REACTIVE STRUCTURES IN WOOD AND HIGH-YIELD PULPS .4. DAYLIGHT-INDUCED OXIDATION OF STILBENE STRUCTURES IN THE SOLID-STATE

In order to mimic the light-induced yellowing of stilbene structures present in hydrogen peroxide bleached high-yield pulps, two monohydroxystilbenes have been synthesized and irradiated with daylight in the solid state on filter paper. The key step in the reaction sequence seems to be an electron transfer-proton transfer process leading to the formation of a stilbene phenoxyl radical. Subsequent oxidation gives rise to a cation which can add water and after loss of methanol is converted into an ortho-quinone. By hydrogen donation and subsequent addition to the stilbene double bond, thiol groups like that in mercaptoacetic acid could be used to capture all radical species formed, and thus prevent the formation of coloured products. Other major reaction pathways leading to the formation of non-coloured products were also identified.