1983 Volume 37 Issue 12 Pages 1102-1108
If either the pKa value of a phenolic compound in the extractives becomes lower or its HLB value higher, as is generally expected, there is a tendency to decrease in its residual amounts in sulfate pulps by being surrounded by the neutral carrier and therefore, protected from alkaline attack. Direct comparison of the speck areas appeared in pulps as a result of aggregation of phenolic molecules dose not seem to give a clear-cut relation among speck area, pKa, and HLB value. However, this is realized by comparing the speck areas S based on a certain amount of residual phenol, R i. e. S/R ratio as shown in Figure 5 and 6. The lower the pKa value of a phenol and also the higher the HLB value of it, the greater ability for aggregation of the phenolic molecules is observed.
A sterochemical environment around the phenolic hydroxyl group was shown to be an additional and important factor for aggregation, and the greater steric hindrance of a phenol could afford less speck area. The reason for giving no speck area in the case of ferruginol and its derivatives, differently from other phenols, may be ascribed to great contribution of the steric hindrance in addition to the relatively low HLB value. Hydrogen bond formation through 12-hydroxyl group to afford an aggregate is prevented firstly from neighbouring 13-isoprophyl group and secondly from interaction between 11-H and 1β-H. Colored substances produced by the treatment of ferruginol with chlorine dioxide, therforfore, do not give any visible speck but disperse uniformly in bleached pulps to lower the brightness.
