Chemical elements
    Amorphous Sulphur
    Colloidal Sulphur
    Physical Properties
    Chemical Properties
      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
      Sulphur Trioxide
      Pyrosulphuric Acid
      Sulphuric Acid
      Persulphuric Anhydride
      Persulphuric Acid or Perdisulphuric Acid
      Permonosulphuric Acid
      Amidopermonosulphuric Acid
      Thiosulphuric Acid
      Polythionic Acids
      Dithionic Acid
      Trithionic Acid
      Tetrathionic Acid
      Pentathionic Acid
      Wackenroders Solution
      Hexathionic Acid
      Polythionic Acids
      Sulphur Sesquioxide
      Hydrosulphurous Acid
      Nitrogen Sulphide
      Nitrogen Persulphide
      Nitrogen Pentasulphide
      Nitrogen Chlorosulphide
      Trithiazyl Chloride
      Thiotrithiazyl Chloride
      Dithiotetrathiazyl Chloride
      Nitrogen Bromosulphide
      Thiotrithiazyl Bromide
      Thiotrithiazyl Iodide
      Thiotrithiazyl Nitrate
      Thiotrithiazyl Hydrogen Sulphate
      Thiotrithiazyl Thiocyanate
      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
      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
      Azidodithiocarbonic Acid
      Cyanogen Monosulphide
      Cyanogen Trisulphide
      Sulphur Thiocyanate
      Disulphur Dithiocyanate
      Thiocyanic Acid
      Dithiocyanic Acid
      Trithiocyanuric Acid
      Perthiocyanic Acid

Pyrosulphuryl Chloride, S2O5Cl2

Rose first prepared Pyrosulphuryl Chloride, S2O5Cl2, in 1838 by the interaction of sulphur trioxide and sulphur monochloride. It is formed by the action of many chlorides on sulphur trioxide; sulphur monochloride, thionyl chloride, silicon tetrachloride, phosphorus pentachloride, phosphorus oxychloride, sodium chloride and carbon tetrachloride all yield the desired product when treated with sulphur trioxide at a suitable temperature. With sodium chloride a mixture of pyrosulphuryl chloride and sodium pyrosulphate is obtained, whilst with the exception of carbon tetrachloride and phosphorus pentachloride, which are converted into oxychlorides, all the remaining chlorides are changed into oxides:

5SO3 + S2Cl2 = S2O5Cl2 + 5SO2;
2SO3 + SOCl2 = S2O5Cl2 + SO2;
2SO3 + PCl5 = S2O5Cl2 + POCl3;
6SO3 + 2P0Cl3 = 3S2O5Cl2 + P2O5;
2SO3 + 2SiCl4 = S2O5Cl2 + Si2OCl6,
followed by 6SO3 + Si2OCl6 = 3S2O5Cl2 + 2SiO2;
4SO3 + 2NaCl = S2O5Cl2 + Na2S2O7;
2SO3 + CCl4 = S2O5Cl2 + COCl2.

The most convenient process is to add a mixture of sulphur trioxide and fuming sulphuric acid gradually to hot carbon tetrachloride, the product being purified by fractional distillation, followed by treatment with sodium chloride to remove any chlorosulphonic acid and subsequent redistillation, preferably under reduced pressure. Fuming sulphuric acid reacts with carbon tetrachloride at 150° C. with formation of chlorosulphonic acid and carbonyl chloride. The chlorosulphonic acid then reacts with more carbon tetrachloride thus:

CCl4 + 2SO3HCl = S2O5Cl2 + 2HCl + COCl2.

When chlorosulphonic acid is dehydrated by the action of phosphorus pentoxide or pentachloride, pyrosulphuryl chloride is obtained:

Cl.SO2.O = Cl.SO2.O.SO2Cl + H2O.

Pyrosulphuryl chloride is a colourless, rather viscous liquid, which in the air fumes less strongly than sulphur trioxide. It boils at 152° to 152.5° C. under 766 mm. pressure, at 57° C. under 30 mm., and at 52° C. under 15 mm., without appreciable decomposition if dry.

D04 = 1.872, D204 = 1.837; = -37.5° to -37° C.; n19D = 1.449. From vapour density determinations it is known that at 180° C. the molecular weight is normal but that at higher temperatures decomposition occurs. The liquid chloride is exothermic with respect to its elements, the heat of formation, according to Ogier, being 159,400 calories, but according to Konowalov 188,200 calories. The specific heat of the liquid is 0.258, and the molecular heat of vaporisation according to the last-named investigator is 7550 calories, a figure more in accordance with Trouton's Rule than the high value of 13,160 calories given by Ogier.

When passed through a red-hot tube the vapour is almost entirely decomposed into sulphur dioxide, sulphur trioxide and chlorine. Vapour density determinations at various temperatures, and analyses of the decomposition products, indicate that decomposition proceeds according to the equations:

S2O5Cl2 = SO3 + SO2 + Cl2,
and S2O5Cl2 = SO3 + SO2Cl2,

the former reaction occurring to a small extent at 200° C. in the presence of sulphur dioxide and chlorine, but giving place at higher temperatures to the second reaction, when

SO2Cl2 SO2 + CI2

follows and decomposition is complete at 360° C.

The liquid chloride is only gradually attacked by water, giving sulphuric and hydrochloric acids, but if the relative quantity of water is very small, two reactions occur,

S2O5Cl2 + H2O = 2HClO + 2SO2,
SO2 + 2HClO = H2SO4 + Cl2,

such solutions having oxidising properties.

Like sulphuryl chloride, pyrosulphuryl chloride can convert many elements, e.g. sulphur, phosphorus, antimony and mercury, into the corresponding chlorides, with simultaneous formation of sulphur dioxide and trioxide. In the reaction between pyrosulphuryl chloride and phosphorus pentachloride or trichloride, there are obtained phosphorus oxychloride, sulphur dioxide and chlorine.

Pyrosulphuryl chloride is not miscible with sulphuric acid, but when sealed together in a tube the two liquids become homogeneous in the course of a few weeks, the sulphuric acid undergoing dehydration:

S2O5Cl2 + H2SO4 = 2Cl.SO2.OH + SO3.

Hydrogen bromide, iodide and sulphide are oxidised to the corresponding elements, various reduction and hydrolytic products of the pyrosulphuryl chloride being formed at the same time. Phosphine also causes reduction of pyrosulphuryl chloride with production of sulphide of phosphorus.

With chromates, chromyl chloride is produced:

K2CrO4 + S2O5Cl2 = CrO2Cl2 + K2S2O7.

Selenium is oxidised to a selenium sulphur oxytetrachloride.

From the chemical behaviour of the substance and especially its relationship to chlorosulphonic acid, it is evident that pyrosulphuryl chloride may be regarded as chlorosulphonic anhydride, Cl.SO2.0.SO2.Cl. Grignard and Muret consider that the properties of the compound are best accounted for by the formula


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