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MCPA
Herbicide
HRAC O WSSA 4; phenoxycarboxylic acid
NOMENCLATURE
MCPA
Common name MCPA (BSI, E-ISO, F-ISO, WSSA); 2,4-MCPA ((m) France); 2M-4Kh (USSR); metaxon* (former name, USSR); MCP (JMAF)
IUPAC name (4-chloro-2-methylphenoxy)acetic acid
Chemical Abstracts name (4-chloro-2-methylphenoxy)acetic acid
CAS RN [94-74-6] EEC no. 202-360-6 Development codes BAS 010H; BAS 141H (both BASF); L065 (Marks)
MCPA-dimethylammonium
CAS RN [2039-46-5]
MCPA-2-ethylhexyl
CAS RN [29450-45-1]
MCPA-sodium
CAS RN [3653-48-3], formerly [11100-01-9] and [11114-06-0] EEC no. 222-895-9
PHYSICAL CHEMISTRY
MCPA
Composition Tech. grade is 85-99% pure. Mol. wt. 200.6 M.f. C9H9ClO3 Form Off-white crystals with a mild phenolic odour (tech.). M.p. 119-120.5 ºC; 115.4-116.8 °C (99.5 % purity) V.p. 2.3 ´ 10-2 mPa (20 ºC); 4 ´ 10-1 mPa (32 °C) KOW logP = 2.75 (pH 1), 0.59 (pH 5), -0.71 (pH 7) (25 ºC) Henry 5.5 ´ 10-5 Pa m3 mol-1 (calc.) S.g./density 1.41 (23.5 °C) Solubility In water 395 (pH 1), 26.2 (pH 5), 273.9 (pH 7), 320.1 (pH 9) (all in mg/l, 25 °C). In diethyl ether 770, toluene 26.5, xylene 49, heptane 5, methanol 775.6, dichloromethane 69.2, n-octanol 218.3 (all in g/l, 25 °C). Stability The acid is chemically very stable. Forms water-soluble alkali-metal and amine salts, although precipitation of calcium or magnesium salts may occur in hard water. Photochemical DT50 (artificial sunlight) 25.4 d (25 °C). pKa 3.07
MCPA-butotyl
Mol. wt. 300.8 M.f. C15H21ClO4 Solubility Readily soluble in organic solvents.
MCPA-dimethylammonium
Mol. wt. 245.7 M.f. C11H16ClNO3
MCPA-2-ethylhexyl
Mol. wt. 312.8 M.f. C17H25ClO3 Form Non-viscous brown liquid, with a strong ester odour. B.p. 350 °C V.p. 2.7 ´ 10-1 to 1.3 ´ 101 mPa (18-45 °C) S.g./density 1.07 (20 °C) F.p. 159 °C (Tag closed cup)
MCPA-potassium
Mol. wt. 238.7 M.f. C9H8ClKO3
MCPA-sodium
Mol. wt. 222.6 M.f. C9H8ClNaO3 Solubility In water 270 g/l. In methanol 340, benzene 1 (both in g/l).
COMMERCIALISATION
History Its plant-growth regulating activity reported by R. E. Slade (Nature (London), 1945, 155, 498). Introduced as a herbicide by ICI Plant Protection Division (now Syngenta AG) and, later, numerous other firms. Manufacturers Atanor; Atul; BASF; Dow AgroSciences; Istrochem; Marks; Nufarm B.V.; Nufarm UK; Sannong
APPLICATIONS
Biochemistry Synthetic auxin (acting like indolylacetic acid). Mode of action Selective, systemic, hormone-type herbicide, absorbed by the leaves and roots, with translocation. Concentrates in the meristematic regions, where it inhibits growth. Uses Post-emergence control of annual and perennial broad-leaved weeds (including thistles and docks) in cereals (alone or undersown), herbage seed crops, flax, rice, vines, peas, potatoes, asparagus, grassland, turf, under fruit trees, and on roadside verges and embankments, etc., at 0.28-2.25 kg/ha. Control of broad-leaved and woody weeds in forestry. Control of aquatic broad-leaved weeds. Often used in combination with other herbicides. Phytotoxicity Phytotoxic to vines, vegetables, cotton, and ornamentals. Formulation types EC; SL; SP.
MCPA
Selected products: 'Agricorn' (FCC); 'Empal' (Unicrop); 'Meadowman II' (mixture of sodium, potassium and diethylammonium salts) (Barclay); 'Sanaphen-M' (Dow AgroSciences); 'Selectyl' (Agriphar); mixtures: 'Butoxone DB Extra' (+ 2,4-DB) (sodium and potassium salts) (Marks); 'Hyprone-P' (+ mecoprop-P+ dicamba) (as mixed sodium and potassium salts) (Agrichem Int.)
MCPA-dimethylammonium
Selected products: 'Actril M75' (Bayer CropScience); 'Agritox 50' (Nufarm UK); 'Agroxone' (Marks); 'Aminex pur' (Istrochem); 'Dicopur M' (Nufarm GmbH); 'Kailan' (Bayer CropScience); 'Spear' (Headland); 'U 46 M-Fluid' (BASF); mixtures: 'Erbitox Combi' (+ 2,4-D-dimethylammonium) (Siapa); 'Optica Trio' (+ mecoprop-P+ dichlorprop-P-dimethylammonium) (mecoprop-P also as dimethylammonium salt) (Marks); 'U 46 Combi Fluid' (+ 2,4-D-dimethylammonium) (BASF)
MCPA-2-ethylhexyl
Selected products: 'Brominal Plus' (Bayer CropScience); 'MCP Ester' (Dow AgroSciences); mixtures: 'Bronate' (+ bromoxynil octanoate) (Bayer CropScience)
MCPA-potassium
Selected products: 'Blagal' (Bayer CropScience); 'Erbitox E30' (Siapa)
MCPA-sodium
Selected products: 'Chiptox' (Bayer CropScience); 'Erbitox E30' (Siapa)
OTHER PRODUCTS
MCPA
'Agricorn 500' (FCC); 'Circium' (salt) (Nufarm UK); 'Pamex' (Crystal); 'Phenoxylene 50' (salt) (Bayer CropScience) mixtures: 'Alistell' (+ 2,4-DB+ linuron) (Syngenta); 'Aminex D' (+ dicamba) (Istrochem); 'Aniten Combi' (+ dicamba+ flurenol) (Siegfried); 'Archer' (+ MCPB+ bentazone) (Headland); 'Banlene Super' (+ mecoprop-P+ dicamba) (as salts) (Bayer CropScience); 'Blespring Combi' (+ mecoprop+ bromoxynil octanoate+ dicamba) (Siapa); 'Brioxil Super' (+ bromoxynil octanoate+ ioxynil octanoate) (Aragro); 'Cedar' (+ 2,4-DB) (Headland); 'Chardex' (+ clopyralid-olamine) (MCPA as amine salt) (Dow AgroSciences); 'Cleanrun 2' (+ dicamba+ dichlorprop) (Scotts UK); 'Field Marshal' (+ mecoprop-P+ dicamba) (United Phosphorus); 'Glisompa' (+ glyphosate) (Probelte); 'Legumex Extra' (+ 2,4-DB+ benazolin-ethyl) (salts) (Bayer CropScience); 'Lonpar' (+ 2,4-D+ clopyralid-olamine) (2,4-D and MCPA as amine salts) (Dow AgroSciences); 'Maestro' (+ bromoxynil+ dicamba) (Nufarm SA); 'Mazide Selective' (+ dicamba+ maleic hydrazide) (Vitax); 'Mircam Plus' (+ mecoprop-P+ dicamba) (Nufarm UK); 'Nocweed' (+ mecoprop-P+ dicamba) (Bayer CropScience); 'Nox-MCP' (+ propanil) (Crystal); 'Outrun' (+ mecoprop-P+ dicamba) (SumiAgro); 'Pasturol Plus' (+ mecoprop-P+ dicamba) (FCC); 'Polo' (+ 2,4-D) (Headland); 'Quad-Ban' (+ mecoprop+ dicamba) (Quadrangle); 'Quattro' (+ bromoxynil) (Nufarm SA); 'Relay P' (+ mecoprop-P+ dicamba) (Headland); 'Sable' (+ glyphosate-isopropylammonium) (Aragro); 'Setter' (+ 2,4-DB+ benazolin) (Dow AgroSciences); 'Spearhead' (+ clopyralid+ diflufenican) (Bayer CropScience); 'Tribute' (+ mecoprop-P+ dicamba) (Nomix-Chipman); 'Trireme' (+ mecoprop-P+ dicamba) (Nufarm UK); 'Tritox' (+ mecoprop-P+ dicamba) (Scotts UK); 'Tropotox Plus' (+ MCPB) (Nufarm UK); 'UPL Camppex' (+ mecoprop-P+ 2,4-D+ dichlorprop) (United Phosphorus); 'UPL Grassland Herbicide' (+ mecoprop-P+ dicamba) (United Phosphorus) Discontinued products: 'Methoxone' * (Zeneca); 'Cirsium' * (Mirfield) mixtures: 'Banlene Plus' * (+ mecoprop+ dicamba) (Stefes, AgrEvo, Schering); 'Camppex' * (+ mecoprop+ 2,4-D+ dichlorprop) (United Phosphorus Ltd); 'Docklene Super' * (+ mecoprop-P+ dicamba) (Stefes); 'Docklene' * (+ mecoprop+ dicamba) (Stefes); 'Herrisol' * (+ mecoprop+ dicamba) (Bayer); 'Marks 2,4-DB Extra' *" (+ 2,4-DB) (sodium and potassium salts) (Marks); 'MSS Mircam Plus' * (+ mecoprop-P+ dicamba) (Mirfield); 'Pasturol' * (+ mecoprop+ dicamba) (FCC); 'Relay' * (+ mecoprop+ dicamba) (Headland); 'Sirocco' * (+ mecoprop-P+ bifenox) (Bayer); 'Springcorn Extra' * (+ mecoprop+ dicamba) (FCC); 'Tribute' * (+ mecoprop+ dicamba) (Nomix-Chipman)
MCPA-dimethylammonium
'Mega M' (Nufarm B.V.) mixtures: 'Dicopur Combi' (+ 2,4-D-dimethylammonium) (Nufarm GmbH); 'Duplosan Super' (+ mecoprop-P+ dichlorprop-P-dimethylammonium) (mecoprop-P also as dimethylammonium salt) (BASF); 'Optica Combi' (+ mecoprop-P) (mecoprop-P also as dimethylammonium salt) (Marks) Discontinued products: 'MB-M750' * (Nufarm Whyte); 'Rhomene' * (Nufarm Whyte) mixtures: 'U 46 Super' * (+ mecoprop+ dichlorprop) (BASF)
MCPA-2-ethylhexyl
'Dagger' (Riverdale); 'Mxl' (Agsco); 'Sword' (Platte) mixtures: 'Bison' (+ bromoxynil octanoate) (Agriliance); 'Bronate Gel' (+ bromoxynil heptanoate+ bromoxynil octanoate) (Bayer CropScience); 'Brox-M' (+ bromoxynil octanoate) (Albaugh); 'Buctril M' (+ bromoxynil heptanoate+ bromoxynil octanoate) (Bayer CropScience); 'Cheyenne' (+ fenoxaprop-P-ethyl) (Bayer CropScience); 'Curtail M' (+ clopyralid) (Dow AgroSciences); 'Dakota' (+ fenoxaprop-P-ethyl) (Bayer CropScience); 'Frontline' (+ florasulam) (Dow AgroSciences); 'Midas' (+ imazapic+ imazapyr) (BASF); 'Paragon' (+ picolinafen) (BASF); 'Spectrum' (+ clopyralid+ florasulam) (Dow AgroSciences); 'Tiller' (+ 2,4-D-2-ethylhexyl+ fenoxaprop-P-ethyl) (Bayer CropScience) Discontinued products: 'Printormona' * (Nufarm Whyte); 'Rhonox' * (Nufarm Whyte) mixtures: 'Cheyenne' * (+ fenoxaprop-ethyl; fenoxaprop) (Hoechst); 'Stampede Cm' * (+ propanil) (Dow AgroSciences); 'Tiller' * (+ 2,4-D-isoctyl+ fenoxaprop-P-ethyl) (AgrEvo)
MCPA-potassium
'Valcer 40' (IQV) mixtures: 'Agtryne MA' (+ terbutryn) (Crop Care); 'Bellmac Plus' (+ MCPB) (MCPB also as potassium salt) (United Phosphorus Ltd); 'Hycamba Plus' (+ mecoprop+ dicamba-potassium) (mecoprop-P also as potassium salt) (Agrichem Int.); 'Hymec Triple' (+ mecoprop-P+ dichlorprop-P) (dichlorprop-P and mecoprop-P also as potassium salts) (Agrichem Int.); 'Hysward-P' (+ mecoprop+ dicamba-potassium) (mecoprop-P also as potassium salt) (Agrichem Int.); 'Redipon Extra' (+ dichlorprop-potassium) (United Phosphorus Ltd); 'Redlegor' (+ 2,4-DB-sodium) (United Phosphorus Ltd); 'Staraminex' (+ fluroxypyr-2-butoxy-1-methylethyl) (Istrochem) Discontinued products: 'Cydexone 400' * (Nufarm Whyte); 'Rambasan 400' * (Nufarm Whyte)
MCPA-sodium
Mixtures: 'Acumen' (+ MCPB-sodium+ bentazone-sodium) (MCPA may be as potassium or dimethylammonium salts) (BASF); 'Agrichem DB Plus' (+ 2,4-DB-sodium) (Agrichem Int.); 'Butoxone Plus' (+ MCPB-sodium) (Marks, Headland); 'Trifolextra' (+ MCPB-sodium) (BASF)
ANALYSIS
Product analysis (acid or salts) by i.r. spectrometry (AOAC Methods, 17th Ed., 971.07, CIPAC Handbook, 1985, 1C, 2137), by hplc (ibid., 1985, 1C, 2139; AOAC Methods, 17th Ed., 980.07) by liquid/liquid chromatography (CIPAC Handbook, 1985, C, 2138; 1980, 1A, 477), by glc of a derivative (CIPAC Handbook, 1985, 1C, 2143, 2257; 1994, F, 292-319) or by titration (ibid., 1985, 1C, 2137); esters by similar methods (ibid., 1985, 1C, 2145); FAO Specification 2/TC/S/F (1992). Mixtures with 2,3,6-TBA by titration or chromatography of a derivative (CIPAC Handbook, 1985, C, 2148). 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 a derivative (J. Lest, Anal. Methods Pestic., Plant Growth Regul. Food Addit., 1967, 5, 439; Anal. Methods Pestic. Plant Growth Regul., 1972, 6, 663) or by hplc (M. Meier et al., Fresenius' Z. Anal. Chem.,1989, 334(3), 235).
MAMMALIAN TOXICOLOGY
IARC ref. 30, 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.
MCPA
Oral Acute oral LD50 for rats 700-1160 mg/kg. Skin and eye Acute percutaneous LD50 for rats >4000 mg/kg. Not irritating to skin; irritating to eyes. Not a skin sensitiser. Inhalation LC50 (4 h) for rats >6.36 mg/l. NOEL (24 mo) for rats 20 ppm (c. 1.33 mg/kg daily), for mice 100 ppm (c. 18 mg/kg daily). Water GV 2 mg/l (TDI 0.5 mg/kg b.w.). Toxicity class WHO (a.i.) III; EPA (formulation) III EC classification Xn; R22| Xi; R38, R41: (for salts and esters, Xn; R20/21/22)
MCPA-2-ethylhexyl
Skin and eye A skin irritant. Not a skin sensitiser (guinea pigs). Inhalation LC50 for rats >4.5 mg/l.
ECOTOXICOLOGY
MCPA
Birds Acute oral LD50 for bobwhite quail 377 mg/kg. Sub-acute dietary LC50 (5 d) for bobwhite quail and mallard ducks >5620 ppm. Fish LC50 (96 h) for rainbow trout 50-560, bluegill sunfish >150, carp 317, silverside 220 mg/l. Daphnia LC50 (48 h) >190 mg/l. Algae EC50 for Selenastrum capricornutum >392 mg/l. Other aquatic spp. LC50 for pink shrimp (Panaeus duorarum) 231 mg/l. Bees LD50 0.104 mg/bee. Worms LD50 (14 d) for Eisenia foetida 325 mg/kg soil.
ENVIRONMENTAL FATE
Animals In rats, following oral administration, MCPA is rapidly absorbed and excreted almost exclusively in the urine, with only a small proportion in the faeces. Only moderate metabolism occurs, and there is only a small amount of conjugate formation. Plants In winter wheat, MCPA is hydroxylated at the methyl group with formation of 2-hydroxymethyl-4-chlorophenoxyacetic acid. This may be further degraded to the benzoic acid, prior to ring opening. Soil/Environment In soil, degraded to 4-chloro-2-methylphenol, followed by ring hydroxylation and ring opening. DT50 <7 d after initial lag phase. Duration of residual activity in soil is c. 3-4 mo, following an application rate of 3 kg/ha.
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