Organic Phosphorus Compounds 59. A new method for the synthesis of phosphonic dichlorides

Heating of thiophosphonic dichlorides, RP(S)Cl 2 , R CH 3 , C 2 H 3 , C 2 H 5 , with a molar equivalent of SOCl 2 under pressure at 150° for 5 to 8 h yields phosphonic dichlorides in quantitative yield. In addition sulfur and sulfur dichloride is formed according to the equation:\documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm RP}\left({\rm S} \right){\rm Cl}_{\rm 2} + {\rm SOCl}_{\rm 2} \to {\rm RP}\left({\rm O} \right){\rm Cl}_{\rm 2} + {\rm SCl}_{\rm 2} + {\rm S} $$\end{document}This method is particularly useful for the preparation of CH 3 P(O)Cl 2 since it was observed that chlorination of CH 3 P(O)(OCH 3 ) 2 with PCl 5 yields CH 3 OP(O)Cl 2 as a by‐product which is difficult to separate from CH 3 P(O)Cl 2 . On the other hand chlorination of methylphosphonic acid with PCl 5 also gives pure CH 3 P(O)Cl 2\documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm CH}_{\rm 3} {\rm P}\left({\rm O} \right)\left({{\rm OH}} \right)_2 + 2{\rm PCl}_{\rm 5} \to {\rm CH}_{\rm 3} {\rm P}\left({\rm O} \right){\rm Cl}_{\rm 2} + 2{\rm HCl} + {\rm 2POCl}_{\rm 3} $$\end{document} .