Isomerization of cycloheptane, cyclooctane, and cyclodecane catalyzed by sulfated zirconia—comparison with open-chain alkanes
The skeletal isomerization of cycloalkanes with the number of carbons greater than six, cycloheptane, cyclooctane, cyclodecane, and cyclododecane, was performed over sulfated zirconia in liquid phase at 50 °C. A main product of methylcyclohexane was formed from cycloheptane via a protonated cyclopropane intermediate, protonated [4.1.0]bicycloheptane, together with small amounts of trans-1,2-dimethylcyclopentane, cis- and trans-1,3-dimethylcyclopentanes, 1,1-dimethylcyclopentane, and ethylcyclopentane. A major product from cyclooctane was ethylcyclohexane via a protonated cyclobutane intermediate, protonated [4.2.0]bicyclooctane, followed by cis-1,3-dimethylcyclohexane in addition to small amounts of trans-1,2-, -1,3-, -1,4-dimethylcyclohexanes, 1,1-dimethylcyclohexane, and methylcycloheptane. The detailed reaction-paths for cycloheptane and cyclooctane were shown after additional examinations in reactions of methylcyclohexane, ethylcyclopentane, ethylcyclohexane, and 1,2-dimethylcyclohexane. Cyclodecane was dehydrogenated into cis- or trans-decaline with the evolution of a dihydrogen. Cyclododecane was converted into lots of products, more than 30 species.