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Two successive degradation steps involving Na 2 Cr 2 O 7 /AcOH and RuO 4 were carried out on a Type II-S kerogen from the Miocene Monterey Formation (California) after pre-saponification of the ester bonds by KOH/MeOH treatment. Detailed gas chromatography (GC) and gas chromatography–mass spectrometry (GC–MS) analysis of the soluble acids revealed significant qualitative and quantitative variation of the various types of products obtained from the two different degradation steps. Maleimides (lH-pyrrole-2,5-diones), dominated by Me,Et-maleimide, were the major degradation products released by Na 2 Cr 2 O 7 /AcOH oxidation indicating that their precursors, probably tetrapyrrole pigments, occur ether- as well as sulfur-bound in the kerogen. On the other hand, a scarcely reported homologous series of 2-methyl- n -alkanoic acids (C 8 –C 27 ) was identified as the most prominent series of carboxylic acids obtained after RuO 4 oxidation. The results support the high specificity of the RuO 4 oxidation method in revealing information on the nature of the alkyl chains substituting the aromatic moieties in the kerogen structure and point to the presence of aryl–alkyl ether groups in the kerogen. The significance of the lipid composition of the kerogen is further discussed in terms of biomarker information and their original attachment to the macromolecular structure.

Ruthenium tetroxide oxidation was applied to sulfur-rich kerogens from the Nordlinger Ries, southern Germany, to provide complementary structural information about the nature of alkyl substituents attached to aromatic moieties. The oxidation products contained series of straight-chain monocarboxylic acids (C8–C29), α,ω-dicarboxylic acids (C7–C26), isoprenoid acids (C14–C21, except C18), non-isoprenoid branched acids (mainly iso and anteiso C11–C18 acids), 3β-carboxysteroids (C28–C31) and steroid ketones (C27–C30). Furthermore, 4-hydroxy-4,8,12,16-tetramethylheptadecanoic acid γ-lactone, 6,10,14-trimethylpentadecan-2-one, and 10-oxo-n-octadecanoic acid were identified. The oxidation products are discussed in terms of their original contribution to the macromolecular structure. The results support previous suggestions that alkyl–aryl ether groups are present in the kerogen, probably as a result of O-alkylation between phenols and aliphatic precursors. Of particular interest, however, is the identification of a predominant homologous series of 2-methyl n-alkanoic acid methyl esters (C9–C28) in one of the samples. The release of this scarcely reported series of branched acids points toward the specificity of RuO4 oxidation revealing structural information on the alkyl chains substituting the aromatic moieties in the kerogen structure, and implies that some of the bound lipids were contributed by sulfate-reducing bacteria.

In an attempt to obtain a greater insight into the structure of Monterey kerogen, partially oxidized kerogen concentrates obtained from Na2Cr2O7glacial CH3COOH stepwise oxidation were examined by Fourier transform infrared (FT-i.r.) analysis. The results show that the kerogen samples contain condensed aromatic systems to which are attached OH and Oalkyl functional groups, and also indicate that the majority of N and S atoms are within the ring structure. It was found that the carbonyl, aromatic and ether groups are not affected while CH2 groups are lost upon oxidation. Furthermore, it was concluded that in kerogen oxidation, organic sulphur can be fixed as inorganic sulphate in the presence of COO− in a manner similar to coal oxidation.

Green River shale kerogen was degraded by a careful five-step oxidation with sodium dichromate in glacial acetic acid. Products isolated from each oxidation step were examined by capillary gas chromatography and combined gas chromatography-mass spectrometry. The analyses revealed the presence of several homologous series. Saturated normal monocarboxylic acids (C 6 C 35 ) and saturated normal α,ω-dicarboxylic acids (C 4 C 33 ) were the major constituent series, while isoprenoid acids (C 14 C 21 , except C 18 ), iso and anteiso acids (C 6 C 16 ), branched dicarboxylic acids (C 20 C 29 ), triterpenoidal acids (C 27 C 33 ), cyclic, and oxo-acids were the minor constituent series. Moreover, a few aromatic acids, branched ketones, heterocyclic compounds, as well as a series of (C 25 C 30 ) n -alkanes were identified. The results were discussed in terms of the qualitative and quantitative variations of the products with duration of oxidation. The data corroborate the conclusion of a predominantly open chain crosslinked aliphatic structure for Green River kerogen, and indicate that aromatic structures are mainly in the form of isolated phenyl and tolyl groups. The results further confirm the presence of etioporphyrin as a significant constituent in the kerogen studied.