Geochemical origin of organic sulfur compounds: Reaction of phenylalanine with elemental sulfur
Abstract Organic sulfur compounds were produced when the aromatic amino acid phenylalanine, as a model protein hydrolysate, was reacted with elemental sulfur under conditions that, although severe, might be considered geochemically plausible. Reactions were carried out in sealed tubes at 135°C and at 212°C for times varying between 17.5 and 571 hours both in the presence and absence of aqueous sodium hydroxide. Reactions occurred under all conditions, yielding complex multicomponent mixtures which included hydrocarbons, compounds containing the three elements C, H and S and compounds containing the four elements C, H, S and N. Initiation of the reaction did not require aqueous sodium hydroxide but in its presence the reaction was essentially complete in about 135 hours at the higher temperature. Long-term products tended toward enrichment in components of higher molecular weight yielding ionic masses up to 355 m/e, about twice that of the parent amino acid. Although unable to provide unequivocal molecular structures, mass spectra showed ionic masses that are consistent with representatives of nine of the 13 classes of sulfur compounds known to exist in crude oils. The exploratory experiments suggest that thermal reaction between the two abundant primary-source materials proteins and elemental sulfur may well be of geochemical significance in the genesis of many of the sulfur compounds found in contemporary crude petroleum.