Reactions of ketones on oxide surfaces. I. Reaction sequence of cyclohexanone on alumina

Abstract

The reaction of cyclohexanone on alumina is investigated at various temperatures and contact times. The poisoning of the surface of pure alumina as well as of alumina impregnated with different amounts of sodium is also studied. The main reaction products are a dimeric aldol condensation product and cyclohexene. The reaction sequence of cyclohexanone on alumina involves first a rapid polymerisation of cyclohexanone on the surface. At low temperatures, hydrogen transfer from the polymer to cyclohexanone is responsible for the formation of cyclohexene, the polymer itself being converted to coke which poisons the surface. At higher temperatures the disproportionation of cyclohexanone is the dominant mechanism for the formation of cyclohexene. Cyclohexanol itself is not formed under the reaction conditions employed. Conditions of low acidity and temperature favour the formation of the dimer.