Abstract
Benzyl phenyl ether (PhOCH2Ph, BPE), a model for related structural features in lignin and low-rank coal, has been immobilized in MCM-41 hexagonal mesoporous silicas having pore diameters of 2.7, 2.2, and 1.7 nm. Pyrolysis studies conducted at 275 °C have revealed that the free-radical reaction pathways previously observed on nonporous Cabosil silica remain operative in the MCM-41 silicas. The BPE pyrolysis rate is slightly slower (ca. 2- fold) in these nanoporous solids than on Cabosil, which is correlated with a corresponding decrease in the rate of radical formation by homolysis of the weak O−C bond. Two rearrangement pathways dominate the chemistry and account for ca. 67 mol % of the products at all pore sizes studied, which is markedly increased compared with the corresponding Cabosil case (ca. 50 mol %). The first pathway is recombination of the incipient benzyl and phenoxyl radicals to form surface-immobilized benzylphenol isomers, 1. The second pathway involves an O−C phenyl shift in surface-attac...
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