Tannins and Leather

The phenols were localised by evaporating the solvent and marking the zones of reduced fluorescence in short-wave UV-light (254 nm). After then spraying with 

Fast Blue Salt B (1% aqueous solution), the layer was dried, briefly exposed to ammonia and finally sprayed with cone, hydrochloric add. Evaluation was performed a few minutes after reaction. The colour change on staiuling also furnished miditional information. A 1% methanolic solution of the phenols 1-8 in Table 3 was u d for comparison. Each time 1 jid was applied on the ri t side and 1 pi of the DESAGA colour test solution aloi side. 

The thermal behaviour of free phenols and tho linked to skin powder via hydrogen bonds is of interest for the interpretation of the thermofractograms of tannins and leather. The results of such experiments are summarised below in Table 3 under a) andb). 

The mono- and diphenols and pyrogallol appear undecomposed in various temperature ranges in the TFG. Phlorogjucinol is partly decomposed into resorcinol. Gallic acid sublimes in the range 170—240 °C, undergoing partial decarboxylation into pyrogallol at over 200 C. 

Hydrogen bond formation with proteins (ddn powder) di laces the zonal maxima clearly to higher temperature ranges. The behaviour of individual tannins and their structural units in the temperature gradient is given in Table 4  

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