Lignins spruce, yield

More recently, Brauns and Seiler (12), (13) extracted native lignin from spruce wood and then homogenized the wood in a colloidal mill. A suspension of approximately one gram of colloidal wood per liter of water was obtained. After the colloidal wood was changed to a solid form, it was found that its cell structure was completely destroyed. However, extraction of this wood with ethyl alcohol at room temperature did not yield further quantities of native lignin. These investigators have also reported the isolation of a lignosulfonic acid-carbohydrate compound. 

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). 

Somewhat variable results were obtained with Norway spruce since optimum conditions were not used on all runs. However, the fractions of soluble lignin were roughly as above, although the yields of total soluble lignin were lower. 

Fig. 4-1. Examples of classical methods indicating a phenylpropanoid structure of lignin. (A) Permanganate oxidation (methylated spruce lignin) affords veratric acid (3,4-dimethoxybenzoic acid) (1) in a yield of 8% and minor amounts of isohemipinic (4,5-dimethoxyisophtalic acid) (2) and dehydrodiveratric (3) acids. The formation of isohemipinic acid supports the occurrence of condensed structures (e.g., /3-5 or y-5). (B) Nitrobenzene oxidation of softwoods in alkali results in the formation of vanillin (4-hydroxy-3-methoxybenzaldehyde) (4) (about 25% of lignin). Oxidation of hardwoods and grasses results, respectively, in syringaldehyde (3,5-dimethoxy-4-hydroxybenzaldehyde) (5) and p-hydroxybenzaldehyde (6). (C) Hydrogenolysis yields pro-pylcyclohexane derivatives (7). (D) Ethanolysis yields so-called Hibbert ketones (8,9,10, and 11).

Saiz-Jimenez et al. (1987) applied analytical pyrolysis-gas chromatography to recent and buried alder, oak, and spruce woods. In comparison with the native woods, the yields of pyrolysis products from the guaiacyl and syringyl lignins were significantly higher in the alder and oak woods, while for spruce, this increase was less significant. 

Lundquist and Kirk (1971) treated spruce lignin with the acidolysis reagent at reflux temperature for 4, 8, and 24 h Ketol la (Fig 6 11) predominates in the 4-h acidolysis mixture (yield, 4 6% of the lignin) and prolonged treatment does not result in any appreciable increase in the yield of acidolysis monomers The yields of the primary ketols la and 2a (Fig 6 11) from birch lignin (a typical... 

Oxidative degradation of native lignin samples (MWL) from spruce and from aspen at varying pH and reaction times during the alkylation step has shown, however, that an optimum yield of products (including dimethyl ester 7) is obtained under the conditions stated above, i.e., reaction at pH 11 for 24h (Gellerstedt, unpubl.). The reason for this discrepancy in the results from model compounds and lignins is not known. 

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