Fluophosphoric Acid

The tendency of fluorine to replace oxygen in oxyacids, which is exemplified in such compounds as hydrofluoboric acid, is shown to some extent in the acids of phosphorus.

Salts of fluophosphoric acid are prepared by the action of alkali fluorides on phosphorus pentachloride. The reaction between NH₄F and PCl₅ proceeds with some violence at 80°-110° C. The product, NH₄PF₆, is dissolved in cold water, precipitated by nitron acetate, and again converted into the ammonium salt by the addition of ammonia and extraction of the organic base with chloroform. The alkali fluorides, KF and NaF, gave less violent reactions and smaller yields of fluophosphate. These salts resemble perchlorates chemically and halides in crystalline form.