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.

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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.

1. Conductometric titrations of the model compounds IV, V, VI and VII provided reconfirmation of the previously reported findings that simple guaiacol-type phenolic hydroxyl group I was conductometrically titratable, while non-guaiacyl phenolic hydroxyl group belonging to type II was conductometrically untitratable. 2. It was thus further confirmed, that the separate estimation of both type-I and -II phenolic hydroxyl groups of lignosulfonic acid by the method of conductometric titration is possible in combination with the ultraviolet absorption spectra taken simultaneously with the conductometric titration without any dilution of the solution. 3. As we have now considerable accumulation of facts supporting the existence of o,o′-diphenol type phenolic hydroxyl group in lignin, three water-soluble model compounds VIII, IX and X were titrated conductometrically. Phenolic hydroxyl groups of IX and X were found to be conductometrically titratable. Of the two phenolic hydroxyl groups of the model compound VIII only one was found to be titratable. 4. A brief theoretical consideration of the conductometric titration of extremely weak acid (phenol) having pK values larger than 9 were made. As is evident from Fig. 12, which shows theoretical conductometric titration curves of phenols having pK values 9∼12, one can calculate the equivalence-point in so far as the pK values of the phenols are smaller than 10; it is, however, impossible to find the equivalence-point when pK values are larger than 10. As the calculated titration curve for pK 12 is nearly linear, it is expected that the pK value of phenolic hydroxyl group of type II is 12 or larger.

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.