NOMENCLATURE

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

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)

COMMERCIALISATION

History Herbicide introduced by FMC Corp.  Patents US 4405357  Manufacturers FM

APPLICATIONS

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. 

ANALYSIS

Product by gc with FID or hplc with u.v. detection. Details and residue methods reviewed (A. W. Chen in Comp. Anal. Profiles, Chapt. 6). 

MAMMALIAN TOXICOLOGY

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

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

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).