Polarographically active structural fragments of lignin. I. Monomeric model compounds

Electrochemical properties of compounds modeling typical structural units of lignin were determined by differential pulse polarography in dimethylsulfoxide with tetrabutylammonium perchlorate as a supporting electrolyte. p-Quinonemethides; derivatives of cinnamyl aldehyde and cinnamic acid; aromatic aldehydes, ketones, diketones, and carboxylic acids; isoeugenol; and coniferyl alcohol were studied. Structural effects on the reduction potentials of lignin units were estimated. The potentials, which correspond to the first polarographic peak, varied from -0.8 (p-quinonemethide) to -2.8 V (coniferyl alcohol). The compounds containing nonconjugated carbonyl or carboxyl groups were not polarographically active. The autoprotonation reaction had a profound effect on the electrochemical reduction of compounds containing hydroxyl groups.