THE FORMATION OF ISOPRENOID SULFUR-COMPOUNDS DURING DIAGENESIS - SIMULATED SULFUR INCORPORATION AND THERMAL TRANSFORMATION

The mechanism of natural sulfur incorporation into organic matter duri ng early diagenesis was studied by simulation reactions carried out wi th three isoprenoid aldehydes under phase transfer catalysis (PTC) of ammonium polysulfide at ambient temperatures. The aldehydes were phyte nal (4), an alpha,beta-unsaturated aldehyde formed by mild oxidation o f phytol (3), citral (5), a monoterpene dienal, and 2H-dihydrocitronel lal (6), a saturated monoterpene aldehyde. All three aldehydes gave po lysulfide cross-linked macromolecules. The structures of the macromole cular substances were studied by the analysis of the products formed b y MeLi/Mel depolymerization. The structures of these products are simi lar to the products formed by the same method from sulfur-rich macromo lecular structures identified in immature sediments. Thermal decomposi tion experiments of the macromolecular products of the alpha,beta-unsa turated aldehydes gave the corresponding isoprenoid thiophenes. The C2 0 isoprenoid thiophenes formed from 4 are found in many natural immatu re sediments. A mechanism for the formation of these thiophenes is pre sented. These results give additional chemical support to the importan t role of inorganic polysulfide anions as molecular binders in nature. The results suggest that thermal processes that follow the incorporat ion of sulfur may play an important role in transforming the early for med sulfur-containing compounds into thermally stable structures. The results also provide a possible new pathway for phytol degradation in sulfide-rich environments and for the formation of C20 isoprenoid thio phenes.