The petroporphyrins of a Cretaceous oil |
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| Authors: | B Didyk YIA Alturki CT Pillinger G Eglinton |
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| Institution: | Organic Geochemistry Unit, School of Chemistry, University of Bristol, Bristol Great Britain |
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| Abstract: | The petroporphyrins of a Cretaceous crude oil, La Paz, from western Venezuela are shown to be a mixture of etio and DPEP homologues (C27-C39) maximising at C30 and C31, respectively. Minor amounts of rhodoporphyrins (C30-C39) are also present. Thin-layer chromatography afforded fractions which have been shown by mass spectrometry to contain up to 80% of a single-molecular-weight species. Oxidative degradation of La Paz petroporphyrins to maleimides and mass-spectrometric study of t.l.c. fractions indicate that some of these porphyrins are to a great extent incompletely substituted. Dealkylation reactions have presumably played an important role in their geologic history. Furthermore, the relative simplicity of the alkyl substitution pattern of the La Paz petroporphyrins suggests that transalkylation reactions have not taken place to any significant extent.The fraction of petroporphyrins isolated from the asphaltenes contains a higher proportion of the DPEP homologues than do the total petroporphyrins isolated from the original crude oil. |
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