibility of the biomimetic approach is illustrated by the preparation of a DHP that is enriched in coniferaldehyde entities and one that i...

When heated under anaerobic conditions, aqueous solutions of the polyoxometalate anion α-(SiVW 11 O 40 ] 5- (POM ox , 1), supplied as the salt K 5 [SiVW 11 O 40 ].12H 2 O, selectively delignify unbleached mixed-pine kraft pulps. During delignification, 1 is reduced hy residual lignin to α-[SiVW 11 O 40 ] 6- (POM red 2) : α-[SiVW 11 O 40 ] 5- + 1e- → α-[SiVW 11 O 40 ]6-, E o = +0.69V vs. NHE. Model studies suggest that phenolic (hydroxylated phenyl) groups present in residual lignin are substrates for the reduction of 1. Reactions of 1 with phenolic arylglycerol β-aryl ethers and other phenolic lignin models suggest that anaerobic POM degradation of residual lignin may occur via sequential single-electron oxidation reactions of phenolic substructures, first to cyclohexadienyl radicals and subsequently to cyclohexadienyl cations. Hydrolysis of these cationic intermediates results in alkyl-side-chain cleavage, a likely route to polymer degradation.

Summary Dehydrogenation polymers (DHPs) were prepared from coniferyl alcohol (CA), sinapyl alcohol (SA), and a mixture of coniferyl and sinapyl alcohol. The polymers were fully acetylated and their carbon NMR spectra were compared. Comparison of the 13C NMR spectra of the DHPs with those of authentic tri- and tetralignols facilitated the assignment of about 85% of the 117 reported signals. Most of the unassigned signals were those from syringyl units. Major differences between the DHP prepared from CA and a pine milled wood lignin were: a relative deficiency of s-O-4 linkages and a predominance of s-5, s-s, and CA end units in the DHP. In contrast, there was no significant quantity of SA end units in a DHP prepared from SA. A major conclusion of the study confirmed that DHPs prepared from CA are relatively poor models of natural lignins isolated from gymnosperms.

Typical solution-state 13C NMR spectra of lignins obtained with relatively modern instrumention contain well over 100 signals. The use of classical lignin model compounds is no longer sufficient for accurate interpretation of these spectra. Ultimately, the only valid models for etherified C9 units in lignin (which account for about 80% of the lignin polymer) must be at least trimeric or tetrameric, depending on the linkages involved. One approach that can be used involves NMR substituent effects. This approach avoids tedious syntheses while retaining the much-needed accuracy of chemical shift correlations between models and natural lignins. Appropriate substituent effects have been calculated by the use of an extensive NMR database of dimeric, trimeric and tetrameric lignin model compounds. Effects related to acetylation and solvent have also been determined. For example, accurate chemical shift data for an underivatized milled-wood lignin (MWL) in DMSO-d6 can be determined on the basis of the ch...

Summary Paris-Grignon, Lignin polymer model Dehydrogenation polymer The structures of novel lignin polymer models prepared from coniferin or coniferyl alcohol under conditions that approximate cell wal1 Signification were characterized by thioacidolysi s. The linkageof monolignol (DHP) type analysis by thioacidolysi s indicates that the structure of these polylignols approximated that of -. Monolignol glucoside native lignin more closely than did the structure of polylignols prepared by the conventional method Coniferyl ulcohol from coniferyl alcohol. Among v:arious possible factors affecting the structure of polylignols during Thioacidolysis polymerization under the present experimental conditions, the important ones appears to be: pH of the medium in which dehydrogenativc polymerization of coniferyl alcohol takes place; relative concentrations of monomer and oligomer radicals; and the carbohydrate matrix in which polymerization occurs.

Treatment of coniferyl alcohol with iron, cobalt, or manganese salts gave a variety of oligolignols and polylignols (DHPs). Conditions could be adjusted to favor high or low molecular weight products and to give different inter-unit linkage distributions. Oxidation with iron and manganese salts generally gave structures containing β-O-4, β-5, and β-β linkages. Oxidation with iron and manganese salts under highly alkaline conditions also generated α-O-4 structures. The cobalt salt K3Co(CN)6 was unique in that a novel β-γ linkage was generated in high yield. Reactions in the absence of solvent also resulted in the formation of oligolignols and DHPs.

Guaiacyl-type lignin polymer models were prepared from coniferin by the action of β-glucosidase and peroxidase, with hydrogen peroxide generated in situ through the action of oxygen and glucose oxidase on the glucose liberated from the coniferin. Polylignols were also prepared from coniferyl alcohol using procedures modified to more closely correspond to conditions prevailing in the cell wall environment. The structure of these novel polylignols approximated that of native lignin more closely than did the structure of polylignols prepared by the conventional method from coniferyl alcohol.

The lignin peroxidases (LiPs) of white-rot basidiomycetes are generally thought to catalyze the oxidative cleavage of polymeric lignin in vivo. However, direct evidence for such a role has been lacking. In this investigation, 14C- and 13C-labeled synthetic lignins were oxidized with a purified isozyme of Phanerochaete chrysosporium LiP. Gel permeation chromatography of the radiolabeled polymers showed that LiP catalyzed their cleavage to give soluble lower-M(r) products. To a lesser extent, the enzyme also polymerized the lignins to give soluble higher-M(r) products. This result is attributable to the fact that purified LiP, unlike the intact fungus, provides no mechanism for the removal of lignin fragments that are susceptible to repolymerization. LiP catalysis also gave small quantities of insoluble, perhaps polymerized, lignin, but in lower yield than intact P. chrysosporium does. 13C NMR experiments with 13C-labeled polymer showed that LiP cleaved it between C alpha and C beta of the propyl side chain to give benzylic aldehydes at C alpha, in agreement with the cleavage mechanism hypothesized earlier. The data show that LiP catalysis accounts adequately for the initial steps of ligninolysis by P. chrysosporium in vivo.

Threo and erythro isomers of 3-acetoxy-1-(4-acetoxy-3-methoxyphenyl) -1- (9,10-dihydro-10-hydroxy-9-oxoanthracen-10-yl) -2-(2-tnethoxyphenoxy)-propane 8 have been synthesized. These compounds are appropriate model compounds for adducts between anthranol (9-hydroxyanthracene) and quinone raethides of β-aryl ether units in the lignin polymer. Adducts of this type are believed to result from side reactions during the anthraquinone-accelerated pulping of wood and may contribute to extensive losses of anthraquinone from the pulping system. The 13C NMR chemical shift3 of C-10 in the threo and erythro isomers of β are 44.1 and 47.5 ppm relative to tetramethylsilane. Peaks with corresponding chemical shifts appeared in a spectrum of an acetylated adduct prepared from lignin and 9,10- 3C labelled anthranol. As in model systems the threo isomer predominated.

(m, 2 H), 3.55-3.98 (m, 1 H), 3.03 (br s, 1 H), 1.15-2.25 (m, 6 H); mass spectrum (70 eV), m/e 141; exact mass calcd for C7HllN02 141.0790, found 141.0790. cis-2-(Hydroxyacetyl)cyclopentanol (34): mp 62-64 “C; IR (Nujol) 3600-3050, 1710 cm-’; NMR (CDC13, 300 MHz) 6 4.50-4.60 (m, 1 H), 4.35 (AB q, 2 H, J = 19 Hz), 3.12 (br s, 1 H), 2.82 (dt, 1 H, J = 9.5,4.85 Hz), 2.51 (br s, 1 H), 1.60-2.15 (m, 6 H); mass spectrum (70 eV), m/e 144, 126; exact mass calcd for C7H1,,02 (C,H1203 H20) 126.0681, found 126.0681. cis -2-Hydroxycyclopentanecarboxylic acid (35): mp 53 “C (lit.m mp 52-53.4 “C); IR (melt) 3600-2400,1720 cm-’; NMR (CDC13/D,0, 90 MHz) 6 4.33-4.63 (m, 1 H), 2.60-3.00 (m, 1 H), 1.60-2.15 (m, 6 H); mass spectrum (70 eV), m/e 130, 112; exact mass calcd for CsH8O2 (C6HlOO3 HzO) 112.0524, found 112.0524.

The quinone methide from guaiacylglycol-β-guaiacyl ether [l-(3-methoxy-4-hydroxyphenyl)-2-(2-methoxyphenoxy)ethanol] formed carbon-carbon bonded adducts with both anthrone and anthrahydroquinone (AHQ). It was found that the anthrone adduct [l-(3-methoxy-4-hydroxyphenyl)-1-(anthracen-9-one-10-yl)-2-(2-methoxyphenoxy)ethane] was much more resistant to alkaline degradation than the corresponding AHQ-adduct Jl-(3-methoxy-4-hydroxyphenyl)-l-(10-hydroxyanthracen-9-one-10-yl)-2-(2-methoxyphenoxy)ethane]. It was demonstrated, by NMR spectroscopy that analogous anthrone and AHQ adducts formed with milled wood lignin and had relative alkaline stabilities consistent with those observed with the model adducts. At 10° C the AHQ-lignin adduct partially decomposed to the Y-monoacetates of coniferyl alcohol and p_-coumaryl alcohol which subsequently reacted with excess AHQ to give the novel adducts, trans-1-(3-methoxy-4-hydroxyphenyl)-3-(10-hydroxyanthracen-9-one-10-yl)propene, and trans-1-(4-hydroxyphenyl)-3-(1...

Spent liquor fractions from soda and soda/anthraquinone cooks of loblolly pine wood meal were examined by C-13 NMR spectroscopy. The material which precipitated from the liquors at pH 7 as well as that remaining in solution were acetylated and fractionated on a styrene-divinylbenzene gel column. This technique was an attempt to simplify spectral interpretation and to elucidate the distribution of anthracenyl structures within the spent liquor components. The NMR spectra of fractions of the precipitated material revealed that anthracenyl structures chemically bound to lignin increased with decreasing molecular weight (MW), whereas, polysaccharide content decreased markedly with decreasing MW. The NMR spectra of the soluble material had no anthracenyl peaks, but did contain a significant peak at 105 ppm. This is in the same location as a predominant peak observed in C-13 NMR spectra of hardwood lignins, and which has been assigned to C2 and C6 of syringyl structures. However, in the present study t...

Extensive loss of anthraquinone (AQ) or the active catalyst anthrahydroquinone (AHQ) from the AQ –- AHQ catalytic cycle has been explained in part by side reactions leading to the reaction product anthrone (anthracen-9-one), followed by subsequent formation of adducts with lignin quinone methides. Degradation of an adduct between anthrone and the quinone methide of guaiacylglycerol-β-guaiacyl ether, under soda pulping conditions, resulted in a complex mixture of products. The mixture included 3-guaiacylbenzanthrone, bianthronyl, bianthrone, guaiacol, AQ, trans-coniferyl alcohol, trans-coniferylaldehyde, cis- and trans-1-(3-methoxy-4-hydroxyphenyl)-2-(2-methoxyphenoxy)ethene, vanillin, and 2-methoxy-4-vinylphenol. C-13 NMR studies of lignins isolated from soda/AQ spent liquors indicated the presence of residual anthrone adducts and a significant content of chemically attached AQ.

The number average structure and the molecular weight distribution of phenol-formaldehyde prepolymers for use in synthesis of tannin-based adhesive resins were determined with 1H- and 13C-NMR spectroscopy and gel permeation chromatography of acetylated resins. These methods were used to determine differences in phenol-formaldehyde prepolymens prepared under different reaction conditions. Quantitative 13C-NMR techniques provided a detailed analysis of the structure of a phenol-formaldehyde prepolymer.

Le compose threo-(acetoxy-4 methoxy-3 phenyl)-1 (dihydro-9,10 hydroxy-10 oxo-9 anthryl-10)-1 (methoxy-2 phenoxy)-2 propane presente une rotation genee dans le spectre RMN a temperature ambiante