Characterization of the polyphenolics related to the colour of western redcedar (Thuja plicata Donn) heartwood

Three quarters of the western red cedar's heartwood colour is due to a poly meric material easily isolated by methanol extraction. The nature of this p olymer has not been fully investigated and published information is contrad ictory. Our initial examination of the coloured polymer by pyrolysis-gas ch romatography, combined with mass spectrometry, indicated that the polymer w as guaiacyl in nature and thus similar to softwood lignin. However, analysi s by infrared spectroscopy indicated the presence of both lignin and lignan like moieties. To clarify this issue a more detailed analysis was conducte d using nuclear magnetic resonance spectroscopy (H-1 NMR, P-31 NMR, C-13 NM R). Analysis of the spectra and comparison with the spectra of plicatic aci d and a product from mild acid treatment of plicatic acid, indicated that t he polymeric fraction was derived almost entirely from lignans. During poly mer formation, the highly reactive pyrocatechol moiety in the plicatic acid is destroyed, leaving a guaiacyl-like polymer. The reaction mechanism appe ars to proceed via an ortho-quinone intermediate followed by polymerization .