Are Imidazoles Versatile or Promiscuous in Reactions With Organophosphates? Insights From the Case of Parathion

Abstract

Is the broad mechanistic versatility of imidazole towards organophosphates (OPs), that has inspired many catalysts and sensors, beneficial? Herein, a thorough analysis is given seeking to unravel this puzzle. For OPs from the P=O family, imidazole attacks the phosphorus atom exclusively (N-phosphorylates). With the P=S family which are less reactive, an unusual N-alkylation predominates. Surprisingly, imidazole reacts with methyl parathion exclusively at the aliphatic carbon, whilst for the ethylated analogue parathion, imidazole reacts by two pathways: at both the phosphorus and aliphatic carbon, with predominance for the latter. The preference for the electrophilic center can be modulated by the pH. Overall, a mechanistic structure-related trend is observed: imidazole tends to prefer other electrophilic centers than the phosphorus for less reactive OPs. Moreover, this gives important insights concerning the challenging chemistry of imidazole alkylation and the outcomes for monitoring systems that depend on the detection of degradation products. Finally, a thorough comparison with the literature is presented seeking to understand how imidazole reacts towards various OPs. We suggest that the promiscuity of imidazole boosts up its versatility.

Nucleophilic Neutralization of Organophosphates: Lack of Selectivity or Plenty of Versatility?

“…[63] Another study investigated the reaction kinetics of IMZ with Parathion and Methyl parathion in aqueous solution by NMR, mass spectrometry, kinetics and theoretical calculations. [64,65] In these cases, the kinetics followed by UV-vis spectroscopy present unexpected results (Figure 17), since the expected Red lines represent fitting between kinetic data and Catalan's paramethers [62] using multiple regression. B. TSSs and energy barriers (kcal mol À 1 ) for the reactions of both tautomers of 4(5) HMZ with DEDNPP obtained at B3LYP/6-31 + G(d, p) level of theory.…”

“…By another perspective, the neutralization process of unwanted stockpiles of Methyl parathion, for example, can be used as a source for synthesizing alkylimidazoles. [65] Table 1 presents a summary of the results for the reactions of IMZ with the family of Parathion and Paraoxon. According to the results we could rationalize that methyl group and sulfur atom drive the reaction to the aliphatic group and the oxygen [65] and (c) Paraoxon (pH 8.98; 25 °C) [55] with IMZ in aqueous solution.…”

“…[65] Table 1 presents a summary of the results for the reactions of IMZ with the family of Parathion and Paraoxon. According to the results we could rationalize that methyl group and sulfur atom drive the reaction to the aliphatic group and the oxygen [65] and (c) Paraoxon (pH 8.98; 25 °C) [55] with IMZ in aqueous solution. Partially reproduced with permission from ref [65].…”

“…Summary of some reactions of IMZ with P=O and P=S organophosphates. [55,56,64,65] and ethyl group drive the reaction to the phosphorus atom. These results are extremely enlightening since they show how promiscuous and versatile the IMZ can be, as well as the organophosphate.…”

Enhancement of organophosphate degradation by electroactive pyrrole and imidazole copolymers

“…Among different catalysts, materials based on imidazole (IMZ) and its derivatives have shown excellent behavior in the detoxification of OPs [19], biomimicking the histidine imidazole in the protein phosphorylation [20,21]. The histidine imidazole in protein enzymes is the most versatile catalytic group, with a pKa near 7, it can act as an acid, base or nucleophilic catalyst [22,23]. Several studies confirmed that cleavage of phosphate esters can be catalyzed by the presence of IMZ, with catalytic increments around 10 5 -fold [10,14,22], combined with the advantages of complete regeneration of the initial catalyst and formation of less toxic compounds.…”