SULFUR-BINDING IN RECENT ENVIRONMENTS .1. LIPID BY-PRODUCTS FROM NI2BDESULFURIZATION

Selected geochemically relevant model compounds were subjected to the nickel boride desulphurization method. Poor hydrogenating properties o f this agent were observed in the case of sterically hindered double b onds. Apart from its desulphurizing properties, a significant number o f functionalities present in lipid compounds were transformed on treat ment with nickel boride. Ketones were reduced to their alcohols wherea s aldehydes were partly converted to their ketals. Although alcohols a nd esters were unaffected by this agent, a nearby unsaturation (i.e., position ar) resulted in the loss of the alcohol group and cleavage of the ester bond, respectively. The significance of these results was d emonstrated by desulphurization experiments on polar fractions from tw o recent sediment extracts. The main compound among the apolar product s obtained, phytane, was found to be quantitatively derived from phyto l and not, as may be presumed, from its macromolecularly sulphur-bound precursor. The results of this work show that compounds generated by nickel boride desulphurization of polar fractions from lipid extracts, particularly from recent sediments, are not necessarily derived from their sulphur-bound precursors. Conclusions with regard to the palaeoe nvironmental significance of the hydrocarbons formed, therefore, shoul d be made with caution. (C) 1997 Elsevier Science Ltd.