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Pyrophosphoryl chloride is used as an alternative reagent to POCl3 in a variation on the Vilsmeier formylation. But, purchasing it from a chem supply is rather expensive, so this preparation might be useful for some.
10.81g of phosphorus pentachloride are introduced into 14.07g of dichlorophosphoric acid (molar ratio of the acid to phosphorus pentachloride is 2:1), the mixture placed in a distillation flask and immediatelly connected with a vacuum distillation apparatus. By the application of water pump vacuum and cooling of the receiver and of the cold trap attached thereto with solid carbon dioxide, the hydrogen chloride formed was sucked off from the reaction mixture and the resultant phosphorus oxychloride continuously distilled off at 20°C and condensed in the receiver and cold trap. The last traces of phosphorus oxychloride formed are finally driven off by a gentle warming of the distillation flask. The receiver is then changed and the pyrophosphoryl chloride formed is distilled over.
Yield: 12.24g (93.6% of theory)
60.74g of phosphorus oxychloride are mixed with 5.71mL of water (molar ratio of phosphorus oxychloride to water is 1:0.8). After the amount of HCl gas equivalent to the added amount of water has been liberated (standing for 24 h at 20°C), 53.01g of the ''hydrated phosphorus oxychloride'' are mixed with 31.86g of phosphorus pentachloride and further reacted and worked up as described as in example 1.
Yield: 24.87g (71.2% of theory)