Pathways and Kinetics of Anisole Pyrolysis Studied by NMR and Selective 13C Labeling. Heterolytic Carbon Monoxide Generation

概要

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By applying [13]C and [1]H NMR spectroscopy the pyrolysis of site-selectively [13]C-enriched (H3[13]CO[12]C6H5) and normal anisole compounds was studied in the dark at 0.001–1.0 M (M, mol dm[−3]) and at 400–600 °C (supercritical conditions). Conversion of the [13]C-labeled methyl group was confined to the methoxy-originated fragments, [13]CO and [13]CH4, and the reactive intermediate, H[13]CHO*. The normal phenyl group, [12]C6H5– was converted to benzene, [12]C6H6 and phenol, [12]C6H5OH without ring disintegration. The pyrolysis consists of two elementary steps: (1) the rate-determining unimolecular ether-bond fission (k1) to generate the fragmented product C6H6 and energized intermediate H[13]CHO* through the intramolecular proton transfer from the methoxy group to the phenyl, and (2) the fast bimolecular disproportionation (k2) through the intermolecular proton/hydride transfer from H[13]CHO* to H3[13]COC6H5 to produce [13]CO, [13]CH4, and C6H5OH. CO is generation by the heterolytic (ionic) mechanism in contrast to the homolytic (radical) one via the phenoxy radical intermediate (C6H5O•) in the literature despite the agreement of the rate constant (k1) and the activation energy.
Chemical Society of Japanの論文
2012-01-15