Kinetics of abiotic hydrolysis of isoxaflutole: influence of pH and temperature in aqueous mineral buffered solutions.
A kinetic study of the chemical hydrolysis of isoxaflutole [5-cyclopropyl-4-(2-methanesulfonyl-4-trifluoromethylbenzoyl)is oxazol e (IFT)], a new herbicide recently developed by Rhône-Poulenc Agro, in buffered, sterile aqueous solutions was carried out in the dark at 295, 308, and 323 K and at nine pH values between 1.8 and 10.1. Samples were analyzed by HPLC-UV. The decrease in IFT concentration was accompanied by an increase in the concentration of its diketonitrile derivative (DKN). Obeying pseudo-first-order kinetics, isoxaflutole hydrolysis increased with increasing pH and temperature: for 295 K and pH 9.3 the rate of degradation was 100-fold faster than at pH 3.8. Using the Arrhenius equation, the rate constants K(obsd), activation energies E(a), and entropies DeltaS() were calculated, and plotting log(K(obsd)) against pH showed that the effect of pH varied with temperature. According to DeltaS() values the mechanism of the reaction was found to be different with respect to pH range. The benzoic acid derivative, known as a degradation product of DKN in plants, was not detected in the present study.
Beltran
E
E
Laboratoire de Chimie Analytique, Faculté de Pharmacie, 15 avenue Ch. Flahault, 34060 Montpellier, France.
Fenet
H
H
Cooper
J F
JF
Coste
C M
CM
D002021:Buffers; D006540:Herbicides / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007555:Isoxazoles / Q000737:chemistry*; D007700:Kinetics; D012996:Solutions; D013696:Temperature
D002021:Buffers; D006540:Herbicides; D007555:Isoxazoles; D012996:Solutions; C415327:isoxaflutole