Oxygen bleaching of kraft pulp is becoming widespread in JaPan to reduce pulp lignin content and chlorine consumption in the production of fully bleached kraft pulp. Further reduction of the chlorine consumption is required from the standpoint of environmental protection. As an effective method for reducing it, pretreatment of kraft pulp with nitrogen dioxide has been proposed. However, the mechanism of its action is not clear. The objective of this research is to learn more about the mechanism. When vanillyl alcohol and veratryl alcohol were treated with NO, in heterogeneous systems under mild conditions, vanillyl alcohol easily decomposed while veratryl alcohol was stable. From vanillyl alcohol, 4-nitroguaiacol and 4,6-dinitroguaiacol (2-methoxy-4,6-dinitrophenol) were formed. A major reaction of veratryl alcohol and 1-(3,4-dimethoxyphenyl)-2-(2-methoxy-4-methylphenoxy) propan-1-ol was oxidation of a benzyl alcohol group to an a-carbonyl group. Nitration was a minor reaction, indicating that nitration of nonphenolic lignin units occurs to a very limited extent in NO2 pretreatment of kraft pulp. It is therefore unlikely that the enhancement of oxygen delignification by NO2 can be explained by the mechanism proposed by Lindeberg and Walding.
