Trithiophosphonic acids

Trithiophosphonic acids (RPS3H2) are thermally unstable compounds, undergoing decomposition reactions at temperatures sometimes as low as — 10°C depending upon the electronic and steric properties of the R substituent. Decomposition usually occurs via a condensation reaction (similar to that observed for dithiophosphinic acids - Equation 21) to give the di-thiadiphosphatene disulfide and eliminate H2S (Equation 35).48 Similar to dithiophosphinic acids, their metal and ammonium salts are far more thermally stable and are therefore the preferred synthetic target in most cases. 

The fe-ester derivatives of trithiophosphinic acids, RP(S)(SR )2, have also been studied and, similar to the metal and ammonium salts, show enhanced thermal stability compared to their parent acids. Trithiophosphonic acid Zj zA (tr im e t lr y 1 s i 1 y 1) esters have been synthesised from organo-/u.v(trim-ethylsilyl)phosphanes with elemental sulfur in toluene (Equation 40).53 These 6z,s(silyl esters) can be readily converted into the parent trithiophosphinic acid by a very slow, controlled reaction with water or methanol.53... 

Several cyclic trithiophosphonic acid systems have been prepared using Lawesson s reagent (LR) and similar reactants. Such products include (86 R = CxH40Me-4) from 4-amino-2-hydroxybenzoic acid whilst l-diphenylmethylene-2-(l//)-naphthalenone... 

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