POLAROGRAPHY AND COULOMETRY, IN DIMETHYLSULFOXIDE, OF NITRIC ACID OXIDATION PRODUCTS FROM SOIL HUMIC ACID

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Abstract
Conventional aqueous and nonaqueous polarography were of little help in directly determining easily reducible functional groups thought to exist in natural soil humic acids. Partial degradation of soil humic acid by nitric acid oxidation produced polarographically feasible sub-units, however. The oxidation products, which dissolved in nonaqueous dimethylsulfoxide, yielded polarographic reduction waves that compared closely with those of nitrobenzoic acids. The oxidation products exhibited solubility properties which differ considerably from those reported for coal humic acid suggesting that the oxidation products of soil humic acid may be more uniform in size and less condensed than those from coal humic acid. Coulometric determination of the resulting aromatic nitro groups gave a value of 9.4% for the concentrated nitric acid nonoxidizable aromatic content of the original soil humic acid. Significance of this low value is that the hard-core aromatics of soil humic materials may be appreciably less than other (indirect) chemical methods have led us to conclude. The relative ease of oxidation indicated that a major part of the aromatics present were of such structure as to be degradable through oxalic acid to CO2.

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