Analysis of Polyphenol-Derived Aromatics in Eucalypt Woods

Abstract

Methods for the determination of polyphenols in wood by chemically degrading the wood and measuring the reaction products by gas chromatography (GC) were explored. A four-step procedure, based on permanganate oxidation of ethylated wood, allowed the estimation of polyflavonoids and related polyphenols as the methyl ethoxybenzoates IVa-c. Euaalyptua marginata heartwood gave methyl 3,4-diethoxybenzoate (IVb) in 2.71 yield, which was the highest value obtained from the eucalypt woods tested. Estimation of hydrolysable tannins as the methyl esters of tri-O-ethyl gallic acid and 4,4′,5,5′,6,6′-hexaethoxydiphenic acid, formed by methylation of the alkaline hydrolysis products of ethylated wood with diazomethane, was attempted. Applied to eucalypt woods, the method gave the methyl gallate in yields of up to 0.62, but the diphenic acid was obtained, in trace amounts, only from wood which had been ethylated for an extended period. The two methods are more suited to the determination of specific polyphenolic structures rather than the total polyphenol content of woods. A second approach to the analysis of diphenic acid moieties in ellagitannins based on alkaline decarboxylation to 2,2′,3,3′,4,4′-hexahydroxybiphenyl (V) and estimation of the hexahydroxybiphenyl (HHBP) by GC of its silylated derivative, was unsuccessful because the HHBP reacted with wood components.