Plant growth regulator, phenylurea
Common name thidiazuron (BSI, E-ISO, (m) F-ISO, ANSI)
IUPAC name 1-phenyl-3-(1,2,3-thiadiazol-5-yl)urea
Chemical Abstracts name N-phenyl-N'-1,2,3-thiadiazol-5-ylurea
CAS RN [51707-55-2] Development codes SN 49 537 (Schering)
Mol. wt. 220.2 M.f. C9H8N4OS Form Colourless, odourless crystals. M.p.
210.5-212.5 oC (decomp.) V.p. 4x10-6 mPa (25 oC) (Langmuir method) KOW
logP = 1.77 (pH 7.3) Henry 2.84x10-8 Pa m3 mol-1 (calc.) Solubility In
water 31 mg/l (pH 7, 25 oC). In hexane 0.002, methanol 4.20,
dichloromethane 0.003, toluene 0.400, acetone 6.67, ethyl acetate 1.1
(all in g/l, 20 oC). Stability Rapidly converted to photoisomer,
1-phenyl-3-(1,2,5-thiadiazol-3-yl)urea, in presence of light (l
>290 nm). Hydrolytically stable at room temperature from pH 5-9. No
decomposition in accelerated storage stability study (14 d, 54 oC).
History Plant growth regulator reported by F. Arndt et al. (Plant
Physiol., 1976, 57, Supplement, p. 99). Introduced by Schering AG (now
Bayer CropScience). Patents DE 2506690; DE 2214632 Manufacturers Bayer
Biochemistry Cytokinin activity. Mode of action Plant growth
regulator, absorbed by the leaves, which stimulates formation of an
abscission layer between the plant stem and the leaf petioles, causing
the dropping of entire green leaves. Uses Used for defoliation of
cotton, in order to facilitate harvesting; applied at 0.21 kg/ha per
season. Formulation types EC; WP; SC. Selected products: 'Dropp'
'Separate' (Feinchemie Schwebda) mixtures: 'Ginstar' (+ diuron) (Bayer
CropScience); 'Harvade-4198' (+ dimethipin) (Crompton); 'Leafless' (+
dimethipin) (Crompton) Discontinued products mixtures: 'Dropp Ultra' *
(+ diuron) (Aventis)
Product analysis by hplc. Residues determined by hplc or by glc with
ECD of a derivative. Details available from Bayer CropScience.
Oral Acute oral LD50 for mice >5000, rats >4000 mg/kg. Skin and
eye Acute percutaneous LD50 for rats >1000, rabbits >4000 mg/kg.
Mild eye irritant; non-irritating to skin (rabbits). No skin
sensitisation (guinea pigs). Inhalation LC50 (4 h) for rats >2.3
mg/l air. NOEL (90 d) for rats 200 mg/kg diet; (1 y) for dogs 100
mg/kg diet. No significant effects observed in a 2 y carcinogenicity
study in mice and a 3-generation reproduction study in rats. Other
Acute i.p. LD50 for rats 4200 mg/kg. Non-mutagenic. Toxicity class WHO
(a.i.) U; EPA (formulation) III
Birds Acute oral LD50 for Japanese quail >3160 mg/kg. Dietary LC50
(8 d) for bobwhite quail and mallard ducks >5000 mg/kg diet. Fish
LC50 (96 h) for rainbow trout >19, bluegill sunfish >32 mg/l.
Daphnia LC50 (48 h) >10 mg/l. Bees Non-toxic to honeybees. Worms
LC50 (14 d) for earthworms >1400 mg/kg.
Animals In rats and goats, metabolism involves hydroxylation of the
phenyl group, followed by formation of water-soluble conjugates.
Following oral administration, the compound is excreted in the urine
and faeces within 96 hours. Plants Only small amounts of residue
(normally <0.1 mg/kg) are likely in cottonseed. Soil/Environment
Strongly adsorbed by soil. DT50 in soil c. 26-144 d (aerobic), 28 d
(anaerobic). Essential soil microbial processes are only temporarily
influenced, if at all.