phlobaphenes

A disadvantage of this synthetic tannin is its complete incapability of dissolving phlobaphenes, which is even so far extended as to precipitate otherwise easily soluble tannins when adding it to solutions of the latter in comparatively large proportions; here, again, the salts are responsible for this behaviour, their large quantities effecting a salting out of the natural tannins.

Synthetic Tannins Georg Grasser

The varying phlobaphene contents of the tannins easily afford an explanation of the different properties above alluded to: the mangrove phlobaphenes are dark coloured bodies, those of mimosa, maletto, and chestnut are of lighter colour, and the last-named tanning materials enumerated above are either devoid of phlobaphenes or possess them only as very light coloured bodies.

Synthetic Tannins Georg Grasser

If, now, the quebracho extract be treated with sulphite and bisulphite in the usual way, the phlobaphenes are solubilised, but the reducing effect of the bisulphite tends to brighten the colour of the otherwise dark coloured phlobaphenes as well as that of the soluble tannins, and a reddish-yellow coloured extract results, imparting its own colour to the pelt.

Synthetic Tannins Georg Grasser

This clearly proves that free and condensed phenolsulphonic acids as such are not capable of completely solubilising phlobaphenes, whereas the sodium salts of free and condensed phenolsulphonic acids possess this property.

Synthetic Tannins Georg Grasser

In order to demonstrate whether the sulphonic acids and their salts are capable of solubilising the insoluble or sparingly soluble anhydrides of the tannins (the phlobaphenes) before and after condensation, the following experiments were carried out: --

Synthetic Tannins Georg Grasser

As regards the capability of the naphthalenesulphonic acids of dissolving phlobaphenes, the following results were obtained: -- solid

Synthetic Tannins Georg Grasser

The dark coloured phlobaphenes present, on account of their insolubility, will have no influence on the colour of the leather.

Synthetic Tannins Georg Grasser

It is hence possible that the plants may employ formaldehyde as a methylation medium, and produce these insoluble condensation products for the purpose of ridding themselves of the poisonous phenols and aromatic hydroxy acids (and tannins), in addition to oxidising processes whereby phlobaphenes, ellagic acid, etc., are formed.

Synthetic Tannins Georg Grasser

The precipitate formed, consisting of quebracho phlobaphenes, was separated from the liquid by decantation, and purified by washing it several times with water.

Synthetic Tannins Georg Grasser

The salt contents of Neradol D, therefore, constitute an advantage in this respect, that not only may Neradol D be mixed with solutions of any natural tannin without insolubles being thereby deposited, but it may also be added in large quantities to a tannin solution with the result that the sparingly soluble and wholly insoluble constituents (phlobaphenes) are completely brought into solution.

Synthetic Tannins Georg Grasser