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The rate constants and free energies of activation of the acid‐and base‐catalyzed reactions of floroglucinolic and resorcinolic flavonoid A rings of pine and wattle tannins, respectively, as well as the model compounds resorcinol, floroglucinol, and catechol, with formaldehyde, acetaldehyde, propionaldehyde, n‐butyraldehyde, isobutyraldehyde, and furfural, were obtained. Second‐order kinetics were found to fit these reactions. Indication and proof of the existence of unstable aldehyde ether bridges and their fast rearrangement at ambient temperature to alkyl bridges for fast‐reacting phenols or phenolic compounds, such as tannins, were obtained for the first time. The dependence of the reaction kinetics on the concentration of OH‐ catalyst was investigated. Anomalies in the behavior of wattle tannin with aldehydes and n‐butyraldehyde with phenols were observed and partially explained. The results led to a slightly different interpretation of the wattle tannin flavonoid structure.

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