Tannin-resorcinol mixtures

In Resin Manufacture. Proper control of the exothermic reaction of formaldehyde with the tannin/resorcinol mixtures is essential. Full water cooling should be applied already at temperatures as low as 25 to 30 °C, otherwise, without it, a 1-ton industrial batch can sometimes pass from ambient to 80 °C in less than 2 minutes I have seen the stainless steel door of a reaction vessel fly 20 meters into the air as a consequence of this mistake, and the operator was lucky The vessel may easily explode or the reaction mixture boil over through the condenser, if the reaction is not properly controlled at its beginnings. 

Ordinates t]s — Vo)ho (in % of the initial value), or Vsivoivo is in this case always the viscosity of the corresponding tannin - water or resorcinol-water mixture). 

Flavonoid acetates and methyl ethers have been separated by WEmoES and Toribio [236] using solvent II (Table 166). Catechin-resorcinol condensation products in particular can be resolved in this way [236]. Catechin acetate diastereoisomers and the acetates of oUgomeric flavonoid tannins such as the acetates of dicatechin and anhydro-catechin can be thus detected with certainty [56]. The acetates of the more highly condensed compounds remain at the start point. Plant extracts containing catechins and flavonoid tannins are best acetylated initially by 15 h treatment with acetic anhydride/absolute pyridine at room temperature. Solvent II or chloroform-ethyl acetate (90 + 10) can be used with silica gel columns for preparative separation of such mixtures. 

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