Disproportionation and Isomerization in Dehydartlon of Cyclohexanol over Trifluoroacetic Acid/Alumina Catalysts

Author: Cheng-Hsia WangCheng-Hsia Wang(Department of Chemistry)

Abstract：

The acidities of two silica aluminas and thirteen aluminas were com-pared using the dehydration of cyclohexanol at 350°C. Acidic catalysts tend to give disproportionation products (methylcyclopentane and cyclohexane) and skeletal isomerization products (the three methycyclopentenes and methylenecyclo-pentane) with the initial dehydration product (cyclohexene). The least acidic aluminas give only cyclohexene. The catalysts are arranged in the order of their acidities as reflected in the amount of the disproportionation and skeletal isomerization products. This ranking method for alumina catalysts provides a convenient, direct way of evaluating the acidity level of a particular alumina catalyst.
Acetic acid has a poison effect on acidity of alumina, the probe reaction giving only cyclohexene. Trifluroacetic acid, on the other hand, has a great enhancement effect on acidity of alumina, the probe reaction giving a great deal of disproportiona-tion and skeletal isomerization products. This effect persists or is further enhanced upon regenerations.

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