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

The mechanism of natural sulfur incorporation into organic matter during early diagenesis was studied by simulation reactions carried out with three isoprenoid aldehydes under phase transfer catalysis (PTC) of ammonium polysulfide at ambient temperatures. The aldehydes were phytenal (4), an alpha,beta-unsaturated aldehyde formed by mild oxidation of phytol (3), citral (5), a monoterpene dienal, and 2H-dihydrocitronellal (6), a saturated monoterpene aldehyde. All three aldehydes gave polysulfide cross-linked macromolecules. The structures of the macromolecular substances were studied by the analysis of the products formed by MeLi/Mel depolymerization. The structures of these products are similar to the products formed by the same method from sulfur-rich macromolecular structures identified in immature sediments. Thermal decomposition experiments of the macromolecular products of the alpha,beta-unsaturated aldehydes gave the corresponding isoprenoid thiophenes. The C20 isoprenoid thiophenes formed from 4 are found in many natural immature sediments. A mechanism for the formation of these thiophenes is presented. These results give additional chemical support to the important role of inorganic polysulfide anions as molecular binders in nature. The results suggest that thermal processes that follow the incorporation of sulfur may play an important role in transforming the early formed 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 thiophenes.