Structure-Activity-Relationships of Synthetic Organic Tanning Agents

In this paper the structure of various syntans are studied and compared to natural tanning agents. Following structure-property relationships were found in reference to tanning efficiency: - Although many natural tannins contain methoxy groups, we could not positively proof a tanning effect of methoxy groups as such. - The spacer group between the phenol moieties does play a role in tanning. Comparing different spacers the benzyliden spacer proofed to be most beneficial for shrinkage temperature. However based on physicochemical properties (solubility, accessibility) the methylene and sulfon spacer appear more favorable. - Natural tannins frequently contain higher oxidized moieties based on catechol or pyrogallol. Trials showed that their influence on the shrinkage temperature was less pronounced than the effect on lightfastness of the obtained leathers, with the phenol based product giving best lightfastness. - The molecular weight of condensates influences the tanning capacity. We used products of three different molecular weights all containing the sodium salt of phenolsulfonic acid and achieved shrinkage temperatures that differed significantly and increased with molecular weight of the condensate.