PERMANGANATE OXIDATION OF HUMIC ACIDS, FULVIC ACIDS, AND HUMINS EXTRACTED FROM Ah HORIZONS OF A BLACK CHERNOZEM, A BLACK SOLOD, AND A BLACK SOLONETZ SOIL

Humic acid, fulvic acid, and humin fractions extracted from a Black Chernozem, a Black Solod, and a Black Solonetz soil were methylated with diazomethane and oxidized with permanganate solution. The oxidation products were extracted into ethyl acetate, separated by preparative gas chromatography, and identified by comparing their mass and micro-IR spectra with those of authentic specimens. Total yields of oxidation products followed the order humic acids > humins > fulvic acids. The products resulting from the oxidation of humic and fulvic acids averaged 63% benzenecarboxylic, 32% phenolic, and 5% aliphatic carboxylic acids. The oxidation products from humins averaged 76% benzenecarboxylic but only 20% phenolic and 4% aliphatic carboxylic acids, indicating some differences in the chemical structure of humins from those of humic and fulvic acids. The most prominent compounds produced by the oxidation of the humic acids were hydroxy benzenepentacarboxylic and benzenetetracarboxylic acids. In general, differences in the distribution of the major oxidation products between the three major fractions were greater than those within individual humic fractions. Thus, the chemical structures of humic acids extracted from three different soils appeared to be more similar to each other than to those of fulvic acid and humin fractions from the same soil. The same was true for fulvic acids and humins extracted from the different soils. Between 79 and 95% of the oxidation products were identified. The oxidation products may have originated from (a) condensed lignin structures, (b) complex structures of microbiological origin, and/or (c) polymeric structures consisting of benzenecarboxylic and phenolic acids held together by hydrogen-bonding.