Tolclofos-methyl

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An organic thiophosphate that is 2,6-dichloro-4-methylphenol in which the hydrogen of the hydroxy group group has been replaced by a dimethoxyphosphorothioyl group.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 DT₅₀ 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 DT₅₀ 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).

Pesticide Type

Fungicide