REACTIONS OF P-BENZOQUINONE ON TIO2(001) SINGLE-CRYSTAL SURFACES - OLIGOMERIZATION AND POLYMERIZATION BY REDUCTIVE COUPLING

Reduction and coupling reactions of benzoquinone on sputter-reduced TiO2(001) surfaces yield benzene, biphenyl, terphenyl, and phenol as volatile products. Like the reductive coupling of monofunctional aldehydes and ketones, reductive coupling of benzoquinone requires titanium cations in oxidation states below +4; activity for this chemistry is strongly quenched by oxidation of reduced surfaces by annealing at 750 K and above. Unlike monofunctional carbonyl compounds, benzoquinone can undergo multiple coupling events, as shown by the production of terphenyl. Both TPD and XPS results suggest that substantial amounts of higher phenylene oligomers are also produced and remain on the surface even at high temperatures. Thus reductive coupling of benzoquinone may provide a route for synthesis of a surface layer of p-polyphenylene, a conductive polymer.