Herbicide Clomazone

NOMENCLATURE Clomazone

Common name clomazone (BSI, ANSI, draft E-ISO, (f) draft F-ISO)

IUPAC name 2-(2-chlorobenzyl)-4,4-dimethyl-1,2-oxazolidin-3-one; 2-(2-chlorobenzyl)-4,4-dimethylisoxazolidin-3-one 

Chemical Abstracts name 2-[(2-chlorophenyl)methyl]-4,4-dimethyl-3-isoxazolidinone 

Other names dimethazone* CAS RN [81777-89-1] Development codes FMC 57 020 

PHYSICAL CHEMISTRY Clomazone

Mol. wt. 239.7 M.f. C₁₂H₁₄ClNO₂ Form Clear, colourless to light brown, viscous liquid. M.p. 25 ºC B.p. 275 ºC V.p. 19.2 mPa (25 ºC) K_OW logP = 2.5 Henry 4.19 ´ 10^-3 Pa m³ mol^-1 S.g./density 1.192 (20 ºC) Solubility In water 1.1 g/l. Miscible with acetone, acetonitrile, chloroform, cyclohexanone, dichloromethane, methanol, toluene, heptane, dimethylformamide. Stability Stable at ambient temperatures for at least 2 y; stable at 50 ºC for at least 3 mo. In sunlight, DT₅₀ >30 d in aqueous solution. F.p. 70-75 ºC (closed cup) 

APPLICATIONS Clomazone

Biochemistry Inhibits carotenoid biosynthesis; target enzyme not known. Mode of action Selective herbicide, absorbed by the roots and shoots and translocated upward. Susceptible species emerge but are devoid of pigmentation. Uses Control of broad-leaved and grass weeds in soya beans, peas, maize, oilseed rape, sugar cane, cassava, pumpkins, and tobacco. Applied pre-emergence or pre-plant incorporated. Phytotoxicity Foliar contact or vapours may cause visual symptoms of chlorosis to nearby sensitive plants. Formulation types CS; EC; WP. Compatibility Compatible with many other herbicides, e.g. metribuzin, linuron, chloramben, alachlor, trifluralin, pendimethalin, metolachlor, oryzalin or ethalfluralin. Selected tradenames: 'Command' (FMC); mixtures: 'Commence' (+ trifluralin) (FMC); 'Brasan' (+ dimethachlor) (Syngenta); 'Cozor Trio' (+ dimethachlor+ napropamide) (Syngenta)

MAMMALIAN TOXICOLOGY Clomazone

Oral Acute oral LD₅₀ for male rats 2077, female rats 1369 mg/kg. Skin and eye Acute percutaneous LD₅₀ for rabbits >2000 mg/kg. Practically non-irritating to eyes (rabbits). Inhalation LC₅₀ (4 h) for rats 4.8 mg/l. NOEL (2 y) for rats 4.3 mg/kg daily. ADI 0.043 mg/kg (proposed). Toxicity class WHO (a.i.) II; EPA (formulation) III 

ECOTOXICOLOGY Clomazone

Birds Acute oral LD₅₀ for bobwhite quail and mallard ducks >2510 mg/kg. LC₅₀ (8 d) for bobwhite quail and mallard ducks >5620 ppm. Fish LC₅₀ (96 h) for bluegill sunfish 34, Atlantic silverside 6.26, rainbow trout 19 mg/l. Daphnia LC₅₀ (48 h) 5.2 mg/l. Algae EC₅₀ (48 h) 2.10 mg/l. Other aquatic spp. LC₅₀ for pink shrimp 8.9, eastern oyster 5.3 mg/l. Worms LC₅₀ (14 d) for Eisenia foetida 156 mg/kg. 

ENVIRONMENTAL FATE Clomazone

Soil/Environment DT₅₀ in soil c. 30-135 d. K_oc 150-562, suggesting clomazone would be mobile in soil; however, in field trials it was found not to leach beyond the top 10 cm of soil (J. Rosenwald et al., Proc. 9th IUPAC Int. Congr. Pestic. Chem., London, 1998, 6A-006).