dimethoate (257)
Insecticide, acaricide
organophosphorus
NOMENCLATURE
Common name dimethoate (BSI, E-ISO, (m) F-ISO, ANSI, ESA, JMAF); fosfamid (USSR)
IUPAC name O,O-dimethyl S-methylcarbamoylmethyl phosphorodithioate; 2-dimethoxyphosphinothioylthio-N-methylacetamide
Chemical Abstracts name O,O-dimethyl S-[2-(methylamino)-2-oxoethyl] phosphorodithioate
CAS RN [60-51-5] EEC no. 200-480-3 Development codes EI 12 880 (Cyanamid); L 395 (Montedison); BAS 152J (BASF) Official codes OMS 94; OMS 111; ENT 24 650
PHYSICAL CHEMISTRY
Composition Tech. grade is 95% pure. Mol. wt. 229.3 M.f. C5H12NO3PS2 Form Colourless crystals; (tech., white to greyish crystals). M.p. 49 篊; (tech., 43-45 篊) B.p. 117 篊/0.1 mmHg V.p. 0.25 mPa (25 癈) KOW logP = 0.704 Henry 1.2 ?10-6 Pa m3 mol-1 S.g./density 1.277 at 65 篊 Solubility In water 23.3 (pH 5), 23.8 (pH 7), 25.0 (pH 9) (all in g/l, 20 篊). Readily soluble in most organic solvents, e.g. in alcohols, ketones, benzene, toluene, chloroform, dichloromethane >300, carbon tetrachloride, saturated hydrocarbons, n-octanol >50 (all in g/kg, 20 篊). Stability Relatively stable in aqueous media at pH 2-7. Hydrolysed in alkaline solutions; DT50 12 d (pH 9). Decomposes on heating, forming the O,S-dimethyl analogue.
COMMERCIALISATION
History Insecticide reported by E. I. Hoegberg & J. T. Cassaday (J. Am. Chem. Soc., 1951, 73, 557; Ital. Agric., 1955, 92, 747). Introduced by American Cyanamid Co. (who sold rights to Wilbur Ellis), by BASF AG, by Boehringer Sohn (now BASF AG), and by Montecatini S.p.A. (now Isagro S.p.A). Patents US 2494283 to Cyanamid; DE 1076662 to Celamerck; GB 791824 to Montedison Manufacturers Cheminova; Mico; Rallis; Shaw Wallace; Sinon
APPLICATIONS
Biochemistry Cholinesterase inhibitor. Mode of action Systemic insecticide and acaricide with contact and stomach action. Uses Control of a wide range of Acari, Aphididae, Aleyrodidae, Coccidae, Coleoptera, Collembola, Diptera, Lepidoptera, Pseudococcidae and Thysanoptera in cereals, citrus, coffee, cotton, fruit, grapes, olives, pastures, beetroot, potatoes, pulses, tea, tobacco, and vegetables. Also used for control of flies in animal houses. Phytotoxicity Non-phytotoxic when used as directed, except to some varieties of lemon, peach, fig, olive, walnut, hop, tomato, bean, cotton, and pine. Russetting is possible with Red Delicious and Golden Delicious apples, and with some ornamentals. Formulation types EC; GR; UL; WP; Aerosol. Compatibility Incompatible with alkaline materials and with sulfur-based formulations. Selected tradenames: 'Perfekthion' (BASF); 'Rogor' (Isagro); 'Afidox' (Lucava); 'Cekutoate' (Cequisa); 'Danadim' (Cheminova); 'Diadhan' (Dhanuka); 'Dicentra' (Sanonda); 'Dimezyl' (Agriphar); 'Efdacon' (Efthymiadis); 'Hilthioate' (Hindustan); 'Robgor' (Ramcides); 'Romethoate' (Rotam); 'Tara 909' (Shaw Wallace); 'Teeka' (Nagarjuna Agrichem)
OTHER TRADENAMES
'Dygon' (Wilbur-Ellis); 'Rebelate' (BASF); 'Agrothoate' (Agrochem); 'Barclay Dimethosect' (Barclay); 'Chimigor' (Diachem); 'Cropgor' (Crop Health); 'Dimeton' (AgroSan); 'Oligor' (Papaeconomou); 'Parrydimate' (Parry); 'Pelethon' (GreenCrop); 'Portman Sysdim 40' (Portman); 'Rogor Dragon' (Agricultura Nacional); 'Rogor L' (Chemiplant); 'Vidithoate' (Vipesco) mixtures: 'Rogodial' (+ phenthoate) (Isagro); 'Salut' (+ chlorpyrifos) (BASF); 'Decis D' (+ deltamethrin) (Aventis); 'Maktion' (+ methidathion) (Makhteshim-Agan); 'Vegehon' (+ fenvalerate) (Agros); 'Vibam' (+ fenobucarb) (Vipesco); 'Wing Tip' (+ chlorpyrifos) (Probelte) Discontinued names: 'Cygon' * (Wilbur-Ellis); 'Roxion' * (Wilbur-Ellis); 'Champ' * (Searle India) mixtures: 'Atlas Sheriff' * (+ chlorpyrifos) (Atlas)
ANALYSIS
Product analysis by glc (CIPAC Handbook, 1980, 1A, 1225; CIPAC Proc., 1981, 3, 204, 211; CIPAC Handbook, 1992, E, 69-72). Residues determined by glc (Analyst (London), 1977, 102, 858; 1980, 105, 515; 1985, 110, 765; J. E. Boyd, Anal. Methods Pestic. Plant Growth Regul., 1972, 6, 357; Man. Pestic. Residue Anal., 1987, I, 3, 6, S8, S13, S17, S19; Anal. Methods Residues Pestic., 1988, Part I, M5, M12).
MAMMALIAN TOXICOLOGY
Reviews FAO/WHO 77, 79 (see part 2 of the Bibliography). Oral Acute oral LD50 for rats 387, mice 160, rabbits 300, guinea pigs 350 mg/kg. Skin and eye Acute percutaneous LD50 for rats >2000 mg/kg. Non-irritating to skin (rabbits). Inhalation LC50 (4 h) for rats >1.6 mg/l air. NOEL (2 y) for rats 5.0 mg/kg diet (0.2 mg/kg daily). ADI (JMPR) 0.002 mg/kg b.w. (sum of dimethoate and omethoate, expressed as dimethoate) [1996]. Toxicity class WHO (a.i.) II; EPA (formulation) II EC hazard Xn; R21/22
ECOTOXICOLOGY
Birds Acute oral LD50 for male pheasants 15, quail 84, chickens 108, female mallard ducks 40 mg/kg. Fish LC50 (96 h) for mosquito fish 40-60, rainbow trout 6.2, bluegill sunfish 6 mg/l. Daphnia LC50 (24 h) 4.7 mg/l; NOEC (24 h) 1 mg/l. Algae EC50 (72 h) for Selenastrum capricornutum 282.3 mg/l; NOEC (72 h) 30.5 mg/l. Bees Toxic to bees. LD50 (oral and topical) 0.1-0.2 mg/bee.
ENVIRONMENTAL FATE
EHC 90 (WHO, 1989), 63 (WHO, 1986; a general review of organophosphorus insecticides). Dimethoate degrades with short half-life in soil, water and plants. When used correctly, exposure of the population through air, food or water is negligible. Animals In mammals, metabolism follows the same pattern as in plants. Plants In plants, oxidised to O,O-dimethyl-phosphorothioate and hydrolysed to O,O-dimethyl-phosphorodithioate, -phosphorothioate, and -phosphate. The ester group is demethylated and the methylamino group is hydrolytically cleaved. Oxidation of dimethoate gives the corresponding oxone (omethoate q.v.), which is classified as toxic and a strong cholinesterase inhibitor, and which appears to show similar rapid degradation in environmental compartments as dimethoate. Soil/Environment Adsorption and desorption constants have been shown to be a linear function of soil silt content. Koc ranges from 16.25 (sandy loam) to 51.88 (sand/loamy sand). Aerobic DT50 2-4.1 d. Photolytic DT50 on soil surface 7-16 d. Low potential for leaching to groundwater because of rapid degradation in soil. |
