Condensed Tannins. Structure of the “Phenolic Acids”

Conifer barkderived Condensed tannins can be used in formulating adhesives. Under some extraction conditions and during normal adhesive formulation, the tannin is exposed to strongly alkaline conditions. Alkaline rearrangement results in partial or total rearrangement of tannins of the procyanidin class to “phenolic acids” which have less phloroglucinol functionality. This makes the tannin less suitable for use in adhesives since it is the phloroglucinolicring that gives tannins their characteristic high reactivity with formaldehyde and/or hydroxybenzyl alcohols. The extent of rearrangement depends on the pH and temperature of the solution, more severe conditions give a greater extent of reaction. The Structure of the phenolic acids was determined using 13C NMR.