Uses
Mevinphos is used to control chewing and sucking insects in a
wide range of crops.
Definition
ChEBI: Mevinphos is a dialkyl phosphate and an organophosphate insecticide. It has a role as an EC 3.1.1.7 (acetylcholinesterase) inhibitor, an acaricide, an agrochemical and an avicide. It is functionally related to a methyl 3-hydroxybut-2-enoate.
Metabolic pathway
Technical mevinphos consists of two stereochemical isomers in the
E:Z ratio of about 7:3. Mevinphos is characterised by a high rate of metabolic
breakdown, such that crops can be harvested within a few hours
of its application. The compound is also rapidly translocated within
plants. There are considerable differences in the metabolism of the two
isomers. In general, the E-isomer (the more toxic, more active acetylcholinesterase
inhibitor and more effective insecticide) is detoxified more
quickly in plants but more slowly in animals. The major route of
detoxification in plants is through hydrolysis to give dimethyl phosphate
and methyl acetoacetate with hydrolysis of the carboxylic ester
function being of lesser importance. Demethylation of the more toxic Eisomer
via a glutathione-based transalkylation reaction is an important
route in mammals, whereas the 2-isomer is hydrolysed to dimethyl
phosphate .
Degradation
Mevinphos is hydrolysed in alkaline solutions (PM). The DT50s for the
technical material at pH 6, 7 and 10 were 94 days, 30 days and 8 hours
respectively (Porter et al., 1964). The E-isomer (1) is hydrolysed more
quickly than the Z-isomer (2). Under alkaline conditions, the products
of hydrolysis of the E-isomer were shown to be dimethyl phosphate (3),
monomethyl phosphate (4), acetone (S), the E-mevinphos carboxylic acid
(6) and the desmethyl E-mevinphos carboxylic acid (7). A small amount of
desmethyl E-mevinphos (8) was also detected. The Z-isomer gave very
little of the desmethyl Z-mevinphos carboxylic acid (10) indicating that
the attack of hydroxyl ion on the 2-isomer was almost entirely on phosphorus,
whereas there was additional nucleophilic attack on the carboxylic
ester function in the case of the E-isomer which was shown to gwe
dimethyl phosphate (3) and acetone (5). Acid hydrolysis resulted in
demethylation of both isomers with the desmethyl E-mevinphos (8)
and desmethyl Z-mevinphos (9) being detected in addition to dimethyl
phosphate (3) and monomethyl phosphate (4) (Spencer et al., 1958) (see
Scheme 1).
