Experiments were carried out with the object of condensing o-, m-, and p-cresolsulphonic acids with formaldehyde in various ways; no essential differences could be detected as regards the mode of reaction or the properties of the intermediary and end-products as compared to those of phenolsulphonic acid. Similarly, condensation of different samples of crude cresol containing varying quantities of o-, m-, and p-cresol did not yield end-products sufficiently different to justify describing them in detail.
E. Relative Behaviour of an Alkaline Solution of Bakelite and Natural
Tannins
Phenolsulphonic acid was condensed with a little formaldehyde, and the reddish pasty condensation product dissolved in caustic soda. This alkaline solution of bakelite was exactly neutralised with acetic acid and mixed with strong solutions of an untreated quebracho extract. It was observed that the solubility of the quebracho extract was not increased by this treatment, but the faintly acidic character of the natural tannin caused the bakelite to be thrown down as an insoluble precipitate.
Crude phenolsulphonic acid, when added to a solution of the quebracho extract referred to, does not increase the solubility of the latter, which even deposits considerable amounts of insoluble tannin particles.
Quite different properties are exhibited by sodium phenolsulphonate, which completely converts quebracho tannin into a water-soluble substance, the aqueous solution of which deposits no insolubles. The partly neutralised condensation product of phenolsulphonic acid and formaldehyde exhibits similar properties [Footnote: Grasser, Collegium, 1913, 521, 478.] (see later).
F. Dicresylmethanedisulphonic Acid (Neradol D) [Footnote: Ger, Pat., 291, 457; Austr. Pat., 61, 057.]
Neradol D is a viscous liquid, measuring about 33° Bé., which is similar to extracts of natural tannins. One of its characteristics is its phenolic odour; it is completely soluble in water, forming a clear, semi-colloidal solution, but is insoluble in all organic solvents with the exception of alcohol, glacial acetic acid and ethyl acetate, which dissolve all but its inorganic constituents. The latter owe their presence to the neutralisation of the crude Neradol with caustic soda, and are composed of sodium salts of the sulphonic acid in addition to Glauber salts.
The aqueous solution of Neradol D shows properties similar to those exhibited by solutions of natural tannins and reacts as follows:—[Footnote: Grasser, Collegium, 1913, 520, 413.]
Methyl orange Acid reaction.
Barium chloride White precipitate, insoluble in HNO_3.
Ferric chloride Deep blue coloration.
Silver nitrate Slight opalescence.
Bromine water No precipitate.
Formaldehyde hydrochloric acid No precipitate.
Gelatine Complete precipitation.
Aniline hydrochloride Strong precipitate.
The reactions with ferric chloride and gelatine should be especially noted, since they are analogous to those given by natural tannins. On the other hand, the reactions with BaCl_2, bromine water and formaldehyde hydrochloric [Footnote: Stiasny carries out the reaction with formaldehyde-hydrochloric acid as follows:—50 c.c. of the tannin solution, plus 5 c.c. concentrated hydrochloric acid and 10 c.c. formaldehyde (40 per cent.) are heated under reflux condenser for ten minutes; most natural tannins are completely precipitated (Collegium, 1906, 435; 1907, 52 et 188).] acid prove the different chemical composition of Neradol D as compared to that of the natural tannins.