Premium
Reactivity of the insecticide chlorpyrifos‐methyl toward hydroxyl and perhydroxyl ion. Effect of cyclodextrins
Author(s) -
Vico Raquel V.,
de Rossi Rita H.,
Buján Elba I.
Publication year - 2009
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.1502
Subject(s) - chemistry , cyclodextrin , reactivity (psychology) , reaction rate constant , nucleophile , medicinal chemistry , hydrogen peroxide , hydrolysis , kinetics , aqueous solution , substrate (aquarium) , reaction rate , organic chemistry , catalysis , medicine , physics , alternative medicine , oceanography , pathology , quantum mechanics , geology
The reactivity of Chlorpyrifos‐Methyl ( 1 ) toward hydroxyl ion and the α ‐nucleophile, perhydroxyl ion was investigated in aqueous basic media. The hydrolysis of 1 was studied at 25 °C in water containing 10% ACN or 7% 1,4‐dioxane at NaOH concentrations between 0.01 and 0.6 M ; the second‐order rate constant is 1.88 × 10 −2 M −1 s −1 in 10% ACN and 1.70 × 10 −2 M −1 s −1 in 7% 1,4‐dioxane. The reaction with H 2 O 2 was studied in a pH range from 9.14 to 12.40 in 7% 1,4‐dioxane/H 2 O; the second‐order rate constant for the reaction of HOO − ion is 7.9 M −1 s −1 whereas neutral H 2 O 2 does not compete as nucleophile. In all cases quantitative formation of 3,5,6‐trichloro‐2‐pyridinol ( 3 ) was observed indicating an S N 2(P) pathway. The hydrolysis reaction is inhibited by α ‐, β ‐, and γ ‐cyclodextrin showing saturation kinetics; the greater inhibition is produced by γ ‐cyclodextrin. The reaction with hydrogen peroxide is weakly inhibited by α ‐ and β ‐cyclodextrin ( β ‐CD), whereas γ ‐cyclodextrin produces a greater inhibition and saturation kinetics. The kinetic data obtained in the presence of β ‐ or γ ‐cyclodextrin for the reaction with hydroxyl or perhydroxyl ion indicate that the main reaction pathway for the cyclodextrin‐mediated reaction is the reaction of HO − or HOO − ion with the substrate complexed with the anion of the cyclodextrin. The inhibition is attributed to the inclusion of the substrate with the reaction center far from the ionized secondary OH groups of the cyclodextrin and protected from external attack of the nucleophile. Sucrose also inhibits the hydrolysis reaction but the effect is independent of its concentration. Copyright © 2008 John Wiley & Sons, Ltd.