This is the first report of metal complexes that promote the degradation of sulfur-containing organophosphate neurotoxins with the benefits of heterogeneous catalysis and phosphorus recovery. Three strategies are presented that begin with a supported molybdenum(VI) peroxide polymer (Mo-Y(s)) made from the immobilization of a Mo(s)/H2O2(aq) mixture on a tetrammine-polystyrene support. The Mo-Y(s) support degrades phosphorothioate pesticides, and one of the products, diethyl phosphite, is a commodity chemical. Specifically, Mo-Y(s) degrades phosphorothioate pesticides of the form (EtO)2P(=S)(OAr) that include parathion, coumaphos and diazonin. Two common themes in this ethanolysis are the production of diethyl phosphite ((EtO)2P(H)) and the corresponding oxon ((EtO)2P(=O)(OAr)). In connection with diethyl phosphite production, various strategies (i.e. solvent, nature of phosphorothioate) will be presented that favor phosphite production over the oxon byproduct. The second strategy uses Mo-Y(s) towards the ethanolysis of the VX analog O,S – diethylphenyl phosphonothioate (DEPP). The ethanolysis with H2O2 yields only P – S bond scission to yield diethylphenyl phosphonate and ethyl sulfate. Activation parameters of DEPP ethanolysis by Mo-Y(s) and by the model compound oxodiperoxo(pyridine-2-carboxylato)molybdate(VI) suggest the rate determining step for DEPP ethanolysis is sulfur oxidation to form an intermediate phoshonothioate S-oxide that subsequently undergoes nucleophilic attack by the ethanol solvent to form diethylphenyl phosphonate and ethyl sulfate. The third strategy entails catalytic hydrolysis of DEPP by the monomeric MoO42- molybdate; this is the first case of homogeneous phosphonothioate hydrolysis by a high oxidation state group VI complex under mild conditions (pH 7, 30 oC). Hydrolysis by MoO42- yields ethylphenyl phosphonate resulting from exclusive P – S scission which is the preferred bond cleavage. The mechanism for this hydrolysis was modeled with density functional theory methods. In this scheme the oxoanion of MoO42- attacks the phosphorus center of DEPP in a SN2(P) fashion to form a mixed molybdate-phosphonate anhydride intermediate; this is followed by rapid hydrolysis. DFT calculations at the G++(d,p) level indicate this nucleophilic route is a viable pathway for the catalytic hydrolysis of DEPP by MoO42. The initial and rate determining SN2(P) nucleophilic attack was successfully modeled that included a transition state search.

Neurotoxin degradation and phosphorus recovery by molybdenum(VI) complexes through heterogeneous and homogeneous catalysis

256th National Meeting (2018)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.