Synthesis of mixed phosphorotrithioates from white phosphorus

Abstract

The first general and high-yielding synthesis of mixed phosphorotrithioates (R¹S)₂P(O)SR² involving white phosphorus, disulfides, and alkyl halides is presented, which provides the shortest and environmentally benign method to synthesize these compounds of practical importance. Only one method for the formation of (R¹S)₂P(O)SR² from elemental phosphorus has been developed. Here, with the use of KOH as a base and DMSO–toluene as a solvent, various disulfides couple readily with white phosphorus to give O-potassium S,S-dialkylphosphorotrithioates (R¹S)₂P(S)OK in almost quantitative yields, which react with alkyl halides to form (R¹S)₂P(O)SR² in high yields. The reaction is characterized by the complete conversion of white phosphorus. Moreover, this method can be easily adapted to large-scale preparation. Our mechanistic data suggest that the attack of RSK on S,S,S-trialkyl phosphorotrithioates and subsequent C–S bond cleavage, the Michaelis–Arbuzov-like dealkylation, are the key steps in the formation of (R¹S)₂P(S)OK.