2275-23-2

Vamidothion is a colorless crystalline substance,. It is readily soluble in water (4 kg/L) and most organic solvents except aliphatic hydrocarbons. Log Kow = 0.12. It decomposes in strong alkaline and acidic media.

Vamidothion is a phosphorothioic insecticide for apples and potatoes.

Vamidothion is a systemic insecticide used to control Homoptera in cotton, fruit and rice.

ChEBI: An organic thiophosphate that is N-methyl-2-[(2-sulfanylethyl)sulfanyl]propanamide in which the thiol group has been converted to the corresponding O,O-dimethyl thiophoshate. Formerly used as an inse ticide and acaricide, it is no longer approved for use within the European Union.

Systemic. Acetylcholinesterase (AchE) inhibitor.

Pyriproxyfen formulations demonstrate persistent efficacy. For example, a water-based 5.3% pyriproxyfen spot-on formulation applied to cats was reported to completely prevent the hatching of flea eggs for at least 46 days after treatment and continued to provide greater than 96% control until day 60 (57). Because pyriproxyfen is efficacious at very low concentrations, trace amounts of the chemical, when transferred from treated pets to their environments, are sufficient to inhibit the development of larvae.

The synthesis of vamidothion involves a two-step process. The first step is the synthesis of the intermediate, 2-((2-hydroxyethyl)thio)-N-methylpropanamide. The second step is the phosphorylation of this intermediate to yield vamidothion.
Step 1: Synthesis of Synthesis of 2-((2-hydroxyethyl)thio)-N-methylpropanamide (Intermediate 1).
In a round-bottom flask equipped with a magnetic stirrer and a reflux condenser, dissolve ethyl 2-mercaptopropionate (1 equivalent) in a suitable solvent such as ethanol. Add sodium ethoxide (1.1 equivalents) to the solution and stir for 15 minutes at room temperature. To this solution, add 2-chloroethanol (1.2 equivalents) dropwise. Heat the reaction mixture to reflux for 4-6 hours. Monitor the reaction progress by Thin Layer Chromatography (TLC). After completion, cool the reaction mixture to room temperature and remove the solvent under reduced pressure. Extract the crude product with a suitable organic solvent (e.g., ethyl acetate) and wash with brine. Dry the organic layer over anhydrous sodium sulfate and concentrate to obtain the crude ethyl 2-((2-hydroxyethyl)thio)propanoate. Dissolve the crude ethyl 2-((2-hydroxyethyl)thio)propanoate in an excess of a 40% aqueous solution of methylamine. Stir the mixture at room temperature for 24-48 hours. After completion, extract the product with dichloromethane. Wash the organic layer with water and brine. Dry the organic layer over anhydrous sodium sulfate and concentrate under reduced pressure to yield the crude 2-((2-hydroxyethyl)thio)-N-methylpropanamide.
Step 2: Synthesis of Vamidothion
In a three-necked flask equipped with a mechanical stirrer, a dropping funnel, and a thermometer, dissolve the crude 2-((2-hydroxyethyl)thio)-N-methylpropanamide (1 equivalent) in a suitable anhydrous solvent (e.g., toluene) under a nitrogen atmosphere. Cool the solution to 0-5 °C in an ice bath. Add a base such as triethylamine (1.2 equivalents) to the solution. Slowly add O,O-dimethylphosphorochloridothioate (1.1 equivalents) dropwise, maintaining the temperature below 10 °C. After the addition is complete, allow the reaction mixture to stir at room temperature for 12 16 hours. Upon completion, filter the reaction mixture to remove the triethylamine hydrochloride salt. Wash the filtrate with a saturated solution of sodium bicarbonate and then with brine. Dry the organic layer over anhydrous sodium sulfate and concentrate under reduced pressure to obtain crude vamidothion.

Vamidothion is mainly metabolised via oxidation to its sulfoxide; further oxidation to the corresponding sulfone has been observed in houseflies but occurs much less readily than with other thioether-containing organophosphates (e.g. phorate). The sulfoxide is then hydrolysed via P-S and C-S bond cleavage to give the thiol or hydroxyl derivatives and dimethyl phosphate and O,O-dimethyl phosphorothioate respectively. O-Demethylation apparently occurs as a major degradation process in plants but has not been observed in soil or in animals. N-Demethylation and hydrolysis to the corresponding carboxylic acid, such as occurs with dimethoate, does not apparently happen in the case of vamidothion.

Vamidothion is decomposed in strongly acidic or alkaline media (PM). Barceld et al. (1993) examined the photolysis of vamidothion in water containing 2-4% methanol and 5% acetone as a photosensitiser irradiated by a xenon arc (suntest) lamp. Metabolites were analysed and characterised by HPLC, thermospray MS and UV (diode array) spectra. The main degradation product identified was vamidothion sulfoxide (2). This product of vamidothion photolysis is shown in Scheme 1.

The acute oral LD₅₀ for rats is 64–105 mg/kg. Inhalation LC50 (4 h) for rats is 1.73 mg/L air. ADI is 8 μg/kg b.w.

Insecticide; Acaricide