Oxydemeton-methyl

Description

Oxydemeton-methyl, i.e., demeton-S-methyl sulfoxide, is a colorless oil, bp 106 ?C/0.01 mm Hg, vp 3.8 mPa (20 ?C). It is miscible with water and soluble in most organic solvents, except petroleum ether. Log Kow = ?0.74(21 ?C). Oxydemeton-methyl is relatively stable in acidic media but hydrolyzed in alkalinemedia;DT₅₀ values (22 ?C) at pH 4, 7, and 9 are 107, 46, and 2 d, respectively.

Chemical properties

Oxydemeton methyl is a colorless to amber-colored liquid. Oxydemeton methyl is relatively slowly hydrolyzed in acidic media, but rapidly hydrolyzed in alkaline media.
Oxydemeton methyl is miscible with water; readily soluble (10–100 g/ 100 mL) in dichloromethane, 2-propanol, and toluene; and practically insoluble (＜1 g/100 mL) in n-hexane.

The Uses of Oxydemeton-methyl

Oxydemeton-methyl is used to control sucking insects on fruit, vines, vegetables, cereals and ornamentals.

The Uses of Oxydemeton-methyl

A metabolite of Demeton-S-methyl (D231370). An organophosphorus pesticide biomarker.

The Uses of Oxydemeton-methyl

Systemic and contact insecticide and acaricide used to control spider mites and other insects on vegetables and some ornamentals.

Definition

ChEBI: Oxydemeton-methyl is an organic thiophosphate and an organothiophosphate insecticide. It has a role as an EC 3.1.1.7 (acetylcholinesterase) inhibitor, an acaricide and an agrochemical. It is functionally related to a 2-(ethanesulfinyl)ethanol.

General Description

Clear amber liquid.

Air & Water Reactions

Water soluble. DEMETON-S-METHYL SULFOXIDE may be rapidly hydrolyzed by alkali .

Reactivity Profile

Organophosphates such as DEMETON-S-METHYL SULFOXIDE are susceptible to formation of highly toxic and flammable phosphine gas in the presence of strong reducing agents such as hydrides. Partial oxidation by oxidizing agents may result in the release of toxic phosphorus oxides.

Fire Hazard

DEMETON-S-METHYL SULFOXIDE is flammable.

Safety Profile

Poison by ingestion, skin contact, intravenous, and intraperitoneal routes. Human mutation data reported. When heated to decomposition it emits very toxic fumes of POx and SOx. See also other demeton entries.

Environmental Fate

Soil. The sulfoxide group is oxidized to the sulfone and oxidative and hydrolytic cleavage of the side chain gives dimethylphosphoric and phosphoric acids (Hartley and Kidd, 1987). Oxamyl was degraded by the microorganism Pseudomonas putida in a laboratory study using cultured bacteria (Zeigler, 1980).
Plant. In asparagus, oxydemeton-methyl was converted to the corresponding sulfone (Szeto and Brown, 1982).
Chemical/Physical. Oxydemeton-methyl can be converted to the corresponding sulfone by hydrogen peroxide (Cremlyn, 1991). Emits toxic fumes of phosphorus and sulfur oxides when heated to decomposition (Sax and Lewis, 1987).

Metabolic pathway

Oxydemeton-methyl is the primary thiooxidation metabolite of demeton- S-methyl. It is further oxidised rapidly to demeton-Smethylsulfon in all media. The major route of further metabolism of both sulfoxide and sulfone is via hydrolysis to the sulfoxide and sulfone thiols. Stage I1 metabolism of these thiol hydrolysis products proceeds via oxidation and conjugation and is different in soil, plants and animals. In plants the thiols are conjugated, whereas in animals they are mainly methylated and oxidised to sulfoxides, sulfones and sulfonic acids. Demethylation is an important route in mammals; however, the compound is sufficiently polar for much to be excreted in the urine unchanged. Demethylation has also been reported to occur in plants.

Metabolism

Almost 99% of orally administered oxydemeton-methyl to animals is excreted within 48 h in the urine. It is oxidized to the sulfone, followed by hydrolytic cleavage of the P?S bond. The thiol metabolites are conjugated or methylated. O-Demethylation is also an important degradation route both inmammals and plants. Oxydemeton-methyl is rapidly degraded in soils.

Degradation

Oxydemeton-methyl is relatively slowly hydrolysed in acidic media but rapidly hydrolysed under alkaline conditions. Half-lives at pH values 4,7 and 9 were 107,46 and 2 days respectively (PM). Under sterile aqueous conditions oxydemeton-methyl was degraded to give the oxidised hydrolysis product bis[2-(ethylsulfinyl)ethyl] disulfide (2) (Ziegler et al., 1980) (Scheme 1).

Toxicity evaluation

The acute oral LD₅₀ for rats is about 50 mg/kg. Inhalation LC50 (4 h) for rats is 0.47 mg/L air. NOEL (2 yr) for rats is 1 mg/kg diet (0.05 mg/kg/d). ADI is 0.3 μg/kg b.w. for the sum of oxydemeton-methyl, demeton-S-methylsulfone, and demeton-S-methyl.