Phosphorus recovery addresses issues of sustainability and organophosphate (OP) remediation in the environment. We present two recovery strategies that use a polystyrene-supported molybdate complex (Mo-Y). Raman and energy dispersive X-ray analysis indicate the Mo-Y surface contains both oxo and diperoxo functionalities. To that end, the coordination complex hydrogen oxodiperoxo(pyridine-2-carboxylato) molybdenum(VI) (1) was employed as a solution model for the supported catalyst. Phosphorothioates of the form ArOP(S)(OR)₂ were subjected to oxidative degradation by molecule 1 and Mo-Y. In the case of the agricultural pesticide diazinon, the degradation yields diethyl phosphite, a commodity OP. This is an example of recycling toxic OP pesticides into a commodity chemical. Both DFT and O18-labeling studies were employed to elucidate mechanistic pathways for diazinon (2) degradation. This proceeds through a phosphorothiooxirane intermediate (3), and this contribution presents detailed evidence to support hydrolysis of 3 and subsequent departure of the pyrimidinol leaving group. Further sulfide oxidation of the intermediates yields diethyl phosphite and sulfate as the final products. The second target OP is glyphosate (4) which is the leading agricultural herbicide. Glyphosate’s connection with non-Hodgkin’s lymphoma and its ubiquity in the environment requires looking at its fundamental chemistry of degradation. To that end, both Mo-Y and molecule 1 degrade 4 into formaldehyde, formate, glycine and phosphate. The traditional degradation products of 4, sarcosine and aminomethylphosphonic acid are not seen which indicates a new degradation pathway that recovers a ubiquitous wide-spectrum herbicide into a usable phosphate. In addition, an intermediate compound, N-methylene glycine is evident that has not been previously reported. This represents a novel degradation pathway for this herbicide promoted by the coordination compound and its corresponding polymer support. Implications for these OP degradations towards phosphate recovery will also be highlighted.

Louis Kuo

Professor, Lewis Clark College

Appearances