Herbicide
HRAC  F2 WSSA  28; triketone



NOMENCLATURE
Common name mesotrione (BSI, pa ISO)
IUPAC name 2-(4-mesyl-2-nitrobenzoyl)cyclohexane-1,3-dione 
Chemical Abstracts name 2-[4-(methylsulfonyl)-2-nitrobenzoyl]-1,3-cyclohexanedione 
CAS RN [104206-82-8]  Development codes ZA 1296 (Zeneca)

PHYSICAL CHEMISTRY
Mol. wt. 339.3  M.f. C₁₄H₁₃NO₇S  M.p. 165 °C  V.p. 5.69 × 10^-3 mPa (20 °C).  Solubility In water 2.2 (pH 4.8), 15 (pH 6.9), 22 (pH 9) (all in g/l, 20 °C).  Stability Stable to hydrolysis (pH 4 - 9).  pKa 3.12

APPLICATIONS
Biochemistry p-Hydroxyphenyl pyruvate dioxygenase inhibitor, which ultimately affects carotenoid biosynthesis. Selectivity in maize derives from differential metabolism.  Mode of action Uptake is foliar and via the root, with both acropetal and basipetal translocation. Symptoms are whitening of leaves, followed by necrosis of the meristematic tissue.  Uses Under development for pre- (at 100-225 g/ha) and post- (at 70-150 g/ha) emergence control of broad-leaved weeds, such as Xanthium strumarium, Ambrosia trifida, Abutilon theophrasti, and Chenopodium, Amaranthus and Polygonum spp., and some grass weeds, in maize.  Formulation types SC.

MAMMALIAN TOXICOLOGY
Oral Acute oral LD₅₀ for male and female rats >5000 mg/kg.  Skin and eye Acute percutaneous LD₅₀ for male and female rats >2000 mg/kg.  Inhalation LC₅₀ >5 mg/l. 

ECOTOXICOLOGY
Birds Acute oral LD₅₀ for bobwhite quail >2000, mallard ducks >5200 mg/kg.  Fish LC₅₀ (96 h) for bluegill sunfish and rainbow trout >120 mg/l. 

ENVIRONMENTAL FATE
Soil/Environment Stable to hydrolysis under sterile conditions at pH 5-9, with <10% degradation after 30 d (25 °C). Aqueous photolysis DT₅₀ (sterile) 84 d. Soil adsorption is significantly influenced by pH and % o.c; K_oc 387 (soil pH 4.6) to 19 (pH 7.7); K_d is linear with % o.c and ranges from 1-5. Degradation is influenced by soil pH; DT₅₀ 31.5 d (pH 5.0, % o.c. 2.0) to 4.0 d (pH 7.7, % o.c. 0.9). Environmental fate may be determined by soil pH and half-life as the only important parameters. See R. A. Wichert et al., Proc. Br. Crop Prot. Conf. - Weeds, 1999, 1, 105; and J. Dyson et al., Proc. 9th IUPAC Int. Congr. Pestic. Chem., London, 1998, 2, 6A-021.