Pyrithiobac-sodium

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Chemical Identification | General Product Information | Physical & Safety Data

Chemical Identification

Common Name

Pyrithiobac-sodium

中文通用名

嘧草硫醚

IUPAC

sodium 2-chloro-6-(4,6-dimethoxypyrimidin-2-ylthio)benzoate

CAS

sodium 2-chloro-6-[(4,6-dimethoxy-2-pyrimidinyl)thio]benzoate

CAS No.

123343-16-8

Molecular Formula

C₁₃H₁₀ClN₂NaO₄S

Molecular Structure

General Product Information

Category

Herbicides > Aromatic acid herbicides

Activity

Herbicide.Pyrithiobac-sodium is primarily a post-emergence herbicide though it can be used from pre- to post-emergence since the compound exhibits residual activity. It is taken up rapidly by roots and shoots and has greatest activity when applied at the 1-3 leaf stage of the weeds. Death occurs 10-14 days after application. Activity is enhanced by the addition of adjuvants such as: non-ionic surfactants; silicon-type adjuvants; and crop oil concentrates. Tank mixes with bromoxynil and/or glyphosate have extended pyrithiobac sodium's weed control spectrum and it is suitable for use on cotton genetically modified to be tolerant to these herbicides. Pyrithiobac has, however, been shown to be antagonistic to some other herbicides in tank mixes. FMC recommends that pyrithiobac-sodium is applied with clomazone pre-emergence, or early post-emergence following clomazone.

When applied post-emergence, pyrithiobac-sodium does not damage the cotton crop at the recommended use rate. Some chlorosis and stunting has been observed, but the quality and yield of cotton is not affected. It is safe to rotational crops. Early-season insecticides can be applied in mixtures or in sequence with pyrithiobac-sodium without crop injury, although some weakening of the cotton fibre has been observed. In field trials, pyrithiobac-sodium gave better control of weeds than commercial standards at lower application rates.

CropUse

CropUses:
cotton

Cotton	35 g ai/ha (pre-emergence)
	70 g ai/ha (post-emergence)

Physical & Safety Data

Physical Properties

Molecular weight:348.7; Physical form:White solid. Density:1.609; Composition:Tech. is >93%. Melting point:233.8-234.2 °C ( decomp.); Vapour pressure:4.80 × 10-6 mPa (25 °C); Partition coefficient(n-octanol and water):logP = 0.6 ( pH 5), -0.84 ( pH 7); pKa:2.34; Solubility:In water 264 ( pH 5), 705 ( pH 7), 690 ( pH 9), 728 (unbuffered) (all in g/l, 20 °C). In acetone 812, methanol 270 × 103, n-hexane 10, dichloromethane 8.38 (all in mg<; Stability:Stable in water (32 d, pH 5-9, 27 °C) and to heat (15 d at 54 °C).

Toxicology

Oral:Acute oral LD₅₀ for male rats 3300, female rats 3200 mg/ kg. Percutaneous:Acute percutaneous LD₅₀ for rabbits >2000 mg/kg. Non-irritating to skin; irritating to eyes (rabbits). Inhalation: LC₅₀ (4 h) for rats >6.9 mg/l. Phytotoxicity:Non-phytotoxic to cotton when applied as directed. ADI:( JMPR) 0.1 mg/ kg b.w. [1999].

Environmental Profile

Ecotoxicology:
Algae: EC₅₀ (5 d) for Selenastrum capricornutum 107µg/l; NOEC for S. capricornutum 22.8 mg/l.Bees: LD₅₀ (48 h, contact) >25µg/bee.Birds:Acute oral LD₅₀ for bobwhite quail >2250 mg/ kg b.w. Dietary LC₅₀ (5 d) for mallard ducks and bobwhite quail >5620 mg/ kg50 (48 h) >1100 mg/l.Fish: LC₅₀ (96 h) for bluegill sunfish >930, rainbow trout >1000, sheepshead minnow >145 mg/l.

Environmental fate:
Animals:More than 90% of radiolabelled pyrithiobac, applied orally and intravenously at 5 mg/ kg to rats, was excreted in urine and faeces within 48 h; the major excreted metabolite was the O-desmethyl derivative. PyrithiSoil:Microbial and photochemical degradation play a major role in degradation in the environment; DT₅₀ in silty soil 60 d. K_d 0.32 (sandy loam), 0.60, 0.38, 0.75 (3 silty loam soils).Plant:Amounts of pyrithiobac-sodium in cotton leaves rapidly decreased, following foliar application; at 62 dat, no residues were found; major metabolites found in foliage were the phenol formed by mono-demethylation, and its glucose conjugate. WATER SOLUBILITY: Soluble, 1% wt/wt (pH 5.6)
Fate in soil:
Pyrithiobac-sodium is degraded primarily by soil microbes. It has a soil half-life of approximately 60 days.

Fate in aquatic systems:
Pyrithiobac-sodium is degraded photochemically in water.

Transport Information

Signal Word:WARNING; Hazard Class:II(Moderately hazardous)