Molecular compounds generated by ruthenium tetroxide oxidation and preparative off line thermochemolysis of lignite humic acids from South Moravia: Implications for molecular structure

The composition of humic acids (HAs) isolated from a South Moravian lignite deposit was examined via thermochemolysis and RuO4 oxidation. The combination of thermochemolysis with TMAH and TEAAc shows that fatty acids were mostly in a “free” form, tightly trapped within the humic acid organic network. Humic acids contain also trapped hydrocarbons. The relative distributions of these compounds confirm their higher plant origin. RuO4 oxidation resulted in a lipophilic fraction containing mainly fatty acids. The hydrophilic fractions released upon RuO4 oxidation comprised mostly aliphatic C2–C9 dicarboxylic acids and hydroxy acids related to short methylene bridges, to bridges between aromatic and/or oxygenated moieties such as aliphatic chains of ligneous units.