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dalapon
Herbicide
HRAC N WSSA 26; halogenated alkanoic acid
NOMENCLATURE
dalapon
Common name dalapon (BSI, ANSI, WSSA, Canada, Germany, (m) France); proprop (Republic of South Africa); DPA (JMAF); 2,2-dichloropropionic acid (used in most other countries)
IUPAC name 2,2-dichloropropionic acid
Chemical Abstracts name 2,2-dichloropropanoic acid
CAS RN [75-99-0] EEC no. 200-923-0
dalapon-sodium
CAS RN [127-20-8]
PHYSICAL CHEMISTRY
dalapon
Mol. wt. 143.0 M.f. C3H4Cl2O2 Form Colourless liquid. B.p. 185-190 ºC V.p. 0.01 mPa (20 ºC) Stability Subject to hydrolysis; slight at 25 ºC, but comparatively rapid ³50 ºC; so aqueous solutions should not be kept for any length of time. Alkali causes dehydrochlorination above 120 ºC. pKa 1.74-1.84, depending on the ionic strength of the solution.
dalapon-sodium
Mol. wt. 165.0 M.f. C3H3Cl2NaO2 Form Pale-coloured, hygroscopic powder. M.p. Decomposes >191 ºC V.p. <1.7 ´ 10-1 mPa (25 °C) S.g./density 1.74 (20 °C) Solubility In water 629 g/kg (25 ºC). In ethanol 110, methanol 369, acetone 3.25, benzene 0.02, diethyl ether 0.16 (all in g/kg, 25 ºC). Stability Stable <150 °C.
COMMERCIALISATION
dalapon-sodium
History The sodium salt introduced as a herbicide by Dow Chemical Co. (now Dow AgroSciences) and by BASF AG (both no longer manufacture or market it). Patents US 2642354 to Dow Manufacturers Hodogaya
APPLICATIONS
Biochemistry Inhibits lipid synthesis (not ACCase inhibition). Mode of action Selective systemic herbicide, absorbed by the leaves and roots, with translocation via both the symplastic and apoplastic systems throughout the plant. Uses Dalapon-sodium is used for control of annual and perennial grasses (including couch grass) on non-crop land (embankments, roadside verges, industrial sites, railway tracks, irrigation channels, ditches, etc.), in orchards (pome fruit, stone fruit, bush fruit, citrus fruit, nuts), olive groves, vineyards, forestry, bananas, sugar cane, rhubarb, asparagus, potatoes, peas, soya beans, beet, oilseed rape, flax, maize, sorghum, coffee, tea, rubber, cotton, and ornamental shrubs. Control of reeds, sedges, rushes, halophytes, and semi-aquatic grass weeds in water courses. Application rates range from 37 kg/ha (non-crop areas) to 2-5 kg/ha (citrus). Formulation types GR; SP; WP. Compatibility Should not be used in combination with oils or contact herbicides, as activity will be diminished due to reduction in translocation. Selected products: 'Diserbo Canali' (Siapa); 'Vilapon' (Vipesco)
OTHER PRODUCTS
dalapon
'Dalacide' (Diachem) Discontinued products: 'Basfapon' * (BASF); 'Basinex P' * (BASF); 'Dowpon' * (DowElanco); 'Gramevin' * (Cyanamid); 'Radapon' * (DowElanco)
ANALYSIS
Product analysis (dalapon or salts) is by decomposition of a complex formed with mercury(II) nitrate and copper(II) nitrate and subsequent titration with acid (AOAC Methods, 17th Ed., 962.06), or by glc of a suitable ester (Herbicides,1977, p. 45); sodium and magnesium salts by rplc (AOAC Methods, 17th Ed., 984.06; CIPAC Handbook, 1988, D, 54). Residue analysis is by glc of a suitable ester (G. N. Smith & E. H. Yonkers, Anal. Methods Pestic., Plant Growth Regul. Food Addit., 1964, 4, 79; Anal. Methods Pestic. Plant Growth Regul., 1972, 6, 621; Rückstandsanal. Pflanzenschutzmitteln, 28-1, 28-6).
MAMMALIAN TOXICOLOGY
Reviews The toxic effects of dalapon have been reviewed (E. E. Kenaga, Residue Rev., 1974, 53, 104).
dalapon-sodium
Oral Acute oral LD50 for male rats 9330, female rats 7570, female mice >4600, female guinea pigs 3860, female rabbits 3860, cattle >4000 mg/kg. Skin and eye Acute percutaneous LD50 for rabbits >2000 mg/kg (85% formulation). Moderately irritating to skin and eyes (rabbits). Inhalation LC50 (8 h) >20 mg/l of 25% solution of formulated product. NOEL In 2 y feeding trials, no effect was observed in rats receiving 15 mg/kg daily, but there was a slight increase in kidney weight at 50 mg/kg daily. Toxicity class WHO (a.i.) U (for dalapon); EPA (formulation) II EC classification (for dalapon) Xn; R22| Xi; R38, R41| R52, R53
ECOTOXICOLOGY
dalapon-sodium
Birds Acute oral LD50 for chickens 5660 mg/kg. Dietary LC50 (5 d) for mallard ducks, Japanese quail, and pheasants >5000 mg/kg diet. Fish LC50 (96 h) for rainbow trout, goldfish, and channel catfish >100, carp >500, guppies >1000 mg/l. Algae EC50 (72 h) >100mg/l. Bees Non-toxic to honeybees. Worms LC50 (14 d) >1058 mg/kg dry soil.
ENVIRONMENTAL FATE
Animals In mammals, following oral administration, dalapon is rapidly eliminated. In dogs, following a single oral dose of 500 mg, 65-70% is excreted within 2 hours. Plants In plants, dalapon-sodium does not undergo significant degradation. Soil/Environment In soil, readily undergoes microbial degradation involving dechlorination and liberation of CO2 (B. E. Day et al., Soil Sci., 1963, 95, 326). Following an application rate of 22 kg/ha, duration of residual activity in soil is c. 3-4 months.
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