Comparative kinetics of the induced radical autocondensation of polyflavonoid tannins. II. Flavonoid units effects

Comparative kinetics of the radical autocondensation induced by SiO2 on a series of polyflavonoid tannins, namely, pine, pecan, mimosa, quebracho, gambier, sumach, and on the catechin monomer as a model compound were carried out by electron spin resonance. The induced radical autocondensation appeared to be independently catalyzed by the known base mechanism, as well as SiO2 and Lewis acid attack directly at the heterocycle oxygen. The reaction...