ORGN 112 |
| Our research involves probing the impact of surface confinement in nonporous and mesoporous silicas on the kinetics and mechanisms of organic free-radical reactions. Previous studies of the pyrolysis of silica-immobilized 1,3-diphenylpropane (DPP) at 375 °C revealed a free radical chain mechanism whose rate is sensitive to surface coverage and, hence, the rate of hydrogen transfer propagation steps on the surface. In the presence of co-attached spacer molecules containing reactive benzylic C-H bonds (e.g. diphenylmethane), the DPP pyrolysis rate is dramatically accelerated compared with surfaces containing inert spacers (e.g. biphenyl and naphthalene). Rapid serial hydrogen transfer steps on the surface result in radical intermediates being relayed across the surface, which overcomes normal diffusional constraints. In the current study, we examine the influence of spacer molecular orientation on the rate of the hydrogen transfer, radical relay process through the use of a hydroaromatic spacer molecule, fluorene, attached to the surface at different positions on the aromatic ring. The impact of surface curvature is also explored through the comparison of nonporous silica (Cabosil) and mesoporous silica supports (MCM-41) of varying pore size (1.6 – 2.8 nm). |
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Process R&D, Physical Organic Chemistry, Heterocycles, Aromatics, Metal-Mediated Reactions
8:00 PM-10:00 PM, Sunday, March 25, 2007 Hyatt Regency Chicago -- Riverside Center, Poster
Division of Organic Chemistry |