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

Meta- and Pyro-phosphorous Acids






The acids HPO2 and H4P2O5 may be regarded as partly dehydrated forms of orthophosphorous acid. In their modes of preparation and properties they recall somewhat the meta- and pyro-phosphoric acids.

Metaphosphorous Acid

Metaphosphorous Acid was produced during the spontaneous combustion of dry phosphine in dry oxygen at a low pressure, probably according to the equation

PH3 + O2 = H2 + HPO2

It was deposited on the walls of the vessel in feathery crystals, which were readily hydrated by water giving H3PO3.

Pyrophosphorous Acid

Pyrophosphorous Acid has been made by treating PCl3 with a little water, or by shaking the syrupy acid with a slight excess of PCl3 and evaporating in a desiccator over KOH and P2O5. The crystalline acid was very deliquescent. Secondary phosphites when heated gave pyrophosphites with loss of water, thus

2BaHPO3 = Ba2P2O5 + H2O

By the addition of the theoretical quantity of sulphuric acid the unstable H4P2O5 was obtained.

Sodium dihydropyrophosphite was prepared by heating sodium hydrogen phosphite in a vacuum at 160° C.:—

2NaH2PO3 = Na2H2P2O5 + H2O

The free acid was hydrated to phosphorous acid in solution with evolution of 4.9 Cals. per mol of H4P2O5. Hydration was accelerated by strong acids. The dihydrogen pyrophosphite of sodium, Na2H2P2O5, similarly gave NaH2PO3. The acid appears to be dibasic, the salt Na2H2P2O5 being formed by neutralisation, with evolution of 14.3 Cals. per mol of water formed in the equation

H4P2O5 + 2NaOH = Na2H2P2O5 + 2H2O

Other salts of this acid have been prepared. As in the case of phosphorous acid the structure may be symmetrical or unsymmetrical, thus

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