Uranyl Bromide, UO₂Br₂

When uranous oxide is heated in a current of bromine vapour a mixture of Uranyl Bromide, UO₂Br₂, and uranous bromide is formed. The former can be extracted with ether, and obtained as yellowish-green fluorescent needles by evaporation of the solution. It is obtained in aqueous solution by the action of bromine water on uranous oxide, or of hydrobromic acid on uranic oxide; yellow needles of the heptahydrate, UO₂Br₂.7H₂O, separate on concentrating the solution. Uranyl bromide is very deliquescent and is decomposed in moist air to hydrated uranic oxide and hydrobromic acid; in dry air it gradually evolves bromine. The solution in water decomposes on keeping, and deposits the yellow hydrate of uranic oxide. When heated, it evolves bromine and hydrogen bromide, and leaves a brick-red residue of uranous oxide.

The double chlorides, K₂(UO₂)Br₄.2H₂O and (NH₄)₂(UO₂)Br₄.2H₂O, have been prepared by acting upon solutions of the alkali uranates with hydrobromic acid. They are separated as yellowish-brown crystals.

Uranyl bromate does not appear to be stable. If a solution of uranyl sulphate is treated with barium bromate, and the filtrate after removal of the precipitate is subjected to evaporation, bromine escapes and a syrupy liquid remains which appears to be a basic bromate.