Definition
ChEBI: An organic thiophosphate that is O,O-diethyl hydrogen phosphorothioate in which the hydrogen of the hydroxy group is replaced by a 5-phenyl-1,2-oxazol-3-yl group.
Description
Isoxathion is a pale yellow liquid, bp 160 ?C/0.15 mm
Hg, vp <0.133mPa (25 ?C). Solubility in water is 1.9 mg/L
(25 ?C). It is readily soluble in most organic solvents. Log
Kow = 3.88. It is unstable to alkali.
Uses
Isoxathion is used as a pesticide.
Uses
Isoxathion is used to control sucking pests, leaf miners and some
chewing pests in a variety of fruit, vegetables and ornamental plants.
Synthesis
The industrial production of isoxathion begins with the synthesis of a substituted phenol derivative, which undergoes thiophosphorylation using reagents such as O,O-dimethyl phosphorochloridothioate to introduce the organophosphate moiety. This step is typically carried out under controlled temperature and anhydrous conditions to prevent hydrolysis and ensure high yield. The resulting intermediate is then subjected to aromatic substitution with a heterocyclic compound, often a pyridyl or thiazole derivative, to enhance insecticidal potency and selectivity.
Metabolic pathway
The principal route of isoxathion metabolism in soil, plants and mammals
is by hydrolysis, probably via the oxon to 3-hydroxy-5-phenylisoxazole
which is rapidly conjugated in both plants and rats. In soils, and to a
lesser extent in plants and mammals, further metabolism of 3-hydroxy-
5-phenylisoxazole proceeds via opening of the isoxazole ring to give
various metabolites of which benzoic acid is one of the more important.
De-ethylation of the phosphate moiety has not been observed.
Metabolism
The principal degradation route of isoxathion in animals,
plants, and soil is cleavage of P?O-isoxazole through
oxidative desulfuration to the oxon followed by hydrolysis
to 3-hydroxy-5-phenylisoxazole, which is conjugated in
both plants and rats.
Degradation
Isoxathion is unstable to alkalis (PM). The hydrolysis product, 3-hydroxy-
5-phenylisoxazole (2), yielded 5-phenyl-3H-oxazolin-2-one (3) as the
major photoproduct via a photolytic rearrangement (Nakagawa et al.,1974).
Toxicity evaluation
The acute oral LD50 for rats is 112 mg/kg. NOEL
(2 yr) for rats is 1.2 mg/kg b.w. DT50 in soil is 9–40 d.
