Studies on the Formation of Complex Oxidation and Condensation Products of Phenols. A Contribution to the Investigation of the Origin and Nature of Humic Acid. Part I. Studies of the Reactivity of Simple Monocyclic Quinones
Proceedings of the Royal Society A
In spite of numerous investigations the chemical nature of the humic acids remains obscure, and one result of the defects of our knowledge is the loose application of the term " humic acid 55 in the literature. For example, the definition given by S. Odenf in his excellent monograph, might also cover any brown or brownish-black substance of unknown constitution." It has long been known that oxidation of certain tannins and other phenolic compomids yields products (phlobaphenes) resembling humic
... s) resembling humic acids, and it has been plausibly suggested that humic acids and these products of oxidation aud condensation are chemically related. Among the recent advocates of a carbocyclic structure for the humic acids may be mentioned Fischer and Eller. Fischer! advanced the theory that humic acids arise from the aromatic constituents of plants. He considered that the most important source is lignin, the aromatic nature of which has been conclusively demonstrated by Klason and by Freudenberg. Eller § pointed out the very close similarities between the 4 4 natural humic acids " and " artificial humic acids55 obtained from different phenols on oxidation by per sulphates in alkaline solution. The £* humic acids " obtained from sugar when treated with strong acids behave in an entirely different manner and belong to a quite different series of compounds. || Eller found that certain phenols when oxidized under varied conditions in alkaline solution yield a " humic acid " of constant composition. He assumed t " Die Huminsauren," etc., Dresden, 1919, pp. 21 and 31. % 4 Brennst.