ISSN:
0022-3832
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
Spruce wood lignin has molecular weight of the order of magnitude of 10,000-100,000. Furthermore, it is bonded, to a large extent, if not completely, with the polysaccharides of the wood. It is formed by enzymatic dehydrogenation of coniferyl alcohol I. The mesomeric forms II-IV of the radical produced stabilize themselves by combining together to form dimers, the largest proportion of which - owing to the preponderant occurrence of the form III - are quinone methides. The latter stabilize themselves intramolecularly, steric arrangements permitting, forming ethers like V and VI. In the case of the quinone methide VIII alone, an intramolecular stabilization is impossible; this methide is stabilized by addition of water or of a hydroxyl group of the carbohydrates. In the latter case, an etherlike carbohydrate compound is formed which contains a phenolic group and which can hence be incorporated into lignin on further dehydrogenation. Substance VIII can also add on coniferyl alcohol, substance V, or other phenols, and hence it condenses units without further loss of hydrogen (XII and XIII). All of the processes described thus far proceed automatically after the formation of the radicals. The new building units thus formed (V, VI, and other similar units) can also be welded together by renewed dehydrogenation or by the formation of more quinone methides which give rise to addition reactions. By means of this combination of dehydrogenative condensation with addition of phenols and alcohols to quinone methides formed intermediarily, lignin grows to a polymolecule, grafting itself in the process onto the polysaccharides. The path of formation of the molecule also explains the extraordinarily great differences between the oligomeric building units, although in the case of conifer lignin they all proceed from the one substance, coniferyl alcohol. The branching of lignin is explained by the addition reaction. The sequence of the units is fully random, since no matrix provides for a definite order.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/pol.1960.1204815037
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