Ring-Opened Products from Reaction of Lignin Model Compounds with UV-Assisted Peroxide

Abstract

Reaction of a range of guaiacyl, syringyl, veratryl and 3,4,5-trimethoxyphenyl lignin model compounds with UV-alkaline peroxide gave rise to 26 aliphatic acids which were identified by gas chromatography-mass spectrometry. The acids derived from scission of the aromatic rings, and their total yields were less than 10% from most model compounds. The acids were both monocarboxylic and dicarboxylic. with either saturated or unsaturated carbon chains, and were variously substituted with hydroxyl, methoxyl and alkyl groups. There were more aliphatic acid products identified in the reaction mixtures of guaiacyl and syringyl lignin models than in those from veratryl and 3,4.5-trimethoxyphenyl models, although high numbers of products were not always reflected in the total yields. The identification of more products from phenols than from their methyl ethers reflects the degree of their degradation, and is consistent with the involvement of the superoxide radical anion as a reaction intermediate.