1. Condensation Induced by Heat
If phenolsulphonic acid is heated in vacuo at 130° C. for twenty hours, condensation takes place [Footnote: Austr. Pat., 64,479.] without the addition of any condensing agent, and an anhydride of the
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HSO_3 HSO_3
composition is formed. This product is a viscous liquid, possessing a very corrosive action. Added to a solution of gelatine, a light, fine flocculent precipitate is thrown down. Analysed by the shake method of analysis, the tannin content of the product equals about 46 per cent. Its strongly acidic and hence swelling character does not express qualities consistent with the conception of suitability for tanning purposes: a sample of the product was therefore partly neutralised to the acidity of Neradol D, when the shake method of analysis yielded the following figures:—
Tanning matters 21.5 per cent. Soluble non-tannins 48.3 " Water 30.2 " ——————— 100.0 per cent.
This partly neutralised sulphonic acid represents a white, pasty mass, which is not particularly easily soluble in water, yielding a solution of milky appearance. Treated with the usual tannin reagents, it exhibits the following characteristics:—
Gelatine Light Flocculent precipitate.
Bromine water Compete fixation.
Ferric chloride Cherry-red coloration.
Lead acetate Very slight Percipitate, insoluble HNO_3.
Aniline hydrochlonde Slight percipitate.
Solutions of this product in concentrations from 1°-8° Bé. exerted no tanning action whatever, whereas more concentrated solutions (15° Bé.) converted pelt in eight days into a leather very similar to a Neradol D leather in colour and feel, but considerably harder.
In order to determine its phlobaphene-solubilising effects, samplesof the product were mixed with concentrated quebracho extract in the proportions 5,10, 20, and 30 per cent. on the weight of extract, and the following observations made:—5 and 10 per cent. were without effect, 20 and 30 per cent. showed some solubilising tendency, but on diluting the mixture with water the quebracho was completely thrown out of solution. Apparently this anhydride is, in this respect also, quite different from the partly neutralised diphenylmethanedisulphonic acid.
2. Condensation with Sulphur Chloride