Oxidation of HF with KMnO4 and possible misconceptions about HF

Abstract

Is hydrogen fluoride or its aqueous solution really incompatible with KMnO4? If so, in what respect (meaning why)? This contribution seeks to answer the previous question that was posed some 20 years ago on the pages of the Journal of Chemical Education. The previous conclusion was that KMnO4 cannot oxidize fluoride anions to elemental fluorine. However, this does not prevent the possibility of another type of reaction occurring between HF and KMnO4. In brief, the reaction of HF(aq) and KMnO4(s) cannot occur with concentrated HF(aq), where w(HF) ≈ 0.4. However, the reaction of liquefied hydrogen fluoride, HF(l) and KMnO4(s) appears to produce Mn2O7(l), which is explosive even at moderate temperatures. The same applies to aqueous solutions of HF where w(HF) ≥ 0.6. In this contribution, some details are further explained and the spreading of some misconceptions is, hopefully, hampered. In addition, some authors described HF as a "flammable and explosive" substance, which is even worse than claiming that "water is flammable and explosive".

Keywords

• fluorine, generation of; hydrogen fluoride; potassium permanganate; permanganic acid; manganese(VII) oxide, water elimination; redox reactions; flammability of HF