A facile route of formation of lignin-carbohydrate complexes during alkaline pulping

2,3,4,6-tetra-O-methyl-D-glucose was treated at high temperature and strong alkaline conditions in order to create cc, P-unsaturated structures through beta-elimination of a methoxyl group. This reaction led to two major products which were analyzed by NMR spectroscopy as 3-deoxy-2,4,6-tri-O-methyl-alpha-D-erythro-2-hexenopyranose and 3-deoxy-2,4,6-tri-O-methyl-alpha-D-threo-2-hexeno-pyranose. These compounds were then mixed with 2-methoxy-4-methylphenol (creosol), under conditions close to those used in kraft pulping. It was shown by GC/MS that the unsaturated sugars produced by beta-elimination were able to give alcohols and carboxylates by a Cannizzaro reaction and to condense with creosol. Two kinds of nucleophilic addition were involved in the formation of lignin-carbohydrate complexes (LCC). These reactions both led to high alkali resistant carbon-carbon bonds and may explain how LCC are formed during kraft pulping.