2KReO4 + 10HBr + 2KBr + 3H3PO2 → 2K2[ReBr6] + 3H3PO3 + 5H2O
Potassium perrhenate react with hydrogen bromide, potassium bromide and hypophosphorous acid to produce hexabromidorhenate(IV) potassium, phosphorous acid and water. Hydrogen bromide and Hypophosphorous acid - concentrated solutions. The reaction takes place in a boiling solution.