Lignin structures in normal and compression wood. Evaluation by thioacidolysis using ethanethiol and methanethiol

The chemical structure of lignin in normal and compression wood of spruce has been studied. Thioacidolysis using both methanethiol and ethanethiol as nucleophiles was used for degradation. The results showed that these nucleophiles work equally well in thioacidolysis, but that methanethiol gives a somewhat higher yield than ethanethiol. In spruce compression wood, several of the monomeric, dimeric and trimeric products were structurally elucidated using gas chromatography-mass spectrometry analysis of the desulphurated thioacidolysis products. Some of the oligomeric structures contained a p-hydroxyphenyl unit, but most of the material seemed to be present in non-condensed beta-O-4 structures. A catechol structure was found and the results also indicated the presence of beta-5 stilbene structures in native spruce lignin.