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.

1. Hydrogen sulphide cooking of α-guaiacyl propanol (VI) gave bis(1-(4-hydroxy-3-methoxyphenyl)-1-propyl) monosulphide (VIII) and disulphide (VII). 2. Vanillyl monosulphide was decomposed with alkali at 130°. Vanillin, vanillyl alcohol and the secondary products from vanillyl alcohol were identified. 3. The mechanism of the kraft cooking process was discussed and a new mechanism was proposed.

The amount of the phenolic hydroxyl group of the lignin in situ was estimated to be about one per 5-6 methoxyl. Phenolic hydroxyl group of low sulphonated lignosulphonic acid is the same as that of the lignin in situ. There exist two types of phenolic hydroxyl groups (I) and (II) in lignin and lignosulphonic acid, the former being conductometrically titratable and the latter untitratable. With several lignosulphonic acid preparations, the ratios of these two types of phenolic hydroxyl groups were measured, the ratio being 1: 1 with lignin in wood, low sulphonated lignosulphonic acid, and birch α-lignosulphonic acid and about 3: 7 with α-acid of gymnosperm origin. The structures of these two types of phenolic hydroxyl groups were suggested.

It was shown that the UV-absorption spectrum of thiolignin must be explained by assuming the existence of the carbonyl group, the double bond conjugated with the nucleus and the carboxyl group attached directly to the nucleus. The amount of the phenolic hydroxyl group and the carboxyl group of thiolignin were estimated by methylating with diazomethane and subsequently hydrolyzing the methylated lignin with alkali.

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