Condensed Phosphoro, Phosphono and Phosphinothioates

In the case of simple ester derivatives, the transition (9.493b) (9.493a) represents the well-known thiolo thiono rearrangement, and the P-S-P linkage is only stable when P=0 is absent. 

The thiono form of cyclic esters is also generally the most stable (9.496), bnt there are some exceptions. The dioxaphosphorinane derivatives (9.497) can be obtained in a relatively stable thiolo form which only very slowly reverts to the thiono isomer. 

Polyphosphorothioic acids and their salts have generally not been well characterised. They presumably exist in thiono rather than thiolo form. 

The cyclic phosphoromonothioic tetramer (9.499) has only been observed in aqueous solution where it exists in tautomeric forms. 

Monothiopyrophosphates (9.494) can be obtained from salts of phosphorothionic esters and dial-kylphosphorochloridates (9.501), or by reaction (9.502). 

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