Singlet oxygen in the photodegradation of lignin models

The photochemical oxidation of lignin models in the presence of singlet oxygen nas studied. The treatment of the non-phenolic beta-O-4 aryl ether derivatives 6, 7, and 8 in the presence of both oxygen and Rose Bengal gave products deming from a formal beta-C-O cleavage formation. By this way the derivatives 12. 13, and 15 were obtained, The photochemical oxidation of the phenolic beta-O-4 aryl ehter 9 gave the same type of product confirming that, in this case, the presence of the carbonyl group is not indispensable to have the cleavage reaction. The use of the model compound 10 showed that. When the phenoxy part of the molecule shows a lower reactivity towards singlet oxygen, the oxidation of the phenol moiety to hydroquinone call occur. The photochemical behaviour of these model compounds can be rationalised from a reaction of singlet oxygen with the phenoxy part of the molecule. (C) 1997 Published by Elsevier Science Ltd.