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;DT
50 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.
Uses
Oxydemeton-methyl is used to control sucking insects on fruit,
vines, vegetables, cereals and ornamentals.
Uses
Systemic and contact insecticide and acaricide used to control spider mites and
other insects on vegetables and some ornamentals.
Uses
A metabolite of Demeton-S-methyl (D231370). An organophosphorus pesticide biomarker.
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 LD
50 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.
