Singlet oxygen-mediated degradation of lignin - Isolation of oxidation products from steam-exploded lignin from straw

Four-hour irradiation of steam-exploded lignin from straw in the presence of singlet oxygen gave product showing high molecular weights. The only product obtained in low yield was the lactone 1. Irradiation of the same lignin sample for longer times allowed to obtain higher quantity of the same compound. The largest amount of the lactone was obtained after 24 h irradiation. This behaviour can be explained considering that lignin from straw can be easily oxidised by singlet oxygen and that I can be obtained from the singlet oxygen oxidation of 5-5' units in the lignin. (C) 2002 Elsevier Science B.V. All rights reserved.