Fundamental Study of Relative Delignification Efficiencies (I): Conventional Pulping Systems

ABTRACT

Reactions of a β-aryl ether model 1 [l-(4-guaiacyl)-2-(O-guaiacyl)-l,5-pentanediol] provide relative rates of pulping reactions that involve quinone methides (QMs). Model 1 was reacted under soda, kraft, soda/anthraquinone (AQ), and sulfite conditions. All alkaline conditions displayed the same lignin model disappearance rate, indicating a common rate determining step — QM formation. The results indicate that reactions between pulping reagents and QM are reversible in most cases and that anthahydroquinone (AHQ) was the most effective reagent at facilitating β-aryl ether cleavage. Alkaline sulfite cooks of 1 gave a similar product distribution as a soda cooks of 1; however, an α-sulfonate 11 &;lsqb;l-(4-guaiacyl)-2-(O-guaiacyl)-5-hydroxypentane-l-sulfonic acid] was the predominant product when 1 was reacted under neutral sulfite conditions. Model 11 reverted back to a QM at high pH values. All of the sulfite cooks of 1 showed only low levels of β-aryl ether cleavage. This paper is the first in a three-part study designed to examine β-aryl ether cleavage in multicomponent pulping systems (e.g., alkaline sulfite/AQ/methanol [ASAM]).