Pyrazophos

Chemical Properties

Pure product is colorless crystals. m.p. 51~53℃, relative density 1.348 (25℃), vapor pressure >0.133×10-3Pa (20℃), 0.221×10-3Pa (50℃). solubility at 20℃: acetone 121.2%, toluene >98%, ethyl acetate 89.8%, ethanol 9.5%, hexane 1.1%, water 0.42% (0.03%). Also soluble in benzene, xylene, carbon tetrachloride, trichloroethylene and other organic solvents. It is easy to decompose under acidic and alkaline conditions, but it will not produce obvious decomposition phenomenon when stored under dry conditions for 2 years.

Uses

Pyrazophos is a systemic fungicide that provides both protective and curative control of various fungal diseases such as powdery mildew (Podosphaera) on apples, stone fruits, bush fruits and strawberries, Erysiphe in cucurbits and tomatoes, Uncinula on vines and leaf blotch (Rhynchosporium) in cereals.

Uses

Pyrazophos is an anticholinesterase pesticide used on fruits and vegetables and can be determined by gas chromatography/mass spectrometry and liquid chromatography with fluorescence detection.

Uses

Fungicide.

Production Methods

Pyrazophos is commercially produced by reacting O,O-diethyl phosphorochloridothioate with 2-hydroxy-5-methylpyrazole-3-carboxylate ethyl ester (prepared from ethyl acetoacetate and hydrazine followed by selective oxidation and esterification) in the presence of triethylamine or potassium carbonate in acetone or toluene, forming the phosphorothioate ester linkage. The crude product undergoes neutralisation, aqueous washing, and vacuum distillation to yield pyrazophos.

Definition

ChEBI: A member of the class of pyrazolopyrimidines that is the ethyl ester of 2-[(diethoxyphosphorothioyl)oxy]-5-methylpyrazolo[1,5-a]pyrimidine-6-carboxylic acid. A fungicide used to control Erysiphe, Helminthosporium and ital>Rhynchospium in cereals.

Mechanism of action

Systemic with protective and curative action. Phospholipid biosynthesis inhibitor.

Metabolic pathway

Limited information is available to describe the degradation and metabolic fate of pyrazophos. Hydrolytic cleavage of the P-O-pyrazolopyrimidine linkage is the primary metabolic pathway. Oxidative desulfuration of pyrazophos to pyrazophos-oxon is only a minor pathway, observed in the plant metabolism study (Scheme 1).

Metabolism

Its mode of action is believed to be the inhibition of melanin biosynthesis and the development of appressoria by fungal conidia. Formulation is available as emulsifiable concentrate (EC: 30%). Application rates on Oidium spp. are in the range of 15–30 g a.i./hl.

Degradation

Pyrazophos (1) is hydrolysed in acidic or alkaline solution (PM).

Pesticide Type

Fungicide