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

Chlorosulphonic Acid, Cl.SO2,OH

In 1854 the discovery of chlorosulphonic acid by Williamson, by the interaction of hydrogen chloride and sulphur trioxide, was of especial interest. Ideas of valency were immature and undeveloped, and for the systematisation of the knowledge of organic and inorganic compounds reference was made to various types such as HCl, H2O and H3N, from which other substances could be regarded as derived by substitution of one or more of the hydrogen atoms by other atoms or groups of atoms. Chlorosulphonic acid was the first example of a compound derived simultaneously from two types, namely from hydrogen chloride and water by the replacement of a hydrogen atom from each by the group SO2.

The following methods are available for the preparation of chlorosulphonic acid: (1) The substance can be obtained by the gradual action of moisture (e.g. atmospheric moisture) on sulphuryl chloride; a similar reaction occurs with sulphuric acid and is more easily regulated:

SO2Cl2 + H2O = Cl.SO2.OH + HCl,
SO2Cl2 + H2SO4 = 2Cl.SO2.OH.

To the former reaction is also to be ascribed the formation of chlorosulphonic acid when moist chlorine and sulphur dioxide are passed over platinum at a red heat.

(2) Concentrated or fuming sulphuric acid also gives rise to chlorosulphonic acid when treated with phosphorus pentachloride:

H2SO4 + PCl5 = Cl.SO2.OH + POCl3 + HCl;

other acid chlorides such as phosphorus oxychloride, phosphorus trichloride, sulphuryl chloride, pyrosulphurvl chloride, sulphur oxytetrachloride, and even sulphur monochloride, give a similar result.

(3) Even chlorine alone will act on sulphuric acid, giving chlorosulphonic acid, as also will hydrogen chloride on sulphur trioxide or on a mixture of sulphuric acid and phosphorus pentoxide. Indeed, the interaction of hydrogen chloride and sulphur trioxide in the presence of sulphuric acid provides the most convenient method for preparing chlorosulphonic acid, the product being purified by distillation in an atmosphere of hydrogen chloride, followed by fractional crystallisation:

Cl2 + H2SO4 = Cl.SO2.OH + HCl;
HCl + SO3 = Cl.SO2.OH.

Chlorosulphonic acid is a colourless fuming liquid of sharp, unpleasant odour. It boils at 151° to 152.5° C. at 765 mm., or at 74° to 75° C. at 19 mm., and it melts at -81°to -80°C.; D04 = 1.784, D204 = 1.753. At the boiling-point the vapour density is normal, but marked dissociation occurs at higher temperatures, e.g. at 200° C., with formation of sulphur trioxide and hydrogen chloride. Referred to solid sulphur trioxide and gaseous hydrogen chloride, the formation of chlorosulphonic acid is exothermic to the extent of 14.4 Calories per gram- molecule; the specific heat at ordinary temperatures is 0.282 and the latent heat of vaporisation 12.8 Calories per gram-molecule.

When heated strongly, the vapour of chlorosulphonic acid undergoes decomposition into sulphur trioxide and hydrogen chloride or, at higher temperatures, into sulphur dioxide, sulphuric acid and chlorine; under suitable conditions, e.g. at 180° to 210° C. in a sealed tube or especially readily in the presence of certain catalysts such as mercury or mercuric chloride, platinum chloride, copper, iodine or sulphur, the liquid substance undergoes disruption into sulphuryl chloride and sulphuric acid.

Water causes very vigorous hydrolysis to sulphuric acid and hydrogen chloride, the action being much more rapid than with pyrosulphuryl chloride:

Cl.SO2.OH + H2O = HCl + SO2(OH)2.

Hydrogen sulphide is readily decomposed by chlorosulphonic acid with formation of sulphur, sulphur monochloride and sulphuric acid; the reaction may be expressed as

2H2S + 2Cl.SO2.OH = S2Cl2 + 2H2O + S + H2SO4,

but is probably more complex.

Chlorosulphonic acid possesses a strong chlorinating power and converts sulphur, phosphorus, arsenic, antimony and tin into the corresponding chlorides, sulphur dioxide together with sulphuric and hydrochloric acids being simultaneously produced. With sulphur and with yellow phosphorus interaction occurs at the ordinary temperature, often becoming uncontrollable with the latter element.

With sulphuric acid and phosphorus pentachloride, respectively, fuming sulphuric acid and pyrosulphuryl chloride are obtained; in the latter case the effect is one of dehydration, and a similar result is producible with phosphorus pentoxide:

Cl.SO2.OH + H2SO4 = O(SO2.OH)2 + HCl;
2Cl.SO2.OH + PCl5 = O(SO2Cl)2 + POCl3 + 2HCl;
2Cl.SO2.OH + P2O5 = O(SO2Cl)2 + 2HPO3.

Potassium sulphate, when warmed with chlorosulphonic acid, yields potassium pyrosulphate, the reaction being analogous to that of sulphuric acid with the chloro-acid; silver nitrate is vigorously converted into silver chloride, with concurrent formation of nitrosulphonic acid.

At the ordinary temperature chlorosulphonic acid dissolves sodium chloride, displacing hydrogen chloride and forming sodium chlorosulphonate, this reaction being due to its acidic nature. It is of interest that ammonium chlorosulphonate can be synthesised by the action of sulphuryl chloride on aminosulphonic acid at 100° C.

The simple acidic nature of chlorosulphonic acid is also manifested in the existence of corresponding ethereal salts, the ethyl ester Cl.SO2.OC2H5 being obtainable indirectly by the action of phosphorus penta-chloride on ethyl hydrogen sulphate (ethylsulphuric acid), C2H5O.SO2.OH, or by the interaction of sulphuryl chloride and ethyl alcohol:

C2H5O.SO2.OH + PCl5 = Cl.SO2.OC2H5 + POCl3 + HCl;
SO2Cl2 + C2H5OH = Cl.SO2.OC2H5 + HCl.

From its general behaviour it is clear that chlorosulphonic acid is closely related to sulphuric acid. Like the latter acid, but with more vigour, it attacks aromatic hydrocarbons with formation of organic sulphonic acids of the structure R.SO2.OH and sulphones of the structure , where R represents an aromatic organic radical such as phenyl (C6H5). From these and other reactions the conclusion may be drawn that in chlorosulphonic acid the chlorine atom must be directly attached to sulphur, and therefore that the constitution must be represented as

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