Studies on the Cooking Mechanism of Wood. XV. Mannich Reaction on Lignin Model Compounds and the Estimation of the Amount of the Simple Guaiacyl Nucleus in Thiolignin

Mannich reactions on many lignin model compounds revealed that 1) model compounds of type (I) give without exception Mannich base with substituent at fifth position in very high yield, 2) those of type (II) do not react, 3) carboxyl group having phenolic hydroxyl group to its para position is split off as carbon dioxide and dimethylaminomethyl group is introduced to the same position, 4) methylol group having phenolic hydroxyl group to its para position reacts with dimethylamine resulting in the formation of dimethylaminomethyl group at the same position, 5) other groups remain intact even when phenolic hydroxyl group exists in para position, and 6) no reaction occurs when the phenolic hydroxyl group is etherified. By applying the Mannich reaction with dimethylamine on thiolignin, it has been concluded that about 25–40% of the phenolic hydroxyl group of thiolignin belongs to the simple guaiacol nucleus of type (I) having no C–C bond at its fifth position, admitting some uncertainty concerning the amount of carboxyl group having free phenolic hydroxyl group in its para position.