INTERACTION OF SULFUR-DIOXIDE AND NITRIC-OXIDE WITH PHOTOIRRADIATED WOOD SURFACES

Photoinduced free radicals on a southern pine sur-face were examined b y electron spin resonance (ESR) spectroscopy. Phenoxy and carbon radic als were generated in cellulose, hemicelluloses, and lignin. While mos t of the phenoxy radicals were stable at 25 C, carbon and alkoxy radic als were unstable at that temperature. Nitric oxide readily reacted wi th carbon and alkoxy radicals to produce nonradical nitroso and nitrit e products, respectively. However, only a portion of carbon radicals r eacted with sulfur dioxide to produce sulfonyl radicals. Alkoxy radica ls were reactive with sulfur dioxide to produce sulfite radicals. Sulf onyl and sulfite radicals were unstable at 25 C and terminated rapidly to form sulfinic acid and sulfonate ester, respectively. Phenoxy radi cals were inert toward sulfur dioxide and nitric oxide. Reaction mecha nisms among photoinduced free radicals, sulfur dioxide, and nitric oxi de are discussed.