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Formaldehyde condensation products of model phenols for conifer bark tannins

Informally Refereed

Abstract

Gel permeation chromatography of the condensation products of phenols and formaldehyde proved effective in understanding the reactions of condensed tannins with formaldehyde. Rates of condensation of phloroglucinols, resorcinols, catechols, (+)catechins, and (-)epicatechin were examined to determine if methylol-tannins from southern pine bark could be prepared as resin intermediates. The phloroglucinols (models for the A-ring of pine bark tannins) were so much more reactive than were the resorcinols (models for the a-ring of wattle tannins), that preparation of methylol-tannins from pine bark tannins seems unlikely even though this approach has been applied succesfully to synthesis of resins from wattle tannins. The methylol content of catechin-formaldehyde condensation products was very low. The catechol B-ring was unreactive under conditions in which condensations of pine bark tannins could be controlled. although there is much less steric hindrance of the a-ring of (-)epicatechin than of (+)catechin, differences in the rates of condensation of these isomers were nont detected. GPC and H-NMR spectra of (+)catechin condensation products showed that a dimer formed rapidly and that further condensation occurred more slowly.

Citation

Hemingway, Richard W.; McGraw, Gerald W. 1978. Formaldehyde condensation products of model phenols for conifer bark tannins. Journal of Liquid Chromatography, Vol. 1(2): 163-179
Citations
https://www.fs.usda.gov/research/treesearch/24238