Liquefaction Mechanism of β-O-4 Lignin Model Compound in the Presence of Phenol under Acid Catalysis. Part 1. Identification of the Reaction Products

Abstract

Summary Guaiacylglycerol-β-guaiacyl ether (GG) was used as a lignin model compound to study the liquefaction reaction mechanism of lignin in the presence of phenol under the catalysis of several typical acids such as sulfuric, phosphoric and oxalic acids. The reaction products were isolated by silicagel column chromatography and high performance liquid chromatography (HPLC). The structures of the obtained compounds were identified by means of GC-MS, 1H-NMR, 13C-NMR, 1H-1H COSY, HMBC and HMQC. As a result, about 30 compounds were obtained as the main reaction products. It was found that their structural characteristics were significantly different from those yielded at the non-catalyzed liquefaction (Lin et al. 1997a), and independent on the acid species. The dominant products were guaiacylglycerol-α-phenyl-β-guaiacyl ethers, followed by guaiacol, triphenylethanes, diphenylmethanes, benzocyclobutanes and phenylcoumarans. The structural characteristics and yields of these main reaction products indicated that condensation between phenol and GG in its C-α and further cleavages in both the β-O-4 linkage and Cβ–Cγ bonding could be the dominant reaction pathways.