To obtain more detailed information on their chemical structures, a humic acid, extracted from a Black Chernozemic O horizon, and a fulvic acid, extracted from a Podzol Bh horizon, were oxidized by allowing them to react with 10 percent aqueous peracetic acid solution for 4 hr at 80°C. The oxidation products were extracted into organic solvents, methylated, separated by column, thin-layer, and preparative gas chromatography, and identified by matching their mass and microinfrared spectra with those of authentic specimens.
The major humic acid oxidation products were phenolic acids (isolated in fully methylated forms, 4.3 percent) and benzenecarboxylic acids (as methyl esters, 15.2 percent). The fulvic acid yielded 4.1 percent phenolic compounds and 7.3 percent benzenecarboxylic acids (as methyl esters). In addition, small amounts of fatty acid (as methyl esters) and aliphatic dicarboxylic acids (as methyl esters) were isolated. The peracetic acid oxidation of unmethylated humic and fulvic acids produced essentially similar compounds and in similar yields as did alkaline KMnO4 and CuO-NaOH oxidations of methylated humic substances. Neither muconic acid-type compounds nor maleic or fumaric acid-type derivatives, whose formation is often associated with peracetic acid oxidation, were detected. Peracetic acid oxidation was found to be a simple, convenient and rapid method that provides worthwhile information on the chemical structure of humic substances.
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