Perfluoboric acid

This acid is not known, but several perfluoborates have been prepared.

Potassium fluohyperborate, K₄B₄F₄O₁₁.H₂O, is prepared by dissolving the compound B₂O₃.2KF in cold water, adding a slightly alkaline solution of hydrogen peroxide, then adding alcohol and stirring. The dry salt is a white, crystalline solid. The aqueous solution is alkaline and slowly evolves oxygen; dilute sulphuric acid added to the solution liberates hydrogen peroxide. Concentrated sulphuric acid decomposes the substance, ozonised oxygen being evolved.

The potassium salt, K₂B₂F₂O₆.H₂O or O₂(BF.O.OK)₂.H₂O, and the ammonium salt, (NH₄)₂B₂F₂O₆.3H₂O, have also been obtained.