HRAC O WSSA 4; phenoxycarboxylic acid
Common name 2,4-D (BSI, E-ISO, (m) F-ISO, WSSA); 2,4-PA (JMAF)
IUPAC name (2,4-dichlorophenoxy)acetic acid
Chemical Abstracts name (2,4-dichlorophenoxy)acetic acid
CAS RN [94-75-7] EEC no. 202-361-1
IUPAC name 2-butoxyethyl (2,4-dichlorophenoxy)acetate
CAS RN [1929-73-3] EEC no. 217-680-1
IUPAC name butyl (2,4-dichlorophenoxy)acetate
CAS RN [94-80-4] EEC no. 202-364-8
IUPAC name dimethylammonium (2,4-dichlorophenoxy)acetate
CAS RN [2008-39-1] EEC no. 217-915-8
IUPAC name bis(2-hydroxyethyl)ammonium (2,4-dichlorophenoxy)acetate
CAS RN [5742-19-8] EEC no. 227-256-8
IUPAC name ethyl (2,4-dichlorophenoxy)acetate
IUPAC name 2-ethylhexyl (2,4-dichlorophenoxy)acetate
CAS RN [1928-43-4] EEC no. 217-673-3 Development codes N208 (Marks)
IUPAC name 2-methylpropyl (2,4-dichlorophenoxy)acetate
CAS RN [1713-15-1] EEC no. 216-992-5
IUPAC name octyl (2,4-dichlorophenoxy)acetate (mixed octyl isomers)
CAS RN [25168-26-7] (formerly [1280-20-2]) EEC no. 246-704-3
IUPAC name isopropyl (2,4-dichlorophenoxy)acetate
CAS RN [94-11-1] EEC no. 202-305-6
IUPAC name sodium (2,4-dichlorophenoxy)acetate
CAS RN [2702-72-9] EEC no. 220-290-4
IUPAC name tris(2-hydroxyethyl)ammonium (2,4-dichlorophenoxy)acetate
CAS RN [2569-01-9] EEC no. 219-911-1
Composition Tech. is 96% pure. Mol. wt. 221.0 M.f. C8H6Cl2O3 Form Colourless powder, with a slight phenolic odour. M.p. 140.5 ºC V.p. 1.86 10-2 mPa (25 °C, OECD 104) KOW logP = 2.58-2.83 (pH 1), 0.04-0.33 (pH 5) Henry 1.32×10-5 Pa m3 mol-1 (calc.) S.g./density 1.508 (20 °C) Solubility In water 311 (pH 1), 20 031 (pH 5), 23 180 (pH 7), 34 196 (pH 9) (all in mg/l, 25 °C). In ethanol 1250, diethyl ether 243, heptane 1.1, toluene 6.7, xylene 5.8 (all in g/kg, 20 ºC); in octanol 120 g/l (25 °C). Insoluble in petroleum oils. Mono-n-butylamine salt: In water 18 g/l (30 ºC). Stability 2,4-D is a strong acid, and forms water-soluble salts with alkali metals and amines. Hard water leads to precipitation of the calcium and magnesium salts, but a sequestering agent is included in formulations to prevent this. Photolytic DT50 (simulated sunlight) 7.5 d. pKa 2.73
Mol. wt. 321.2 M.f. C14H18Cl2O4
Mol. wt. 277.1 M.f. C12H14Cl2O3
Mol. wt. 266.1 M.f. C10H13Cl2NO3 M.p. decomp. c. 120 °C Solubility In water 3 kg/l (20 ºC). Soluble in alcohols and acetone. Insoluble in kerosene and diesel oil.
Mol. wt. 326.2 M.f. C12H17Cl2NO5
Mol. wt. 249.1 M.f. C10H10Cl2O3
Composition Isomeric with 2,4-D-isoctyl; sometimes these names are used interchangeably. Mol. wt. 333.3 M.f. C16H22Cl2O3 Form Golden yellow, non-viscous liquid, with a sweet, slightly pungent odour. M.p. <-37 °C B.p. >300 °C (decomp.) V.p. 47.9 mPa (25 °C) KOW logP = 5.78 (25 °C) Henry 1.8 Pa m3 mol-1 (calc.) S.g./density 1.148 (20 °C) Solubility In water 0.086 mg/l (25 °C). Miscible with most organic solvents. Stability Hydrolysis DT50 <1 h. Stable to light, DT50 >100 d. Stable at 54 °C. F.p. 171 °C (Cleveland open cup)
Mol. wt. 277.1 M.f. C12H14Cl2O3
Composition Isomeric with 2,4-D-2-ethylhexyl; sometimes these names are used interchangeably. Mol. wt. 333.3 M.f. C16H22Cl2O3 Form Yellowish-brown liquid, with a phenolic odour. B.p. 317 °C S.g./density 1.14-1.17 g/ml (20 °C) Solubility In water 10 mg/l. F.p. 171 °C
Mol. wt. 263.1 M.f. C11H12Cl2O3 Form Colourless liquid. M.p. 5-10 ºC and 20-25 ºC (two forms) B.p. 130 ºC/1 mmHg V.p. 1.4 Pa (25 ºC) Solubility Practically insoluble in water. Soluble in alcohols and most oils.
Mol. wt. 243.0 M.f. C8H5Cl2NaO3 Solubility In water 18 g/l (20 ºC).
Mol. wt. 370.2 M.f. C14H21Cl2NO6 M.p. 142-144 ºC Solubility In water 4.4 kg/l (30 ºC).
Biochemistry Synthetic auxin (acting like indolylacetic acid). Mode of action Selective systemic herbicide. Salts are readily absorbed by the roots, whilst esters are readily absorbed by the foliage. Translocation occurs, with accumulation principally at the meristematic regions of shoots and roots. Acts as a growth inhibitor. Uses Post-emergence control of annual and perennial broad-leaved weeds in cereals, maize, sorghum, grassland, established turf, grass seed crops, orchards (pome fruit and stone fruit), cranberries, asparagus, sugar cane, rice, forestry, and on non-crop land (including areas adjacent to water), at 0.28-2.3 kg/ha. Control of broad-leaved aquatic weeds. The isopropyl ester can also be used as a plant growth regulator to prevent premature fruit fall in citrus fruit. Phytotoxicity Phytotoxic to most broad-leaved crops, especially cotton, vines, tomatoes, ornamentals, fruit trees, oilseed rape and beet. Formulation types EC; GR; SP; SL.
Product analysis of 2,4-D, salts, esters and mixed combination products by acid-base titration, by glc (CIPAC Handbook, 1985, 1C, 2060, 2257; 1994, F, 292-319; Herbicides 1977, pp. 6-21), by rplc (AOAC Methods, 17th Ed., 971.07, 976.03, 978.05, 984.07; CIPAC Handbook, 1985, 1C, 2060; 1988, D, 51), by hplc (ibid., 1983, 1757), or by i.r. spectrometry (ibid., 1998, H, 131). Free phenol impurity determined by glc (CIPAC Handbook, 1994, F, 197), hplc (ibid., 1994, F, 362) or electrochemically (ibid., 1994, F, 368). Residues determined by glc of derivatives (Pestic. Anal. Man., 1979, I, 201-D; Anal. Methods Pestic. Plant Growth Regul., 1972, 6, 630) or by hplc (M. Meier et al.,Fresenius Z. Anal. Chem.,1989, 334, 235). In drinking water, by conversion to methyl ester with diazomethane, then glc with ECD (AOAC Methods, 17th Ed., 992.32).
Reviews FAO/WHO 77, 79, 80, 82, 92 (see part 2 of the Bibliography). Toxicity and hazards to man, domestic animals and wildlife have been reviewed (J. M. Way, Residue Rev., 1969, 26, 37). IARC ref. 15, 41; Suppl. 7 class chlorophenoxy herbicides classified as 2B, based on epidemiology of production. More recent evidence (M. Kogevinas et al., Am. J. Epidemiol., 145(12), 1061 (1997)) relates this to dioxin contamination of early production. Not relevant to current processes.
Oral Acute oral LD50 for rats 639-764, mice 138 mg/kg. Skin and eye Acute percutaneous LD50 for rats >1600, rabbits >2400 mg/kg. Skin and eye irritant (rabbits). A skin sensitiser (guinea pigs). Inhalation LC50 (24 h) for rats >1.79 mg/l. NOEL (2 y) for rats and mice 5 mg/kg b.w.; (1 y) for dogs 1 mg/kg b.w. ADI (JMPR) 0.01 mg/kg b.w. [2001, 1997]; 0.01 mg/kg b.w.  (sum of 2,4-D and its salts and esters, as 2,4-D); [EEC] 0.05 mg/kg b.w. (2001). Water GV 30 g/l (based on ADI). Toxicity class WHO (a.i.) II; EPA (formulation) II EC classification Xn; R22| Xi; R37, R41| R43| R52, R53: (for salts Xn; R22| Xi; R41| R43| N; R51, R53; for esters Xn; R22| R43| N; R50, R53)
Oral Acute oral LD 50 for rats 949 mg/kg. Skin and eye LD50 for rats >2000 mg/kg; not a skin irritant (rabbits); severe irritant to eyes (rabbits). Inhalation LC50 (4 h) for rats >3.5 mg/l air.
Oral Acute oral LD50 for rats 896 mg/kg. Skin and eye Dermal LD50 for rabbits >2000 mg/kg. Slight eye irritant. A skin sensitiser (guinea pigs). Inhalation LC50 (4 h) for rats >5.4 mg/l air. ADI Due to toxicological equivalence to 2,4-D, ADI is assumed to be equivalent to that for 2,4-D.
Oral Acute oral LD50 for rats 650 mg/kg. Skin and eye Acute percutaneous LD50 for rats >3000 mg/kg. NOEL for rats 1250, dogs 500 mg/kg diet.
Oral Acute oral LD50 for rats 700 mg/kg.
Oral Acute oral LD50 for rats 666-805 mg/kg.
Birds Acute oral LD50 for wild ducks >1000, Japanese quail 668, pigeons 668, pheasants 472 mg/kg. LC50 (96 h) for mallard ducks >5620 mg/l. Fish Some formulations (e.g. esters) are toxic to fish, whilst others are not. LC50 (96 h) for rainbow trout >100 mg/l. Daphnia LC50 (21 d) 235 mg/l. Algae EC50 (5 d) for Selenastrum capricornutum 33.2 mg/l. Other aquatic spp. EC50 (14 d) for Lemna gibba 0.58 mg/l. Bees Not toxic to bees; LD50 (oral) 104.5 g/bee. Worms LC50 (7 d) 860 mg/kg; NOEC (14 d) 100 g/kg. Other beneficial spp. Harmless to Trichogramma cacoeciae, Poecilus cupreus, Aleochara bilineata.
Birds Acute oral LD 50 for bobwhite quail 500 mg/kg. Oral LC50 for bobwhite quail >5620 ppm. Fish LC50 (96 h) for rainbow trout 100 mg/l. Algae EC50 for Selenastrum capricornutum 51.2 mg/l. Bees LD50 (contact) >100 µg/bee; (oral) c. 94 µg/bee.
Birds Acute oral LD50 for mallard ducks 663 mg/kg. Dietary LC50 (5 d) for bobwhite quail and mallard ducks >5620 ppm. Fish LC50 for fathead minnow, bluegill sunfish and rainbow trout greater than solubility in water. Daphnia EC50 (48 h) 5.2 mg/l. Algae EC50 for Skeletonema costatum 0.23, Navicula pelliculosa 4.1, Selenastrum capricornutum and Anabaena flos-aquae >30 mg/l. Other aquatic spp. EC50 (14 d) for Lemna gibba 0.5 mg/l. Bees LD50 (contact) >100 µg/bee; (oral) >100 µg/bee.
Fish LC50 (96 h) for cut-throat trout 0.5-1.2 mg/l.
Birds Acute oral LD50 for wild ducks >2025 mg/kg.
EHC 29 (WHO, 1984), 84 (WHO, 1989). EHC 84 concludes that, when used as recommended, 2,4-D does not appear to produce direct toxic effects on any animal species. Animals In rats, following oral administration, elimination is rapid, and mainly as the unchanged substance. Following single doses of up to 10 mg/kg, excretion is almost complete after 24 hours, although, with higher doses, complete elimination takes longer. The maximum concentration in organs is reached after c. 12 hours. Plants In plants, metabolism involves hydroxylation, decarboxylation, cleavage of the acid side-chain, and ring opening. Soil/Environment In soil, microbial degradation involves hydroxylation, decarboxylation, cleavage of the acid side-chain, and ring opening. Half-life in soil <7 d. Koc c. 60. For a review of environmental aspects of 2,4-D, see Environmental Health Criteria 84 (WHO, 1989). Rapid degradation in the soil prevents significant downward movement under normal conditions.
Soil/Environment Rapidly hydrolysed in soil and water to the parent acid; DT50 <1 d.