PHOTOCHEMISTRY OF A MODEL LIGNIN COMPOUND - SPIN-TRAPPING OF PRIMARY PRODUCTS AND PROPERTIES OF AN OLIGOMER

alpha-Guaiacoxylacetoveratrone, 1, was selected as a model of a lignin structure component for photolysis and free radical spin trapping stu dies. The 3,4-dimethoxyphenacyl radical, Ar-COCH2, 2, thermally genera ted from alpha-bromoacetoveratrone with trimethyltin, was spin trapped by phenyl-tert-butylnitrone (PBN), and the spin-trapped radical ident ified by ESR and mass spectroscopy. Spin trapping by PBN of radical ph otoproducts from 1 gave a mixture of trapped radicals, according to ES R. These were separated as their hydroxylamines and identified by liqu id chromatography/mass spectroscopy (LC/MS) under chemical ionization (CI) conditions. This LC/MS (CI) method identified the same phenacyl f ragment, 2 (reduced), as well as a fragment tentatively attributed to a spin-trapped guaiacoxyl radical, chemically reduced to the hydroxyla mine. Extended direct photolysis of 1 yields colored paramagnetic olig omers. The synthesis of yphenyl)-2-(4-hydroxy-3-methoxyphenylethanone( 10), a rearranged, recombination photoproduct of 1, is described. A pa thway for formation of oligomers as unstable dimers of 10 is presented .