Ruthenium-ions-catalyzed oxidation of an immature asphaltene: Structural features and biomarker distribution

Covalent structural features and the biomarker content of an immature aspha ltene originating from a saline lake deposit in China have been explored in ruthenium-ions-catalyzed oxidation. This process converts aromatic-attache d aliphatic appendages to their carboxylic acid derivatives, the carboxylic group representing the site of attachment to the aromatic ring. The kinds of products were similar to those found from mature crude oil asphaltenes w ith slightly but significantly different distributions. The main structural features identified were, in decreasing order of importance, alkenyl bridg es between aromatic carbons (including aromatic condensed cyclohexanes) fol lowed by aromatic-attached n-alkyl, isoprenoid, and alpha-C-1-C-3 branched n-alkyl side chains. The major cyclic biomarkers detected were all attached to aromatic carbons by a single C-C bond and comprised gammacerane, C-27-C -35 hopanes, C-27-C-29 regular steranes, 4-methyl steranes, C-20-C-23 pregn anes, C-20-C-24 cheilanthanes, etc., each with a specific position in the m olecule as the attachment site. Additional products-as found with other asp haltenes-were benzene di-through hexacarboxylic acids, useful indicators of the mode of aromatic condensation in the asphaltene.