Carbon Oxybromide, COBr₂

Carbon oxy-bromide COBr₂, is obtained in an impure condition by the interaction of phosphorus or boron tribromide and carbon oxychloride, and also in small quantities by the union of carbon monoxide and bromine in presence of aluminium bromide, or under the influence of the silent electric discharge. The rate of combination of the dry gases is very slow; probably no reaction would take place between them in the complete absence of water. Carbon oxybromide is best obtained5 by slowly dropping concentrated sulphuric acid into carbon tetrabromide heated to about 160° C., and redistilling the product after contact with metallic antimony:

CBr₄ + H₂SO₄ = COBr₂ + 2HBr + SO₃.

Carbon oxybromide is a colourless, mobile, fuming liquid of density 2.45 at 15° C. It boils at 64°-65° C. with slight decomposition; it is more stable towards water than carbonyl chloride; like the latter, it reacts with dimethyl aniline to form dye-stuffs.