Carfentrazone-ethyl

Triazolinone

NOMENCLATURE

Common name carfentrazone (BSI, E-ISO, (f) F-ISO, ANSI, for the carboxylic acid) IUPAC name ethyl (RS)-2-chloro-3-[2-chloro-5-(4-difluoromethyl-4,5-dihydro-3-methyl-5-oxo-1H-1,2,4-triazol-1-yl)-4-fluorophenyl]propionate
Chemical Abstracts name ethyl α,2-dichloro-5-[4-(difluoromethyl)-4,5-dihydro-3-methyl-5-oxo-1H-1,2,4-triazol-1-yl]-4-fluorobenzenepropanoate

CAS RN [128639–02–1] ethyl ester; [128621–72–7] acid

PHYSICAL CHEMISTRY
Composition ≥90% pure (EU Rev. Rep.). Mol. wt. 412.2 M.f. C15H14Cl2F3N3O3; C13H10Cl2F3N3O3 (acid) Form Very viscous yellow-orange liquid. M.p. –22.1 °C B.p. 350–355 °C/760 mmHg V.p. 1.6 × 10-2 mPa (25 °C); 7.2 × 10-3 mPa (20 °C) Kow logP = 3.36 Henry 2.47 × 10-4 Pa m3 mol-1 (20 °C, calc.) S.g./density 1.457 (20 °C) Solubility In water 12 μg/ml (20 °C), 22 μ;g/ml (25 °C), 23 μ;g/ml (30 °C). In toluene 0.9, hexane 0.03 (both in g/ml, 20 °C); miscible with acetone, ethanol, ethyl acetate and dichloromethane. Stability Hydrolytic DT50 3.6 h (pH 9), 8.6 d (pH 7), stable (pH 5). Aqueous photolytic DT50 8 d. F.p. 229 °C (SCC)

APPLICATIONS
Biochemistry Acts by inhibition of protoporphyrinogen oxidase, leading to membrane disruption. Mode of action Absorbed by foliage, with limited translocation. Uses Post-emergence control in cereals of a wide range of broad-leaved weeds, especially Galium aparine, Abutilon theophrasti, Ipomoea hederacea var. hederacea, Chenopodium album and several mustard species, at 9–35 g/ha. Also for desiccation of potatoes, at 60 g/ha. Phytotoxicity Good tolerance in wheat, barley and rice. Formulation types EC; SG; WG; WP; EW.

ENVIRONMENTAL FATE
Animals In rats, c. 80% of the administered dose is rapidly absorbed and excreted in the urine within 24 hours. The major metabolite was the corresponding acid. Further metabolism appears to involve oxidative hydroxylation of the methyl group or dehydrochlorination to form the corresponding cinnamic acid. Plants Rapidly converted to the free acid, which is hydroxylated and then oxidised at the triazolinone methyl to form the dibasic acid; DT50 (carfentrazone-ethyl) <7 d, DT50 (carfentrazone) <28 d. Soil/Environment Broken down in the soil by microbial action; not susceptible to photodecomposition or volatility following soil application. Strongly adsorbed to sterile soils (Koc 750±60 at 25 °C). In non-sterile soils, rapidly converted to the free acid, which has low soil binding (Koc 15–35 at 25 °C, pH 5.5). In the laboratory, soil DT50 is a few hours, degrading to the free acid, which in turn has DT50 2.5–4.0 d.

MAMMALIAN TOXICOLOGY
Oral Acute oral LD50 for female rats 5143 mg/kg. Skin and eye Acute percutaneous LD50 for rats >4000 mg/kg. Minimally irritating to eyes; non-irritating to skin (rabbits). No skin sensitisation (guinea pigs). Inhalation LC50 (4 h) for rats >5 mg/l. NOEL (2 y) for rats 3 mg/kg daily. ADI (EC) 0.03 mg/kg b.w. [2003]; (EPA) aRfD 5 mg/kg b.w., cRfD 0.03 mg/kg b.w. [1998]. Other Non-mutagenic in the Ames test. Toxicity class WHO (a.i.) III (company classification) EPA (formulation) III, IV EC classification N; R50, R53 

ECOTOXICOLOGY
Birds LD50 for bobwhite quail >2250 mg/kg. LC50 for mallard duck >5620 ppm. Fish LC50 (96 h) 1.6–43 mg/l, depending on species. Daphnia EC50 (48 h) 9.8 mg/l. Algae EC50 5.7–17 μg/l, depending on species. Other aquatic spp. EC50 (96 h) for eastern oysters 2.05, mysid shrimps 1.16 ppm. EC50 (14 d) for Lemna gibba 0.0057 mg/l. Bees LD50 (oral) >35 μg/bee; (contact) >200 μg/bee. Worms LC50 >820 mg/kg soil.