Herbicide

HRAC  C1 WSSA  5; 1,2,4-triazinone

NOMENCLATURE

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

IUPAC name 3-cyclohexyl-6-dimethylamino-1-methyl-1,3,5-triazine-2,4-(1H,3H)-dione 

Chemical Abstracts name 3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4-(1H,3H)-dione 

CAS RN [51235-04-2]  EEC no. 257-074-4  Development codes DPX A3674 (Du Pont) 

PHYSICAL CHEMISTRY

Mol. wt. 252.3  M.f. C12H20N4O2  Form Colourless, odourless crystals.  M.p. 115-117 ºC  B.p. Decomposes on distillation.  V.p. 0.03 mPa (extrapolated) (25 ºC); 8.5 mPa (86 ºC)  KOW logP = 1.2 (pH 7)  S.g./density 1.25  Solubility In water 33 g/kg (25 ºC). In chloroform 3880, methanol 2650, benzene 940, dimethylformamide 836, acetone 792, toluene 386, hexane 3 (all in g/kg, 25 ºC).  Stability Stable in aqueous media between pH 5 and pH 9 and below 37 ºC. Decomposed by strong acids and strong alkalis. Stable to light. 

COMMERCIALISATION

History Herbicide reported by T. J. Hernandez et al. (Proc. North Cent. Weed Control Conf., 1974, p. 138). Introduced by E. I. du Pont de Nemours Co.  Patents US 3902887  Manufacturers Du Pont

APPLICATIONS

Biochemistry Photosynthetic electron transport inhibitor at the photosystem II receptor site.  Mode of action Non-selective, primarily contact herbicide, absorbed by the leaves and roots, with translocation acropetally.  Uses A post-emergence contact herbicide effective against many annual and biennial weeds and, except for Sorghum halepense, most perennial weeds, at 6-12 kg a.i./ha. Used for selective control in alfalfa, pineapples, sugar cane and in plantations of certain coniferous species; also on non-crop areas, but not on sites adjacent to deciduous trees or other desirable plants.  Phytotoxicity Should not be used for weed control in larch (Larix spp.) or in areas planted with deciduous species.  Formulation types GR; SL; SP.  Selected tradenames: 'Velpar' (Du Pont)

OTHER TRADENAMES

Mixtures: 'Oustar' (+ sulfometuron-methyl) (Du Pont)

ANALYSIS

Product analysis by hplc or by glc with FID (C. L. McIntosh et al., Anal. Methods Pestic. Plant Growth Regul., 1984, 13, 267). Residues determined by glc (idem, ibid.; R. F. Holt, J. Agric. Food Chem., 1981, 29, 165). In drinking water, by gc with FID (AOAC Methods, 1995, 991.07). 

MAMMALIAN TOXICOLOGY

Oral Acute oral LD50 for rats 1690, guinea pigs 860 mg/kg.  Skin and eye Acute percutaneous LD50 for rabbits >5278 mg/kg. Reversible irritant to eyes (rabbits); non-irritating to skin (guinea pigs).  Inhalation LC50 (1 h) for rats >7.48 mg/l.  NOEL (2 y) for rats 200, mice 200 ppm; (1 y) for dogs 200 ppm.  Toxicity class WHO (a.i.) III; EPA (formulation) II  EC hazard Xn; R22| Xi; R36| N; R50, R53 

ECOTOXICOLOGY

Birds Acute oral LD50 for bobwhite quail 2258 mg/kg. Dietary LC50 (8 d) for bobwhite quail and mallard ducklings >10 000 mg/kg diet.  Fish LC50 (96 h) for rainbow trout 320-420, fathead minnow 274, bluegill sunfish 370-420 mg/l.  Daphnia LC50 (48 h) 442 mg/l.  Bees Not toxic to bees; LD50 >60 mg/bee. 

ENVIRONMENTAL FATE