The synthesis of O,O-bistrimethylsilyl S-trihalogenomethyl phosphorothioates

Abstract

O,O-Bistrimethylsilyl S-trihalogenomethyl phosphorothioates are formed quantitatively in the pure state from the reaction between bistrimethylsilyl phosphite and trihalogenomethylsulphenyl chlorides, CCl_3-nF_nSCl (n = 1–3) in dry benzene or toluene. The corresponding di-isopropyl S-trihalogenomethyl phosphorothioates (PrⁱO)₂P(O)SCCl_3–n′F_n are likewise obtained from di-isopropyl phosphite with significant advantage in yield and purity over other methods. Bromotrimethylsilane smoothly converts these isopropyl esters into the corresponding trimethylsilyl esters to give an alternative synthesis of the title compounds. Chemical ionisation mass spectrometry of these esters provides valuable structural information and, for the isopropyl esters, generates a family of ammonia-containing ions. The bis-silyl esters hydrolyse rapidly and spontaneously in water under acidic, neutral, and mildly basic conditions although the expected S-trihalogenomethyl phosphoro-thioates decompose too rapidly to permit their characterisation.