Description
Thiometon is the thion (P=S) analog of demeton-Smethyl.
It is a colorless oil, bp 104 ?C/0.3 mm Hg, vp
39.9 mPa (20 ?C). The water solubility is 200 mg/L (27 ?C).
It is highly soluble inmost organic solvents except alkanes.
Log Kow = 3.15. It is hydrolyzed in alkaline and acidic
media; DT50 (25 ?C) values at pH 3, 6, and 9 are 25, 27,
and 17 d, respectively.
Uses
Thiometon is used to control sucking insects and mites on a wide
range of crops.
Definition
ChEBI: Thiometon is an organic thiophosphate, an organothiophosphate insecticide and an organosulfur compound. 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-(ethylsulfanyl)ethanethiol.
Metabolic pathway
Thiometon is the thion (P=S) analogue of demeton-S-methyl. Consequently,
many of the biotransformations of hometon are similar
to those of demeton-S-methyl to which it is oxidised in animals. It is also
the dimethyl analogue of disulfoton. However, thiooxidation in soil
and plants appears to be more facile than oxidative desulfuration to
the oxon so that its metabolism is analogous to phorate and disulfoton
in that the compound is first thiooxidised to thiometon sulfoxide and
sulfone which are oxidatively desulfurated to oxydemeton-S-methyl and
demeton-S-methylsulfon respectively.
Degradation
Thiometon is more easily hydrolysed in alkaline media than in acid. The
DT50 values at pH 3，6 and 9 were 25,27 and 17 days at 25 °C (PM). The
rates of hydrolysis at pH values 5.7 and 8.5 for thiometon, disulfoton,
demeton-S-methyl and diazinon catalysed by alumina and three different
forms of iron oxide were determined by Dannenberg and I'ehkonen
(1998). Products were analysed by GC-MS. In the presence of oxygen, the
expected thiol product of hydrolysis of the former three compounds, 2-
ethylthioethanethiol(2), was not observed at any stage during the course
of the reaction. Instead it was found to dimerise to the disulfide (3). Under
nitrogen, the main product of disulfoton hydrolysis was an ethylated thiol
which was probably formed via nucleophilic attack of the thiol (2) on
disulfoton, although the experiment was not performed with thiometon
itself.
Toxicity evaluation
The acute oral LD50 for rats is
70–120 mg/kg. Thiometon is metabolized oxidatively in
plants, forming demeton-S-methyl sulfoxide and sulfone,
which are the active principles.
