Polarographically active structural fragments of lignin. II. Dimeric model compounds and lignins

Lignin model dimers representing all typical interunit linkages in lignin (beta-O-4, alpha-O-4, alpha-O-gamma, beta-5, 5-5, beta-beta, stilbene, enol ether) were characterized by differential pulse polarography (DPP) and cyclic voltammetry (CV) in DMSO. Polarographic activity was registered for alpha-(C=O)-beta-O-4 structures and conjugated double bonds in stilbene and enol ether structures. A structure-chemical reactivity correlation diagram is drawn based on the studies of one- and two-unit model structures of lignin. Peaks in differential pulse polarograms of lignin were assigned to certain functional groups and bond types based on the comparison between the data obtained on model compounds and selectively chemically modified [NaBH4, LiAlH4, CH2N2, (CH3O)(2)SO2] lignin samples.