Toward Heterogeneously Catalyzed Detoxification of Phosphotriesters: Insights from Kinetics and Theoretical Calculations

A mixed Mg2+/Al3+ oxide featuring an incipient spinel phase was employed in the catalytic decomposition of a range of phosphate triesters, including the neurotoxic biocide chlorpyrifos methyl O-analog, with estimated catalytic effects up to 104-fold. The target reaction, namely, the transesterification with 1-propanol, was conveniently chosen as a means to convert toxic organophosphorus substrates into trialkyl phosphates structurally related to a family of flame retardants. Catalytic efficiency depends upon the stereo-electronic properties of the substrate, with both leaving group ability and geometric factors displaying pivotal effects on the rate constants. To evaluate the adsorption of 1-propanol/propoxide and the phosphotriester methyl paraoxon over the MgAl2O4(100) surface, density functional theory calculations with periodic boundary conditions were performed, which showed that the most probable reactants’ conformation prior to the reaction is such that propoxide is bound to a Mg2+ center with a ju...