Chemical elements
  Phosphorus
    Isotopes
    Energy
    Preparation
    Applications
    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
      Alkylphosphines
      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
      Phosphine
      Pyrophosphoric Acid
      Phosphoric acids
    Slow Oxidation
    Phosphatic Fertilisers

Phosphorus Trifluoride, PF3






Some early indications were obtained that phosphorus reacted with fluorides of zinc and lead, and that the fluoride resulting was a gas. This gas was prepared in 1884 by heating lead fluoride with copper phosphide in a brass tube. It is also produced by the action of fluorides of zinc, silver or lead on phosphorus trichloride or tribromide. One of the most convenient methods of preparation is by the reaction between arsenic trifluoride, which is easily prepared and purified, and phosphorus trichloride, thus:—

PCl3 + AsF3 = PF3 + AsCl3

The apparatus consists of a distillation flask fitted with a tap-funnel. The side-tube of the flask is sealed to a condensing wash-bottle, which can be cooled in a mixture of solid carbon dioxide and alcohol, and the wash-bottle is joined to a condenser which is immersed in liquid air. After the whole apparatus has been thoroughly dried, the arsenic trifluoride is allowed to drop into the trichloride. The vapours of these two compounds are removed in the first condenser, and the phosphorus trifluoride is solidified in the second.

Phosphorus trifluoride can also be made by the action of lead fluoride on phosphorus trichloride and by the decomposition of the pentafluoride by means of electric sparks.

The composition has been established by the vapour density and by analysis. The fluoride is a colourless gas which does not fume in the air, and is highly poisonous. It condenses to a colourless liquid at -95° C. and freezes to a white solid at -160° C. The heat of formation is 106.2 to 109.7 Cals. per mol, therefore much greater than that of the trichloride, and the trifluoride also proves to be the more stable of the two compounds. It can be decomposed by electric sparks with deposition of phosphorus and formation of the pentafluoride, thus:—

5PF3 = 3PF5 + 2P

It can be reduced by heating with hydrogen:—

PF3 + 3H2 = PH3 + 3HF

and also by heating with silicon or boron:—

4PF3 + 3Si = 3SiF4 + 4P

but is not reduced by heating with sulphur, phosphorus or arsenic. It is not affected by the metals copper, mercury, iron, cobalt and nickel at ordinary temperatures, but the same metals give phosphides at a red heat. It is completely absorbed by sodium at the melting- point of this metal.

Phosphorus trifluoride is easily oxidised. Although it does not burn in air it can be exploded with oxygen by electric sparks, one volume of the gas mixed with half a volume of oxygen giving one volume of phosphorus oxyfluoride:—

PF3 + ½O2 = POF3

It combines vigorously with all the halogens giving mixed pentahalides (q.v.). It is hydrolysed very slowly by cold water, rather more quickly by boiling water, and quickly by aqueous alkalies, giving in the last case alkali fluoride and phosphite. It was considered by Moissan and by Berthelot that the first product of hydrolysis was a fluophosphoric acid (q.v.), the potassium salt of which was fairly stable.


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