Pure Hydrofluoboric acid has never been produced but aqueous solutions of HBF4 can be produced by dissolving boric acid in hydrofluoric acid solution in aqueous solution at 20-25 °C. Three equivalents of HF react to give the intermediate boron trifluoride and the fourth gives Hydrofluoboric acid.
B(OH)3 + 4 HF → H3O+ + BF4− + 2 H2O
Aqueous solutions of Hydrofluoboric acid can also be prepared by treating impure hexafluorosilicic acid with solid boric acid followed by removal of precipitated silicon dioxide. Anhydrous solutions can be prepared by treatment with acetic anhydride.
Hydrofluoboric acid is the principal precursor to fluoroborate salts, which are typically prepared by acid-base reactions. The inorganic salts are intermediates in the manufacture of flame-retardant materials, glazing frits, and in electrolytic generation of boron. HBF4 is also used in aluminum etching and acid pickling.
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