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

Heating of thiophosphonic dichlorides, RP(S)Cl2, R  CH3, C2H3, C2H5, with a molar equivalent of SOCl2 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: This method is particularly useful for the preparation of CH3P(O)Cl2 since it was observed that chlorination of CH3P(O)(OCH3)2 with PCl5 yields CH3OP(O)Cl2 as a by‐product which is difficult to separate from CH3P(O)Cl2. On the other hand chlorination of methylphosphonic acid with PCl5 also gives pure CH3P(O)Cl2 .