Dichlofenthion (IUPAC name: O-2,4-Dichlorophenyl O,O-diethyl phosphorothioate) is a phosphorothioate which is primarily used as a pesticide and nematicide. Dichlofenthion (IUPAC name: O-2,4-Dichlorophenyl O,O-diethyl phosphorothioate) is a phosphorothioate which is primarily used as a pesticide and nematicide.