Uses
Tolclofos-methyl is a non-systemic organophosphorus fungicide
with both protective and curative activities that control soil-borne diseases
caused by Rhizoctonia solani, Corticium rolfsii, Tphula incamata and Typhula
ishikariensis in/on potatoes, sugar beet, cotton and peanuts.
Uses
Agricultural fungicide.
Production Methods
In industrial production, tolclofos-methyl is synthesised by reacting 2,6-dichlorophenol with phosphorus oxychloride to form a chlorinated phosphorochloridate intermediate. This intermediate is then esterified with methanol under controlled conditions to yield the final compound, tolclofos-methyl.
Definition
ChEBI: An organic thiophosphate that is 2,6-dichloro-4-methylphenol in which the hydrogen of the hydroxy group group has been replaced by a dimethoxyphosphorothioyl group. Tolclofos-methyl is a phospholipid biosynthesis inhibitor and fungicide that is used for co
trolling soil-borne diseases caused by Typhula incarnata, Corticium rolfsii, Typhula ishikariensis, and Rhizoctonia solani.
Mechanism of action
Nonsystemic with contact action showing protective and curative properties. Lipid peroxidation inhibitor.
Metabolic pathway
Tolclofos-methyl underwent common degradation and metabolic pathways
in water, soil, plants and animals. These reactions are well
documented for most organophosphorus compounds and include oxidative
desulfuration, hydroxylation/oxidation of the 4-methyl group
to the alcohol and carboxylic acid, cleavage of the P-O-aryl linkage,
O-demethylation and conjugation. In addition to the above reactions,
photolytic isomerisation to the thionate (P=S) was also observed. A
schematic presentation of the primary metabolic pathways for tolclofosmethyl
is illustrated in Scheme 1.
Degradation
[
14C-phenyl]Tolclofos-methyl(1) was stable to hydrolytic degradation at
pH 5, 7 and 9 at 22°C with DT
50 values of 139, 417 and 238 days,
respectively. Higher temperature led to a more rapid hydrolysis and two
hydrolysis products were detected. O-Demethylation and oxidative desulfuration
were the major reactions to yield 2,6-dichloro-p-tolyl methyl
hydrogen phosphorothioate (2) and toclofos-methyl oxon (O-2,6-dichlorop-
tolyl O,O-dimethyl phosphate, 3), respectively. Cleavage of the P-O-aryl
linkage yielded 2,6-dichloro-4-methylphenol(4) as a minor degradation
product (WHO, 1994).
Tolclofos-methyl degraded in water under natural sunlight irradiation
with DT
50 values of 44 days (in distilled water), 15-28 days (in natural
river and pond water) and less than 2 days in 2% acetone/water. The
major degradation reactions included oxidative desulfuration to yield
compound 3 and O-demethylation to yield compound 2. The major
photodegradation products in river and pond waters and soil thinlayer
surfaces were compounds 2, 3, 4 and the O-demethylated 3 (2,6-
dichloro-p-tolyl methyl hydrogen phosphate, 5) (Mikami et al., 1984).
In acetone solution, demethylation of the isomerisation product [2,6-
dichloro-p-tolyl O,S-dimethyl phosphorothioate (6)] yielded 2,6-dichlorop-
tolyl S-methyl hydrogen phosphorothioate (7) and 2,6-dichloro-p-tolyl
dihydrogen phosphate (8) as the major photodegradates (Mikami et al.,
1984).
Toxicity evaluation
Its acute oral toxicity is very low in comparison with
a thio-ester type of other organophosphorus fungicides
(edifenphos, iprobenfos, and pyrazophos).
