Herbicide

HRAC  E WSSA  14; diphenyl ether

NOMENCLATURE

fomesafen

Common name fomesafen (BSI, draft E-ISO, ANSI); fomésafène ((m) draft F-ISO)

IUPAC name 5-(2-chloro-a,a,a-trifluoro-p-tolyloxy)-N-methylsulfonyl-2-nitrobenzamide 

Chemical Abstracts name 5-[2-chloro-4-(trifluoromethyl)phenoxy]-N-(methylsulfonyl)-2-nitrobenzamide 

CAS RN [72178-02-0]  EEC no. 276-439-9  Development codes PP021 (ICI) 

PHYSICAL CHEMISTRY

fomesafen

Mol. wt. 438.8  M.f. C15H10ClF3N2O6S  Form White crystals.  M.p. 219 °C  V.p. <4 ´ 10-3 mPa (20 °C)  KOW logP = 2.9 (pH 1), <2.2 (pH 4-10)  Henry <2 ´ 10-7 Pa m3 mol-1 (pH 7, 20 °C)  S.g./density 1.61 (20 °C)  Solubility In pure water c. 50, <10 (pH 1-2), 10 000 (pH 9) (all in mg/l, 20 ºC).  Stability Stable in storage for at least 6 months at 50 ºC. Decomposed by light. Stable at pH 3 and 11 (40 °C). Stable to aqueous photolysis for 32 d (pH 7, 25 °C).  pKa 2.83 (20 ºC); forms water-soluble salts (e.g. fomesafen-sodium) 

fomesafen-sodium

Mol. wt. 460.7  M.f. C15H9ClF3N2NaO6S 

COMMERCIALISATION

History Herbicide reported by S. R. Colby et al. (Proc. Int. Congr. Plant Prot., 10th, 1983, 1, 295). Introduced by ICI Plant Protection Division (now Syngenta AG).  Patents EP 3416  Manufacturers Syngenta

APPLICATIONS

Biochemistry Protoporphyrinogen oxidase inhibitor.  Mode of action Selective herbicide, absorbed by both leaves and roots, with very limited translocation in the phloem.  Uses Early post-emergence control of broad-leaved weeds in soya beans. Applied at 200-400 g/ha.  Phytotoxicity Non-phytotoxic to soya beans and to other crops such as beans of the genus Phaseolus and the leguminous cover crops Pueraria and Calapogonium.  Formulation types SL.  Selected tradenames: 'Flex' (Syngenta); 'Flexstar' (Syngenta); 'Reflex' (Syngenta)

OTHER TRADENAMES

fomesafen-sodium

Mixtures: 'Fusiflex' (+ fluazifop-P-butyl) (Syngenta); 'Reflex T' (+ terbutryn) (Syngenta); 'Tornado' (+ fluazifop-P-butyl) (Syngenta); 'Twister' (+ fenoxaprop-P-ethyl+ fluazifop-P-butyl) (Syngenta); 'Typhoon' (+ fluazifop-P-butyl) (Syngenta)

ANALYSIS

Product analysis by hplc with u.v. detection. Residue analysis in soil by hplc; in crops by tlc, hplc or nmr. Details available from Syngenta. 

MAMMALIAN TOXICOLOGY

fomesafen

Oral Acute oral LD50 for male rats 1250-2000, female rats 1600 mg/kg.  Skin and eye Acute percutaneous LD50 for rabbits >1000 mg/kg. Mild skin irritant; mild to moderate eye irritant (rabbits). Extreme skin sensitiser (Magnusson & Kligman test), not a skin sensitiser (ear/flank Stevens test, guinea pigs).  Inhalation LC50 (4 h) for male rats 4.97 mg/l.  NOEL (2 y) for rats 5 mg/kg b.w. daily; (18 mo) for mice 1 mg/kg b.w. daily (liver tumours in mice due to peroxisome proliferation - not relevant to man); (6 mo) for dogs 1 mg/kg b.w. daily. NOEL developmental toxicity for rabbits 2.5 mg/kg b.w. daily.  ADI 0.05 mg/kg.  Other Genotoxicity negative. Not oncogenic.  Toxicity class WHO (a.i.) III; EPA (formulation) III  EC hazard Xn; R22 

fomesafen-sodium

Oral Acute oral LD50 for male rats 1860, female rats 1500 mg/kg.  Skin and eye Acute percutaneous LD50 for rabbits >780 mg/kg.  Other Not oncogenic. 

ECOTOXICOLOGY

fomesafen

Birds Acute oral LD50 for mallard ducks >5000 mg/kg. Dietary LC50 (5 d) for mallard ducks and bobwhite quail >20 000 mg/kg.  Fish LC50 (96 h) for rainbow trout 170, bluegill sunfish 1507 mg/l.  Daphnia EC50 (48 h) 0.33 g/l.  Algae EC50 170 mg/l.  Bees Low oral and contact toxicity to bees. LD50 (oral) ³50 mg/bee; (contact) ³100 mg/bee.  Worms LC50 (14 d) >1000 mg/kg. 

ENVIRONMENTAL FATE