Identification and geochemical significance of demethylated highly cyclized regular polyprenoids in oils and source rocks

Autor: J.M. Trendel, Jacques Connan, A. Charrié-Duhaut, Philippe Schaeffer, Daniel Dessort, Pierre Adam, Pierre Albrecht, E. Grosjean
Přispěvatelé: Institut de Chimie de Strasbourg, Université de Strasbourg (UNISTRA)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS)
Jazyk: angličtina
Rok vydání: 2007
Předmět:
Zdroj: Organic Geochemistry
Organic Geochemistry, Elsevier, 2007, 38 (9), pp.1501-1515. ⟨10.1016/j.orggeochem.2007.05.009⟩
ISSN: 0146-6380
DOI: 10.1016/j.orggeochem.2007.05.009⟩
Popis: Polycyclic polyprenoid hydrocarbons and related demethylated compounds have been identified in severely altered bitumen from oil stained rocks of Upper Jurassic/Lower Cretaceous age. They occur as three series, one homologue of which has been isolated and structurally characterized from nuclear magnetic resonance (NMR) studies. They comprise hydrocarbons demethylated at the A/B ring junction, compounds demethylated at rings E/F/G and a novel series of compounds demethylated at both the ring A/B junction and the ring E/F/G junction, identified for the first time. The occurrence in a number of unaltered and biodegraded oils and source rocks of Upper Jurassic/Lower Cretaceous age, of non-demethylated hydrocarbons, together with related series demethylated at rings E/F/G, indicates that the demethylation process is unlikely to be related to a late degradation process, but rather results from the early transformation of precursors bearing functionalised methyl groups on rings E/F/G. In contrast, polycyclic polyprenoid hydrocarbons demethylated at the A/B ring junction occur only in the most biodegraded samples, suggesting that this demethylated series is formed at later stages of alteration by further demethylation of both non-demethylated compounds and compounds demethylated at rings E/F/G. In addition, a novel series of carboxylic acids related to the polycyclic polyprenoids has been tentatively identified using gas chromatography–mass spectrometry (GC–MS) and comprises both non-demethylated and demethylated structures at rings E/F/G. It is proposed that the acids represent alteration products of polyprenoids bound to aromatic sub-units from macromolecular material that have been released upon severe oxidation during exposure to biodegradation/weathering.
Databáze: OpenAIRE
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