NOMENCLATURE
Common name isoxaflutole (BSI, E-ISO, (m) F-ISO) IUPAC name 5-cyclopropyl-1,2-oxazol-4-yl α,α,α-trifluoro-2-mesyl-p-tolyl ketone; 5-cyclopropyl-4-[2-methylsulfonyl-4-(trifluoromethyl)benzoyl]isoxazole
Chemical Abstracts name (5-cyclopropyl-4-isoxazolyl)[2-(methylsulfonyl)-4-(trifluoromethyl)phenyl]methanone CAS RN [141112–29–0] Smiles code CS(=O)(=O)c1cc(ccc1C(=O)c2cnoc2C3CC3)C(F)(F)F
PHYSICAL CHEMISTRY
Composition Tech. is c. 98% pure. Mol. wt. 359.3 M.f. C15H12F3NO4S Form Off-white or pale yellow solid. M.p. 140 °C V.p. 1 × 10-3 mPa (25 °C) Kow logP = 2.34 Henry 1.87 × 10-5 Pa m3 mol-1 (20 °C) S.g./density 1.42 (20 °C) Solubility In water 6.2 mg/l (pH 5.5, 20 °C). In acetone 293, dichloromethane 346, ethyl acetate 142, n-hexane 0.10, toluene 31.2, methanol 13.8 (all in g/l, 20 °C). Stability Stable to heat (14 d at 54 °C) and to light. Hydrolysis DT50 11 d (pH 5), 20 h (pH 7), 3 h (pH 9). Aqueous photolysis DT50 40 h.
APPLICATIONS
Biochemistry Rapidly metabolised in plants, and in the soil, by opening of the isoxazole ring, to form a diketonitrile, which is the active species (K. E. Pallett et al., Pest Manag. Sci., 2001, 57, 133, and refs. therein); this is a p-hydroxyphenyl pyruvate dioxygenase inhibitor. This enzyme converts p-hydroxyphenyl pyruvate to homogentisate, a key step in plastoquinone biosynthesis. Inhibition leads to indirect inhibition of carotenoid biosynthesis, giving rise to chlorosis of new growth.
Mode of action Systemic by either root or foliar uptake.
Uses Broad-spectrum grass and broad-leaved weed control in maize and sugar cane. Applied at 75–140 g/ha pre-emergence or pre-plant; the spectrum can be enhanced by mixture with other active ingredients.
Formulation types SC; WG; WP.
ANALYSIS
Residues in plants, soil or water by hplc/uv, gc/ms or lc/ms/ms (Resid. Anal. Methods; Environ. Chem. Methods).
ENVIRONMENTAL FATE
Animals Rapidly absorbed and metabolised in the rat, goat and hen, following oral administration. The main product eliminated in both urine and faeces in the rat and goat and in the excreta of the chicken was the diketonitrile metabolite. Elimination was relatively rapid in all three species, with very low to moderate levels of residues being found in the tissues, with the higher levels being located in the principal organs of metabolism and excretion. Plants Plant metabolism study demonstrated that residue levels at harvest are very low, and comprise mainly a non-toxic metabolite. Soil/Environment In laboratory soil studies, degradation proceeds via hydrolysis and microbial degradation, with final mineralisation to CO2. Mean DT50 (lab., aerobic, 20 °C) for isoxaflutole 2.3 d; for its biologically active diketonitrile metabolite 46 d. Mean field DT50 for isoxaflutole 1.3 d; for diketonitrile 11.5 d. Mean Koc for isoxaflutole 112 l/kg; for diketonitrile 109 l/kg. Isoxaflutole and its major metabolites are potentially mobile in soil under simulated high rainfall; however, field studies indicate that residues remain in the surface horizons; after 4 months, virtually no residues remain in the soil.
TOXICOLOGICAL & ENVIRONMENTAL REVIEWS
EU Rev. Rep. SANCO/3136/99, Apr. 2003. EPA Fact Sheet, Sep. 1998. EU Status (1107/2009) Approved, 2003/68/EC as amended by 2004/65/EC; proposed extension to 31 Jul 2016.
MAMMALIAN TOXICOLOGY
Oral Acute oral LD50 for rats >5000 mg/kg. Skin and eye Acute percutaneous LD50 for rabbits >2000 mg/kg. Not a skin irritant; minimal eye irritation (rabbits). Not a skin sensitiser. Inhalation LC50 (4 h) for rats >5.23 mg/l. NOEL (2 y) for rats 2 mg/kg daily. ADI (EC) 0.02 mg/kg b.w. [2003]; (EPA) cRfD 0.002 mg/kg [1998]. Other Non-mutagenic, non-neurotoxic. EPA (formulation) III EC classification R63| N; R50, R53
ECOTOXICOLOGY
Birds Acute oral LD50 (14 d) for quail and mallard ducks >2150 mg/kg; dietary LC50 (8 d) >5000 ppm. Fish LC50 (96 h) for rainbow trout >1.7, bluegill sunfish >4.5 ppm. Daphnia LC50 (48 h) >1.5 ppm. Algae EC50 for Selenastrum capricornutum 0.016 mg/l. Other aquatic spp. EC50 (96 h) for eastern oysters (Crassostrea virginica) 3.4 mg/l, mysid shrimps (Mysidopsis bahia) 18 μg/l. Bees LD50 (oral and contact) >100 μg/bee. Worms Non-toxic at 1000 mg/kg.
