PHOTOREACTIVITY OF LIGNIN MODEL COMPOUNDS IN THE PHOTOBLEACHING OF CHEMICAL PULPS .1. IRRADIATION OF PHENYL)-2-(3'-METHOXYPHENOXY)-1,3-DIHYDROXYPROPANE IN THE PRESENCE OF SINGLET OXYGEN SENSITIZER OR HYDROGEN-PEROXIDE IN BASIC METHANOL SOLUTION

The irradiation of 1-(veratryl)-2-(3'-methoxyphenoxy)glycerol in alkal ine methanol solution was performed in the presence of hydrogen peroxi de (UV and visible light) and sensitized by methylene blue (MB) in the presence of O-2 (visible light). The photoproducts were analysed by g as chromatography-mass spectrometry (GC-MS). The beta-O-4 ether bond c leavage, which usually occurs in reactions involving singlet oxygen, w as not operative, since the corresponding phenol 3 was detected in tra ce amounts only and the carbonyl derivative 4 was not detected at all. Irradiation in the presence of MB/O-2, induced the oxidation of the b enzyl group into a carbonyl function and produced the hydroxymethylati on of one benzene ring of compound 1. In contrast, such reactivity was not observed when 1 was irradiated in the presence of H2O2; neverthel ess, hydroxylation of one benzene ring was detected. For both types of irradiation, four stereoisomers were formed. The mass spectrum showed the addition of hydrogen peroxide to the B benzene ring of compound 1 . This is the most important reaction, and was ascribed to the radical addition of a superoxide anion assisted by the hydroxyl groups in the beta or gamma positions of the glycerol moiety. (C) 1997 Elsevier Sci ence S.A.