Phosphorus trichloride is only partially miscible with bromine; two layers are formed, which, on the addition of iodine, combine with evolution of heat and the formation of a reddish solid resembling PBr5:—
PCl3 + 2½Br2 + ½I2 = PBr5 + ICl3
A mixture of PCl3 and Br2 in molecular proportions when moderately cooled (to 10° C. or thereabouts) deposited crystals having the composition PCl3Br2. These melted at 35° C. with decomposition and separation into two layers. The compound resembles phosphorus pentabromide (q.v.) in appearance. When brought into contact with water it is said to give first HOBr, HBr and PCl3, also POBr3 and POCl.
At lower temperatures still more bromine can be combined, giving compounds such as PCl2Br3 by displacement of chlorine and PCl2Br5.
Many other addition compounds have been reported by various workers. By mixing bromine with phosphorus trichloride, heating on the water-bath and then cooling to about -5° C. brown needle-shaped crystals have been obtained, the analysis of which leads to the formula PCl3Br8. By allowing this compound to stand with PCl3 in a sealed tube for some days red crystals separated which had the composition PCl3Br4. |