A PHOTOCHEMICAL STUDY OF AN O-METHYLATED ALPHA-CARBONYL BETA-1 LIGNIN MODEL DIMER - 1,2-DI(3',4'-DIMETHOXYPHENYL)ETHANONE (DEOXYVERATROIN)

The photochemistry of 1,2-di(3′,4′-dimethoxyphenyl)ethanone (deoxyveratroin) (1) (an O-methylated α-carbonyl β-1 lignin model dimer) was examined. Its photochemical reactivity was studied in both liquid (benzene and ethanol) and solid (adsorbed on lignin-free fibres) states in degassed or aerated media. In degassed benzene and fibres, 1 is photochemically transformed into several identified compounds (monomeric to tetrameric units) and a coloured mixture of higher molecular weight fractions. The structures and titration of the photoproducts are well explained by Norrish type 1 cleavage and photoreduction of the carbonyl group. The presence of oxygen inhibits the reductive mechanism and leads to veratric acid by trapping the ketyl and desyl radicals. The observation of a low disappearance quantum yield of 1 in degassed ethanol is attributed to the presence of a low-lying π,π* triplet state as shown by phosphorescence. © 1990.