Interaction of Sulfur Dioxide and Nitric Oxide with Photoirradiated Wood Surfaces
Keywords:ESR, electron spin resonance, cellulose, hemicelluloses, lignin, sulfonyl radical, sulfite radical, nitroso, nitrite, sulfinic acid, sulfonate ester
AbstractPhotoinduced free radicals on a southern pine surface were examined by electron spin resonance (ESR) spectroscopy. Phenoxy and carbon radicals were generated in cellulose, hemicelluloses, and lignin. While most of the phenoxy radicals were stable at 25 C, carbon and alkoxy radicals were unstable at that temperature. Nitric oxide readily reacted with carbon and alkoxy radicals to produce nonradical nitroso and nitrite products, respectively. However, only a portion of carbon radicals reacted with sulfur dioxide to produce sulfonyl radicals. Alkoxy radicals were reactive with sulfur dioxide to produce sulfite radicals. Sulfonyl and sulfite radicals were unstable at 25 C and terminated rapidly to form sulfinic acid and sulfonate ester, respectively. Phenoxy radicals were inert toward sulfur dioxide and nitric oxide. Reaction mechanisms among photoinduced free radicals, sulfur dioxide, and nitric oxide are discussed.
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