Some spontaneous reactions of OO-dimethyl S-ethylthioethyl phosphorothiolate and related compounds in water and on storage, and their effects on the toxicological properties of the compounds

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Abstract
OO-Dimethyl S-ethylthioethyl phosphorothiolate and its diethyl homolog, thionate isomer, sulfoxide and sulfone were purified by solvent-extraction procedures, and their purities tested. Their oral and intravenous LD50 values to rats and I50 values against cholinesterase were determined. On storage or in water the intravenous toxicities of all but the sulfone increased 40- to 100-fold, owing to the formation of alkylsulfonium derivatives. Thus the thioethyl thiolates alkylated themselves to alkylsulfonium thiolates; the dimethylthioethyl thiolate appeared to be in dynamic equilibrium with its thionate isomer, with which it reacted to give a sulfonium derivative; and the sulfoxide gave some thioethyl thiolate, which was also alkylated to sulfonium compounds. The sulfone was stable. The alkylsulfonium compounds were very powerful anticholinesterases, very toxic by intravenous injection (LD50 values of 0.01-0.06 mg/kg), but much less toxic orally. Sulfonium compounds present in amounts below the limits of physical and chemical detection can interfere with biochemical and toxicological observations. The importance of using biochemical tests of purity is stressed. The effects of these facile reactions of the study of biochemical and toxicological effects are pointed out with reference to insecticidal action, analysis of residues in crops and the practical precautions which have to be taken to obtain reproducible LD50 values by intravenous injection.