Acetal lignins

As can be seen from Fig 2b, the solid state C-13 nmr spectrum of T. aestivum also shows sets of enhanced resonances at 61 ppm and 169.6-174.9 ppm respectively (24). However, their relative intensities are very different from that observed for L. leucocephala. Indeed, it can immediately be seen that very little reduction of the administered precursor to hydroxymethyl analogues (at 61 ppm) has occurred. On the other hand, the dominant resonances at 169.6 and 174.9 ppm are coincident with bound hydroxycin-namic acids (e.g. ferulic 5a) and its esters (31). Subsequent analysis of its isolated acetal lignin derivative (32) indicated that much of the lignin contained hydroxycinnamate residues (33). 

Hydrolysis of the Acetal Lignins. The lignins (400 mg.) were dissolved in a solution of 28 ml. of dioxane and 12 ml. of water acidified with hydrochloric acid to a concentration of 0.5A, and the solution was boiled under reflux for 2 hours. After cooling, the solution was poured into water (about 200 ml.), the precipitate was separated by centrifugation and purified by reprecipitation from dioxane (15 ml.) into water (150 ml.). After centrifugation the lignin was dried in vacuo over P2Ob at 65°C. 

Table V. Hydrolysis of Acetal Lignins (Alkoxyl Measurements)...

Poly(vinyl acetate)/lignin and poly(e-caprolactone)/lignin blends were prepared by casting chloroform solutions of PVAc (Mw 140 kDa) and PCL (Mw 80 kDa) mixtures containing 9-30% by weight of lignin (Table 2). 

Alkaline methanolysis of graft vinyl acetate-lignin copolymers (Samples LVAO, LVAl, and LVA60) led to the corresponding water-soluble vinyl alcohol copolymers, whose lignin content, as determined by the absorption at 280 nm, resulted to be substantially higher than in the parent VAc copolymer samples hydrolyzed samples, respectively, thus demonstrating however the formation of copolymer macromolecules. 

Functional Group Analysis. The total hydroxyl content of lignin is determined by acetylation with an acetic anhydride—pyridine reagent followed by saponification of the acetate, and followed by titration of the resulting acetic acid with a standard 0.05 W sodium hydroxide solution. Either the Kuhn-Roth (35) or the modified Bethge-Liadstrom (36) procedure may be used to determine the total hydroxyl content. The aUphatic hydroxyl content is determined by the difference between the total and phenoHc hydroxyl contents. 

Further Preparative Reactions. When pulps are to be used in the production of materials that do not retain the original fiber stmcture, such as rayon or ceUulose acetate film, the lignin, hemiceUulose, and other components must be reduced to the lowest possible concentrations. A surfactant (ionic or nonionic) is often added during a hot, weakly alkaline extraction step after chlorination. Another approach, sometimes used in addition to the surfactant step, is to treat the pulp with 6—10% NaOH after most of the oxidative bleaching is finished. This treatment removes most of the hemiceUulose. In most purification plants the final stage includes use of sulfuric acid chelators are optional. 

Cellulose Esters Epoxy Resins Lignins Polystyrene Poly (2-vinyl pyridine) Polyvinyl Chloride Polymethyl methacrylate Polyphenylene Oxide Phenolics Polycarbonate Polyvinyl Acetate, etc. Polyvinyl butyral SBR rubber, etc., etc. 

At3g06550 - are deficient in wall-bound acetate. It would be interesting to test their resistance, lignin depositions and other physiological parameters under the influence of pathogens. It may be that these experiments will make clear the role of polysaccharide acetylation. 

Wood chips can also be utilized as such to produce bioethanol. The cellulose and hemicellulose material is hydrolyzed in the presence of acids (H2SO4, HCl, or HCOOH) or enzymes to yield glucose and other monosaccharides [16]. Lignin is separated by filtration as a solid residue and the monosaccharides are fermented to ethanol, which, in turn, is separated from water and catalyst by distillation. Ethanol can be used not only as energy source but also as a platform component to make various chemicals, such as ethene and polyethene. Today green acetaldehyde and acetic acid from wood-derived bioethanol is manufactured by SEKAB Ab, at the Ornskoldsvik Biorefinery of the Future industrial park. 

An alternative possibility is that of the biorefinery. In this concept a few key chemicals would be isolated from a small number of process steps. Whilst there are many possibilities for this, in one example the raw material, say com, could be cmshed to release oil (the first key product). The resulting mass could then be fermented to give several key platform chemicals such as ethanol, lactic acid and acetic acid. This attractive concept would be more viable if all the cellulose and lignin components could be efficiently used in the fermentation process. 

The plant cell wall contains different types of polysaccharides, proteins (structural glycoproteins and enzymes), lignin and water, as well as some inorganic components (1, 14-16). The plant cell suspensions, however, grow as a population of cells with a primary cell wall(17). The main components of these walls are cellulose-free polysaccharides and pectic polysaccharides in particular, which constitute 1/3 of their dry weight. (18). Some fragments, e g. methanol, acetic, ferulic and p-cumaric acids, are connected with the pectic polysaccharides by ester bonds with the carboxylic and hydroxylic groups. 

Lignin, brown coal polymer of methacrylic acid, methacrylamide, hydroxyethyl acrylate, hydroxypropyl acrylate, vinyl acetate, methyl vinyl ether, ethyl vinyl ether, N-methylmeth-acrylamide, N,N-dimethylmethacrylamide, vinyl sulfonate, or 2-acrylamido-N-methylpropane sulfonic acid free radical polymerization of a water-soluble vinyl monomer in an aqueous suspension of coals [705,1847]... 

The quinone methide can also be generated in situ, at least in aqueous NaOH, directly from the peracetate, as hydrolysis of the phenolic acetate is faster than the benzylic acetate (see an example in Section 12.5.3). This method was used to demonstrate the addition of anthrahydroquinone (AHQ) and anthranol to (actual polymeric) lignin quinone methides in studies elucidating the anthraquinone (AQ)-catalyzed 8-0-4-aryl ether cleavage mechanisms in alkaline pulping.64-66... 

Lu, F. Ralph, J. Preliminary evidence for sinapyl acetate as a lignin monomer in kenaf. J. Chem. Soc., Chem. Commun. 2002, 90-91. 

Repeated methylation of bagasse native lignin with dimethyl sulfate yielded a product with a 29-1 % methoxyl content. Four such methyl-ations did not change this value. However, the infrared spectrum of this derivative still revealed a small absorption band at 3400 cm1. Thus, it appeared that at least one hydroxyl group could not be methylated. Treatment of this methylated product with acetic anhydride and pyridine gave an acetate, which did not exhibit an absorption band at 3400 cm-1. Consequently, a tertiary hydroxyl group, which can be acetylated but not methylated, seems to be present in this lignin. 

Bagasse Native Lignin in 95% Ethyl Alcohol Bagasse Native Lignin in 0 02 N Alkali — Acetate of Bagasse Native Lignin in 95% Ethyl Alcohol. 

The support for a chemical linkage between cellulose and lignin in wood, presented by Hibbert and co-workers (90), is based on their treatment of oak wood with acetic anhydride, glacial acetic acid and catalytic amounts of sulfuric acid. A fraction soluble in dioxane was found to have, after several precipitations, the same composition of lignin, cellulose and pentosan as that of the wood itself. 

Pyrolysis has a long history in the upgrading of biomass. The dry distillation of hardwood was applied in the early 1990s to produce organic intermediates (methanol and acetic acid), charcoal and fuel gas [3]. Today s processes can be tuned to form char, oil and/or gas, all depending on the temperature and reaction time, from 300 °C and hours, to 400-500 °C and seconds-minutes, to >700 °C and a fraction of a second [3, 19, 23, 24], The process is typically carried out under inert atmosphere. We illustrate the basic chemistry of pyrolysis by focusing on the conversion of the carbohydrate components (Fig. 2.4). The reaction of the lignin will not be covered here but should obviously be considered in a real process. Interested readers could consult the literature, e.g., [25]. Pyrolysis is discussed in more details elsewhere in this book [26],... 

---