SINGLET OXYGEN IN THE PHOTODEGRADATION OF LIGNIN MODELS

The photochemical oxidation of lignin models in the presence of single t 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 photoch emical oxidation of the phenolic beta-O-4 aryl ehter 9 gave the same t ype of product confirming that, in this case, the presence of the carb onyl group is not indispensable to have the cleavage reaction. The use of the model compound 10 showed that. When the phenoxy part of the mo lecule shows a lower reactivity towards singlet oxygen, the oxidation of the phenol moiety to hydroquinone call occur. The photochemical beh aviour of these model compounds can be rationalised from a reaction of singlet oxygen with the phenoxy part of the molecule. (C) 1997 Publis hed by Elsevier Science Ltd.