An improved ruthenium tetroxide oxidation of marine and lacustrine kerogens: possible origin of low molecular weight acids and benzenecarboxylic acids

Incorporation and condensation of low molecular weight biomolecules, including the effect of Maillard reactions, are considered to play a role in kerogen formation, but the details of this process are not fully understood. We used an improved ruthenium tetroxide (RuO4) oxidation procedure to determine the molecular composition of marine and lacustrine kerogens. We characterized some of the low molecular weight compounds and recovered benzenecarboxylic acids (BCAs) from the products. To clarify the origin of the products from the kerogens, we used the same RuO4 oxidation procedure to examine model melanoidins, fatty acids (FAs), amino acids and galactose. The results indicated that short chain (C2–C5) α,ω-dicarboxylic acids were major compounds in the kerogen products and that their precursor molecules might be melanoidins or unsaturated FAs. A maximum at C9 for the α,ω-dicarboxylic acids was identified only in the oxidation products from the lacustrine kerogens. We attributed this result to the difference between marine and lacustrine kerogens with respect to precursor unsaturated FAs. The BCAs produced from the kerogens are possibly produced from melanoidin-derived material in the kerogens. The C21 and C23 α,ω-dicarboxylic acids from a lacustrine (Lake Biwa) kerogen suggest that resistant biopolymers from green microalgae contributed to kerogen formation.