Kinetics of chemical degradation of isoxaflutole: influence of the nature of aqueous buffers (alkanoic acid/sodium salt vs phosphate)

• Published in: Pest management science Vol. 57; no. 4; pp. 366 - 371
• Main Authors: Beltran, Estelle, Fenet, Hélène, Cooper, Jean-François, Coste, Camille-Michel
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 01.04.2001; Wiley
• Subjects: Agronomy. Soil science and plant productions; analysis; aqueous solutions; basic catalysis; Biodegradation, Environmental; Biological and medical sciences; Buffers; Carboxylic Acids; Carboxylic Acids - chemistry; Cathartics; Cathartics - chemistry; chemical degradation; chemistry; diketonitrile derivative; Fundamental and applied biological sciences. Psychology; general catalysis; herbicides; Herbicides - analysis; Herbicides - chemistry; Hydrogen-Ion Concentration; isoxaflutole; Isoxazoles; Isoxazoles - analysis; Isoxazoles - chemistry; new products; Phosphates; Phosphates - chemistry; Potassium Compounds; Potassium Compounds - chemistry; Sodium Bicarbonate; Sodium Bicarbonate - chemistry; Soil and water pollution; Soil science; Water; Substituent effect; General base catalysis; Isoxazole derivatives; Pollutant behavior; Pesticides; Acetate; Chemical degradation; Buffer solution; Herbicide; Chemical reaction kinetics; Benzoic acid derivatives; Sodium Hydrogenphosphates; Potassium Dihydrogenphosphates; Ionic strength; Aqueous medium; Environment impact; Concentration effect; Alkanoic acid; Position effect; Degradation product; Chemical weed control
• ISSN: 1526-498X; 1526-4998
• DOI: 10.1002/ps.300

A kinetic study of the chemical degradation of isoxaflutole (5‐cyclopropyl‐1,2‐oxazol‐4‐yl ααα‐trifluoro‐2‐mesyl‐p‐tolyl ketone) into its diketonitrile derivative (DKN), which is its active herbicide principle, in organic buffers at different pH values was carried out using a HPLC/UV detection method. The values of the pseudo‐first‐order rate constants Kobs for the reaction were calculated and compared with those previously obtained in inorganic buffers. In both cases, Kobs was found to be dependent on pH and temperature, but at pH 5.2 the degradation of isoxaflutole in CH3COOH/CH3COONa buffers was considerably faster than in KH2PO4/Na2HPO4 buffers, indicating that the compound was sensitive to the nature of the reagents used to prepare buffered solutions. The influence of phosphate and acetate concentrations and the influence of the R‐substituent in RCOOH/RCOONa buffers were investigated. For the HA/A− buffers studied, the values of Kobs were linearly dependent on HA and A− concentrations, which meant that the degradation of isoxaflutole was subject to general catalysis. The values of Kobs were also found to be dependent on the number and the position of the CH3 groups of the R‐substituent. The known degradation product of DKN (a benzoic acid derivative) was not detected throughout this study. © 2001 Society of Chemical Industry