Edifenphos

Description

Edifenphos is an organochlorine rice fungicide. It is moderately soluble in water and is volatile. Based on its chemical properties it is not expected to leach to groundwater. It is not usually persistent in either soil or water systems. Edifenphos is moderately toxic to mammals it is also a neurotoxin and an acetyl cholinesterase inhibitor. It is moderately toxic to fish and poses more of a risk to aquatic invertebrates.

Chemical Properties

Industrial product is yellow to light brown transparent liquid with bad odor. b.p.154℃/1.33Pa, relative density 1.23 (20℃), refractive index n22D1.61. It can be soluble in methanol, ethyl ether, chloroform, acetone, benzene, xylene and other organic solvents, insoluble in water. b.p.154℃/1.33Pa, relative density 1.23 (20℃), refractive index n22D1.61. It can be soluble in methanol, ethyl ether, chloroform, acetone, benzene, xylene and other organic solvents, insoluble in water. b.p.154℃/1.33Pa, relative density 1.23 (20℃), refractive index n22D1.61. Stable in acidic condition, easy to hydrolyze or ester exchange reaction in alkaline condition, especially when the temperature is higher.

Uses

Fungicide.

Uses

Edifenphos is a foliar applied contact fungicide that provides both protective and curative control of rice blast diseases caused by Pyricularia oryzae. It also controls ear blight and stem rot in rice.

Definition

ChEBI: An organic thiophosphate that is the O-ethyl-S,S-diphenyl ester of phosphorodithioic acid. Used to control a variety of fungal diseases on rice including blast, ear blight and stem rot. Edifenphos i moderately toxic to mammals and fish but poses more of a risk to aquatic invertebrates.

Production Methods

Edifenphos is commercially synthesised through the esterification of diphenyl dithiophosphoric acid with ethanol. This process involves reacting phosphorus pentasulfide with phenol to produce diphenyl dithiophosphoric acid, which is then treated with ethanol to form edifenphos.

Mechanism of action

Phospholipid biosynthesis inhibition, foliar applied with protective and curative action

Metabolic pathway

Hydrolytic cleavage of the P-0 and P-S linkages affords the major degradation and metabolic pathways of edifenphos. A unique transesterification reaction yielded tri-S-phenyl and di-O-ethyl phosphorus esters as minor products in soil and plant test systems (Scheme 1).

Degradation

The hydrolytic DT₅₀ values of edifenphos (1) at pH 7 and 9 at 25 °C were 19 and 2 days, respectively (PM). [³⁵S]Edifenphods egraded rapidly in aqueous solution when exposed to UV light at 25-28 °C [DT₅₀ ca. 3 days (light exposed) vs. 19 days (dark control)]. Cleavage of the P-S linkage is the primary degradation pathway. Thiophenol (2) was further oxidised to form diphenyl disulfide (3), possibly during sample extraction, isolation and analysis. Stepwise cleavage of the P-S and P-O linkages yielded O-ethyl S-phenyl hydrogen phosphorothioate (4), S-phenyl dihydrogen phosphorothioate (5), benezenesulfonic acid (6) and sulfuric acid as major ³⁵S-containing products, whereas O-ethyl dihydrogen phosphate (7) and phosphoric acid were recovered from the phosphorus portion of the molecule (Murai, 1977).

Toxicity evaluation

Edifenphos shows no delayed neuropathic symptoms. Safety intervals between spray and harvest for rice are 21 days in Japan with 0.2 mg of MRL (Maximum Residue Limit).

Pesticide Type

Fungicide