Aerobic oxidation of secondary pyridine-derivative alcohols in the presence of carbon-supported noble metal catalysts

Pt/C and PtBi/C catalysts prepared on a synthetic mesoporous carbon were evaluated in the oxidation of secondary aromatic alcohols (1-phenylethanol, α-methyl or phenyl pyridinemethanol) with air in different dioxane/water mixtures at 100 °C under 10 bar air. The observed activity for all substrates over both types of catalysts was strongly improved with the addition of water to the dioxane solvent as a result of different interactions of the alcohols with the metallic surface in the apolar dioxane solvent or polar aqueous medium. A promoting effect of bismuth was observed for all substrates. However, the reaction rate was also dramatically influenced by the nature of the aromatic moiety, the nature of the α-group, and the position of the substituent on the pyridine moiety. As a general rule the reactivity was meta < para ≪ ortho and the pyridine derivatives with a phenyl group were more reactive. α-Phenyl-2-pyridinemethanol was totally converted to 2-benzoylpyridine with a selectivity of 96% in dioxane/water 50/50 vol% in the presence of a 2.7% Pt–0.9% Bi/C. Nevertheless, platinum leaching was detected, which could be limited with the promotion by bismuth.