Reactions of Phosphorus Monothio Acids With Aliphatic Diazo Compounds

Reactions of phosphorus monothio acids with diazomethane, diazoacetone, diphenyldiazomethane, and diazofluorene have been studied. The ratio of the yields of the S- and O-derivatives QS/QO has been found to be dependent on three factors: i) the nature of substituents at phosphorus - with electron-donor substituents raising the O-derivative yield and the quantity log (QS/QO) varying as εσ of the substituents; (ii) stability of alkyldiazonium and carbocation - with QO increasing with the carbocation stability; and (iii) polarity of the medium - the O-derivative yield rises with dielectric permeability of the medium and QS/QO has been found to be a linear function of 1/D. The most probable mechanism has been established as proton transfer from the acid to the diazocompound followed be formation of the S-derivative and the O-derivative. The former results from an SN2 reaction of the alkyldiazonium cation with the thiol-thione anion within the ion pair. The O-derivative arises from the thiol-thion anion and the carbocation; the latter resulting from decomposition of the alkyldiazonium cation within the ion pair.