Phosphonothioates, a class of sulfur containing organophosphates, have applications ranging from chemical warfare agents to common pesticides. As potent inhibitors of acetylcholinesterase, these compounds pose a serious threat to human health. Sodium molybdate has been found to accomplish phosphonothioate degradation under mild aqueous conditions, with P-S specific bond scission and modest turnover. The primary aim of this research is to gain a better mechanistic understanding of how sodium molybdate facilitates phosphonothioate hydrolysis. Specifically, the goal is to discern between two possible mechanisms: one involving nucleophilic attack by the molybdate oxoanion, and the other involving molybdate oxygen (Lewis Acid) activation. To this end, several studies with sodium molybdate were conducted. These include tracking the hydrolytic fate of 18O-labeledO,S-diethyl phenylphosphonothioate, investigating the structure-activity relationship for the hydrolysis of phosphonothioates, and determining the thermodynamic parameters of activation for the hydrolysis of O,S-diethyl phenylphosphonothioate. The results obtained thus far do not definitively disprove either mechanism hypothesis. However, they do provide important clues about the process, and will guide the interpretation of a key future study. In addition to the primary focus on sodium molybdate, this research included extending the 18O labeling study to include lanthanum triflate-promoted phosphonothioate degradation. Several inquiries also examined the effectiveness of various other molybdenum (VI) oxide compounds and sodium tungstate in promoting the degradation of phosphonothioates and specific common pesticides.

Degrading organophosphate toxins: Fundamental studies of molybdate-mediated phosphonothioate hydrolysis

251st National Meeting (2016)

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