The Potassium Permanganate Oxidation of Methylated and Unmethylated Humic Acids Extracted from Solonetz, Solod and Chernozem Ah Horizons

Humic acids were extracted from Ah horizons of a Solonetz, a Solod, and a Chernozem soil. A portion of each extracted humic acid was methylated in order to make it more resistant to attack by electrophilic KMnO 4 . Both the methylated and unmethylated humic acids were then oxidized with KMnO 4 . The oxidation products were extracted into ethyl acetate and separated by preparative gas chromatography into relatively pure components, which were then analyzed by mass spectrometry and micro‐infrared spectrophotometry. A matching of the mass and IR spectra and gas chromatographic retention times of the isolated components with those of authentic specimens led to their identification. The most prominent compounds produced by the oxidation of methylated humic acids were 1,3,5‐benzenetricarboxylic acid and a complex phenolic acid, tentatively identified as propanone‐hydroxy‐methyl acetoxy‐benzene‐dicarboxylic acid. These two compounds accounted for between 18 and 23% of the original methylated humic acids. The main products resulting from the oxidation of unmethylated humic acids were benzenetri‐, benzenetetra‐ and benzenepenta‐carboxylic acids, which constituted between 10 and 12% of the weights of the original unmethylated humic acids. The results show that methylation of humic acids prior to oxidation is a useful procedure which substantially increases the yields and types of oxidation products. From the similarities in analytical data and in the quality of the oxidation products, we conclude that the three humic acids have similar chemical structures, yielding benzenecarboxylic and phenolic acids on oxidation. These compounds either originate from more complex structures or they exist in the humic acids in the forms in which they were isolated, held together by hydrogen bonds.