Bismuth Oxybromide, BiOBr

Bismuth Oxybromide, or Bismuthyl Bromide, BiOBr, can be obtained by the action of water on a solution of bismuth tribromide in hydrobromic acid; it is also believed to be formed by heating together bismuth tribromide and bismuth trioxide. By a suitable modification of the former method, the crystalline oxybromide may be obtained. The precipitated substance is obtained as a snow-white, amorphous powder of density (at 20° C.) 6.7. The crystalline form is colourless and transparent, density (at 15° C.) 8.082. It melts at a bright red heat, at which temperature bismuth tribromide volatilises; it darkens on exposure to light; it is insoluble in water, but dissolves in moderately dilute hydrobromic acid; it is decomposed by potassium hydroxide as follows:

BiOBr + KOH ⇔ BiO.OH + KBr

Two other oxybromides have been reported, namely, Bi₈O₁₅Br₆ and Bi₁₁O₁₃Br₇ (or 7BiOBr.2Bi₂O₃), but their identities have not been confirmed.

Bismuth oxybromides are partially reduced to metal when heated to a dull red heat in a current of dry ammonia.

A basic salt, bismuth oxybromate, or bismuthyl bromate, BiOBrO₃, has been obtained (mixed with some bismuthyl hydroxide, BiO.OH) by the prolonged action of an aqueous solution of bromic acid upon bismuth hydroxide. The mixture is a white, amorphous, insoluble powder which loses water between 150° and 200° C. and decomposes violently when strongly heated, leaving a residue of bismuth oxy-bromide. At the same time there is formed a soluble product, the solution of which decomposes on evaporation, with evolution of bromine, while the small amount of residue which is obtained decomposes at once in the air.