The pesticide Diazinon (DZN) is a toxic compound of the class of organophosphates (OF’s) used as an acaricide and fungicide. Its half-life (t1/2) is greater than 17 months (60 ºC). In this context, Imidazole (IMZ) stands out as a powerful nucleophile/catalyst in OF's dephosphorylation reactions. For the reaction of DZN with IMZ in the pH range 3-10, catalytic increments of 1000 times and t1/2 less than 3 h were obtained, with the ionic form of IMZ being the most reactive. Nuclear Magnetic Resonance Analysis - 31P NMR Indicates that the reaction at pH 5 (with an ionic species from IMZ - pKa ~ 7) leads to the formation of one phosphorylated product, suggesting that IMZ acts as general acid catalyst helping water nuleophilic attack on phosphorus. At pH 8, IMZ becomes promiscuous, leading to the formation of 3 phosphorylated products, suggesting that IMZ acts as: i) nucleophile in the aliphatic carbon of DZN, forming a diester derived from DZN and ii) general basic catalyst, helping the water attack on the phosphorus of DZN and the diester formed in i). Even though promiscuous, IMZ acts in an incredibly versatile way in reactions with DZN, exercising multiple catalysis and modulating the mechanisms according to pH, outlining new possibilities for detoxification and monitoring.

Dephosphorylation reactions of organophosphate pesticide diazinon with imidazole: kinetics and mechanistic insights

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