A.C. Kock-van Dalen

Quenching of labile functionalised lipids by inorganic sulphur species: evidence for the formation of sedimentary organic sulphur compounds at the early stages of diagenesis

Abstract The bitumen of the Jurf ed Darawish Oil Shale has been analysed for organic sulphur compounds (OSC). A number of OSC are reported for the first time: several C 28 8, C 37 and C 38 2,5-dialkylthiolanes and -thiophenes and 2,6-di- n -alkylthianes, and C 19 branched thiophenes possessing the 9-methyloctadecane carbon skeleton. A number of these compounds were identified by synthesis of authentic standards. All the OSC compound classes mentioned exhibit structural isomer distributions dominated by a limited number of all theoretically possible isomers. This provides direct evidence for the formation of these OSC by abiogenic sulphur incorporation into functionalised lipids at the early stages of diagenesis. Precursors for the OSC identified are suggested. From these observations and from data on the occurrence of other OSC and of sulphur in high molecular weight substances a general model for the incorporation of sulphur into organic matter is proposed. Sulphur incorporation into precursors with double bonds (or other reactive functionalities) will lead to formation of OSC and sulphur-rich high molecular weight substances. Only precursors with two double bonds in favourable position for intramolecular addition of intermediate thiols can yield low molecular weight OSC. Double bond isomerisations by a sequence of H 2 S addition and elimination reactions may play a role in this respect.

Di- or polysulphide-bound biomarkers in sulphur-rich geomacromolecules as revealed by selective chemolysis

Abstract Three types of sulphur-rich high-molecular-weight material in the alkylsulphide, the polar, and the asphaltene fractions isolated from the bitumen of an immature bituminous shale from the Vena del Gesso basin (Italy) were desulphurised using Raney Ni and were treated with MeLi/MeI, a chemical degradation method which cleaves selectively and quantitatively di- or polysulphide linkages. The products formed were characterised by gas chromatography-mass spectrometry. Raney Ni desulphurisation revealed that these S-rich macromolecules are in substantial part composed of sulphur-linked biomarkers with linear, branched, isoprenoid, steroid, hopanoid, and carotenoid carbon skeletons. MeLi/Mel treatment provided evidence that a major part of the total amount of macromolecularly bound biomarkers are linked via di- or polysulphide moieties to the macromolecular network. Since the di- or polysulphide linkages are attached at specific positions of the bound biomarkers it is proposed that they are formed by intermolecular incorporation reactions of HSx− into low-molecular-weight functionalised biological lipids during early diagenesis. The different properties (solubility and molecular weight) of the sulphur-rich macromolecules in the alkylsulphide, the resin, and the asphaltene fractions can be explained simply by differences in degree of sulphur cross-linking.

Occurrence and origin of mono-, di-, and trimethylalkanes in modern and Holocene cyanobacterial mats from Abu Dhabi, United Arab Emirates

n-Alkanes, highly branched isoprenoids, monomethylalkanes (MMAs), dimethylalkanes (DMAs), and trimethylalkanes (TMAs) are the most abundant components in the hydrocarbon fractions of extracts of four modern and two Holocene cyanobacterial mats (t1500 and 5110 ± 170 y bp) collected in Abu Dhabi (United Arab Emirates). The homologous families of MMAs, DMAs, and TMAs were identified by comparison of mass spectral and relative retention time data with published data. DMAs were also identified by synthesis of authentic standards, 3,9-dimethyltricosane, 5,9-dimethyltricosane, and 11,15-dimethylheptacosane. MMAs, DMAs, and TMAs of the cyanobacterial mats can be separated into two groups on the basis of their distribution patterns and structures. MMAs and DMAs in the C16-C22 range are characterized by methyl substituents mainly located at C-6 (or ω6) and C-7 (or ω7) and are derived from cyanobacteria. They are relatively abundant components in the modern cyanobacterial mats, but with increasing age of the mats they become much less abundant. On the contrary MMAs, DMAs, and TMAs in the C24-C45 range are exclusively found in the Holocene cyanobacterial mats. Their longest chains mainly contain an odd number of carbon atoms and they always carry the methyl substituents at odd numbered carbon atoms. The similarity in composition of this very specific group of branched alkanes with that encountered in insect epicuticular waxes suggests that these sedimentary hydrocarbons originate from insects, which probably grazed on the cyanobacterial mats.

The occurrence and identification of series of organic sulphur compounds in oils and sediment extracts. I. A study of Rozel Point Oil (U.S.A.)

A number of novel series of organic sulfur compounds (OSC) have been identified in several oils and sediment extracts including Rozel Point Oil (Bos Elder County, Utah, U.S.A.; Miocene). This oil contains these series in abundance, and the OSC were therefore studied in detail. The aromatic fraction was fractionated using column chromatography, and the fractions obtained were analyzed by GC with simultaneous flame ionization and flame photometric detection (PFD) and by Gas Chromatography/Ma (GC-MS). Series of isoprenoid thiophenes, isoprenoid thiolanes, isoprenoid bithiophenes, isoprenoid thienylthiolanes, isoprenoid benzothiophenes, thiophene and thiolane steranes, 2,5-di-n-alkylthiolanes, 2,6-di-n-alkylthianes and 2,4-di-n-alkylbenzo(b)thiophenes have been identified. The identifications were based on chromatographic and mass spectral data, response on the FPD, carbon skeleton determination by desulfurization and in some cases on mass spectral data from, and coinjections with, synthetic compounds. Together, almost 1000 OSC have been identified in the aromatic fraction of this oil. Because the carbon skeletons of the OSC identified have the same structures as the well know hydrocarbons from geological materials (isoprenoid hydrocarbons, steranes, n-alkanes) these compounds are thought to be products of sulfur incorporation reactions into specific precursors.

Origin and diagenetic transformations of C25 and C30 highly branched isoprenoid sulphur compounds : further evidence for the formation of organic sulphur compounds during early diagenesis

Abstract A number of C25 and C30 highly branched isoprenoid (HBI) sulphur compounds (E.G., thiolanes, 1-oxo-thiolanes, thiophenes, and benzo[ b ]thiophenes) with 2,6,10,14-tetramethyl-7-(3-methylpentyl)pentadecane and 2,6,10,14,18-pentamethyl-7-(3-methylpentyl)nonadecane carbon skeletons were identified in sediments, ranging from Holocene to Upper Cretaceous. These identifications are based on mass spectral characterisation, desulphurisation, and, in some cases, by comparison of mass spectral and relative retention time data with those of authentic standards. The presence of unsaturated C25 and C30 HBI thiolanes in a Recent sediment from the Black Sea (age 3–6 × 10 3 a) strongly supports their formation during early diagenesis. The co-occurrence of HBI polyenes (C25 and C30) and unsaturated HBI thiolanes (C25 and C30) possessing two double bonds less than the corresponding HBI polyenes, in this Recent sediment, testifies to the formation of unsaturated HBI thiolanes by a reaction of inorganic sulphur species with double bonds of the HBI polyenes. Furthermore, a diagenetic scheme for HBI sulphur compounds is proposed based on the identification of HBI sulphur compounds in sediment samples with different maturity levels.

The identification of mono-, di- and trimethyl 2-methyl-2-(4,8,12-trimethyltridecyl) chromans and their occurrence in the geosphere

A series of novel mono-, di-and trimethyl 2-methyl-2-(4,8,12-trimethyltridecyl)chromans (MTTC) have been identified in a number of sediment extracts and oils ranging from Pleistocene to Permian. The identifications were based on comparison of mass spectra and Chromatographic data of synthetic methylated MTTC with those of geologically occurring methylated MTTC and coinjections with the synthetic standards. Although the methylated MTTC are structurally related to tocopherols, they do not appear to be their diagenetic derivatives. The distribution of methylated MTTC in sediments and oils seems to depend on the original environment of deposition and may be used as a palaeoenvironmental indicator, e.g. to assess the occurrence of palaeohypersalinity.

Identification of homologous series of alkylated thiophenes, thiolanes, thianes and benzothiophenes present in pyrolysates of sulphur-rich kerogens

The ability of flash pyrolysis-gas chromatography with dual flame ionization and flame photometric detection, and flash pyrolysis-gas chromatography-mass spectrometry, to afford detailed information about the organic sulphur pyrolysis products of kerogens is exemplified through analysis of five different sulphur-rich, type II kerogens. The pyrolysates of these kerogens are extremely complex mixtures. The technique with flame photometric detection yields a chromatogram that shows the distribution of only organic sulphur products in the pyrolysates. However, a considerable loss of sensitivity in flame photometric detection was apparent for higher-molecular-weight compounds. The use of the mass spectrometer as a detector, using characteristic m/z values of organic sulphur compounds for appropriate mass chromatograms, was therefore preferable. Identification of the organic sulphur products was accomplished by sulphur-selective flame photometric detection and comparison of their mass spectral and chromatographic data with those of standard reference compounds. Chromatographic retention time data for 48 standard sulphur compounds (alkylated thiophenes, thiolanes and benzo[b]thiophenes) were determined. Homologous series of 2-alkylthiophenes, 2-alkyl-5-methylthiophenes, 2-alkyl-5-ethylthiophenes, 2-alkylthiolanes, 2-alkylthianes, 2-alkyl-5-methylthiolanes, 2-alkyl-4-methylbenzo[b]thiophenes, 4-alkyl-2-methylbenzo[b]thiophenes and 2-alkyl-benzo[b]thiophenes, through a total carbon number of 22, have been identified through linear Kovats plots and comparison of mass spectral and chromatographic data of the C18 members of these series with those of standard compounds.

Sulphur-bound steroid and phytane carbon skeletons in geomacromolecules: Implications for the mechanism of incorporation of sulphur into organic matter

Sulphur-bound steroid and phytane moieties in macromolecules present in the polar fractions of six immature samples (both crude oils and sediment extracts) have been analyzed using S-selective chemolysis methods and analytical pyrolysis. The identifications of the methylthioethers released from the macromolecule-containing fractions after MeLi/MeI treatment are based on comparison of mass spectral data and chromatographic data with those for synthesized methylthioethers. Evidence is presented that di- or polysulphide linkages are present in geomacromolecules in both sediments and oils and that the location of di- or polysulphide linkages in macromolecularly S-bound moieties is the same as that of monosulphide linkages. Macromolecularly S-bound phytanyl moieties are chiefly bound with S linkages located at the tertiary positions of their carbon skeletons, which indicates that the S incorporation mechanism(s) involve(s) intermediate carbocations. The macromolecularly S-bound steroids are bound with S linkages located mainly at C-2, C-3, C-4, or C-5 of their carbon skeletons, which indicates that the S incorporation took place into sterenes or steradienes—the dehydration products of stanols and stenols, respectively. However, it remains possible that the macromolecularly S-bound steroids with an axial S linkage at C-3 are, in part, resulting from a SN2 reaction of inorganic S species with steryl esters or stanols.

Characterisation of highly branched isoprenoid thiophenes occurring in sediments and immature crude oils

Abstract A number of C 20 and C 25 highly branched isoprenoid thiophenes (HBIT) (i.e. thiophenes with 2,6,10-trimethyl-7-(3′-methylbutyl)dodecane and 2,6,10,14-tetramethyl-7-(3′-methylpentyl)pentadecane carbon skeletons) have been identified in sediments and immature oils from different geographical locations. Eight C 20 and two C 25 HBIT structural isomers were assigned on the basis of mass spectral characterisation, desulphurisation of isolated or mixtures of C 20 and C 25 HBIT and in some cases by comparison of mass spectral and relative retention time data with authentic compounds. Only a limited number of all theoretically possible isomers were present, indicating that these HBIT are probably formed by selective sulphur incorporation reactions into the widely occurring highly branched isoprenoid alkenes.

Lipase-catalysed ammoniolysis of lipids. A facile synthesis of fatty acid amides

Abstract Ammoniolysis of triglycerides to the corresponding fatty acid amides is efficiently catalysed byCandida antarctica lipase (Novozym 435). Thus, olive oil gave 90% of nearly pure oleamide after 72 h at 60°C. Jojoba wax was similarly converted into a mixture ofcis-11-eicosenamide and erucamide together withcis-11-eicosenol andcis-l3-docosenol.