Difluorophosphoric acid

Difluorophosphoric acid is an inorganic compound with the formula HPO2F2. It is a mobile colorless strongly fuming liquid. The acid has limited applications, in part because it is thermally and hydrolytically unstable. Difluorophosphoric acid is corrosive to glass, fabric, metals and living tissue.

A method to make pure difluorphosphoric acid involves heating phosphoryl fluoride with fluorophosphoric acid and separating the product by distillation:
 * POF3 + H2PO3F → 2 HPO2F2

It is prepared by hydrolysis of phosphoryl fluoride:
 * POF3 + H2O → HPO2F2 + HF

Further hydrolysis gives fluorophosphoric acid:
 * HPO2F2 + H2O → H2PO3F + HF

Complete hydrolysis gives phosphoric acid:
 * H2PO3F + H2O → H3PO4 + HF

The salts of difluorophosphoric acid are known as difluorophosphates.