Other
Scientific paper
Oct 1964
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1964gecoa..28.1547b&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 28, Issue 10-11, pp.1547-1552
Other
2
Scientific paper
Studies on the structure of humic acids have been retarded by the lack of suitable degradation procedures that yield aromatic monomers with some side chains intact. A relatively mild degradation under reducing conditions is described which liberates up to 30 per cent of ether-soluble material from soil humic acids and native lignin preparations. The ether-soluble fraction consists of a rich complex of phenolic and phenolic acid monomers, including C 6 -C 1 and C 6 -C 3 units, which have been identified by thin-layer chromatography. Two-way chromatography patterns differ for humic acids of different origins and provide a "fingerprint" technique that may remove some of the current confusion arising from lack of criteria for the characterization of this class of compounds. The contribution of lignin from the overlying vegetation to the formation of humic acid was demonstrated by the presence of relatively unchanged lignin residues. Vanillic, syringic p -hydroxy benzoic, guaiacyl and syringyl propionic acids have been identified. Syringyl residues occur in humic acids formed under deciduous hardwood vegetation (oak), but are absent under coniferous softwoods (pine) where vanillic acid predominates. The assumption that these are lignin-derived components was supported by the complete absence of such residues in humic acid developing in a lignin-free environment below Antarctic clumps of the moss Bryum argenteum . Other degradation products that may be used to distinguish between different humic acids include phloroglucinol, methylphloroglucinol, protocatechuic acid, resorcinol, 3,5-dihydroxybenzoic acid, pyrogallol and orcinol. Several of these can be obtained by degradation of model substances of the C 6 -C 3 -C 6 type. They may represent a flavonoid contribution of the parent vegetation or, alternatively, could be derived from soil microbial syntheses where 1-3-5 substitution patterns are quite common. Native spruce lignin yielded a mixture of 34 compounds. The presence of p -hydroxybenzoic acid confirmed the probable existence of non-methoxylated phenyl residues in soft-wood lignin.
Burges N. A.
Hurst H. M.
Walkden Beryl
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