NOMENCLATURE

Common name diflufenican (BSI, draft E-ISO, (m) draft F-ISO); diflufenicanil ((m) France)

IUPAC name 2',4'-difluoro-2-(a,a,a-trifluoro-m-tolyloxy)nicotinanilide 

Chemical Abstracts name N-(2,4-difluorophenyl)-2-[3-(trifluoromethyl)phenoxy]-3-pyridinecarboxamide 

Other names DFF  CAS RN [83164-33-4]  Development codes M&B 38 544 (May & Baker) 

PHYSICAL CHEMISTRY

Composition ³97% pure.  Mol. wt. 394.3  M.f. C₁₉H₁₁F₅N₂O₂  Form Colourless crystals.  M.p. 159-161 °C  V.p. 4.25 ´ 10^-3 mPa (25 °C, gas saturation method)  K_OW logP = 4.9  Henry 0.033 Pa m³ mol^-1  Solubility In water <0.05 mg/l (25 ºC). Soluble in most organic solvents, e.g. acetone, dimethylformamide 100, acetophenone, cyclohexanone 50, isophorone 35, xylene 20, cyclohexane, 2-ethoxyethanol, kerosene <10 (all in g/kg, 20 ºC).  Stability Stable in air up to melting point. At 22 ºC, very stable in aqueous solution at pH 5, 7 and 9. Fairly stable to photolysis.

COMMERCIALISATION

History Herbicide reported by M. C. C. Ramp et al. (Proc. Br. Crop Prot. Conf. - Weeds, 1985, 1, 23) and by C. F. A. Kyndt et al. (ibid., p. 29). Introduced by May & Baker Ltd (now Aventis CropScience).  Patents EP 53011 

APPLICATIONS

Biochemistry Blocks carotenoid biosynthesis, by inhibition of phytoene desaturase.  Mode of action Selective contact and residual herbicide, absorbed principally by the shoots of germinating seedlings, with limited translocation.  Uses Applied at 125-250 g/ha pre- or early post-emergence in autumn-sown wheat and barley, to control grass and broad-leaved weeds, particularly Galium, Veronica and Viola spp. Normally used in combination with isoproturon or other cereal herbicides.  Phytotoxicity Any slight phytotoxicity is in the form of small transient patches on basal leaves, with no adverse effect on crop development.  Formulation types SC; WP. 

ANALYSIS

Methods have been developed to determine residues in plants and soil (J. Agric. Food Chem. 1991, 39(5), 968-76). 

MAMMALIAN TOXICOLOGY

Reviews Proc. Br. Crop Prot. Conf. - Weeds, 1985, 1, 23-28.  Oral Acute oral LD₅₀ for rats >2000, mice >1000, rabbits >5000 mg/kg.  Skin and eye Acute percutaneous LD₅₀ for rats >2000 mg/kg. Non-irritating to skin and eyes (rabbits).  Inhalation LC₅₀ (4 h) for rats >2.34 mg/l air.  NOEL In 14 d sub-acute trials in rats, no adverse effect observed at 1600 mg/kg b.w. In 90 d feeding trials, NOEL for dogs was 1000 mg/kg b.w. daily, for rats 500 ppm diet.  Other Non-mutagenic in the Ames test.  Toxicity class WHO (a.i.) III (Table 5)  EC hazard R52, R53 

ECOTOXICOLOGY

Birds Acute oral LD₅₀ for quail >2150, mallard ducks >4000 mg/kg.  Fish LC₅₀ (96 h) for rainbow trout 56-100, carp 105 mg/l.  Daphnia LC₅₀ (48 h) - no effect at 10 mg/l.  Algae No growth inhibition of algae (96 h) at 10 mg/l.  Bees Non-toxic by ingestion or contact.  Worms Non-toxic to earthworms. 

ENVIRONMENTAL FATE

Plants In cereals, rapidly metabolised via the nicotinamide and nicotinic acid to CO₂. Following pre-emergence application in autumn, no residues are detectable in the grain and straw after c. 200-250 days.  Soil/Environment In soil, degradation proceeds via the metabolites 2-(3-trifluoromethylphenoxy)nicotinamide and 2-(3-trifluoromethylphenoxy)nicotinic acid to bound residues and CO₂. Half-life varies from 15 to 30 weeks, depending on soil type and water content.