Laboratory simulation of natural sulphurization: I. Formation of monomeric and oligomeric isoprenoid polysulphides by low-temperature reaction of inorganic polysulphides with phytol and phytadienes

Abstract

Natural sulphurization of organic matter was simulated by reactions of phytol, thiophytol, phytadienes, and 1-hexadecene with NaHSx in dimethylformamide for several days at ambient or slightly elevated temperatures. Phytol gave 3-methyl-3-(4,8,12-trimethyltridecyl)-1,2-dithiolane (1) and 4-methyl-4-(4,8,12-trimethyltridecyl)-1,2,3-trithiane (2) in 0.2–0.7 and 0.05-0.3% yield, respectively. Thiophytol was, however, converted to 1 and 2 in 79% yield. A mixture of phytadienes was almost quantitatively converted into polysulphide-linked oligomers consisting of two to ten phytane units (mean molecular weight ca. 1400 daltons) after 5 days at room temperature. 1-Hexadecene was converted under similar conditions into a mixture of 2,2′-dihexadecyl polysulphides in about 17% yield. The formation of the dimers and oligomers is rationalized by a stepwise Markovnikov-type addition of hydrogen polysulphides to isolated or conjugated double bond(s), respectively. Substitution of OH by SxH followed by an intramolecular reaction with the double bond is the main pathway for formation of 1 and 2 from phytol, as proven by the almost complete conversion of thiophytol under these reaction conditions. The structures of the products generated are similar to those of S compounds present in sediments. These results demonstrate that natural sulphurization of organic matter by reaction with inorganic polysulphides can occur under very mild conditions.