NOMENCLATURE

Common name phenmedipham (BSI, E-ISO, ANSI, WSSA, JMAF); phenmédiphame ((m) F-ISO)

IUPAC name methyl 3-(3-methylcarbaniloyloxy)carbanilate; 3-methoxycarbonylaminophenyl 3'-methylcarbanilate 

Chemical Abstracts name 3-[(methoxycarbonyl)amino]phenyl (3-methylphenyl)carbamate 

Other names PMP  CAS RN [13684-63-4]  Development codes SN 38 584 (Schering); ZK 15320; EP-452 

PHYSICAL CHEMISTRY

Composition Tech. grade is >97% pure.  Mol. wt. 300.3  M.f. C₁₆H₁₆N₂O₄  Form Colourless crystals.  M.p. 143-144 ºC; (tech., 140-144 ºC)  V.p. 1.33 ´ 10^-6 mPa (25 ºC)  K_OW logP = 3.59 (pH 3.9)  Henry 5 ´ 10^-8 Pa m³ mol^-1 (calc.)  S.g./density 0.34-0.54 (20 ºC)  Solubility In water 4.7 mg/l (room temperature). Soluble in polar organic solvents. In acetone, cyclohexanone c. 200, methanol c. 50, chloroform 20, benzene 2.5, hexane c. 0.5, dichloromethane 16.7, ethyl acetate 56.3, toluene c. 0.97, 2,2,4-trimethylpentane 1.16 (all in g/l, 20 ºC).  Stability Stable up to 200 ºC. Very stable in acidic media, but hydrolysed in neutral and alkaline media; DT₅₀ (22 ºC) 50 d (pH 5), 14.5 h (pH 7), 10 min (pH 9). In solution (pH 3.8) irradiated at 280 nm, DT₅₀ 9.7 d.  pKa <0.1 

APPLICATIONS

Biochemistry Photosynthetic electron transport inhibitor at the photosystem II receptor site.  Mode of action Selective systemic herbicide, absorbed through the leaves, with translocation primarily in the apoplast.  Uses Used post-emergence, at 1 kg a.i./ha, in beet crops, especially sugar beet, after the emergence of most broad-leaved weeds and before they develop more than 2-4 true leaves; also used on strawberries, spinach, peas, mangold and red beet.  Phytotoxicity Non-phytotoxic to beet crops.  Formulation types EC; SC; oil-SC; SL; WG.  Compatibility Incompatible with alkaline substances. 

ANALYSIS

Product analysis by titration (CIPAC Proc., 1980, 2, 215; CIPAC Handbook 1985, 1C, 2181) or by hplc (ibid.); method available from Aventis. Residues by glc (K. Kossmann & N. A. Jenny, Anal. Methods Pestic. Plant Growth Regul., 1973, 7, 611); in soil by hplc or by hydrolysis to m-toluidine, derivatives of which are determined by glc with ECD or by colorimetry (K. Kossmann, Weed Res., 1970, 10, 340). Details available from Aventis. 

MAMMALIAN TOXICOLOGY

Oral Acute oral LD₅₀ for rats and mice >8000, guinea pigs and dogs >4000 mg/kg.  Skin and eye Acute percutaneous LD₅₀ for rabbits 1000, rats 2500 mg/kg. Not a skin sensitiser.  Inhalation LC₅₀ (4 h) for rats >7.0 mg/l.  NOEL (2 y) for rats 100, dogs 1000 mg/kg; (90 d) for rats and dogs 200 mg/kg diet.  ADI 0.03 mg/kg.  Other Acute i.p. LD₅₀ for rats >5000 mg/kg.  Toxicity class WHO (a.i.) III (Table 5); EPA (formulation) IV 

ECOTOXICOLOGY

Birds Acute oral LD₅₀ for chickens >2500, mallard ducks >2100 mg/kg. Dietary LC₅₀ (8 d) for mallard ducks and bobwhite quail >6000 mg/kg diet.  Fish LC₅₀ (96 h) for rainbow trout 1.4-3.0, bluegill sunfish 3.98 mg/l. LC₅₀ (96 h) for harlequin fish 16.5 mg/l (15.9% EC formulation).  Daphnia LC₅₀ (72 h) 3.8 mg/l.  Algae IC₅₀ (96 h) 0.13 mg/l.  Bees Not toxic to bees; LD₅₀ (oral) >23 mg/bee; (contact) 50 mg/bee.  Worms EC₅₀ (14 d) >156 mg/kg soil.

ENVIRONMENTAL FATE

Animals In mammals, following oral administration, 99% is excreted within 72 hours, mainly in the urine. Hydrolysis to methyl N-(3-hydroxyphenyl)carbamate and conjugation to glucuronides and ethereal sulfates are the major steps in metabolism.  Plants Methyl N-(3-hydroxyphenyl)carbamate is the major metabolite in plants.  Soil/Environment DT₅₀ in soil c. 25 d, DT₉₀ c. 108 d. Metabolites include methyl N-(3-hydroxyphenyl)carbamate and m-aminophenol, and subsequently complexes with soil components (R. Senawana et al., Bull. Environ. Contam. Toxicol., 1971, 6, 322-327). Phenmedipham does not accumulate in soil, nor is there any relevant uptake by following crops. Due to its favourable physico-chemical parameters, no risk of groundwater contamination is to be expected. K_oc 2400.