Reactivity of the Insecticide Chlorpyrifos-methyl towards hydroxyl and perhydroxyl anions. Effect of Cyclodextrins.

RAQUEL V. VICO; RITA H. DE ROSSI; ELBA I. BUJÁN

John Wiley & Sons, Ltd.

Año: 2009 vol. 22 p. 691 - 691

he reactivity of Chlorpyrifos-Methyl (1) toward hydroxyl ion and the alfa-nucleophile, perhydroxyl ion was investigated in aqueous basic media. The hydrolysis of 1 was studied at 25ºC 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 x 10-2 M-1 s-1 in 10% ACN and 1.70 x 10-2 M-1 s-1 in 7% 1,4-dioxane. The reaction with H2O2 was studied in a pH range from 9.14 to 12.40 in 7% 1,4-dioxane/H2O; the second-order rate constant for the reaction of HOO ion is 7.9 M-1 s-1 whereas neutral H2O2 does not compete as nucleophile. In all cases quantitative formation of 3,5,6-trichloro-2-pyridinol (3) was observed indicating an SN2(P) pathway. The hydrolysis reaction is inhibited by alfa-, beta-, and ganma-cyclodextrin showing saturation kinetics; the greater inhibition is produced by ganma-cyclodextrin. The reaction with hydrogen peroxide is weakly inhibited by alfa- and beta-cyclodextrin (beta-CD), whereas ganma-cycl