Lignin isolation from wood

Searching for evidence on the nature of the bond, we conducted a spectroscopic study of lignins isolated from wood by ethanolysis (P) and found, as expected, that 0-keto groups did not appear in the lignins until... 

In this work we have, in a preliminary way, extracted periodate lignin by the continuous dioxane-dimethoxypropane-HCl procedure and obtained only about 11% of a soluble material which had the same infrared spectral characteristics as the lignin isolated from wood. The gel-like residue showed evidence of having undergone the same reaction but remained insoluble. This seemed to indicate that the reaction alone was not enough to confer solubility. 

Lignins. Lignins are amorphous, cross-linked phenolic polymers that occur uniquely in vascular plants and comprise 20-30% of most wood. Lignins isolated from wood are polydisperse, with molecular weights in the range of thousands to hundreds of thousands (4). Lignins are produced almost exclusively from three cinnamyl alcohols, whose structures are shown in Chart I. These structural units have propylphenyl carbon skeletons and differ... 

Thus, most of the degradative reactions of polymeric lignins suggested previously by the analysis of decayed lignin isolated from decayed wood by white-rot fungi were catalyzed by lignin peroxidase. 

Potutkin and associates (14) report changes in the lignin isolated from hot-pressed particleboards compared to that from raw birchwood from which the boards were made. Lignin isolated from boards pressed at 180C showed increased infrared absorption at 800 cirri and 1300-1500 cm"1, which is interpreted to indicate condensation and demethoxylation, respectively. An appearance of a new band at 1370 cm""1 is assigned to aryl-alkyl ether bonds formed by reactions of lignin with other wood breakdown products to yield pseudolignin. 

Jiang J-E, Chang H-m, Bhattacharjee SS, Kwoh DLW (1987) Characterization of residual lignins isolated from unbleached and semi-bleached softwood kraft pulps. J Wood Chem Techno 1 7 81-96... 

Fig. 8.1.3. High-performance size-exclusion chromatograms of acetylated samples of milled wood lignin from pine (—), pine kraft lignin (—) and two samples of residual lignin isolated from pine kraft pulp (-,----). (Yamasaki et al. 1981)...

The earliest expts devoted to the nitration of lignin, previously isolated from wood pulp by means of HC1, were reported by Hagglund (Ref 3). Lignin mixed with fuming nitric acid... 

Cellulose is insoluble in most solvents including strong alkali. It is difficult to isolate from wood in pure form because it is intimately associated with the lignin and hemicelluloses. Analytical methods of cellulose preparation are discussed in the section on Analytical Procedures. ... 

FIGURE 3. C NMR spectra of a cypress log buried in the Okefenokee Swamp, Georgia, a Douglas fir tree that had fallen in the rain forest surrounding Mount Ranier, Washington, and lignin isolated from modern spruce wood by the sodium paraperiodate treatment. 

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