Condensed tannins. 5. The oxidative condensation of (+)-catechin

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Abstract
The autoxidation of (+)-catechin in aqueous solution is relatively slow and is accompanied by an increase in the average molecular weight of the mixture formed. The percentage of (+)-catechin remaining in the oxidation product is estimated and the average molecular weight of the tannins calculated. The autoxidation reaction appears to be complex. Degradation accompanies the condensation reaction and the percentage of phloroglucinol formed is low. The oxidation is accompanied by a "browning" reaction; the product is soluble in methanol and acetone-water, and apparently similar to that which accompanies (+)-catechin in commercial gambier extract. Tannins present in cube gambier from the leaves of Uncaria gambir are shown to be polymeric.