Beech Lignin—Proposal of a Constitutional Scheme

Abstract

The high molecular weight material lignin consists of phenylpropane units linked together by a variety of bond types. During the past eight years, two newly developed degradation procedures have permitted the first direct determinations of the nature of these bonds. The first procedure affords a very mild partial hydrolysis of benzyl ether bonds. Eleven dimeric, trimeric, and tetrameric degradation products were obtained in this way from spruce and beech lignin: they exhibited three different kinds of bonds between the C9 structural units, and their structures have all been elucidated. In the second procedure, the most important kind of bond in lignin, i.e. the arylglycerol-P-aryl ether bond, can be subjected to directed cleavage under mild conditions after introduction of a suitable neighboring group. On application to beech lignin, 91 Yo of the material was degraded giving monomeric to tetrameric phenols. Complete structural elucidation of the twenty dimeric phenols isolated and a knowledge of their relative yields and the yields of the other fractions obtained by gel filtration permitted a structural scheme to be set up for beech lignin in which the Cg structural units are linked together by no less then ten different kinds of bonds. The structural scheme, which can be readily explained biogenetically, has the same elemental composition as natural beech lignin. Further support for the structural scheme comes from a comparison of the "C-NMR spectrum of natural beech lignin and a 3C-NMR spectrum calculated for the proposed structure on the basis of about fifty lignin model substances.

Biomass valorisation by staged degasification

“…This originates from the biogenesis of lignin from the aromatic alcohols coumaryl alcohol, coniferyl alcohol and sinapyl alcohol as the main building blocks, yielding p-hydroxyphenyl (H), guaiacyl (G) and syringyl (S) units in the final lignin structure. For beech (Fagus sylvatica) lignin, the relative content of these three units has been determined as G:S:H = 56:40:4 [33]. For spruce (Picea abies) lignin a ratio of G:S:H = 94:1:5 has been reported [34].…”

Paving the Way for Lignin Valorisation: Recent Advances in Bioengineering, Biorefining and Catalysis

“…Theabsence,oratleast extremely low abundance,ofnoncyclic a-O-4 linkages,i na ddition to the discovery of eightmembered ring structures D2,c onstitutes an important update to the classical models of lignin proposed by Nimz (1974) [182] and Adler (1977). [31,183] These dibenzodioxocin motifs became recognised as crucial branching points in native lignins.…”

Modification de couleur du bois de chênes européens exposés à la lumière solaire

“…Les (Leary, 1968 Le rôle des phénols dans la photodégra-dation des lignines n'est pas encore clairement élucidé (Castellan et al, 1990;Heitner et Schmidt, 1991). L'étude de la photolyse en solution des molécules modèles des lignines a montré que la pré-sence de groupes phénoliques libres n'est pas nécessaire pour induire une forte coloration (Scalbert et al, 1987); -la structure des lignines : la structure des lignines de feuillus contient un nombre plus important d'unités syringyles (Nimz, 1974) alors qu'il y a beaucoup plus de gaïacyls pour les résineux (Adler et Marton, 1959;Adler, 1977 (Hon et Ifju, 1978 (Wengert, 1968;Schmitt, 1984 (Dirckx, 1988 (Bergman, 1969) (Dirckx, 1988;Dirckx et al, 1992) …”