Methamidophos

• Thiophosphoric acid O, S- dimethylesteramid
• O, S- dimethyl phosphoramidothioate
• Tamaron

Colorless solid

Fixed

1.27 g · cm -3

44.9 ° C

Decomposes

• Very slightly soluble in water (> 2000 g · l-1 at 20 ° C)
• Soluble in alcohols and ketones
• Slightly soluble in ether

Risk

• 7.5 mg · kg -1 ( LD50, rat, oral)
• 118 mg · kg -1 ( LD50, Rabbit, transdermal)

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Methamidophos is a chemical compound from the group of Thiophosphorsäureamide and an organophosphate insecticide.

Stereoisomerism

Because methamidophos contains a chiral center at the phosphorus atom, there are two stereoisomers that are mirror image behave, the (R) - enantiomer and the ( S)- enantiomer. As an insecticide, the racemate - a 1:1 mixture of the (R ) enantiomer and the (S)- enantiomer - are used.

Production and representation

Methamidophos is prepared starting from Dimethylphosphordithiosäure ( DMPA), which is chlorinated to O, O- Dimethylchlorthiophosphat ( DMPCT ). This reacts with ammonia and then with either dimethyl sulfate or methyl iodide to the final product.

Properties

Methamidophos is a colorless crystalline substance. The technical product ( about 73 % purity) forms yellowish to colorless crystals having a melting point below 40 ° C. When heated, the compound decomposes without boiling.

Use

Methamidophos is a 1969 introduced systemically acting insecticide and acaricide with a broad spectrum of activity in many cultures. It is used in China in large quantity in the cultivation of rice.

Safety

Methamidophos showed a very high acute toxicity: LD50 (rat, oral): 7.5 mg / kg body weight; LD50 (rat, dermal): 69 mg / kg body weight; LC50 (inhalation rat) 0,063 mg / liter of air ( 4 h). In tests on rats, the typical clinical symptoms ( salivation and lacrimation, difficulty breathing, twitching, convulsions) were observed to cholinesterase inhibition. It turned out to be not irritating to skin and eye irritant and a skin sensitizer than not.