Detoxificação de compostos organofosforados promovida por formamida e 1,2,3-triazol: mecanismos e influência do meio reacional

Abstract

Obsolete stocks of organophosphorus pesticides (Ops) became a global concern due to the severe impact caused on human health and the environment. Thus, exploring efficient detoxifying processes of such compounds is of great interest. In that nucleophilic organocatalysis has been promising for the development of aforementioned processes, it is strategic to understand (I) the reactivity of small nucleophilic scaffolds and (II) the influence of reaction medium in the breakdown of Ops. In this work, I is explored by investigating the reactivity of 1,2,3-triazole anion (3TAZ) towards the breakdown of Paraoxon, whereas the solvolysis of O,O-diethyl- 2,4-dinitrophenyl phosphate (DEDNPP) promoted by formamide (FMD) is proposed to explore II. Systems were evaluated by means of spectrophotometric kinetic studies, 31P nuclear magnetic resonance analyses, and computational calculations mainly at the M06-2x/6-31+G(d,p) level of theory. Regarding I, three plausible nucleophilic pathways were considered: via aliphatic carbon alkylating the nucleophile, via nucleophilic aromatic substitution, and the desired pathway via P–O bond break leading to non-toxic diester after the hydrolysis of the phosphorylated-3TAZ (INT) intermediate. Interestingly, kinetic studies revealed that the breakdown of Paraoxon proceeds exclusively via phosphorus atom — rate enhancements of 2.2 x 102 were observed compared to the neutral hydrolysis of the OP. Calculation results are in agreement with experimental evidence, indicating that the pathway P–O bond cleavage presents the lowest energy barrier compared to the additional channels, although alkaline medium is required to complete the catalytic cycle. Regarding II, regiospecific nucleophilic amidolysis via P–O bond cleavage is observed, leading to non-toxic diester and FMD regeneration. Curiously, water plays antagonistic behavior: while it is key for the breakdown of the reaction intermediate, it inhibits the nucleophilic activity of FMD by hydrogen bonding effects.