/Chlorthiophos/ A reaction mixture of the three isomers: (i) O-2, 4-dichlorophenyl-5-methylthiophenyl O, O-diethyl phosphorothioate; (ii) O-2, 5-dichlorophenyl-4-methylthiophenyl O, O-diethyl phosphorothioate (major component); and (iii) O-4, 5-dichlorophenyl-2-methylthiophenyl O, O-diethyl phosphorothioate.