Isomerization of Cyclohexene Oxide over Solid Acids and Bases

The reaction of cyclohexene oxide over solid acids and bases at 108 °C gave five main products, 1,3-cyclohexadiene (1), cyclohexanone (2), cyclohexanol (3), 2-cyclohexen-1-one (4), and 2-cyclohexen-1-ol (5). SiO2–TiO2 and SiO2–TiO2–MgO were highly active for the isomerization, giving a large amount of 1. TiO2–ZrO2 mainly showed selectivity for the formation of 5, and other catalysts formed both 2 and 5. Of the alumina prepared in four different ways, two were highly active, giving 5 predominantly. The results were discussed in comparison with those for an oxide containing a methyl group on the oxide ring, 1-methylcyclohexene oxide. By the experiment using the deuterated epoxide, 1,2-epoxycyclohexane-3,3,6,6-d4, isotope effects for the formation of 2, 3, 4, and 5 over Al2O3’s, SiO2–TiO2 and solid H3PO4 were observed. It has been concluded that the epoxide is adsorbed on both acidic and basic sites, and that allyl alcohol is formed when both the opening of the epoxide ring and the hydrogen abstraction take place simultaneously, while ketone is formed when the former precedes the latter.