Chemical elements
    Physical Properties
    Chemical Properties
      Alkali Phosphides
      Alkaline Earth Phosphides
      Copper Silver and Gold Phosphides
      Zinc Group Phosphides
      Aluminium Phosphide
      Titanium Group Phosphides
      Tin Phosphides
      Lead Phosphides
      Arsenic Phosphides
      Antimony Phosphides
      Bismuth Phosphides
      Chromium Phosphides
      Molybdenum and Tungsten Phosphides
      Manganese Phosphides
      Iron Phosphides
      Cobalt Phosphides
      Phosphonium Chloride
      Phosphonium Bromide
      Phosphonium Iodide
      Hydrogen Phosphides
      Phosphorus Trifluoride
      Phosphorus Pentafluoride
      Phosphorus Trifluorodichloride
      Phosphorus Trifluorodibromide
      Fluophosphoric Acid
      Phosphorus Dichloride
      Phosphorus Trichloride
      Phosphorus Pentachloride
      Phosphorus Chlorobromides
      Phosphorus Chloroiodides
      Phosphorus Tribromide
      Phosphorus Pentabromide
      Phosphorus Diiodide
      Phosphorus Triiodide
      Phosphorus Oxytrifluoride
      Phosphorus Oxychloride
      Pyrophosphoryl Chloride
      Metaphosphoryl Chloride
      Phosphoryl Monochloride
      Phosphoryl Dichlorobromide
      Phosphoryl Chlorodibromide
      Phosphoryl Tribromide
      Metaphosphoryl Bromide
      Phosphoryl Oxyiodides
      Phosphorus Thiotrifluoride
      Phosphorus Thiotrichloride
      Phosphorus Thiotribromide
      Mixed Phosphorus Thiotrihalides
      Phosphorus Suboxides
      Phosphorus Trioxide
      Phosphorus Dioxide
      Phosphorus Pentoxide
      Hypophosphorous Acid
      Phosphorous Acid
      Meta- and Pyro-phosphorous Acids
      Hypophosphoric Acid
      Tetraphosphorus Trisulphide
      Diphosphorus Trisulphide
      Tetraphosphorus Heptasulphide
      Phosphorus Pentasulphide
      Phosphorus Oxysulphides
      Phosphorus Thiophosphites
      Phosphorus Thiophosphates
      Phosphorus Selenophosphates
      Phosphorus Sulphoselenides
      Diamidophosphorous Acid
      Phosphorus Triamide
      Monamidophosphoric Acid
      Diamidophosphoric Acid
      Triamidophosphoric Acid
      Dimetaphosphimic Acid ≡P=
      Trimetaphosphimic Acid
      Tetrametaphosphimic Acid
      Penta- and Hexametaphosphimic Acid
      Monamidodiphosphoric Acid
      Diamidodiphosphoric Acid
      Triamidodiphosphoric Acid
      Nitrilotrimetaphosphoric acid
      Monothioamidophosphoric Acids
      Thiophosphoryl Nitride
      Di- Tri-imido- and -amido-thiophosphates
      Imidotrithiophosphoric Acid =
      Phosphorus Chloronitrides
      Triphosphonitrilic Chloride
      Tetraphosphonitrilic Chloride
      Pentaphosphonitrilic Chloride
      Hexaphosphonitrilic Chloride
      Heptaphosphonitrilic Chloride
      Triphosphonitrilic Bromide
      Phosphorus Halonitrides
      Phosphorus Nitride
      Pyrophosphoric Acid
      Phosphoric acids
    Slow Oxidation
    Phosphatic Fertilisers

Phosphorus Pentabromide, PBr5

In the presence of excess of bromine phosphorus can form not only the pentabromide but also, according to the thermal diagram, other perbromides. It was discovered early that the presence of some iodine greatly facilitates the combination, probably by the formation of ICl3, thus:—

PCl3 + ½I + 5Br = PBr5 + ICl3

It is also produced by the decomposition of the dibromotrifluoride formed when trifluoride is passed into bromine at -10° C.:—

5PF3Br2 = 3PF5 + 2PBr5


Phosphorus pentabromide is a yellow crystalline solid which melts to a red liquid with decomposition. It fumes in the air. A red form has also been described, but this is probably PBr7.

The densities and specific volumes of the liquid under the pressure of its own vapour were determined in a sealed evacuated glass dilatometer. One set of results was as follows:—

t° C85100130165

From these results and others the coefficient of expansion is calculated as vt-85 = v85{1 + 0.0019(t-85)}

vt-100 = v100{1 + 0.0012t}, up to 165° C.

The vapour is formed with dissociation. The pressures of the total vapour formed were determined by a static method. From the results it was calculated that the boiling- (sublimation) point was 106° C.

The heat of formation

P (solid) +2½Br2 (liq.) = PBr5 (solid) + 63.5 Cals.

was found to be greater than that of PBr3, but less than that of PCl5. The additional heat on combination with the last two atoms of bromine was found to be small.

PBr3 (liq.) + Br2 (liq.) = PBr5 (solid) +20.3 Cals.

The hydrolysis with excess of water produces hydrobromic and phosphoric acids. The heptabromide, PBr7, which was prepared by subliming PBr5 with Br2 in a sealed tube at 90° C., hydrolyses with the production of the same acids and bromine in addition. In the presence of a small amount of water the oxybromide POBr3 may be produced. Hydrogen sulphide by an analogous reaction gave the sulphobromide:—

PBr5 + H2S = PSBr3 + 2HBr

The pentabromide may also be used to replace hydroxyl groups in organic compounds by halogen. Thus:

PBr5 + CH3COOH = POBr3 + CH3COBr + HBr

An ammine, PBr5.9NH3, was formed by passing dry ammonia into a solution of PBr5 in CCl4.
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