Herbicide

HRAC  B WSSA  2; sulfonylurea

NOMENCLATURE

Common name chlorsulfuron (BSI, draft E-ISO, (m) draft F-ISO, ANSI, WSSA)

IUPAC name 1-(2-chlorophenylsulfonyl)-3-(4-methoxy-6-methyl-1,3,5-triazin-2-yl)urea 

Chemical Abstracts name 2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl]benzenesulfonamide 

CAS RN [64902-72-3]  EEC no. 265-268-5  Development codes DPX 4189 (Du Pont); W4189 

PHYSICAL CHEMISTRY

Mol. wt. 357.8  M.f. C12H12ClN5O4S  Form White crystalline solid.  M.p. 174-178 °C  V.p. 3 ´ 10-6 mPa (25 ºC)  KOW logP = -0.99 (pH 7)  Henry 3.0 ´ 10-9 Pa m3 mol-1  S.g./density 1.48  Solubility In water 587 ppm (pH 5), 3.18 g/100g (pH 7) (both 25 ºC). In dichloromethane 1.4, acetone 4, methanol 15, toluene 3, hexane <0.01 (all in g/l, 20 ºC).  Stability Stable to light when dry. Decomposes at 192 ºC. In aqueous solutions, DT50 4-8 w (pH 5.7-7.0, 20 ºC); significant degradation in 24-48 h (pH <5). Hydrolysis is also promoted by polar organic solvents such as methanol and acetone.  pKa 3.6 

COMMERCIALISATION

History Herbicide reported by P. G. Jensen (Weed Control, 1980, 21st, 24). Introduced by E. I. du Pont de Nemours Co.  Patents US 4127405  Manufacturers Du Pont

APPLICATIONS

Biochemistry Branched chain amino acid synthesis (ALS or AHAS) inhibitor. Acts by inhibiting biosynthesis of the essential amino acids valine and isoleucine, hence stopping cell division and plant growth. Selectivity derives from rapid metabolism in the crop. Metabolic basis of selectivity in sulfonylureas reviewed (M. K. Koeppe & H. M. Brown, Agro-Food-Industry, 6, 9-14 (1995)).  Mode of action Selective systemic herbicide, absorbed by the foliage and roots, with rapid translocation acropetally and basipetally.  Uses Control of most broad-leaved weeds and some annual grasses in wheat, barley, oats, rye, triticale, flax, and on non-crop land. Applied pre-emergence, early post-emergence, pre-plant, or early post-plant incorporated, at 9-25 g/ha.  Phytotoxicity Phytotoxic to many broad-leaved crops, particularly sugar beet and brassicas.  Formulation types WG.  Selected tradenames: 'Glean' (Du Pont); 'Telar' (USA) (Du Pont); 'Granonet' (Agrimix); 'Lasher' (Sanonda)

OTHER TRADENAMES

'Caddy' (Du Pont); 'Pilargreen' (Pilarquim); 'Press' (AgroSan); 'Uron' (Probelte) mixtures: 'Finesse' (+ metsulfuron-methyl) (Du Pont); 'Valinate' (+ linuron) (Du Pont)

ANALYSIS

Product analysis by hplc (R. V. Slates & M. W. Watson, Anal. Methods Pestic. Plant Growth Regul., 1988, 16, 53). Residues determined by hplc (idem, ibid.; E. W. Zahnow, J. Agric. Food Chem., 1982, 30, 854) and by immunoassay (Kelly et al., ibid., 1985, 33, 962). Methods for sulfonylurea residues in crops, soil and water reviewed (A. C. Barefoot et al., Proc. Br. Crop Prot. Conf. - Weeds, 1995, 2, 707). 

MAMMALIAN TOXICOLOGY

Oral Acute oral LD50 for male rats 5545, female rats 6293 mg/kg.  Skin and eye Acute percutaneous LD50 for rabbits 2500 mg/kg. Mild eye irritant; non-irritating and non-sensitising to skin.  Inhalation LC50 (4 h) for rats >5.9 mg/l air.  NOEL (2 y) for rats 100, mice 500 mg/kg diet; (1 y) for dogs 2000 mg/kg diet.  ADI 0.05 mg/kg.  Other No oncogenic, mutagenic or teratogenic activity detected in standard tests. Acute i.p. LD50 for rats 1450 mg/kg.  Toxicity class WHO (a.i.) III (Table 5); EPA (formulation) IV (75 WG)  EC hazard N; R50, R53 

ECOTOXICOLOGY

Birds Acute oral LD50 for mallard ducks and bobwhite quail >5000 mg/kg. Dietary LC50 (8 d) for mallard ducks and bobwhite quail >5000 mg/kg diet.  Fish LC50 (96 h) for rainbow trout >250, bluegill sunfish >300 mg/l. LC50 for fathead minnow >300, catfish >50, sheepshead minnow >980 mg/l.  Daphnia LC50 (48 h) 370 mg/l.  Bees LD50 (contact) >25 mg/bee.  Worms LC50 >2000 mg/kg. 

ENVIRONMENTAL FATE