MECHANOCHEMISTRY OF LIGNIN .3. MECHANOCHEMICAL REACTIONS OF BETA-O-4 LIGNIN MODEL COMPOUNDS

Mechanochemical reactions of (β—0—4 units of lignin were discussed on the basis of the results from veratryl glycerol-β-guaiacyl (I) and vanillin (II) ethers and related compounds, which were treated with ceramic ball mill for 1 hr in air. The homolytic cleavage of aryl ether bonds was observed only in the compounds containing para a-carbonyl group. In particular, the cleavage of Cβ—O bond in compound (II) gave vanillin with 18.8% yield. This was followed by the homolytic cleavage of Cα—Cβ to give 3 and 4 and further by emission of formaldehyde to afford 7. However, condensation reaction among radicals also occurred to give 5 and 6.These results suggested that mechanical pulp lignin contained more amounts of para-carbonyl phenol groups compared to those in original wood lignin, and therefore would give significant effect on pulp bleaching with alkaline hydrogen peroxide. © 1990, Walter de Gruyter. All rights reserved.