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

Hydrogen Phosphides

Liquid Hydrogen Phosphide

The analysis of this compound shows that it is hydrogen hemiphosphide, (PH2)x, and the molecular weight corresponds to tetrahydrogen diphosphide, P2H4.

This liquid, which is the cause of the spontaneous inflammability of phosphine prepared by methods (a), (b), (c), was isolated by passing through a freezing mixture the gas resulting from the action of water upon calcium phosphide. The condensate was a mobile liquid having a density of about 1.01 and vaporising between 30° and 40° C. The boiling-point at 735 mm. was found to be 57° to 58° C., and on careful distillation there is no residue. The vapour density (probably of the products of decomposition) is 74.73 to 77.0 and the empirical formula is PH2; hence, on the analogy of hydrazine the constitutional formula has been written as H2=P-P=H2.

The compound is unstable and decomposes when heated; when kept it changes slowly in the dark and quickly in the light into the gaseous and solid hydrides. Since 100 parts by weight give 38 parts of the solid and 62 parts of the gaseous hydride this decomposition may be represented by the equation

5PH2 = 3PH3 + P2H


This is best carried out in a Woulfe bottle having a capacity of about 3 litres and furnished with three necks, through one of which hydrogen is admitted. Through another pieces of calcium phosphide are introduced into water, and the third is fitted with the exit tube which is cooled by a reflux condenser and connected with a spiral tube terminating in a wash-bottle, the whole of which is immersed in a freezing-mixture. Uncondensed gas is ignited in a draught. The bottle is warmed to about 60° C. in a water-bath and the calcium phosphide added as required. 100 grams of Ca3P2 give 3 to 4 c.c. of liquid phosphide.

Solid Hydrogen Phosphide

A yellow solid is formed during the decomposition of potassium phosphide by water, and this solid is formed in many other reactions which yield the other hydrides, possibly as a secondary product resulting from the decomposition of the hemiphosphide by water. It is also formed by the exposure of phosphine to light, and is one of the products of the action of chlorine upon phosphine.


The mixed hydrogen phosphides generated by the action of water on calcium phosphide, in a 3-litre flask through which is passed a current of carbon dioxide, are passed through a condenser to remove most of the water vapour and then through a series of wide glass tubes packed with granular calcium chloride (which must leave no residue when dissolved in hydrochloric acid). The tubes are protected from the light by rolls of paper. After the whole apparatus has been filled with carbon dioxide, the calcium phosphide is introduced into the flask in amount sufficient to give a layer about 1 cm. deep. A steady stream of phosphine is evolved at 60° C., the spontaneously inflammable part of which is immediately decomposed by the calcium chloride with deposition of the solid hydrogen diphosphide. The escaping gas is led directly into the flue and burnt. The solid spreads through the tubes and appears in the final wash-bottle, which contains hydrochloric acid. The apparatus is then again filled with CO2 and the last calcium chloride tube detached and used as the first of the next repeat operation. The contents of the calcium chloride tubes are dissolved in cold dilute hydrochloric acid. The hydrogen phosphide, which usually floats, is filtered off, washed with ice-cold water, then with alcohol and with ether which has been redistilled over sodium. This dissolves a little of the compound to give a yellowish colloidal solution. The solid is filtered off, centrifuged, dried for 12 hours in a vacuum desiccator over P2O5, and kept in a closed vessel of brown glass in a desiccator.


The diphosphide is a yellow powder, which is tasteless, odourless and insoluble in most solvents. It decomposes in the light giving phosphine, and is easily decomposed by heating in an atmosphere of hydrogen. It ignites in air at temperatures between 100° and 200° C.

The empirical formula is (P2H)x. The molar weight, deduced from the lowering of the freezing-point of white phosphorus, corresponds to the formula P12H6. The density is 1.83 at 19° C. The heat of formation from white phosphorus and hydrogen is given as +35.4 Cals.

Chemical Reactions

P12H6 is dissociated when heated above 70° C. in an indifferent gas—into its elements at 175° C. in CO2, or into phosphorus and phosphine at 215° C. The ignition temperature in air is 120° to 150° C. The only liquids which dissolve it without decomposition are phosphorus and P2H4. It dissolves in ammonia at -40° C. with evolution of phosphine. After evaporation of the ammonia a black solid is left which appears to be an ammine of a higher hydrogen phosphide. Like the other phosphides it is easily oxidised by halogens, chlorates and nitric acid.

The hydrogen of this phosphide appears to have a slight acidic character, since the phosphide dissolves in alcoholic alkalies giving deep red solutions which contain polyphosphides, similar to those which are formed by the action of alcoholic alkali on finely divided scarlet phosphorus. These compounds are easily hydrolysed by dilution, or by the addition of acids, with the precipitation of a yellow or reddish mixture of solid hydrogen phosphide and scarlet phosphorus (which possibly contains a suboxide or P4H.OH).

Higher Phosphides of Hydrogen

When the diphosphide is gradually heated to 175° C. in vacuo, or when its ammoniate is heated, a reddish powder is formed to which the composition P9H2 has been assigned:

5P12H6 = 6P9H2 + 6PH3

This compound is fairly stable in dry air, but in moist air is converted into phosphine and phosphoric acid. It dissolves in liquid ammonia. A phosphide P5H2 has also been reported.

Some hydroxyphosphides are formed also by oxidation and hydrolysis of a mixture of phosphorus and phosphorus trichloride, or by the hydrolysis of tetraphosphorus diiodide, P4I2, when this is boiled with water. The solid to which the composition P4H.OH has been assigned dissolves in alcoholic potash giving hydrogen and the potassium salt, P4H.OK.
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