Chemical elements
  Sulphur
    Isotopes
    Energy
    Extraction
    Refining
    Applications
    Allotropy
    Crystalline
    Amorphous Sulphur
    Colloidal Sulphur
    Physical Properties
    Chemical Properties
    Detection
    Estimation
    Compounds
      Hydrogen Sulphide
      Metal Polysulphides
      Hydrogen Polysulphides
      Hydrogen Pentasulphide
      Hydrogen Trisulphide
      Hydrogen Disulphide
      Sulphur Monofluoride
      Sulphur Tetrafluoride
      Sulphur Hexafluoride
      Sulphur Monochloride
      Sulphur Dichloride
      Sulphur Tetrachloride
      Sulphur Monobromide
      Thionyl Fluoride
      Sulphuryl Fluoride
      Fluorosulphonic Acid
      Thionyl Chloride
      Sulphuryl Chloride
      Sulphur Oxytetrachloride
      Pyrosulphuryl Chloride
      Chlorosulphonic Acid
      Thionyl Bromide
      Sodium Sulphoxylate
      Sulphur Dioxide
      Sulphurous Acid
      Sulphites
      Sulphur Trioxide
      Pyrosulphuric Acid
      Pyrosulphates
      Sulphuric Acid
      Persulphuric Anhydride
      Persulphuric Acid or Perdisulphuric Acid
      Perdisulphates
      Permonosulphuric Acid
      Amidopermonosulphuric Acid
      Thiosulphuric Acid
      Thiosulphates
      Polythionic Acids
      Dithionic Acid
      Trithionic Acid
      Trithionates
      Tetrathionic Acid
      Tetrathionates
      Pentathionic Acid
      Pentathionates
      Wackenroders Solution
      Hexathionic Acid
      Polythionic Acids
      Sulphur Sesquioxide
      Hydrosulphurous Acid
      Hydrosulphites
      Nitrogen Sulphide
      Nitrogen Persulphide
      Nitrogen Pentasulphide
      Sulphammonium
      Hexasulphamide
      Nitrogen Chlorosulphide
      Trithiazyl Chloride
      Thiotrithiazyl Chloride
      Dithiotetrathiazyl Chloride
      Nitrogen Bromosulphide
      Thiotrithiazyl Bromide
      Thiotrithiazyl Iodide
      Thiotrithiazyl Nitrate
      Thiotrithiazyl Hydrogen Sulphate
      Thiotrithiazyl Thiocyanate
      Thionylamide
      Sulphamide
      Imidodisulphamide
      Sulphimide
      Sulphonic Acids
      Amidosulphonic Acid
      Imidosulphonic Acid
      Nitrilosulphonic Acid
      Hydroxylamine-monosulphonic Acid
      Nitrososulphonic Acid
      Hydroxylamine-disulphonic Acid
      Hydroxylamine-isodisulphonic Acid
      Hydroxylamine-trisulphonic Acid
      Dihydroxylamidosulphonic Acid
      Sulphazinic Acid
      Sulphazotinic Acid
      Dehydrosulphazotinic Acid
      Nitrosulphonic Acid
      Nitrosulphonyl Chloride
      Nitrosulphonic Anhydride
      Nitrosulphuric Acid
      Nitrosodisulphonic Acid
      Sulphonitronic Acid
      Sulphates of Hydroxylamine
      Hydroxylamine Dithionate
      Hydrazine Dithionate
      Hydrazine Amidosulphonate
      Carbon Subsulphide
      Carbon Monosulphide
      Carbon Disulphide
      Thioformaldehyde
      Thiocarbonic Acid
      Ammonium thiocarbonate
      Thiolcarbonic Acid
      Xanthic Acid
      Perthiocarbonic Acid
      Sodium perthiocarbonate
      Carbonyl Sulphide
      Thiocarbonyl Chloride
      Thiocarbonyl Tetrachloride or
      Carbon Hexachlorosulphide
      Trichloromethyl Disulphide
      Thiocarbonyl Sulphochloride
      Carbon Bromosulphide
      Amino-derivatives of Thiocarbonic Acid
      Dithiocarbamic Acid
      Thiocarbamide
      Azidodithiocarbonic Acid
      Thiocyanogen
      Cyanogen Monosulphide
      Cyanogen Trisulphide
      Sulphur Thiocyanate
      Disulphur Dithiocyanate
      Thiocyanic Acid
      Thiocyanates
      Dithiocyanic Acid
      Trithiocyanuric Acid
      Perthiocyanic Acid
      Perthiocyanogen
      Sulphates

Hydrogen Polysulphides






In 1777 Scheele observed that by the rapid addition of much acid to a solution of sulphur in an alkali it was possible to produce a yellow, pungent, oily substance. Better conditions for the preparation of this substance were first described by Berzelius in 1825, who stated that a concentrated solution of " liver of sulphur " should be added in small quantities to dilute hydrochloric acid. The oily substance, of specific gravity approx. 1.7, is very unstable and is rapidly decomposed on contact with water, although dilute acids, especially hydrochloric acid, exert a distinct preservative action. For many years the oil was regarded as hydrogen pentasulphide, H2S5. When freshly prepared it is completely soluble in cold benzene; it cannot therefore contain any considerable quantity of free sulphur, and as its composition approximates to that of a penta- sulphide, it was natural to come to the conclusion that it might be an impure hydrogen pentasulphide; now, however, the product is not- regarded as a definite compound. It varies in viscosity according to the percentage of sulphur in the original dissolved metallic polysulphide, and widely divergent views have at various times been expressed as to the formula representing its composition.

A discovery that certain alkaloids were capable of producing definite crystalline compounds with hydrogen polysulphide unfortunately failed to elucidate the mystery of the composition of the latter, since the compounds produced did not yield unanimous indications. Thus strychnine yielded a hexasulphide, (C21H22O2N2)2.H2S6, whilst brucine gave two hexasulphides, a red one, (C23H26O4N2)3.(H2S6)2, and a yellow one, (C23H26O4N2)3.H2S6.6H2O, and also an octasulphide, C23H26O4N2.H2S8.2H2O. Furthermore, apart from the fact that these additive compounds were not of one type and that their composition was at first wrongly interpreted, there was the additional disadvantage that their indications did not accord well with the earlier views concerning the formula of hydrogen polysulphide.

Solubility of Sulphur in Hydrogen
Solubility of Sulphur in Hydrogen Di- and Tri-sulphides.
At the beginning of the twentieth century, therefore, there was no certainty as to the formula of hydrogen polysulphide, and, indeed, any formula between the limits H2S2 and H2S8 appeared possible, although the representation H2S5 appeared to be more in favour than any other. Three well-defined compounds, however, have now been isolated, hydrogen disulphide, H2S2, hydrogen trisulphide, H2S3, and hydrogen pentasulphide, H2S5; these will be described; there is also evidence of the existence of hydrogen hexasulphide, H2S6. The alkaloid compounds already mentioned are well-crystallised, stable bodies, and furthermore, the solubility curves for sulphur in the disulphide and trisulphide respectively have been determined between the temperatures -34.72° C. and 55.3° C. and found to be identical; in both cases there is a marked break in the curve at -1.45° C., at which temperature the liquid has a composition very near to that required by the formula H2S6 (i.e. 82.47 per cent, of sulphur not evolved as H2S); (see fig.).


Preparation of Hydrogen Polysulphides

The crude hydrogen polysulphide, or " hydrogen per- sulphide "as it is frequently termed, is best prepared by heating for three hours at 100° C. a mixture of sodium sulphide, Na2S.9H2O, with half its weight of sulphur. The crystalline sulphide melts and the sulphur is gradually dissolved to a deep-red solution of which the solute has a composition between Na2S4 and Na2S5. This solution is mixed with rather less than its own bulk of water and is then introduced as a thin stream into a mixture of dilute hydrochloric acid and ice. The same yellow, oily product is obtained whatever the composition of the dissolved polysulphide, whether Na2S2, Na2S3, Na2S4 or Na2S5.

If the oil is distilled under a pressure of 2 mm. in glass apparatus of which the superficial alkali has been removed by treatment with hydrogen chloride, a distillate amounting to approximately one-sixth of the original bulk can be collected in the usual manner and on analysis proves to be hydrogen trisulphide, H2S3. At the same time a more volatile liquid, actually hydrogen disulphide, H2S2, can be condensed in a second receiver cooled by a mixture of ether and solid carbon dioxide.

The crude persulphide is also formed together with a large proportion of sulphur, when sulphur dioxide either as gas or in solution is reduced by means of hypophosphorous acid.

The pentasulphide, H2S5, has been isolated more recently by decomposing pure anhydrous ammonium pentasulphide with anhydrous formic acid.

General Properties of Hydrogen Polysulphides

All the known hydrogen polysulphides, as well as the crude so-called hydrogen persulphide, are yellow liquids at the ordinary temperature. They are very sensitive towards alkalis, and it is therefore necessary to treat glass vessels intended for their storage (which is often possible only for a few hours) with hydrogen chloride gas. If necessary, the compounds can be dried over calcium chloride, but this also should have received previous treatment with hydrogen chloride.

The compounds burn with a blue flame, giving water and sulphur dioxide. Even at the ordinary temperature they readily decompose into hydrogen sulphide and sulphur, the measurement of the amount of hydrogen sulphide formed from a known weight of a hydrogen polysulphide, when warmed in an atmosphere of hydrogen, supplying the most convenient method of analysis. Dilute acids act as preservatives, but even traces of alkali cause rapid and vigorous decomposition. The addition of alcohols, especially amyl alcohol, also induces rapid decomposition.

Sulphur dissolves in the various hydrogen polysulphides as already described; the solutions deposit crystalline sulphur when cooled or on the addition of benzene. As solutions of sulphur in hydrogen disulphide or trisulphide behave in this way, whereas the fresh crude polysulphide does not yield its excess of sulphur on similar treatment, this supplies further evidence of the existence of a higher polysulphide in the crude " persulphide."

The hydrogen polysulphides are miscible with benzene, toluene, chloroform, bromoform, carbon disulphide, ether and heptane, giving relatively stable solutions, and the use of such solutions has been suggested in place of sulphur chloride for the vulcanisation of caoutchouc at the ordinary temperature. The addition of alcohol to the benzene solutions induces rapid decomposition, with formation of nacreous sulphur, which slowly undergoes conversion into ordinary sulphur. Ketones, nitrobenzene, aniline and pyridine also catalyse the decomposition.
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