A degradação nucleofílica de organofosfatos promovida por 1,2,4 triazol

Abstract

Organophosphates and derivatives are compounds widely used as agrochemicals due to their high stability and considerable efficiency. Despite its importance, the imprudent use and numerous prohibitions motivated by the harm to human health and the environment have required efficient methods of degrading obsolete stocks of pesticides, to avoid poisoning and countless human deaths that occur every year. Nucleophilic substitution is an important method to mitigate the toxicity of organophosphates. In the present study, the degradation of organophosphate diethyl-2,4-dinitrophenylphosphate (DEDNPP) and of the pesticide diethyl-4-nitrophenylphosphate (Paraoxon) promoted by 1,2,4-triazole (TAZ) was investigated by means of kinetic studies, nuclear magnetic resonance (NMR) analyses and computational calculations using density functional theory. Results showed that the rapid degradation of organophosphates is mainly promoted by the anionic form of the nucleophile (TAZ(-)) at pH higher than 8 (optimal at pH = 11). Rate enhancements on the order of 106 and 105 times were observed compared to spontaneous hydrolysis of DEDNPP and Paraoxon, respectively. NMR analyses indicated that the exclusive route of degradation of DEDNPP promoted by TAZ(-) occurs via P–O bond cleavage in a highly synchronous concerted mechanism. Rapid hydrolysis of the phosphorylated intermediate was observed by 31P NMR, leading to the formation of a non-toxic diester and regeneration of TAZ(-) as an authentic catalyst for the reaction. As indicated by computational calculations at the M06-2X/6- 311++G(d,p) level, equivalent nitrogens of the TAZ(-) (1 and 2) are the main nucleophilic center of the anion. Overall, the efficiency and selectivity of TAZ(-) was verified, acting as a detoxifying agent for organophosphates in aqueous medium. Results may instigate the projection of new catalysts for the efficient and rational degradation of organophosphate pesticides.