Peroxidative Oxidation of Lignin and a Lignin Model Compound by a Manganese SALEN Derivative

Abstract

The manganese catalyst, (1R,2R)-(−)-[1,2-cyclohexanediamino-N,N′-bis(3,5-di-t-butylsalicylidene)]manganese(III) chloride, was used to activate H2O2 to oxidize organosolv lignin and a lignin model compound. Oxidation of the β-O-4 lignin model substrate 1-(4-hydroxy-3-methoxyphenyl)-2-(2-methoxyphenoxy)propane-1,3-diol (320.3 m/z) and poplar organosolv lignin resulted in both fragmentation and polymerization processes, likely via phenoxy radical formation. Matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) mass spectrometry (MS) of the reaction products from the β-O-4 model substrate showed oligomers of the substrate with masses of 661.192, 979.355, and 1297.466 m/z that correspond to a dimer, trimer, and tetramer of the β-O-4 model substrate, respectively. Nuclear magnetic resonance (NMR) shows the formation of 5–5 diphenyl and 4-O-5 linkages in the β-O-4 model substrate oxidation products. Gel permeation chromatography (GPC) detected three peaks, corresponding to the β-O-4 model subs...