Laboratory simulation of natural sulphurization: I. Formation of monomeric and oligomeric isoprenoid polysulphides by low-temperature reactions of inorganic polysulphides with phytol and phytadienes
Natural sulphurization of organic matter was simulated by reactions of phytol, thiophytol, phytadienes, and 1-hexadecene with NaHS x 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 S xH 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.