OXIDATIVE DEGRADATION OF LIGNIN BY PHOTOCHEMICAL AND CHEMICAL RADICAL GENERATING SYSTEMS

Oxidation of specifically radiolabeled ¹⁴C-lignins by UV/H₂0₂. Fenton's reagent, photosesitizing riboflavin. UV- and γ-irradiation was examined. In the presence of UV/H₂O₂, a hydroxyl radical (·OH) generating system. ¹⁴C-methoxy. 2-¹⁴C-sidechain] and ¹⁴C-ring labeled lignin were rapidly and extensively degraded as measured by gel filtration of the reaction products on Sephadex LH-20. This suggested that exposure to OH leads to rapid, nonspecific lignin degradation. Rapid degradation of 14C-methoxy, 2-¹⁴C-sidechain] and ¹⁴C-ring labeled lignin also occurred in the presence of the ·OH generating system, Fenton's reagent, confirming the primary role of ·OH in these reactions. Photosensitizing riboflavin, also capable of effecting transformation of organic compounds via Type I hydrogen radical abstractions, caused extensive oxidative degradation of ¹⁴C-methoxy labeled lignin and significant degradation of 2-(¹⁴C-sidechain] and ¹⁴C-ring labeled lignin. In addition, UV- and γ-irradiation caused slower but extensive degradation of the polymers, probably via radical type mechanisms. All of these results indicate that ·OH as well as organic radical generating systems are effective agents for the purpose of degrading this heterogeneous, optically inactive and random biopolymer.