Ruthenium-Ions-Catalyzed Oxidation of an Immature Asphaltene:  Structural Features and Biomarker Distribution

Covalent structural features and the biomarker content of an immature asphaltene originating from a saline lake deposit in China have been explored in ruthenium-ions-catalyzed oxidation. This process converts aromatic-attached 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 with slightly but significantly different distributions. The main structural features identified were, in decreasing order of importance, alkenyl bridges between aromatic carbons (including aromatic condensed cyclohexanes) followed by aromatic-attached n -alkyl, isoprenoid, and α-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 pregnanes, C 20 −C 24 cheilanthanes, etc., each with a specific position in the molecule as the attachment site. Additional products as found with other asphaltenes were benzene di- through hexacarboxylic acids, useful indicators of the mode of aromatic condensation in the asphaltene.