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 Diiodide, P2I4

Phosphorus Diiodide, P2I4, was first prepared by fusing the constituents in equivalent proportions. 50 grams of iodine and 4 grams of red phosphorus are melted in a flask and, after partial cooling, 2.5 grams of white phosphorus are added in small pieces. Or, equal parts by weight of iodine and phosphorus are dissolved in carbon disulphide and the solution is cooled to 0° C., when the compound crystallises. It has also been prepared by the action of iodine on phosphorous oxide:—

5P4O6 + 8I2 = 4P2I4 + 6P2O5


Phosphorus diiodide forms orange-coloured crystals which belong to the triclinic system. The analysis gave (PI2). The vapour density, determined in the presence of nitrogen at a pressure slightly below 100 mm. and at 265° C., was between 18.0 and 20.2 (air = 1), which corresponds to a molecule P2I4. At 15 mm. and 100° to 120° C. the compound dissociates into P2I3 and P. The melting-point was given as about 110° C. The heat of formation is given as

P + I2 (solid) = PI2 + 9.88 Cals.

P2I4 can be ignited in a current of oxygen and burnt to phosphoric oxide and iodine. The hydrolysis appears somewhat complex and yields P, PH3, HI and H3PO3. The phosphine is a secondary product, since by gradual addition to water in the cold neither phosphine nor red phosphorus are formed:—

P2I4 + 5H2O = 4HI + H3PO3 + H3PO2

P2I4 is soluble in CS2 and slightly soluble in liquid H2S. At about 100° C. it reacted with H2S giving HI and a sulphoiodide P4S3I2.
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