Note 60 — Chapter XX · SULPHUR, SELENIUM, AND TELLURIUM

We will mention the following difference between the sulphonic acids and the ethereal acid sulphates (Note 59): the former re-form sulphuric acid with difficulty and the latter easily. Thus sulphovinic acid when heated with an excess of water is reconverted into alcohol and sulphuric acid. This is explained in the following manner. Both these classes of acids are produced by the substitution of hydrogen by SO3H, or the univalent radicle of sulphuric acid, but in the formation of ethereal acid sulphates the SO3H replaces the hydrogen of the hydroxyl in the alcohol, whilst in the formation of the sulphonic acids the SO3H replaces the hydrogen of a hydrocarbon. This difference is clearly evidenced in the existence of two acids of the composition SO4C2H6. The one, mentioned above, is sulphovinic acid or alcohol, C2H5.OH, in which the hydrogen of the hydroxyl is replaced by sulphoxyl = C2H5.OSO3H, whilst the other is alcohol, in which one atom of the hydrogen in ethyl, C2H5, is replaced by the sulphonic group—that is = (C2H4)SO3H·OH. The latter is called isethionic acid. It is more stable than sulphovinic acid. The details as to these interesting compounds must be looked for in works on organic chemistry, but I think it necessary to note one of the general methods of formation of these acids. The sulphites of the alkalis—for example, K2SO3—when heated with the halogen products of metalepsis, give a halogen salt and a salt of a sulphonic acid. Thus methyl iodide, CH3I, derived from marsh gas, CH4, when heated to 100° with a solution of potassium sulphite, K2SO3, gives potassium iodide, KI, and potassium methylsulphonate, CH3SO3K—that is a salt of the sulphonic acid. This shows that the sulphonic acid may be referred to sulphurous acid, and that there is a resemblance between sulphuric and sulphurous acid, which clearly reveals itself here in the formation of one product from them both.