The self-condensation of cyclohexanone and methylcyclohexanones under very high pressure

Abstract

The self-condensations of cyclohexanone and its methyl substituted derivatives were investigated under pressures of 20～50kbar and temperatures of 160～300℃ without solvent and/or catalyst. It was found that 2-cyclohexenylcyclohexanone, 2-cyclohexylidenecyclohexanone, 2, 6-dicyclohexenylcyclohexanone and dodecahydrotriphenylene were produced from the self-condensation of cyclohexanone. Dodecahydrotriphenylene becomes the main product at the higher pressure and the higher temperature. 2, 2'-Methyl-(2-methylcyclohexenyl)-cyclohexanone was obtained from the self-condensation of 2-methylcyclohexanone. The reactivity of 2, 6-dimethylcyclohexanone was also examined and no product was obtained under pressures of 20～50kbar and below temperatures of 250℃. This condensation is assumed to occur in the liquid phase and to proceed through a series of aldol condensation followed by dehydration. This scheme was confirmed from pressure effects, but the mechanism of this condensation cannot be explained merely by the pressure dependence of auto-protolysis. The non-reactivity for 2, 6-dimethylcyclohexanone is reasonable in light of the larger steric hindrance.