The bromine catalysed oxidation of arsenic trifluoride by antimony pentafluoride

Antimony pentafluoride dissolves in excess arsenic trifluoride presumably with the formation of AsF₃·SbF₅ [1,2] and possibly (AsF₃)_nSbF₅ n = 2, [3], 3, [4], in equilibrium with one another and the solvent. However, O. Ruff [5] found in 1906 that in the presence of bromine, antimony pentafluoride oxidises arsenic trifluoride to arsenic pentafluoride with formation of a solid he suggested was SbBrF₄. In the course of our work we investigated this reaction and found that trace quantities of bromine (<0.1 mole per cent) catalyse the formation of arsenic pentafluoride and SbF₃·SbF₅ [6], according to equation (1).AsF₃ + 2SbF₅ = AsF₅ + SbF₃·SbF₅ (1)Reaction (2) is endothermic to the extent of ca. 33 Kcals mole^?1 [7–9], but reaction (1) occurs spontaneously in presence of bromine, being more favourable than reaction (2) by the heat of reaction (3).AsF₃ + SbF₅ = AsF₅ + SbF₃ (2)SbF₃ + SbF₅ = SbF₃·SbF₅ (3)