Carbon tetra-bromide, CBr4, is prepared similarly to the chloride by the action of bromine on carbon disulphide, iodine being in this case the halogen-carrier. A mixture of 2 parts of carbon bisulphide, 14 parts of bromine, and 3 parts of iodine is heated in a sealed tube for forty-eight hours at 250° C., and the product distilled when cold with sodium hydroxide solution. Carbon tetrabromide is a solid, and crystallises from alcohol in white, glistening tablets having an ethereal smell; it has a density of 3.42, melts at 92.5° C., and boils under atmospheric pressure with partial decomposition at 189.5° C., whilst under 50 mm. pressure the boiling-point is 101° C.
Solid carbon tetrabromide exists in two enantiotropic forms, the transition temperature between which is 46°-47° C. |