ON THE DISTRIBUTION OF THE DIASTEREOMERS OF THE STRUCTURAL ELEMENTS IN LIGNINS - THE STERIC COURSE OF REACTIONS MIMICKING LIGNIN BIOSYNTHESIS

Stereochemical studies on the formation of the diastereomers of arylgl ycerol-beta-aryl ether structures during lignin biosynthesis have been carried out with model compounds. The addition of water to quinone me thides of the beta-syringyl ether type gives arylglycerol beta-syringy l ethers with a predominance of the erythro isomer when the pH of the medium is low. Since erythro forms of arylglycerol beta-syringyl ether s are prevalent in hardwood lignins, this indicates that the pH of the medium in which lignin biosynthesis occurs is lower than has been ass umed until now. Equilibration studies with non-phenolic model compound s of the arylglycerol-beta-guaiacyl ether and beta-syringyl ether type s under acidolysis conditions indicate that the erythro predominance o bserved in the syringyl ethers in lignins does not correspond to equil ibrium conditions. A remarkable resistance to acidolysis is observed i n the model compounds of etherified syringylglycerol beta-syringyl eth er type.