ACIDIC PERMANGANATE OXIDATIONS OF LIGNIN AND MODEL COMPOUNDS - COMPARISON WITH OZONOLYSIS

Acidic permanganate oxidation degrades completely the aromatic moieties of lignins and lignin model compounds while a part of the side-chain structures can be recovered intact in the form of carboxylic acids. Thus, threonic acid (6.9%) is obtained from threo-veratrylglycerol, erythronic acid (7,8%) from erythro-veratrylglycerol -(2-methoxyphenyl) ether and glycolic acid (~ 13%) from vanillyl alcohol. Erythronic and threonic acids, in a molar ratio of 0.6:1, were also identified as permanganate oxidation products of black spruce native lignin. Minor oxidation products from lignin and lignin model compounds included glyceric, oxalic, glycolic, tartronic, erythraric, thrcaric, 2,4-dihydroxybutanoic, succinic and malic acids. Ozonation of lignin and an lignin model compounds resulted in the formation of the same products as permanganate oxidation but the yields of erythronic and threonic acids were larger by a factor of more than ten confirming the earlier results of Nakano and coworkers (1982). From black spruce native lignin, the products obtained were; erythronic and threonic acids in the molar ratio of 0.75:1, the minor components identified from model compound oxidations and, in addition, two isomeric 2-hydroxy-3-hydro-xymcthylbutanedioic acids and 3,4-dihydroxybutanoic acid.The former two isomeric acids were also identified as ozonation products of the β-1 model compound 1,2-bis-(3,4-dimethoxyphenyl)-1,3-propanediol. 3,4-Dihydroxybutanoic acid was obtained in larger amounts from the oxidations of Klason lignins and is proposed to be formed from condensed structures in lignin. © 1990, Walter de Gruyter. All rights reserved.