Characterisation of the ruthenium tetroxide oxidation products from the aromatic unresolved complex mixture of a biodegraded crude oil

The monoaromatic, diaromatic and triaromatic fractions of a biodegraded crude oil were oxidised using ruthenium tetroxide to cleave the alkyl substituents attached to aromatic rings. The oxidation products were separated into dichloromethane-soluble monocarboxylic acids, which were subsequently reduced to monodeuterated hydrocarbons for characterisation using gas chromatography–mass spectrometry (GC–MS), and water-soluble dicarboxylic acids. n-Alkanes, methylalkanes, alkylalkanes, alkylcyclohexanes, methylalkylcyclohexanes, isoprenoids and bicyclic compounds were identified in the monodeuterated hydrocarbon samples derived from all three aromatic fractions. Most of these compounds were the same as those observed in the saturate fractions of unbiodegraded crude oils, except for the deuterium atom. Also, in the samples from the diaromatic and triaromatic fractions, numerous aromatic compounds were identified. The main components of the dicarboxylic acid fractions were α,ω-dicarboxylic acids and alkylcyclopentane- and alkylcyclohexane-dicarboxylic acids. The oxidation products represent the alkyl moieties that were attached to aromatic rings in the initial crude oil aromatic fractions