NOMENCLATURE

fenoxaprop-P-ethyl

Chemical Abstracts name ethyl (R)-2-[4-[(6-chloro-2-benzoxazolyl)oxy]phenoxy]propanoate 

CAS RN [71283-80-2]  Development codes Hoe 046360 (Hoechst); AE F046360 (AgrEvo) 

PHYSICAL CHEMISTRY

Mol. wt. 410.4  M.f. C₁₅H₁₈N₆O₆S  Form Colourless to light tan, odourless crystals.  M.p. 194 ºC  V.p. 7.73 ´ 10^-10 mPa (25 ºC)  K_OW logP = 0.89 (pH 7), 1.588 (pH 5)  Henry 6.34 ´ 10^-12 Pa m³ mol^-1 (calc.)  S.g./density 1.6  Solubility In water 50 mg/l (pH 7, 25 ºC). In acetone 1.6, acetonitrile 0.8, ethanol 0.17, methanol 0.35, methylene chloride 3.9, ethyl acetate 0.68 (all in g/l).  Stability Stable at pH 7 and pH 9. Hydrolysis occurs more rapidly at pH 5, DT₅₀ 45 d. Photolysis is not a major degradation pathway. Acidic in reaction.  pKa 4.6 

APPLICATIONS

Biochemistry Branched chain amino acid synthesis (ALS or AHAS) inhibitor. Acts by inhibiting biosynthesis of the essential amino acids valine and isoleucine, hence stopping cell division and plant growth. Selectivity derives from rapid metabolism in the crop. Metabolic basis of selectivity in sulfonylureas reviewed (M. K. Koeppe & H. M. Brown, Agro-Food-Industry, 6, 9-14 (1995)).  Uses Post-emergence control of wild mustard, hempnettle and other broad-leaved weeds in oilseed rape, at 15-20 g/ha.  Formulation types WG. 

ANALYSIS

By hplc. Methods for sulfonylurea residues in crops, soil and water reviewed (A. C. Barefoot et al., Proc. Br. Crop Prot. Conf. - Weeds, 1995, 2, 707). 

MAMMALIAN TOXICOLOGY

Oral Acute oral LD₅₀ for rats >11 000, rabbits >5000 mg/kg.  Skin and eye Acute percutaneous LD₅₀ for rabbits >2000 mg/kg. Non-irritating to skin; slightly irritating to eyes (rabbits). Non-sensitising to skin (guinea pigs).  Inhalation LC₅₀ (4 h) for rats >5.7 mg/l air.  NOEL (90 d) for rats and mice 5000 ppm; (1 y) for rats 500, dogs 3000 ppm; (18 mo) for mice 5000 ppm. Non-oncogenic and non-mutagenic in rats. Non-teratogenic in rats and rabbits.  Toxicity class WHO (a.i.) Table 5; EPA (formulation) Not registered in US 

ECOTOXICOLOGY

Birds Acute oral LD₅₀ for bobwhite quail and mallard ducks >2250 mg/kg. Dietary LC₅₀ (5 d) for bobwhite quail and mallard ducks >5620 mg/kg diet.  Fish LC₅₀ (96 h) for bluegill sunfish and rainbow trout >600 mg/l.  Daphnia LC₅₀ (48 h) 34 mg/l.  Bees Acute toxicity to honeybees >12.5 mg/bee.  Worms Contact LD₅₀ (14 d) for earthworms >1000 mg/kg soil. 

ENVIRONMENTAL FATE

Animals Ethametsulfuron-methyl administered to male and female rats was rapidly metabolised and excreted in the urine and faeces. Half-lives for excretion range from 12 hours in male rats to 21-26 hours in female rats. Less than 0.2% of the dose remains in the tissues five days after dosing at the highest dose level. No preferential accumulation of ethametsulfuron-methyl or its metabolites.  Plants Oilseed rape was treated with 30 g/ha ethametsulfuron-methyl in a glasshouse: total radiolabelled residues in the foliage decreased rapidly from c. 1.0 ppm immediately after treatment to 0.02 ppm after 31 days; DT₅₀ 1-3 h. Two primary metabolites were identified, formed by successive dealkylation; firstly of the ethoxy group, to give the corresponding hydroxytriazine, then of the methylamino substituent. Total radioactive residue in mature oilseed rape was very low (0.008 to 0.012 ppm). No ethametsulfuron-methyl was detected in the seed.  Soil/Environment Soil metabolism (aerobic, lab.) DT₅₀ 9 w; three major metabolites were identified. In soil photolysis studies, sunlight accelerated degradation three-fold relative to dark controls. Aquatic metabolism (aerobic) DT₅₀ 6 mo, (anaerobic) DT₅₀ 2-9 mo, depending on sediment pH. In laboratory soil mobility studies based on soil TLC, soil column leaching, and adsorption/desorption studies, mobility is highly dependent on soil characteristics, primary organic matter content and soil pH. Mobility ranges from very mobile in sandy loam soil to very low mobility in loam soil.