T. Kishimoto, Y. Sano
Delignification Mechanism during High-Boiling Solvent Pulping.
Part 1. Reaction of Guaiacylglycerol-?-Guaiacyl Ether
Summary
A phenolic ?-O-4 type lignin model compound, guaiacylglycerol-?-guaiacyl ether (1) was treated with
70 wt% aq 1,3-butanediol solution at 160–200°C to investigate the delignification mechanism under
HBS (high-boiling solvent) pulping conditions. The following compounds were identified from the reaction
products by use of GC-MS: guaiacol (2), coniferyl alcohol (3), ?-etherified coniferyl alcohols (4)
and ?-etherified guaiacylglycerol-?-guaiacyl ethers (5), but acidolysis products, such as Hibbert's
ketones were not detected. These results strongly suggest that the phenolic ?-O-4 linkage was cleaved
homolytically under HBS pulping conditions. The cleavage of ?-ether exhibited a pseudo first-order rate
behavior. The pseudo first-order rate constants were as follows: k = 0.94 × 10?2 min?1 at 160 °C;
k = 1.97 × 10?2 min?1 at 170°C; k = 3.22 × 10?2 min?1 at 180 °C; k = 9.76 x 10?2 min?1 at 200 °C.
The activation energy was 98.3 kJmol?1. The formation of higher molecular weight compounds was confirmed
by GPC. It is highly probable that the oligomeric products were derived from the recombination
of phenoxy radicals formed by homolysis of the ?-aryl ether.
Holzforschung, Walter de Gruyter
Print ISSN: 0018-3830
Volume: 55, 11/2001
Pages: 611 - 616
Show full article (external site)
Show all available items of this journal
Search
