Mechanisms of Degradation of Paraoxon in Different Ionic Liquids

Abstract

Herein, the reactivity and selectivity of the reaction of O,O-diethyl 4-nitrophenyl phosphate triester (Paraxon, 1) with piperidine in ionic liquids (ILs), three conventional organic solvents (COS), and water is studied by (31)P NMR, UV-vis, and GC/MS. Three phosphorylated products are identified as follows: O,O-diethyl piperidinophosphate diester (2), O,O-diethyl phosphate (3), and O-ethyl 4-nitrophenyl phosphate diester (4). Compound 4 also reacts with piperidine to yield O-ethyl piperidinophosphate monoester (5). The results show that both the rate and products distribution of this reaction depend on peculiar features of ILs as reaction media and the polarity of COS.

The effect of the structure of the anion of an ionic liquid on the rate of reaction at a phosphorus centre

“…Based on Kamlet‐Taft parameters for the corresponding ionic liquids (Table ), this anion can be considered much more coordinating than the previous anions considered ([BF 4 ] − , [PF 6 ] − , and [(CF 3 SO 2 ) 2 N] − ). It is important to note that this ionic liquid 8 was the one that provided the largest rate constant enhancement in, and selectivity for, the S N 2@P pathway in the work of Pavez et al described earlier . As that work also considered nucleophilic attack onto an activated phosphorus species, it was anticipated that a similarly large increase in the rate constant for the ethanolysis of diethyl chlorophosphate 3 might be observed.…”

“…Early studies, whilst not including kinetic data, showed the control of nucleophilic attack of amines and water on phosphorus(III) chloride and subsequent application in preparative chemistry . Subsequently, detailed kinetic analysis of reactions of phosphorus compounds with nitrogen nucleophiles has been reported; Pavez et al considered the reactions of the activated phosphorus species 1 and 2 (Figure ) with amine nucleophiles . While these reactions are complicated—they can involve substitution at the phosphorus centre (S N 2@P), on the aromatic ring (S N Ar), and at the carbon centre adjacent to the oxygen on the ethyl chain (S N 2@C)—rate data were obtained for all of these pathways in a range of ionic liquids and molecular solvents.…”

“…The selectivity for the S N 2@P pathway also changes on moving from a molecular solvent to an ionic liquid, with ionic liquids all providing a higher selectivity for this pathway than the molecular solvents. Activation parameters measured for the reaction of the substrate 2 in representative ionic liquids suggest organisation about, and stabilisation of, the transition state, and kinetic behaviour suggests a change in mechanism in this case [14c] …”

“…Whilst the effect of the cation of the ionic liquid on the associated solvent effects on the reaction shown in Scheme has been investigated, how the structure of the anion might affect the reaction has not been considered. Such effects are worth considering as they allow further solvent design with different interactions that might be introduced; these have been shown to be important in determining such solvent effects previously including particularly in reactions at phosphorus centres . As such, the work described herein investigates how varying the structure of the anion of an ionic liquid can affect the outcome of this reaction.…”

The α-Effect in SNAr Reaction of 1-Fluoro-2,4-dinitrobenzene with Hydrazine: Ground-State Destabilization versus Transition-State Stabilization

“…Aminolysis of carboxylic esters has been reported to proceed through a concerted mechanism or via a stepwise pathway with one or two intermediates (e.g., a zwitterionic tetrahedral intermediate T ± and its deprotonated form T -) depending on the reaction conditions. [13][14][15][16] Reaction of 2,4-dinitrophenyl benzoate with a series of cyclic secondary amines has been reported to proceed through a stepwise mechanism with a change in rate-determining step (RDS) in H 2 O containing 20 mol % DMSO on the basis of a curved Brønsted-type plot 15a but via a concerted mechanism in MeCN on the basis of a linear Brønsted-type plot with β nuc = 0.40.…”