Further investigations on the chemistry of fungal “humic acids”

In view of the considerable interest in laboratory-prepared fungal “humic acids” as possible precursors or incorporated structural components of soil humic substances, we degraded four fungal “humic acids” by the relatively mild alkaline cupric oxide oxidation. The oxidation products were extracted into organic solvents, methylated, separated by thin-layer chromatography and identified on a gas chromatographic-mass spectrometric-computer system.Average yields of major degradation products were: (a) aliphatic compounds, 38 per cent; (b) benzene-carboxylic compounds, 25 per cent; and (c) phenolic compounds, 21 per cent. The remaining 16 per cent consisted of a number of dialkyl phthalates. Our data agree with those that we reported earlier when we degraded a number of fungal “humic acids” by the more drastic alkaline permanganate oxidation and show that fungal “humic acids” are enormously complex organic materials containing aliphatic and aromatic structures, (some of which contain N), but only a relatively small proportion of which is phenolic. Most of the aliphatics isolated consisted of alkanes and fatty acids, which are known to persist in soils over long periods of time and are frequently firmly retained by soil humic substances.