During the preparation of sulphur monochloride, Millon in 1838 obtained a substance which he described as a crystalline sulphur chloride; its formation was due to the presence of moisture during the action, and similar crystals can be formed by introducing a little sulphur monochloride into a flask filled with moist chlorine. The composition of the crystals has since been shown to be represented by Sulphur Oxytetrachloride, S2O3Cl2.
A more convenient method of preparation is to pass chlorine into a mixture of sulphur monochloride with a bimolecular proportion of chlorosulphonic acid at -15° C., until solidification occurs. Probably sulphur tetrachloride is first formed and then reacts with the chlorosulphonic acid:
SCl4 + Cl.SO2.OH = Cl.SO2.O.SCl8 + HCl
Sulphur oxytetrachloride is a pungent, colourless, crystalline solid of m.pt. 57° C., with decomposition. Even when kept at the ordinary temperature it gradually liquefies on account of decomposition into thionyl and sulphuryl chlorides; if decomposed rapidly at higher temperatures, the latter compound is naturally accompanied by or even replaced by its dissociation products.
S2O8Cl2 = SOCl2 + SO2Cl2.
Treatment with water causes hydrolysis to sulphuric and sulphurous acids, together with hydrochloric acid:
S2O3Cl2 + 4H2O = H2SO3 + H2SO4 + 4HCl.
Sulphuric acid reacts with sulphur oxytetrachloride as with sulphuryl chloride, yielding chlorosulphonic acid.
In accordance with its reactions the constitution of sulphur oxytetrachloride must be regarded as represented by Cl.SO2.O.SCl3. |