Configurational isomerization of cis-and trans-1,2-,1,3- and 1,4-dimethylcyclohexanes

Abstract

Configurational isomerization (henceforth isomerization) of cis- and trans-1,2-, 1,3-, and 1,4-dimethylcyclohexanes (henceforth c-1,2,1,3, 1,4 and t-1,2, 1,3, 1,4) has been studied under identical experimental conditions on supported Pt catalyst in the temperature range 373–548 K and partial pressure of hydrogen range 13.3–100 kPa. The effect of temperature and hydrogen pressure on the reaction rates as well as the activation energies were determined. Plotting the rates of isomerization against temperature reveals maxima. The rate of isomerization of t-1,3, increases with increasing hydrogen pressure. Isomers containing axial–equatorial (henceforth a,e) methyl groups were converted at a higher rate than those containig diequatorial methyl groups (henceforth e,e). At lower temperatures the experimental data may be interpreted by the ‘roll-over’ mechanism, while at higher temperatures the π-allyl mechanism proceeding via more unsaturated surface intermediates is invoked.