Chlorthiophos is an organophosphorus pesticide. It is a mixture of isomers: O,O-diethyl-O-(2,5-dichloro-4-methylthio)phenyl phosphorothioate (ca. 73%) O,O-diethyl-O-(4,5-dichloro-2-methylthio)phenyl phosphorothioate (ca. 13%) O,O-diethyl-O-(2,4-dichloro-5-methylthio)phenyl phosphorothioate (ca. 14%) It is extremely poisonous. ...