Mechanistic Studies of Organosulfur (Thiol) Formation in Coastal Marine Sediments
1989; American Chemical Society; Linguagem: Inglês
10.1021/bk-1989-0393.ch015
ISSN1947-5918
AutoresAppathurai Vairavamurthy, Kenneth Mopper,
Tópico(s)Isotope Analysis in Ecology
ResumoStudies were carried out to understand the influence of environmental variations, in particular pH and salinity, on organosulfur (thiol) formation in marine sediments via the Michael addition mechanism. Reactions of HS- and a polysulfide species, S42-, with simple organic molecules containing activated, unsaturated bonds (acrylic acid and acrylonitrile) revealed that polysulfide ions were more reactive than bisulfide ion under conditions typical of marine sediments. Furthermore, polysulfide ion reactions were especially more important for organic Michael acceptors having a terminal carboxyl group (e.g. acrylic acid) than for neutral molecules. Variation of pH influenced reaction rates probably by its effect on the speciation of the reactants. The reaction of HS- with acrylonitrile (a neutral organic molecule) showed maximum reaction rates around neutral pH. However, with acrylic acid the pH maximum was shifted to a lower pH value, close to its pKa, because of the higher reactivity of the undissociated acid. High ionic strength influenced the rate of the addition reaction positively, depending on the polarizability of the organic molecule. This effect suggests that hypersaline palaeoenvironmental conditions would have favored organosulfur formation by the Michael addition mechanism.
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