"The Hydrolysis of the Organophosphate Pesticides Parathion and Paraoxon by the Metallocene Dicyclopentadienyl Molybdenum (IV) Dichloride"

Student Researcher: Nicholas Perera and Kukui Awana

Faculty Advisor: Louis Y. Kuo

We report the first case of an organometallic complex that effectively hydrolyzes the organophosphate pesticides parathion and paraoxon. Parathion and paraoxon are toxic nerve agents biochemically similar to many other pesticides and some chemical warfare agents such as VX and sarin gases. 1H and 31P NMR spectral evidence suggest that the aquated form of the metallocene bis(h5-cyclopentadienyl) molybdenum (IV) dichloride (Cp2MoCl2: Cp=h5C5H5) degrades the organophosphorus pesticides parathion and paraoxon via hydrolytic pathways. These are the first known cases where an organometallic compound has been used to hydrolyze an organophosphate triester or pesticide in aqueous solution.

Cp2MoCl2 promotes the hydrolytic phosphotriester bond cleavage in paraoxon with rate accelerations of 2300 and 27 at pD 7 and pD 3, respectively. The hydrolysis of paraoxon involves an intermolecular (*S? = -49e.u.) nucleophilic attack by hydroxide resulting in phosphorus-oxygen bond cleavage. The products of paraoxon hydrolysis are p-nitrophenol and diethyl phosphoric acid. Cp2MoCl2 promotes hydrolytic carbon-oxygen bond cleavage in parathion via nucleophilic attack by hydroxide with a rate acceleration of 130 and 105 at pD 7 and 3, respectively. The resulting products are ethanol and (O-ethyl O-Hydrogen O-(4-nitrophenyl) phosphorothionate (deethyl parathion). The results herein represent one of the few cases of this type of unusual hydrolytic chemistry, and the first case of an organometallic complex that accelerates organophosphate pesticide hydrolysis.