SULFUR-BOUND STEROID AND PHYTANE CARBON SKELETONS IN GEOMACROMOLECULES - IMPLICATIONS FOR THE MECHANISM OF INCORPORATION OF SULFUR INTO ORGANIC-MATTER

Sulphur-bound steroid and phytane moieties in macromolecules present i n the polar fractions of six immature samples (both crude oils and sed iment extracts) have been analyzed using S-selective chemolysis method s and analytical pyrolysis. The identifications of the methylthioether s released from the macromolecule-containing fractions after MeLi/MeI treatment are based on comparison of mass spectral data and chromatogr aphic data with those for synthesized methylthioethers. Evidence is pr esented that di- or polysulphide linkages are present in geomacromolec ules in both sediments and oils and that the location of di- or polysu lphide linkages in macromolecularly S-bound moieties is the same as th at of monosulphide linkages. Macromolecularly S-bound phytanyl moietie s are chiefly bound with S linkages located at the tertiary positions of their carbon skeletons, which indicates that the S incorporation me chanism(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 inc orporation took place into sterenes or steradienes-the dehydration pro ducts of stanols and stenols, respectively. However, it remains possib le that the macromolecularly S-bound steroids with an axial S linkage at C-3 are, in part, resulting from a S(N)2 reaction of inorganic S sp ecies with steryl esters or stanols.