Labelled organophosphorus pesticides. I. Synthesis of carbon-14 labelled O,O-dimethyl O-(3-methyl-4-nitrophenyl) phosphorothioate (sumithion®)

O,O-Dimethyl O-(3-methyl-4-nitrophenyl) phosphorothioate (I) (Sumithion®), an organophosphorus insecticide, was labelled with carbon-14 individually at the aryl methyl and the phenyl ring. The synthetic procedures are shown in Fig. 1 and 2. Coupling reaction of 3-methoxyphenylmagnesium bromide with methyl-14C iodide followed by O-demethylation gave 3-methyl-14C-phenol, which was nitrosated with sodium nitrite and subsequently oxidized with 30% nitric acid to give 3-methyl-14C-4-nitrophenol in the overall yield of 48% from methanol-14C. Condensation of 3-methyl-14C-4-nitrophenol with O,O-dimethyl phosphorochloridothioate gave Sumithion-(aryl methyl-14C) in 89% yield. Grignard reaction of 1-bromo-3-methoxybenzene-14C6 with methyl iodide afforded 1-methoxy-3-methylbenzene-14C6 in good yield and the latter was converted to Sumithion-(phenyl-14C) by the similar procedures used for the aryl methyl labelling. The overall yield of sumithion-(phenyl-14C) was 43% from 3-bromophenol-14C6.