Thorium Bromide, ThBr₄

Thorium Bromide, ThBr₄, is prepared similarly to the chloride, i.e. by the union of its elements, by acting on a heated mixture of thoria and carbon with bromine vapour, and by brominating thorium carbide at high temperature (Moissan and Martinsen). It may also obtained conveniently by the method of Bourion, which is generally applicable to the preparation of anhydrous metallic bromides from their oxides. This method consists in the simultaneous action of sulphur chloride vapour and hydrogen bromide on the metallic oxide heated to a suitable temperature. Thus a white mass of ThBr₄ is obtained when sulphur chloride vapour at 135° C., mixed with hydrogen bromide, is distilled on to heated thoria, whilst if the temperature is lowered to 125° C. ThOBr₂ results.

Anhydrous thorium bromide forms on sublimation transparent colourless needles of density 5.62. It sublimes in vacuo at 600°-620° C. and boils at about 725° C. It is hygroscopic, and easily soluble in water and alcohol. From a solution of thorium hydroxide in aqueous hydrobromic acid the crystallohydrate ThBr₄.10H₂O was obtained by Jannaseh; other observers have described the hydrates ThBr₄.8H₂O and ThBr₄.7H₂O. According to Chauvenet the dodekahydrate ThBr₄.12H₂O is obtained in needles by evaporating at 100° C. a solution of thorium hydroxide in alcoholic hydrogen bromide, and this salt when dried in the air passes into ThBr₄.10H₂O, which in a vacuum becomes ThBr₄.7H₂O. The heats of solution of the anhydrous salt and the different hydrates are: ThBr₄, 70,190 calories, ThBr.7H₂O, 22,550 calories; ThBr₄.10H₂O, 9,840 calories; ThBr₄.12H₂O, 2,300 calories.

Thorium bromide forms with ammonia the compound ThBr₄.3NH₃, and with pyridine (C₅H₅N)₂H₂ThBr₆.