The generation of quinones from lignin and lignin-related compounds

Lignin and lignin-related compounds were oxidized with potassium nitrosodisulfonate, hydrogen peroxide, and peracetic acid, with the aim of producing o - and p -benzoquinones. Depending on the substrate and oxidant, yields of p -benzoquinones from lignin model compounds were as high as 80-95%. The best yield of p -benzoquinones from lignin (16%) was with the use of potassium nitrosodisulfonate and an aspen hardwood lignin; corresponding yields obtained with hydrogen peroxide and peracetic acid were 0-2%. Electrochemical oxidation was examined briefly and found to be inferior to the chemical oxidants with regard to yields of benzoquinones from lignin models (max. 40%) and from lignin (1%). The nitrobenzene oxidation of several lignin samples revealed that the highest syringaldehyde and combined aldehyde yields (for subsequent oxidation to quinones) were obtained from an organosolv lignin obtained through the acid-catalyzed pulping of aspen with ethanol.