Condensed Tannins: Reactions of Model Compounds with Furfuryl Alcohol and Furfuraldehyde

Abstract

Reaction products of phloroglucinol or catechin with furfuryl alcohol and furfuraldehyde were studied. In reactions of furfuryl alcohol with phloroglucinol, only 2-furyl-1′,3′,5′-trihydroxyphenyl) methane was obtained as product, and 53% of the phloroglucinol was recovered. Reactions of furfuryl alcohol with catechin gave 2-furyl-(8-catechinyl) methane and 2-furyl-(6-catechinyl) methane in 4.0% and 1.5% yields, respectively, while 62% of the catechin was unreacted. Polymeric furans with few catechin moieties made up the oligomeric products (38% of catechin). Reaction of phloroglucinol with furfuraldehyde gave 2-furyl-di(1′,3′,5′-trihydroxyphenyl) methane, an unstable product that readily polymerized during isolation. The solid state ¹³C-NMR spectrum of the higher polymers suggested one phloroglucinol moiety per furan unit, but lower oligomers contained more furan-furan condensation products. Reactions of catechin with furfuraldehyde gave 2-furyl-di(8-cate-chinyl) methane and the two diastereomers of 2-furyl-(6-catechinyl)-(8-catechinyl) methane in low yield, with 65% of the catechin unreacted.