Organophosphorus Compounds Properties & Applications
"Learn about the properties and applications of organophosphorus compounds, including their toxicity to warm-blooded animals and insects. Explore the synthesis of compounds like Schradan and Parathion, their systemic effects, and practical advantages in pest control."
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Organophosphorus Compounds Dr. Geeta Singh Assistant Professor Department of Chemistry D.D.U. Gorakhpur University, Gorakhpur 1
Organophosphorus Compounds Lange and Krueger first time reported the bioactivity of Organophosphorus compounds. Schrader prepared the compounds which are known under the names: Tabun, Soman and Sarin which were used in chemical warfare.
Organophosphorus compounds are toxic to warm blooded animals as well as strongly toxic to insects. Oorganophosphorus compounds are the largest group of pesticides and they have wide spectrum for insecticides due to their efficiency, duration of action, toxicity and range of activity. The important compounds of this series are OMPA, Parathion, Paroxon, Diazinon, Malathion, dichlorvous, chlorpyrifos etc.
Octamethyl pyrophosphoroamidate (Schradan) OMPA Schradan was prepared by partial hydrolysis of tetramethyl chlorophosphonoamidate obtained by reaction of dimethylamine and phosphoryl chloride. H2O + 2R3N + POCl3
Properties and Application Pure commercial product is colorless oily liquid b.p.118-122 o C. It is readily soluble in water as well as in organic solvents, but very stable in aqueous media. OMPA is strongly toxic to warm blooded animals, its LD50 for rats being 8 mg/kg, and is a relatively weak contact insecticide. It is formulated as 30 to 40% aqueous solution. It is not phototoxic but very effective against insects.
Schradan is a systemic insecticide and is translocated from the surface of the sprayed leaves or from the roots into different parts of the plants. This systemic effect has several practical advantages: a. Exposed to the climate like rain , sunshine, atmospheric oxygen etc; b. Hidden insects are effected; c. Pesticide often penetrate the new shoots which develop after spraying, and protects them against insect pests; d. When the chemical is absorbed by the leaf surface it poisons only the pests feeding by suction from the leaf tissues, while useful insects with other modes of feeding are not affected.
O,O-Diethyl-p-nitrophenyl phosphorothioate (Parathion) It was prepared by Schrader by the reaction of diethylphosphorothionochloridate with sodium p-nitrophenolate +
Properties and Application Parathion is a yellow liquid b.p. 116 OC. It is soluble in water at room temperature. It has low toxicity towards warm blooded animals and higher stability against hydrolysis. Its LD50 for rat is 6.4 mg/kg. Its formulation with mineral oils is very effective against various hibernating forms of orchard pests. It is potent against plant lice, flies and caterpillars at concentration 0.0001- 0.0008 %. It is hazardous to bees therefore parathion should not be used during blossom time. Parathion acts as a contact and stomach insecticide. It has no systemic effect. About four hundred pests are known which can be controlled effectively by use of Parathion
Diethyl-p-nitrophenyl phosphate (Paraoxon) It was also prepared by Schrader by the reaction of diethylphosphorochloridate with sodium p-nitrophenolate. As follows: +
Properties and Application The pure compound is an odourless reddish yellow oil, b.p. 148-151 OC. It is soluble in water and readily soluble in most of the organic solvent. It is highly toxic to warm blooded animals LD50 for rat is 3 mg/kg and it is not readily used in agriculture. However it possess strong insecticidal and acaricidal effect. In ophthalmology it is used as miotic agent under the name Mintacol.
O,O-dimethyl dithiophosphate of diethyl mercaptosuccinate (Malathion) Other names: Carbofos, Maldison, Mercaptothion Malathion is an organophosphate insecticide. Malathion is a colorless to amber liquid with a skunk- or garlic-like odor. Malathion may be prepared by reaction of O,O- dimethyldithiophosphoric acid and diethyl maleate. It may also be prepared in single step by the reaction of phosphorus pentasulphide, methanol and diethyl ester of maleic acid. Malathion is liquid b.p. 156-157 C at 0.7 mm Hg and m.p. 2.9 C
Properties and Application Malathion is a broad-spectrum insecticide used to control a variety of outdoor insects in both agricultural and residential settings. It has a broad range of action against other sucking and chewing insects. Malathion is a pesticide that is widely used in agriculture, residential landscaping, public recreation areas. Its great importance is due to its low toxicity to warm blooded animals. Its LD50 for rat is 1200 mg/kg. Malathion is an insecticide of relatively low human toxicity. In the US, it is the most commonly used organophosphate insecticide.
Malathion is used in public health pest control programs such as mosquito eradication in conjunction with diesel fuel to fog an area where there is an infestation of mosquitoes. Malathion is metabolized in insects by enzymatic oxidation to its oxo analogue, malaoxon. This oxidative conversion increases the insecticidal and toxic effect to many times the original values. Malathion is registered for use on food, feed, and ornamental crops and in boll weevil and fruit fly eradication programs. Malathion in low doses (0.5% preparations) is used as a treatment of head lice and body lice.
O CH3O P S CH-COOC2H5 CH3O CH2-COOC2H5 Malaoxon
Diazinon O,O-Diethyl-O-(2-isopropyl-6-methyl-4-pyrimydyl)phosphorothioate It was prepared by condensation of isobutyramide and ethylacetoacetate, yielding 2-isopropyl-4-methyl-oxy-pyrimidine, which is then reacted with O,O-diethyl phosphorothiochlorinate. (C2H5O)2PSCl +
Properties and Application Pure compound is colourless liquid b.p. 83-84 OC. Technical compound contains 95% of pure product. It is lightly soluble in water but readily soluble in petroleum ether, alcohol and xylene. Its LD50 for experimental rat is 50-100 mg/kg. This compound shows promising effect when spread to kill house fly and some agricultural insects.
