Spruce, lignin

In recent years a lot of investigations have been made on this subject. E.g. Maciel and co-workers 41,42) found that several of the most prominent signals in the CP/M AS NMR spectra can be tentatively assigned for Norway spruce lignin to specific carbon atoms in the phenyl propane unit. Further also in the solid state the signals at about 105 ppm are indicative of hardwood. 

Figure 3.3 Partial structure (16 aromatic units) of a spruce lignin fragment.

It would take too much space here to review in detail the numerous methods that have been applied to assay all the functions in lignin this is almost a specialized subject in itself. The prominent work of the Swedish schools in this connection has been well re dewed by A dler (2,7 a). References to the results of analytical work and how they are accurately reflected by his constitutional scheme for spruce lignin are given by Freudenberg (41, 42,43,43a). 

The similarities in the structure and 3neld of the acids obtained by this degradation from natural spruce lignin and a biosynthetic "spruce lignin copolymer (mixed DHP) made in vitro from a mixture of the three -coumaryl alcohols established the general identity of the two preparations 46, 47). 

Depolymerization of C-methylated spruce lignin and methylated birch MWL by lignin peroxidase was reported in the paper describing the discovery of the enzyme (8). Glenn et al. also... 

Products from the direct oxidation of lignin that give information about its structure include acetic, oxalic, and succinic acids, vanillin, vanillic acid, and dehydrodivanillin. Regarding lignin constitution, they are of only minor interest, but the yields in which they are obtained are significant. For vanillin and its derivatives the total yield is about 33% of spruce lignin (24, 36, 37, 38). Two extraordinary products of this direct oxidation deserve special attention—i.e., benzenepentacarboxylic (45) and tricarballylic acids (47), (XXIX) and (XXX). They will be mentioned later in connection with lignenolide (XXVII). 

The yield of guaiacylglycerol 0-coniferyl ether (XXII) 31) probably surpasses even pinoresinol (XIX) and dehydrodiconiferyl alcohol (XVII). So far it has not been obtained in crystalline form, possibly because of its labile benzyl alcohol group. A derivative has been obtained in the crystalline state and has also been synthesized 15). Guaiacylglycerol 0-coniferyl ether also occurs to a small extent in spruce cambium and has been isolated from spruce lignin as a crystalline derivative 42). 

Phenylcoumarone (VIII) has a characteristic ultraviolet and ioniza-tion-Ae spectrum, which enabled us to detect dimeric structures of this type in reaction mixtures obtained when Bjorkman spruce lignin was subjected to acidolysis for 20 hours. From the spectrophotometric estimation of the amount of the phenylcoumarone systems formed, we concluded that from a total of 100 phenylpropane units of Bjorkman lignin, about 20 are involved in phenylcoumaran systems (I) in other words, about every 10th phenylpropane unit is linked to one of its neighbors by the cyclic benzyl aryl ether linkage characteristic of I. 

The theoretical composition deduced for spruce lignin was confirmed by analytical data for several low sulfonated, high molecular weight ligno-sulfonate fractions. The results of these studies are presented in detail in Paperi Pun 47, 443 (1965). 

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